First things first, what you’re doing when “breaking-in” a new performance engine – or any freshly rebuilt engine, for that matter – should be clearly defined. That is one of the largest pieces of misinformation in and of itself, according to Simon. “We must understand what it is we are actually trying to do. Some people think we are trying to bed in the bearings, or crankshaft, and that’s just not the case,” says Simon. “If you end up with metal-to-metal contact between the bearings and crankshaft journals [which would occur in a bedding process], you’re going to cause damage. Once that contact occurs, no amount of gentile running is going to fix that.”

What is actually being done during engine break-in is fairly simple – it’s the controlled bedding, or wearing-in, of the new piston rings on the hone of the cylinder walls. “We are trying to bed those rings so that they achieve a correct seal against the cylinder walls, and we have a relatively narrow window in which to do this,” relates Simon. “Once we achieve that seal, we end up with an engine that creates good power, has low blow-by, and has low oil consumption.”

“We’re using the rough surface of the hone pattern to abrade the rings and make them seat,” Simon explains. The crosshatch pattern of the hone in the cylinder like a file on the outer surface, creating a perfect fit within the bore. While that may sound simple – and really, the actual mechanics of it are – the process to actually achieve that is a delicate balancing act, as that crosshatch is only abrasive for a limited amount of time. “The reason there’s a narrow window is because that hone pattern will be broken down in time,” Simon continues.

Where things get complicated, is the proper way to maximize the effectiveness of that period where the crosshatch is essentially file-fitting the piston rings to the bore. “My process is one which I’ve gone though and developed through my career. It works exceptionally well, and as with most engine builders, I’m a bit superstitious about it,” says Simon. “The worst thing you can do while breaking in an engine is baby the engine or allow it to idle for extended periods, particularly when it’s hot. That will place almost no load on the rings and it will allow that hone pattern to be broken down without actually performing its job.”

 

However, while you don’t want a light load, you also don’t want to go to the other extreme either. “What we want to use is moderate amounts of load and moderate amounts of RPM,” explains Simon. “What happens with moderate loads, is that combustion pressure gets behind those rings, and pushes them out against the fresh hone pattern. That friction against the cylinder wall helps the bedding process along. However, that friction creates a lot of heat, so we need to be careful of that. You don’t want to go straight to wide open throttle and 8,500 rpm.”

Additionally, the lubricant used in the initial break-in period can have a large impact on how well the rings seat., and results in yet another balancing act. “The goal is to use an oil which will allow enough friction for the rings to bed in correctly. Common high-performance synthetic oil is so slippery it will actually inhibit the wear required to bed the rings in. So you don’t want to use super slick full-synthetic oils to break the engine in,” reveals Simon.

He prefers to use mineral-based oil, during break-in, as it will still protect the engine, but not be so super slippery as to be detrimental to the break-in process. There are a number of break-in specific oils on the market, which usually contain other additives to protect other parts of the engine in its early stages of life, and preferences on which one is best are about as varied as the varieties of oil themselves.

One final myth that Simon aims to bust, is extended engine break-in periods. “After a couple hundred kilometers of use, your rings are as bedded in as they’re ever going to be. After that, it’s all downhill, so you might as well get out and start enjoying your engine,” he says. “Exceedingly long break in periods are absolute rubbish.”

 

A helmet is one of those things you hope you never actually need. Many refer to this safety device as a “crash helmet” which is something you certainly never want to use it for, however that is exactly what it is designed to be utilized for. These helmets do a very important thing during a collision — protect your brain.

Even if you haven’t attended medical school, we all know enough anatomy to understand we need our brains to live. So, for obvious reasons this is no place to cut corners and try to save a few bucks. The purchase of a helmet can save your life. So, long story short, spend a couple of dollars on your own brain bucket. It is an easy insurance policy.

I often forget what my helmet is really for. I use my helmet as a place to put sponsor stickers and I use it to concentrate before a race. I close my visor, which is the universal sign for “leave me alone for a minute,” and I sit and think about the task at hand. How do I want to start? How am I going to manage my tires? Which cars am I going to draft with, or who am I going to block? My helmet is my Zen place, but that is not the intention of the design. It is designed to save my life when things go sideways, or worse, upside down.

Certification

When purchasing a helmet there are various options that need to be considered. The first one is the certification. For most car racing enthusiasts you are looking for a Snell SA rating. It is important to understand how helmets are rated as you will see a few different decals on helmets as you are shopping around.

You will see a D.O.T. decal which is really for motorcycle helmets on the public roads. You will see an M rating which is again for motorcycles and you will also see an SA rating. The SA rating also comes with a year associated with it. The year listed on the decal isn’t the year the helmet was manufactured, it is the Snell standards associated with that particular year. You may also run across F.I.A. ratings which come out of Formula 1 and Europe.

So, how in the “snell” did this certification come about? Great question. Pete Snell died in a motor racing accident in 1956 from a rollover collision. Afterwards, a team of doctors, engineers, and scientists got together and, in Snell’s memory, dedicated their work to certifying safety standards in helmets. Since 1957, the Snell Memorial Foundation has been certifying helmets. Why do you care? Because unless your helmet has their certification sticker inside, you ain’t racin’.

To find out how helmets can earn a Snell rating I spoke with Ed Becker, executive director and chief engineer at the Snell Memorial Foundation. The simple answer is helmets are test rated by bashing them into things. One of the tests performed is when a helmet has a 6.1 kilogram metal head placed in it (yes, kilograms because scientists use the metric system), and then the helmet is dropped from 11 feet. Sensors inside the helmet measure the G’s felt by the simulated head. No, they don’t use live humans for this test, for obvious reasons. If the G’s felt are above 243 G’s for a size large helmet, the helmet fails and does not receive a Snell certification.

Ed said helmet manufacturers have their own choice in how they build a helmet, Snell does not mandate a construction process, they only designate the tests the helmet must pass in order to be certified. The goal at Snell is “impact energy management,” which means when the outside of your helmet stops, the inside of the helmet should let your head “ride down” the impact by compressing the inner layer of the helmet, so your brain doesn’t feel the heavy hit.

For the SA 2015 standards, the SA rated helmets are being hit harder than the M rated helmets. Currently, most helmets that arrive at the foundation for testing do pass the tests as the helmet manufacturers engineer the helmets with the Snell standards in mind. However, occasionally helmets do fail, and then they are sent back to the manufacturer for a redesign. Snell rated helmets are safer, because they are tested beyond the government requirements for a basic D.O.T. rating. Those government requirements date back to standards set in 1966 which Ed considers, “Ancient technology.”

Some sanctioning bodies allow you to run an M rated (motorcycle) helmet, however, the recommendation for automobile competition is the SA rating should be used. The motorcycle rated helmets are not designed for impacts with roll cages and are not built with fire-retardant materials. The helmet in this photo, decked out in Girl Power livery, is a Pyrotech SA 2015 rated helmet for auto racing.

Construction/Fitment

Patrick Utt, president of RaceQuip, explained how his helmets are built, “Helmet construction, from inside out, starts with a layer of fire retardant cloth covering a thin layer of soft foam against your head. This covers a 2-inch thick Expanded Polystyrene (EPS) dense foam insert. The EPS liner fits into an outer shell made from one of any various composite materials including fiberglass, Kevlar, and/or carbon fiber. The outer shell has a layer of gelcoat (or clear epoxy) that was sprayed into the mold to ensure the helmet has a good surface finish and releases from the mold more easily. Lastly, a layer of fire retardant paint covers the gelcoat layer.” RaceQuip prides itself for its affordable helmet designs and only builds SA rated helmets.

When deciding which helmet is the right one for you, the best advice I have seen comes from Ken Myers, owner of I/O Port Racing Supplies, who races cars and sells helmets to racers all day long. “If you can go to a store and try the helmet on, you will be much better off versus buying one on the internet and hoping for the best,” he says.

Ken says fitment is the key to being comfortable in the race car. “Size large doesn’t always mean large, and a large helmet in a Pyrotech that fits you doesn’t mean a large helmet in a Bell will fit you the same,” he mentions. “Bell’s higher-end helmets are sized in hat sizes, for example 7 5/8ths. However, just because you wear a 7 5/8ths hat doesn’t mean that same helmet size will fit your head properly. You need to try the different helmets on.”

One of the considerations when buying a helmet is the material the shell is made of. More expensive helmets are made of carbon fiber and are lightweight. Ken Myers says there are some advantages to a lighter helmet in a collision. “The more mass on your head in a collision, the more chance for injuries to the neck. Additionally, lighter helmets are easier on the drivers during long stints behind the wheel, like for endurance racers.”

This advice was echoed by Patrick Utt from RaceQuip, “The weight factor is mostly important to racers who spend an hour or more in the car during a race. The lighter weight is less likely to fatigue the neck muscles.”

Ken did offer this warning about lightweight carbon fiber helmets — not all carbon fiber is actual carbon fiber. “Many helmet manufacturers use a mix of fiberglass, Kevlar, and one layer of carbon fiber on the outside of the helmet to make it appear as if it is made completely with carbon fiber, which it isn’t. A $500 carbon fiber helmet, isn’t really a carbon fiber helmet.”

Ken also indicated that just because a helmet is more expensive, it doesn’t mean that it is actually a safer or better helmet, “All SA 2015 helmets have passed the same criteria to meet that Snell standard. A $250 SA 2015 helmet from Pyrotech met the same standards as a $1,300 SA 2015 Bell Carbon helmet. What matters is does the helmet meet your needs?”

Consider Options

Other things to consider when purchasing a helmet are options. Do you want forced air into your helmet? Then you need to purchase a helmet that allows you to pipe in air. Do you race on a dirt track with a lot of dust? You may want a helmet with less air vents in the front. Do you have a radio in your car? You may want to purchase a helmet that has radio speakers already in it.

Shawn Sampson, racer and owner of Sampson Racing Communications (SRC) outfits teams with radio equipment and sells helmets with radio gear already installed. “I love the Stilo helmet line. It’s the helmet I wear when I am racing in the 25 Hours of Thunderhill. You don’t have to worry about ear buds coming out of your ears; the speakers are built right into the helmet. It works great.”

Other things to consider:  if you race at night, you will want a clear face shield. If you race in a sunny place, you may want a dark or smoked shield. If you are an endurance racer and need to drink water during a race, you may need to add driver hydration to your helmet by routing a tube through the front to a camel pack with water.

There are a lot of things to consider when you make your helmet purchase, so it is crucial to think about all of these options before getting out your credit card. For example, if you are going to road race with the National Auto Sport Association (NASA), you are required to have a full-face helmet. Open-face helmets, which are used frequently in autocross events, are not allowed in wheel-to-wheel road racing with NASA. Knowledge is power — read your rule book!

All SA 2015 helmets are equipped with anchors for HANS-style head and neck restraint devices, which means it is no longer an issue that has to be decided by the customer, your helmet will come with those anchor positions already. New Snell standard helmets won’t be out until around October of 2020 with an SA 2020 rating which will provide even more advances in driver safety. Make sure the helmet you buy is right for what you need. When your car is rolling upside down at 100 miles an hour, that is no time to think to yourself, “Darn, I should have bought a better helmet.”

Good luck with your helmet shopping experience and keep the shiny side up!

 

 

 

 

 

 

 

 

 

 

 

You’ve more than likely heard the terms open deck, semi-closed deck (semi-open), and closed deck before. But, do you know how to identify which design your block uses or why an open-deck that works well for a naturally aspirated build won’t likely last very long if it’s boosted or has nitrous? Which design your engine has will play a major role in the maximum peak cylinder pressure your block can handle, which can be simply translated to maximum power.

Peak cylinder pressure is much greater at the top the of the cylinder, where the combustion event happens. This is in addition to any secondary pressure sources the cylinder might be exposed to, such as forced induction, nitrous, and detonation. Naturally, this is the location that most failures happen, the more pressure you introduce into the cylinder, the more likely the cylinder wall is to bubble, crack, or fail entirely.

The video above, posted by time attack team Jager Racing and featuring Outfront Motorsports, presents the advantages of using a closed deck block on their time attack Subaru WRX STI. The video focuses specifically on the EJ25 motor, but the advantages can be generalized.

Open Deck

An open deck is one of the most common designs found in lower horsepower aluminum blocks. It is the easiest to manufacture and provides the overall best cooling efficiency, due to the coolants ability to make full contact with the surface area of the upper portion of the cylinder. Some will argue that this block has the benefit of weighing less than its two siblings because less material is used, but this weight difference is marginal for most blocks.

The downside to an open deck is that it provides the least amount of structural support at the top of the cylinder walls, where they need it most. This reason alone makes an open deck block the least reliable choice for almost any type of forced induction or nitrous application, and should be left to low compression, naturally aspirated engines and low boost platforms.

Semi-Closed Deck

A semi-closed deck is the most common design found in modern factory turbocharged aluminum blocks, and is stronger than an open deck by adding structural support to the top of the cylinders at four points. Using modern casting techniques, this design can handle respectable boost levels into the mid 30 PSI range and a much higher peak cylinder pressure than an open deck (depending on the application).

Because of the added material around the cylinder walls, this style is more difficult to manufacture and requires more machine work before the cylinders can be installed. Some will argue that the added support joints of a semi-closed deck reduces cooling efficiency and is more prone to cylinder hot spots by limiting the surface area for the coolant to contact. At higher horsepower levels, a semi-closed deck is still prone to failure at the points in between the supporting joints, especially in endurance racing or road racing applications where sustained high temperatures are common.

The most common solution for semi-closed and open deck blocks is installing aftermarket sleeves that can support higher cylinder temps and pressure. This process is pretty expensive, but it is highly recommended that you find a reputable machine shop that has experience with your platform. Sleeving requires a lot of precise machine work to not damage the block, so only the best in your area should be trusted.

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Left: A factory 3.5-liter EcoBoost engine prior to being machined for aftermarket sleeves. Right: A sleeved 3.5-liter EcoBoost engine.

Closed Deck

A closed deck design is generally left to iron blocks and aluminum racing engines. It is the perfect design for fully built, high compression, high revving race engines that require the highest level of structural support available. Common on high level drag race motors, this design is also able to withstand prolonged periods of high heat and cylinder pressure commonly seen in endurance racing and road racing.

A closed deck block is much more expensive and requires an entirely different casting procedure if done from the manufacturer, but can also be modified using pieces that are press fit into position around the water jackets. The latter process requires a custom head gasket, along with precise calculations and machine work to verify that the pieces fit properly and that the water ports are drilled properly to provide adequate flow to efficiently cool the heads.

Many will also note that a closed deck block provides the least amount of cooling capability out of the three. Although this is true to an extent, many of todays closed deck blocks have been put through extensive testing and are designed to guarantee efficient cooling.

Conclusion

Depending on the goals for your build, you may need to sleeve your block or upgrade to a closed deck design. Most modern semi-closed deck blocks can handle very respectable power levels before needing to be sleeved or upgraded, and open deck blocks can handle just about anything you throw at it in naturally aspirated form. But, if you are building a race engine and want the ultimate reliability out of your block, your best option is a closed deck design or aftermarket sleeves (depending on the application and your budget).

If we had to choose one operation that epitomizes the process of engine blueprinting – we can’t think of a better one than setting bearing clearance. This goes far beyond slapping a set of new bearings in the main saddles, torquing the main caps in place, and hoping the crank turns over. Blueprinting clearance means establishing a clearance that is your target number and working the components until this number is achieved. Anything else is just bolting an engine together.

We won’t get into establishing specific clearance goals here because that has been previously covered by EngineLabs. We can offer the standard advice that is tried and true – multiply the crank journal diameter by 0.001-inch. As an example with a small-block Chevy main journal of 2.200-inch – then an oil clearance of 0.0022-inch would be a great place to start.

This discussion will focus on main and rod bearings in a mild, street-driven performance engine that might see occasional high-RPM use, like at the drag strip. Perhaps the first bit of information worth mentioning is that this is the total clearance around the circumference of the bearing. So in the case of a 2.500-inch main bearing with a vertical clearance of 0.0025-inch, this establishes there is only 0.00125-inch clearance between the crank journal and the main bearing at the top and bottom. Under maximum load, the oil is squeezed into a very tiny area of clearance measured with five digits to the right of the decimal point–perhaps as tight as 0.00025-inch. The remainder of the clearance is found on the unloaded side–the top side of the main bearing or the bottom side of a rod bearing.

The large amount of bearing clearance on the opposite side of the load is used to feed oil between the journal and the bearing, which is why producing sufficient clearance is so important. It is this dynamic loading of the bearings that reinforces why attention to detail is so important. There are other considerations such as bearing crush, eccentricity, and bearing materials that demand close scrutiny, but we will focus on how a DIY builder can create professional results by using high-quality measuring tools and working carefully.

We will make some very important assumptions that the block and crankshaft have either been machined or carefully measured to ensure they are straight, with minimal taper, so that our measurements will pay off with a happy engine when assembled.

The first order of business is to measure the crankshaft. We will need a quality outside micrometer, a notebook to record the readings, and a clear, clean work bench. The crank should be clean and ready for assembly. Assuming we’re working with a V8 engine, it’s important to measure the main journals in two locations and record both. If you are really fastidious, it’s a great idea to measure for taper across the journal as well.

Once a journal diameter is established, there are two ways to go about setting up your dial indicator to measure the inside diameter of the bearing housing.

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With the micrometer at a specific journal diameter, use this to zero the dial bore gauge (left). We placed our mic in a bench vise to hold it firmly, protected by a thick rag. Setting the dial bore to zero requires attention-to-detail to make sure the zero is accurate. If you induce an error at this stage, every other measurement will be in error. Next, use the dial bore gauge to measure the inside diameter of the housing bore, in this case, the number two main journal that has been torqued (right). For maximum accuracy, measure bearing clearance only in the vertical. Also check for taper in the rod. We had a poorly resized used rod that had 0.0015-inch taper. This is caused when the rods are not switched on the mandrel and only honed from one side. This creates a taper or bell-mouth in the rod big end. So always check for taper on rebuilt rods.

One way is to set the outside micrometer to a specific journal diameter. Let’s use a 454ci big-block Chevy as an example. With a 0.010-inch-under crankshaft, we measured the number three journal at 2.7387-inch. This is exactly 0.010-inch undersize. We can set the dial bore gauge to read zero at this point and then install and measure the inside diameter of the bearings in the number three main.

The second procedure saves time but could introduce a math error. This process measures all the journals. Then the builder sets the dial bore gauge to one journal size and performs the math to adjust the clearance from the dial bore gauge for the different housing bore diameters. As an example, if we set the dial bore gauge to the 2.7387-inch diameter of journal three, then we would add or subtract the difference of varying sizes of the journals to produce the actual bearing clearance. If the journal is larger than our standard by 0.0002-inch, then we would subtract 0.0002 from the dial bore gauge reading for clearance for that main bearing.

As an example, if we installed 0.010-under bearings and measured the clearances and all was right with the world, the dial bore gauge should read +0.0025-inch (our desired clearance) for all five main journals. But this only happens on TV car shows and magazine engine articles. In a big-block that we recently assembled for a friend, the crank main journals measured as follows:

Main Journal	Journal Diameter	Actual Undersize
1	2.7393	0.0094
2	2.7390	0.0097
3	2.7387	0.0100
4	2.7384	0.0103
5	2.7383	0.0104

None of the crank main journals measured the same and only number three was the technically correct 0.010-inch undersize. Budget and time limitations prevented us from grinding this crank 0.020-under. Instead, we had to deal with this and use multiple size bearing shells to bring the clearances as close as possible.

Let’s first address the clearances for the 0.010-under number three. Measuring the actual clearance using 0.010-under Federal-Mogul bearings, we came up with 0.0027-inch. This was slightly more than our ideal 0.0025 spec but acceptable. The other four created either too much or too little clearance using just 0.010-under bearings.

Some performance bearing companies like Federal-Mogul offer optional bearing sizes such as 0.001 undersize or oversize inserts that make it much easier to set an ideal clearance. In our case, we needed 0.011-inch undersized on some of the journals and 0.009-inch-undersized bearings for the front two. Federal-Mogul offers these and saved our bacon. This allowed us to increase or decrease the clearances to get closer to our ideal. While mixing half-shells is acceptable practice, never mix shells with more than 0.001-inch spread and always stay within the same manufacturer. In other words, never mix a 0.009 bearing shell with an 0.011-inch version.

One down side to performing all these customized clearances is that we were faced with purchasing two (and in our case, three) sets of main bearings for one engine. So do all measuring before you buy the bearings. The same is true with rod bearings.

The best way to fix this would have been to have the engine align honed to establish the proper housing bore diameter. In our case, the engine had to go back together due to deadlines beyond our control so we did the best we could. The final 0.0035-inch clearance is well within factory tolerances, but it is also 0.0005 inch wider than we would prefer. For a mild street motor, this was acceptable. Another reason this will work is that as the thrust bearing, this additional clearance will provide more than enough oil to properly lube the bearing’s thrust surfaces.

It’s also important to point out that housing bore diameter, whether it be the rods or mains, have a big effect on bearing clearance. Incorrect clearances are commonly blamed on the bearings when the reality is the housing bores are improperly sized. When combined with inconsistent crank journal diameters, this tolerance stack-up is the real culprit in nearly all clearance issues. Measuring these parts is the only way to know for sure.

At some point in the Blueprinting series, we will also look at the accuracy of the measurement tools you are using. If your measuring devices are not accurate to at least 0.0002-inch, the actual numbers may not be an accurate reflection of what is really there.

It’s also important to point out that bearing clearance will dictate engine oil viscosity. We will have to over-generalize here, but tighter clearances demand thinner oil while wider clearances will need a higher viscosity oil to establish the proper oil-film thickness to prevent abnormal wear.

Most of the details in this story relate to employing common sense and accurate measurement techniques. Accomplish both of those tasks and your engine will live a long and powerful life.

We are all guilty of installing a flashy part on our hot rod or engine that doesn’t add any power, but we’re convinced the system “runs better” with it installed. Now imagine installing a part that doesn’t directly build power, but its interaction with the engine’s rotating assembly can release power that may have otherwise been wasted energy in the form of vibration, or maybe the part just reduces premature wear on bearings and associated components. This part–the harmonic damper–already exists on every street-driven engine, and is often overlooked as just a mounting point for accessory pulleys or a location for attaching weights for externally balanced engines. The harmonic damper presents a crucial opportunity to optimize your rotating assembly to insure longer life or to free up wasted energy that could be better applied to the tires.

So is it a balancer, or is it a damper? The two terms are used interchangeably, but technically they have different functions. A balancer adds weight to help (externally) balance the lower rotating assembly of an engine, while a damper, quells the vibrations during crankshaft vibration which occur as a function of the combustion process. Keep in mind, while all harmonic balancers are dampers, all dampers are not balancers. Yet for purposes of bench racing, both terms are often used to mean the same part.

                                      
                                       Keeping It Basic

During the combustion process, each piston is forced to move down the cylinder as a result of an explosion contained within the combustion chamber. This stroke imparts a sudden rotational force to the crankshaft. Even though it is a very stout component, a crankshaft is not perfectly rigid. So during these combustion events, the crank will twist slightly in response to each explosion/impact.

This crank twist is analogous to a simple torsion bar with a lever arm at one end. Now assume you hit that lever arm with a hammer. You can imagine there will be some slight twist when you first hit the lever arm, but that would be followed by the arm springing back into place, maybe even vibrating for a short time before coming to rest.

In this example, we have torsional twist followed by torsional vibration (during the spring back event). Torsional twist is a function of part length (inline engines will have a longer crankshaft than V-configurations) and thickness, material shear modulus (think: material stiffness), and Torque (force from combustion x crank throw). Similarly, torsional vibration is a function of part length, torsional stiffness, and polar moment of inertia (think: object’s ability to resist torsion). For a detailed explanation of these phenomena, review Himmelstein’s Technical Memo #8150.

What’s the problem?

Torsional vibration has side effects that are rarely desirable. Because force is transmitted into a crankshaft at discrete points in its rotation (example: every 90 degrees of rotation in a V8 application), the output torque is not continuous, thus creating pulses and torsional vibrations. In the event that these pulses occur around the resonance frequency of a crankshaft, the effects can be multiplied. When this occurs, risk of component failure (broken crank) increases as well as the chance of premature wear of bearings. In some cases those vibrations can be transmitted to other points in the powertrain such as the valvetrain (via timing chain) or down the driveline towards the tires. Either direction isn’t desirable as it can rob power in addition to potentially killing parts.

Technology Options

While a few methods to damping have been invented, the vast majority of automotive OEM and aftermarket companies point towards two solutions for controlling detrimental torsional vibration; elastomeric and viscous damping.

The method for elastomeric harmonic damper construction tends to make them the most cost-effective as an OEM replacement or upgrade. Romac Performance Products specializes in elastomeric harmonic dampers and builds products for mild to full race applications. Construction is rather simple, and consists of four parts: a hub, elastomeric band, outer inertia ring, and snap ring. The hub is constructed to fit over the front of the crankshaft snout with a keyway. The hub will usually have a bolt pattern built into the front face which allows for attachment of accessory pulleys. The backside of the hub may have a cavity built for attaching weights to externally balance the rotating assembly. Applied around the hub is the elastomeric band which is constructed of a rubber polymer. Polymer durometer (hardness) gives Romac the ability to add or subtract damping ability, tune for engine frequency, and long term durability.

Fit to the outside diameter of the elastomer band is the outer inertia ring. This outer inertia ring functions as a small flywheel that wants to remain at constant speed despite the acceleration and deceleration pulses that the crankshaft is experiencing. The elastomeric band between the hub and outer ring allows the outer ring to move slightly independently (or at a more constant speed), while the inner hub runs slightly faster and slower in response to torque pulses. A snap ring is inserted inside of the outer inertia ring in order to keep the band and inertia ring in their respective places.

During operation, the band transmits only part of the vibrational forces from the hub to outer ring, while also converting some of that vibrational energy to heat which is dumped to atmosphere. Romac takes great pride in the fact that all of their harmonic dampers are hand assembled, giving technicians that ability to inspect each assembly for best results.

A good example of viscous harmonic dampers are those offered by Fluidampr. Speaking with Brian Lebarron at Fluidampr, he describes a viscous harmonic damper as “contain[ing] a free rotating inner inertia ring that shears through a thin layer of proprietary silicone. As it shears, destructive vibration is transformed to heat. Heat then radiates through the outer housing to atmosphere.” More simply; the viscous damper includes an outer housing, an inner inertia ring (think free-rotating ring inside the housing), and the housing is filled with a THICK silicone fluid which fills in the gaps between the housing and ring.

Under constant smooth torque applications, the housing and ring spin together. When torque pulses are introduced, the ring wants to continue spinning at a constant speed while the housing is in a constant state of acceleration and deceleration.

The housing and ring speed differences apply a shear force against the silicone fluid between them. The silicone absorbs that shear force in the form of heat which is dumped to atmosphere.

From an OEM perspective, an elastomeric damper covers the vast majority of engines being produced today. The primary reason for this choice is cost of manufacturing as the elastomeric option tends to be constructed of parts which have lower tolerances as well as utilizing raw materials which are more common and don’t demand a premium price. Viscous dampers are often utilized by OEMs in high performance and luxury applications.

Do I Really Need One?

For those familiar with sprint car engines, they know that most sprint competitors don’t utilize a damper at all. Similarly, a minority of drag racers have opted out of a damper with the theory that less rotating mass allows the engine to increase RPM quicker. We’ll keep this discussion at a high level and just point out that sprint and drag engines aren’t intended to see many miles. Careful component selection can help mitigate some overall vibration and ultimate component failures, but the benefits of a damper are undeniable for anybody looking for more than a few quarter-mile passes or a Saturday night main.

Selecting a Damper

Consider the following topics when choosing your next damper:

• Application
  • Daily Driver to Full Race?
    • If a Daily Driver, will stock replacement suffice? Consideration should be given regarding avoiding the previous failure mode.
    • If Performance or Full Race, what type of driving or racing (sprint/endurance)? What types of RPM will the engine see?
  • Function over fashion
    • Always prioritize function. After all, what good is fashion if the chosen damper leads to engine failure? After functional needs are met, feel free to throw all the chrome plating and anodizing as is appropriate.
    • Does the engine need crank pulleys or external balance weights? Will the crank pulleys be attached to the damper body or should they be an integral part of the harmonic damper?
  • Diameter
    • This topic may fall under both Application and Function, but make sure to choose a diameter that meets both functional needs AND will actually fit within the space allotted.
  • SFI or not?
    • If any type of racing or performance is under consideration, an SFI-approved harmonic damper should be a requirement. Many sanctioning bodies will require an SFI 18.1-approved damper. If not, consider what it would be like if a 6-8 pound metal disc came off the front of the engine at high RPM…yeah, don’t skimp here. To understand more about what it takes to comply with SFI 18.1 guidelines refer to SFI -Crankshaft Hub Harmonic Dampers.
  • Budget
    • If you’re rebuilding a daily driver’s engine, that $89 damper from the parts store may be all you need. But if any added performance is your goal, expect to pay according to your intended RPM and speed ranges. That $89 harmonic damper likely will not provide much protection if you’re spinning your engine to 7,000-plus rpm, or hanging a big supercharger on it and doubling or tripling its output. The old saying of “you get what you pay for” is definitely in effect when it comes to harmonic dampers.

In Conclusion

There is a wide variety of choices on the market when it comes to harmonic dampers; from elastomeric to fluid-based, and each one has its place. The ultimate selection is up to you, and your engine will thank you for taking its health into account during the build process.

You don’t need us to tell you that turbochargers are hot. The word on the street is as enticing as it is simplistic. Just stick a turbo on it and you’ll make ridiculous horsepower. We once asked the guru of engine power, Kenny Duttweiler, “How much power can we make with a turbo on a 6.0-liter LS?” His answer was succinct: “How much do you want to make?” That meant that four digit power numbers are achievable. However, in the vein of full disclosure, this won’t be an easy, bolt-on, walk in the park process. If you are motivated, it’s well worth the effort.

We latched on to the learned souls at Garrett Honeywell, who can trace their turbocharger lineage all the way back to 1936; it’s quite obvious they know a little bit about turbochargers. Our story starts with someone who had already taken a stab at adding a turbo to a 6.0-liter LS engine for a street car. Several years ago, Justin Nall decided that a single turbo pushing air into a used, iron 6.0L truck engine seemed like a good idea.

His machine is a choice, Lemonwood yellow ’66 Chevelle with a 4L80E automatic, a decent PTC converter with 3,400 stall, and a 12-bolt rearend filled with a 3.31:1 ring-and-pinion. The car is not particularly light at 3,850 pounds. The engine sports 364 cubic-inches, with a Comp camshaft measuring  .598-inch of lift on the intake and .591-inch of lift on the exhaust, with 234 and 230 degrees of duration at 0.050-inch, respectively. Other components include: Wiseco 10.4:1 pistons, a set of CNC-ported production 243 heads, an Edelbrock Pro Flo intake, and a stock truck throttle body. Overall, the combination is fairly mild. Nall lives in Minnesota, so he puts plenty of miles on his hot rod during the summer months.

At the Summer Nationals event at the state fairgrounds in nearby St. Paul, he also has run the car on the chassis dyno. His initial turbo package was intended as a conservative choice to dip his toes in the turbo waters. Lately he’s decided to up the game with more horsepower, so we thought this would be an excellent way to blaze a trail toward a more aggressive turbocharger. The Chevelle was previously capable of over 650 rwhp, and his goal was to push this to 900 flywheel horsepower; that puts wheel power around 800 to the rear tires. His fuel of choice is E85, because it offers roughly 105 octane, and the engine really loves how the fuel cools the hot compressed air exiting the turbo.

We accessed Garrett’s website, and discovered a wealth of technical information that is divided into areas depending upon your technical level of understanding. If you are just getting into this, then the Basic area will deliver important foundation work for you to understand the concepts. The website also offers intermediate and advanced areas as well, so you can jump right into the area where you are most comfortable.

If you don’t want to run through the math, Garrett also offers its Boost Adviser, which makes the selection process a bit easier. But it’s still a good idea to read this story, because along the way we will explain what all the terms mean and how they are used to help choose a turbo. Many of the details we will discuss here are based on knowing your way around a compressor map. If you’re not familiar with what this is, it’s important to do a little homework by reading all about this on Garrett’s website. But we’ll hit the highlights for you here.

The Important Terminology

A compressor map is a basic X-Y coordinate graph, yet it offers a tremendous amount of important information. The horizontal (X) axis of the map is expressed in airflow in pounds per minute (lbs/min). This is the amount of mass airflow the turbocharger can move. Obviously, the larger the compressor housing of the turbo, the more air it can move. There’s a simple trick that everyone uses when reading the airflow portion of this map. The pounds per minute of air increases moving left to right. If you multiply the lbs/min number x 10, that will roughly represent the amount of horsepower that airflow can deliver. So for our goal of 900 hp, this would be represented by 90 lbs/min of air.

The vertical (Y) scale is expressed as a pressure ratio. This isn’t just that number times sea level air pressure (14.7 psia), but it’s very close. One way to explain this is the pressure ratio is derived as the pressure expressed on your boost gauge divided by the ambient air pressure. If we saw 44.1 psig on our boost gauge and this occurred at sea level with an ambient air pressure of 14.7 psia then dividing 44.1 by 14.7 would equal a pressure ratio of 3.0.

Note that we expressed the above ambient air pressure as 14.7:1 psia. The “a” in psia means absolute pressure. The “g” in psig means pressure as read on a gauge. A typical boost gauge represents ambient air pressure as 0, which is why we have to label the pressure we are talking about. In absolute terms, 44.1 psig is 58.8 psia in absolute pressure (14.7 + 44.1 = 58.8). This will become important once we start wading through the formulas. But don’t worry – it’s not that difficult.

So for Justin Nall’s Chevelle, we’re looking to size a turbo with Garrett that will deliver around 900 flywheel hp. To determine how much airflow we will need, Garrett recommends starting by calculating the actual mass airflow. This will reinforce what we just did with the short-cut but it’s worth running through the numbers.

Air Flow Required

The initial mass airflow calculation uses several variables that we need to know. The first is our estimated horsepower, which is 900. Then it asks for the projected air-fuel ratio and the brake specific fuel consumption (BSFC) number. The BSFC number represents the pounds of fuel consumed per horsepower per hour (lbs/hp/hr). A good, late model naturally-aspirated engine on gasoline will use around 0.45 lbs/hp/hr of fuel. As the number becomes smaller, that means the engine is more efficient and uses less fuel to make the same amount of power.

Because Nall is using E85, which is 85-percent ethanol, this fuel has a lower specific heat content which means we must burn more fuel to make the same amount of power compared to gasoline. So for E85, the BSFC number we will use is a 0.60 number. This means we’re using roughly one-third more fuel to make the same horsepower. This sounds terrible—and it is, if we were in a fuel economy race. But since Nall is focused on making horsepower, this isn’t all that bad. Plus, with a turbocharger, we must add additional fuel to make sure the engine does not experience a lean air/fuel ratio that could damage parts. So add all that up and a BSFC number of 0.60 will work for this application. If we were planning on using a high-octane gasoline, a BSFC of 0.55 would be better.

This calculated number is what we will use to reference mass airflow on the compressor map. Since we’re only using one turbocharger, our goal will require a rather large compressor to move all this air. If we were going with a twin-turbo package, then this number would be divided by two.

AirFlow Requirement (Wa):

Manifold Pressure Required

Now that we have our lbs/min airflow requirement, we can move to Garrett’s next step, which is to calculate the Manifold Absolute Pressure requirement. This is possibly the most complex part of this entire selection process, so we’ll take it nice and easy here. The variables we will need to put into the equation include the displacement in cubic inches (364ci), the maximum engine speed in RPM (6,500), the engine’s volumetric efficiency (VE) that we’ll discuss in a moment, and the intake manifold inlet air temperature in degrees Fahrenheit (150°F).

The proposed inlet air temperature is high, since we’re going to calculate this assuming we’re not running an intercooler. Big power numbers with high boost often demand an intercooler, but to keep things simple, we’re going to assume that the E85 will help cool the incoming air, so we’re going with the 150°F number. If we lowered this inlet air temperature, this would lower the calculated boost pressure required, so in a way, we are being conservative.

Volumetric Efficiency (VE) also demands some explanation. This is a number that we will use to determine the capture ratio of the air flowing through the engine. Because of mechanical inefficiencies, a basic street engine is not going to be 100-percent efficient in using all the air that flows past the throttle body. We’re going to put the VE number at 88-percent – which means we’re not going to capture that last 12-percent of air.

As an example, if we have a cylinder that was completely filled, it could capture 10 lbs/min of air, but the reality is it will only be able to retain 8.8 lbs/min. This has a direct bearing on how much power we can make, so a smaller number will be more conservative, while a larger number decreases the amount of air we need to make the same power.

The temperature required for the calculation will use Kelvin, which is absolute temperature, so to convert from degrees Kelvin to degrees Fahrenheit, we have to add 150 to the Kelvin standard of 460. Plus we are also going to use a gas constant (which is 639.6) to make the equation work. Don’t ask why this is important – that’s another story entirely.

The manifold pressure required will be represented by the abbreviation MAPreq and the equation looks like this:

The result is expressed as absolute pressure (psia). Justin Nall lives in Minnesota, where we found an average atmospheric pressure number for his area of 28.92 inches of mercury which equates to 14.46 psia. Standard sea level pressure (for comparison) is 29.92 inches of mercury. So if we take our calculated 40.48 psia and subtract the ambient air pressure of 14.46, this will give us 26 psig—or the reading we will see on the boost gauge. This would be the theoretical maximum boost required to make 900 hp.

Compressor Discharge

This next step is to calculate the amount of pressure loss that the system will experience between the discharge side of the compressor and the intake manifold inlet. If we were using an intercooler, we would need to know how much pressure would be lost pushing the boosted air through the cooler. But since we are assuming no intercooler here, we can use a basic 1 psi loss of pressure between the compressor outlet and the intake manifold inlet. It’s called P2c because it’s the pressure of the outlet.

The formula looks like this:

P2C Compressor Discharge

• P2c= MAPreq + pressure loss between turbo and intake manifold
• Compressor Discharge Pressure Drop = MAPreq + Delta P loss

Assuming a 1 psi loss:

• P2c = 40.48 + 1 psi
• P2c = 41.48 psia

Compressor Inlet Pressure

Engineers who design turbochargers have to account for all pressure loses which also includes the amount of pressure loss we might experience between the inlet air filter and plumbing that is used on the inlet side of the turbocharger. For this discussion we will assume a 1 psi loss or drop between the ambient air pressure and the actual compressor inlet. Because it’s the first pressure on the inlet side, Garrett calls it “P1c.”

The formula is below:

P1c Compressor Inlet Pressure

• P1c = Ambient Pressure minus (–) Loss Due to Inlet Restriction
• P1c = 14.46 – 1 psi = 13.46 psia

Calculate Pressure Ratio

If you remember earlier in this story, we looked at compressor maps and how the vertical scale is expressed in Pressure Ratio. That’s what we will calculate next. This is actually fairly simple because all we’re doing is dividing the discharge pressure by the inlet air pressure. This will be the pressure ratio that we will plug into our compressor map.

The formula looks like this:

Calculate Pressure Ratio

• P2c / P1c
• 41.48 / 13.46 = 3.08 Pressure Ratio

We now have all the data required to plug into a typical compressor map. Unlike the classic pirate movie where X marks the spot of where to dig for the treasure, there are literally several compressor maps that would appear to work with the numbers that we’ve generated.

The main inputs again are our 108 lbs/min of air required along with a pressure ratio of 3.08. But keep in mind that these are the peak numbers. There are other factors that will have an effect on how the turbocharger operates within the system.
Justin’s experience has shown him that among the more important variables is exhaust backpressure. All turbos generate backpressure and this is especially true with turbos for the street where the exhaust housing is generally sized smaller to help the turbo spool quicker.

This relates to what is called the A/R ratio that relates to the size of the exhaust housing. Larger A/R housings reduce backpressure but also tend to spool slower. According to Garrett, A/R (Area/Radius) describes a geometric characteristic of all compressor and turbine housings. Technically, it is defined as: the inlet (or, for compressor housings, the discharge) cross-sectional area divided by the radius from the turbo centerline to the centroid of that area.

After we produced our numbers, we searched through quite a few turbochargers and selected a turbo that we thought would work – a GTX4508. We shared our numbers with the Garrett engineers and they matched a GTX4294R and a GTX4202R to our application. The engineers said the numbers place the turbo selection somewhere between these three turbos. Garrett’s selection is a more conservative choice than our estimate for the Chevelle and much of this could be considered a compromise between ultimate power and decent manners on the street. Garrett’s recommendation is based on much more direct experience and therefore carries significantly more weight.

The 4202R employs a 76mm inducer and a 102 mm exducer sizes while the larger GTX4508R is sized up with an 80mm inducer and 106mm exducer. The larger wheel means it will spin up slightly slower.

In comparing the GTX4202R to the GTX4508, the more aggressive 4508 moves more air, which moves the chart more to the right. This will make more peak power but likely will not come up on boost as quickly, all else being the same. We don’t have the space here to get into how altering the turbine section might be able to help that, but this also means likely changes in backpressure as well.

In Conclusion

As you can surmise, there’s more than a bit of effort involved with choosing a turbo and there are many other variables that we have not discussed. Hopefully this exercise in turbo matching has helped take some of the mystery out of homing in on the right turbocharger. You might want to run through more than one scenario just to get comfortable with the numbers. Have fun with it and see how changing the numbers has an effect on these boost devices. You can also use the Garrett Boost Adviser program to generate the calculations so you don’t have to slog through all the math. Boost Adviser will ask a few questions and then provide some turbocharger matches based on your input. You can also take the calculations and compare points on the compressor maps to find the selection that suits your application.

All this may appear intimidating at first, but as you work with it and as you learn more about how turbochargers work, more of it will make sense. All these calculations are intended to remove the black magic from choosing a turbocharger.

Let’s create a scenario that could cause any car enthusiast to break out in a cold sweat. You are sitting in your ride at a crowded intersection and your foot is firmly holding the clutch pedal to the floor. When the light turns green, you plan to annihilate the rear tires on your car. You know your car can do it, you’ve got enough horsepower to immediately turn your tires into asphalt crayons. When the light does turn green, you slide your left foot off of the clutch pedal and smash the throttle. But for some reason, something doesn’t seem right. You see smoke billowing from under your car, but the smell is different. It doesn’t smell like tire smoke. At that moment, you see a guy taking video of you smoking your car’s stock clutch instead of the tires. You, my friend, are about to go viral on YouTube as an epic fail.

While the OE clutch in your car worked great when your car was all OE, upgrades tend to put more stress on parts — some of us learn that the hard way, but I digress. Replacing the clutch with another OE unit will probably heed the same results, so it’s time to step up. But, stepping up requires a little knowledge about choosing the right parts.

How do you know what you need if you don’t know what’s available? That’s where we come in. We spoke with clutch professionals from Spec, Mantic, and Quarter Master, to get some insight into different clutch materials and designs, and to find out how you can properly choose the system that is perfect for your car.

When it comes to deciding on a clutch, there are many options available that will technically fit behind your engine, but do you know what parts are the right choice for your application?

Jeff Neal at Quarter Master told us, “The right clutch choice depends on the usage the clutch will see. Our Pro Series is robust, and has a high-torque capacity which is great for road racing.” He continued with, “Our V-Drive clutch is great for those on a tight budget, and is great for short track, road, and rally racing. Then we have our Optimum series clutches, which are designed for high horsepower racing applications.”

When we asked Geoff Gerko of Mantic Clutch, he recommended their organic disc clutch for daily driver cars that see only occasional passes down the dragstrip. If looking for a clutch that is at home on the street or the race track, Geoff says, “Our Sprung Hub, Cushioned Ceremetalic clutch features smooth operation, great drivability, and increased torque capacity containment. This is our most versatile and popular clutch material for the average enthusiast.” Geoff continued, “Our Solid Hub Ceremetalic also features smooth operation, but is best suited for use in purpose-built cars that see frequent track days or consistent bracket racing.”

Last but not least, Shelly Norton of Spec Clutch told us, “Generally speaking, all of our units are built to survive abuse when used within their specified torque ratings. Most of our “staged” clutches are also classified as multipurpose.” Shelly continues, “Our Stage I through Stage III kits are considered street-friendly, but can still be used for many types of racing. Our Stage IV is good for road racing, drag racing, and drifting; and our Stage V is primarily a drag race unit.”

Friction Materials

As the performance of your car increases, so should the characteristics and durability of the material used to make your clutch disc. The following is a brief synopsis of clutch materials available, and when each should be employed. When it comes to a clutch material for racing, Neal says, “We typically recommend a sintered-metallic (bronze) material. This has a very high coefficient of friction with manageable driving characteristics. For street-performance clutches, we offer organic (rag type) materials for a more street-friendly driving experience that delivers race-type friction capability.”

Organically Speaking

Organic material is primarily used to make stock-style clutch discs. Organic material is acceptable for normal driving conditions and usage, but as operating temperatures rise, or you place the clutch under heavy loads (which is usually accompanied by slippage), the clamping ability will fade because the coefficient of friction drops off. In addition, at high RPM and/or when the disc gets hot, they tend to fail structurally.

Bullet Proof

The use of Kevlar material offers a much higher coefficient of friction than organic material, but with some loss in drivability (i.e. it gets grabby when releasing the pedal). This occurs, because, as the coefficient of friction goes up in the disc material, so will the aggressiveness of the material when the clutch is engaged. This usually results in clutch “chatter.” Since Kevlar is compatible with stock flywheels and pressure plates, it makes a good upgrade choice, but using it takes some getting used to in regards to driveability.

Aggressive Grabber

Bronze-metallic materials are the most aggressive materials in regards to clutch friction. Since it is very aggressive, it offers an extended life over Kevlar and organic materials. According to Gerko, “Our Ceremetalic material is our friction material of choice. It engages smoothly, wears well, tolerates the heat, and has a consistent coefficient of friction. This enables us to create clutch kits that accomplish everything for our customers.”

By reducing static pedal pressures, usage of metallic materials can result in a quick and clean clutch engagement. Since metallic materials are the most aggressive materials available, it will also wear the flywheel and pressure plate surfaces much faster. Therefore, they should only be used with a steel or nodular-iron pressure plate and flywheel. If used on the street, this material will cause chatter when the clutch is being engaged.

Iron Age

Sintered iron is an optimal choice for street use, as it has a greater ability to withstand slippage and not lose its friction coefficient. Sintered iron is also preferable for high-horsepower applications and drag racing. When it comes to choosing the clutch material for your car, Norton explains, “We actually have particular materials for particular setups. For instance, we do not have one, two, or even three preferred materials. However, our Stage II-Plus carbon/Kevlar hybrid materials and our Stage III-Plus materials are the most recommended in high-horsepower environments. Likewise, our organic and pure Kevlar materials are the most recommended for mild-power applications.”

Checking On Twins

Not only do you have to choose what material your clutch disc is comprised of, but you also need to decide if you need one, two, or more discs. Clutches are generally rated by their torque-holding capacity. A single-disc clutch will inherently have less holding capacity than a twin disc when based solely on their surface area. According to Norton, “We recommend installing a multi-disc unit when using a single-disc clutch is insufficient. If the clutch works but experiences significantly-reduced wear life, it is insufficient. There are also cases where a single-disc might seem sufficient, but the overall setup can benefit from a smaller-diameter, multi-disc unit to deliver better shifting capabilities or a lower inertia flywheel package for significant rate of RPM and horsepower gains.”

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A multi-disc clutch will inherently have more holding capacity than a single-disc clutch based solely on their surface areas.

Twin-disc clutches are designed to have a lower inertia, but will have higher torque-holding capabilities since they spread the load across more surface area. Twin-disc clutches also tend to be noisier in comparison to their single-disc counterparts. This is because there are more plates and separator discs in the package. Gerko tells us, “The main goal of a multi-disc clutch is to increase clutch surface area without substantially increasing pedal effort.”

A good rule of thumb is that a single-disc clutch is a good all-around performance clutch to use with a stock or mildly-modified engine. Depending on the clutch material used, it will have OE-like engagement and shifting qualities. Twin discs are designed to handle a lot more torque than a stock or aftermarket single disc, and therefore are a better fit in higher horsepower applications. To make the right choice, you will need to know the torque capability of your engine, and consult the clutch manufacturer.

Weighted Rotation

When talking clutches, you have to factor in the flywheel. The flywheel not only has the teeth for starter engagement, it is also an energy-storing device. A heavy flywheel causes the engine’s RPM to climb at a slower rate than a lighter (aluminum) flywheel, but since it also stores more energy because of its mass, the engine’s RPM will not drop as dramatically (like between shifts) as if using an aluminum flywheel.

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A few things to remember: A steel flywheel is heavier and will help the engine retain RPM when shifting. An aluminum flywheel is lighter, and when used, the engine will not have as much rotating mass and will lose RPM much faster when shifting,

Also, a lighter flywheel will allow the engine to spin quicker, but a more dramatic drop in RPM will be noticed (like between shifts), and the lighter weight could also cause an issue if using your car for daily transportation. This is because the lower inertial mass of the lighter flywheel means the car will be harder to get moving from a stop sign or traffic light. Aluminum flywheels are generally used in road or drag race applications where the engine is continually kept at a higher RPM.

Under Pressure

The pressure plate of your clutch system is what applies the clamping force that squeezes the clutch disc against the flywheel. But just like with the flywheel and clutch disc, you have a choice to make. For this article, we’ll focus on the three main types of pressure plates: the long style, the Borg and Beck, and the diaphragm. According to Gerko, “The diaphragm-spring clutch really is a superior design, because the clutch can be designed to steadily increase its clamping load as the disc(s) wear. This is tremendously beneficial in multi-disc applications. It helps the customer get the maximum performance from the clutch before it needs replaced.”

The long-style pressure plate is identified by the three thin fingers that contact the throw out bearing. The long-style pressure plate is typically used in drag race applications, and will deliver a considerably-hard pedal feel. The Borg and Beck style is similar to the long style in that it functions via three fingers, but the difference is it has wider fingers that release plate pressure. According to Neal, “The long-style design is great for high-horsepower applications like drag racing.”

The Borg and Beck style uses rollers under the pressure plate cover. These rollers are forced outward under centrifugal force as the engine spins. This increases the clamping pressure as the engine RPM increases. Finally, a diaphragm pressure plate uses a series of “fingers” (also called a Belleville spring), that completely encompass the center opening of the pressure plate. The main advantage to this style pressure plate is that holding the clutch pedal down at a stoplight is much easier than with a long or Borg and Beck-type pressure plate. “We almost always prefer a diaphragm unit.” says Norton, “Diaphragm clutch technology is superior for the majority of uses. Diaphragm units produce more clamp load, more of the time, with friendly pedal requirements and high RPM capability. Diaphragm pressure plates are also a no-maintenance option.”

The Choice Is Yours

So which flywheel, pressure plate, and clutch material do you think you need now that you’ve smoked your clutch and become a YouTube favorite?

At this point, we have hopefully shed some light on choosing the correct clutch. Now that you have done your homework, know your vehicle, and know the professionals you can trust, all that is left is for you to get the right clutch for your ride.