SPEC Shares How To Choose The Best Possible Clutch, Part 1

Many enthusiasts still prefer to choose their own gears. Whether we’re talking about road racing, autocross, drag racing, or street performance, the ability to manually shift your transmission is still regarded as an advantage by many. This preference and the fact manual transmissions steal less horsepower than comparable automatic gearboxes means the clutch is still a big deal to performance enthusiasts — and will be for a long time to come. Sure, we’ve heard the scuttlebutt about less and less new cars being made available with manuals, but we also see a thriving aftermarket for high-capacity manual boxes, shifters, and of course, clutches.

We have to face some facts here. The clutch is a wear part — it will eventually require replacement. Like brake pads, clutches are designed to work with friction to deliver the desired results. They are made to wear out, but before they do, we want them to perform reliably and predictably.

If you’re one of the proud enthusiasts who still loves rowing gears, what do you consider when it’s time to choose a clutch?

We want a clutch to handle the difficult task of delivering the horsepower we’re making (typically, a lot more than the factory engineered into our cars) and send it to the gearbox smoothly and effectively. This needs to be done without regard to the situation, which (for us enthusiasts) can be pretty hairy sometimes. Grabbing another gear just past redline-level RPM and dropping the clutch pedal is a lot to ask. Yet, we want this exercise-in-awesomeness to be reliably smooth, predictable, and repeatable — no matter how hot the clutch gets from all the fun we’re having.

So, how do we get there? Most of us accept that a good high-performance clutch assembly will cost more than a stock replacement unit. Like tires, we want more performance and we’re willing to pay a bit more for it. Knowing what we want, what we’ve got, and what we’re willing to pay, you’d think we were ready to pull the trigger, right?

Not so fast! There are many different kinds of clutches out there, and you need to get the one that best suits your needs.

We spoke with David Norton, owner of SPEC Clutches to get the inside scoop. Although he is the owner, David is also one of the many enthusiasts working at SPEC. This kind of enthusiast-heavy environment has taken SPEC to a good place, as the people working there want their own cars to work better too, and their product shows this kind of dedication. David assures us that anyone you speak with at SPEC is really into this stuff like we are.

We asked him the kind of questions we know you’d ask him, if you could. His answers are full of good info that will help you get the best possible clutch-per-dollar for your particular hot rod, which is what it’s all about.

TO: Before we begin, can you tell us a bit about SPEC? You started the company, but how did the SPEC brand become synonymous with high-performance?

David Norton:  My wife and I formed SPEC in the year 2000. I was a grassroots racer and street racer through the 1990s, always racing my daily driver in SCCA, NASA, and numerous import drag racing series. I used every clutch in the marketplace and felt like if I improved upon all I didn’t like about those offerings, and incorporated all I did like, we could manufacture a successful product.

Initially, we focused on the Mustang market and quickly moved into the GM LT1/LT4 and LS1 market. From our first event (the Fun Ford Weekend at Bradenton Motorsport Park, and at Desoto Dragway just one year before), we sold more units than we could produce with a single plate-engineer and two disc-builders. We quickly grew from 6 to 33 employees.

Our big break happened when our Stage 3 clutch made the cover of GM High-Tech Performance magazine with the title “Miracle Clutch.” We provided a unit for their “Project Thunderchicken,” a 396ci stroker LT-powered Pontiac Firehawk. They had used everything in the marketplace, and our unit was the only one to hold up to their relentless abuse of the poor bird. We began our expansion into other markets (JDM and European) in 2002. In 2004, we built the 30,000-square-foot production facility we utilize today.

TO: What critical points should a customer focus on when purchasing a new clutch for a performance application?

Norton: There are many benefits to a clutch and flywheel upgrade. However, a clutch change involves more than just the clutch itself, and you will want to do everything right the first time because it is labor-intensive. When a customer calls for a recommendation, we ask how much torque they need it to hold, where they drive the car, and oftentimes about vehicle weight and gearing.

There are several considerations we address when making a recommendation, and the end-user should rank or prioritize these before choosing a high-performance clutch.

A high-performance clutch not only can last a lot longer than an original equipment clutch in a modified car but also outlive an original equipment clutch in an unmodified car! — David Norton

The first consideration is torque capacity, or how much power the unit needs to hold. Capacity is most often the first priority. The proper unit of measure for clutch capacity is pound-feet (lb-ft) of torque — not horsepower. Based on the nature of the modifications, you should be able to determine your torque level. Most of the time, it will be within 15-percent above or below your horsepower.

As an example, let’s use a potential build that should produce 460 lb-ft of torque. It is recommended that a 10- to 15-percent capacity buffer be added to the clutch capacity to allow for underrated modifications, like a heavy torque hit from a nitrous shot, and/or owner’s greed for more power. That buffer can also help maximize clutch life. So a clutch with a 530 lb-ft capacity would be a good choice. Our ratings take into consideration that sticky tires may be used, as well.

The second consideration is drivability (or pedal requirement) and how the clutch feels at engagement. Pedal requirement is not a concern on most late-model hydraulic applications. We are able to produce a lot of clamp load with the lowest possible actuation requirement (a popular feature of our brand). The feel at engagement would be important if the end-user drives the car on the street in a lot of stop-and-go situations. Maximizing streetability calls for a unit with a sprung-hub (dampened) disc and a material configuration that is somewhat forgiving.

The third consideration is life expectancy. It is very hard for a clutch manufacturer to rate or guarantee life expectancy, simply because there are many after-sale factors that determine the wear cycle. Clutch life will be maximized as long as you stay within the clutch capacity buffer and follow seating instructions that accompany a high-performance clutch. It is also best to follow industry-standard installation practices like replacing old bolts, refreshing worn hydraulics, and surfacing or replacing the flywheel. Given instructions are properly followed during and after correct installation, a high-performance clutch not only can last a lot longer than an original equipment clutch in a modified car but also outlive an original equipment clutch in an unmodified car!

The fourth consideration is weight. Most street and track driven cars can benefit from our lightweight-clutch options. The benefits are increased rate of rev and increased horsepower/torque. A lighter clutch alone will not produce any substantial downside. It is a great way to complement your modifications with a part that can produce gains without adding stress to any other part of the car. SPEC offers lightweight-clutch options for many applications in single- and multi-disc configurations.

The final consideration is the price. The value will be based on how you prioritize the above considerations. Basically, a clutch is like taxes. Spend sufficiently now or you will be penalized later.

TO: What are some common mistakes people make when installing a clutch?

Norton: We have seen all the possible mistakes when helping enthusiasts choose a replacement clutch or flywheel: Too much clutch, not enough, too light, too heavy. All can be remedied with a good recommendation. Regardless of where you buy your clutch, SPEC encourages you to call for a recommendation. We have seen almost every installation mistake and practice.

Most Common Clutch Installation Mistakes

The most common clutch installation mistakes are:

  • not replacing used fasteners
  • not using proper bolt torque values
  • installing the disc backward
  • not replacing the pilot bearing in the crankshaft
  • Not replacing the release (throw-out) bearing
  • not resurfacing or replacing the flywheel (replacement is highly recommended in dual-mass applications)
  • contaminating the disc and surfaces by not replacing seeping rear-main crankshaft oil seals
  • applying too much grease to the input shaft (which then gets all over the new friction surfaces)
In Part 2, we will continue our discussion with David Norton and learn more about racier applications, multi-disc clutches, and SPEC‘s in-house flywheel program. We’d like to thank David for his time and knowledge, and we’d encourage you to read Part 2 of this story! There’s a lot more to learn.

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About the author

Scott Parkhurst

Beginning his career in the U.S. Air Force, Scott transitioned from hands on positions assembling air craft and racing engines when he became Tech Editor of Popular Hot Rodding. He was later Editor of Engine Masters and is a published author.
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