Written by Steve Turner
Photography courtesy of ClutchTamer and by the FSC staff
Both bulbs glow. Engines rev and pop against a two-step limiter when two cars head into battle. As the tree moves from yellow to green, clutch pedals release and power jolts back to the rear wheels. The trick with stick-shift machines is managing the clutch release off the line. Part skill and part art, this technique can win or lose the race.
It’s not something that comes easily to every driver or every combination, but what if we told you there was a way to easily dial-in the clutch hit on a manual-transmission car so it dead-hooks every time. You might tell us to shut the front door, and that’s exactly what inspired the product enabling this feat—a screen door closer.
“I was looking to get the most power possible thru a Saginaw four-speed, which at the time was breaking at least once a month. I came up a simple plan to soften the hit of the clutch, it was based on a hydraulic screen door closer that I found at a local hardware store,” Grant Robbins, owner of ClutchTamer, said. “I made a few modifications, named it the ‘Hillbilly Clutch Slipper,’ and it worked great. Back then it got that Saginaw down to 6.51 with a 1.45 60-foot. Pretty sure I could improve on that if I still had the Saginaw setup.”
From there, this piece of inspired ingenuity became the ClutchTamer. The device has been embraced by a wide variety of racers, particularly those in the heads-up ranks that run manual transmissions like the NMRA’s G-Force Racing Transmissions Coyote Stock and Richmond Gear Factory Stock. As you’ll see in the photos here, we contacted several of them to see how using one impacted their racing.
That’s great, of course, but how does this adjustable clutch pedal damper help a car launch with a clutch?
“It’s configured to allow the clutch pedal to be instantly released to a specific point within its ‘sweet spot’ zone. That sweet spot is the zone where the clutch hits/grabs just hard enough to get the car in motion as efficiently as possible. Any harder would result in spinning tires or breaking parts, any softer would slow reaction time and leave e.t. on the table,” Robbins explained. “As the pedal reaches that specific point within that zone, its travel is instantly slowed by a hydraulic cylinder with the effect of extending the time spent within that zone. The goal is to give the car more time to gain speed before the clutch locks up, which helps make the car quicker by keeping rpm up higher where the engine can make more power.”
In a way, the ’Tamer is effectively like installing a higher stall speed torque converter in an automatic car. It allows for enough slip to let the car accelerate, while softening the blow off the line.
Though the original Clutch Tamer is designed for traditional, cable-actuated clutches, the company now offers the HitMaster In-Line Hydraulic Clutch Hit Controller. This unit installs in-line with the hydraulic clutch line and allows the same adjustment as its mechanical cousin.
“The HitMaster in-line hydraulic version allows you to dial back the intensity of that instant initial hit, much like the original ClutchTamer. Let’s say you have an overkill clutch that can hold 1,000 lb-ft behind an engine that only makes 600. If you launch the car and allow that clutch to hit with it’s full 1,000 lb-ft capacity, it’s going to instantly pull an additional 400 lb-ft of inertia out of the rotating assembly, which causes the engine to lose rpm,” Grant Robbins explained. “Extra clutch capacity, beyond what it takes to hold the engine’s torque, that’s what controls how fast the clutch pulls the engine down. Too much extra clutch torque capacity, the clutch either pulls the engine down too fast (bog), knocks the tires loose, or breaks drivetrain parts. But if you dialed the initial hit of that 1,000-lb-ft clutch all the way back to around 700 lb-ft, it still holds all of the engine’s 600 lb-ft of torque, except now it only pulls engine rpm down at a much slower 100 lb-ft rate. Because the car is gaining speed while the clutch is pulling the engine down, the engine doesn’t get pulled down as far,”
So just like the mechanical version, the hydraulic ’Tamer is another tool that helps you dial in your combination for better performance.
“But if you were to use a ClutchTamer or HitMaster to cut the initial hit of that 1,000-lb-ft clutch back to 900 lb-ft, it’s not going to pull the engine down as fast, which gives the car more time to accelerate. The result would look more like line ‘B,’ where the car is able to accelerate to about 20 mph before engine rpm syncs up with vehicle speed (that sync point is where the clutch actually stops slipping),” Robbins added. “That raises bog rpm to about 2,800, where the engine is obviously going to make a lot more power than it did at 1,800 rpm. Backing the hit of that 1,000-lb-ft clutch off to 800 would result in something like line ‘C,’ where the engine stays above 3,700. Now the bog point is up to around 420 horsepower. Back the hit off to around 700 lb-ft and it would look more like line ‘D,’ as the clutch is now only pulling 100 lb-ft of inertia out of the rotating assembly. That extra slip time allows the engine to stay closer to its sweet spot for power production, now it’s up to about 550 horsepower through the low point of the bog.”
Now owners of modern musclecars can employ this system to control launches on cars that are easy to take from stock to beyond-four-digit horsepower with the right combination of upgrades.
Street and Strip
While the ClutchTamer is definitely geared toward the racing crowd, its installation is said to have little impact on day-to-day usability. As such, you could easily run one in your street/strip race car and only see its benefits when you head to the track.
“…Pedal release rates during casual driving are typically a lot slower than a slip controlled drag strip launch, so the driver still has full control over feathering of the clutch pedal for a smooth start,” he said.
That means your weekend warrior will always be ready for battle. However, for those times of competition, you’ll definitely want the right supporting hardware.
“Not for casual driving, just drive it like you did before. You may notice that the clutch pedal takes longer to return to the top when released, but other than that you probably won’t even notice that it’s there,” he added. “For launching at the drag strip, releasing the clutch pedal from a properly adjusted pedal stop is a must for consistency.”
Dialing It In
“A properly dialed in ClutchTamer launch will hit softer than an automatic, but that softer hit lasts longer. Basically it takes a clutch dump launch that’s too intense/violent that wastes a lot of energy, and transforms that launch by spreading the energy release over a longer time period where it can be harnessed more efficiently,” Robbins said. “That’s what makes it so easy to launch on radials when the hit is controlled by a ClutchTamer. That softer launch also makes the car less sensitive to chassis/shock adjustments, so less likely to need expensive shocks to control that softer hit.”
Essentially this device is democratizing the kind of driving skill that an elite few have hone and perfected. It allows adjusting how aggressive the clutch will hit to accommodate for track conditions and should generally make launches more consistent.
“The ability to dial in the hit also makes it possible to launch from pretty much any rpm you want to. Launch rpm is basically stored energy, and the engine has to make the energy that it takes to spin up that rotating assembly,” Robbins added. “A slip-controlled clutch allows for spinning it up much higher prior to the start, which makes more power available to accelerate the car when the clocks are running.”
It may even let you run a setup with less rolling resistance, which should help put more power to the ground once the car is moving down the track.
“Another benefit is there is no need for low air pressures to help absorb the hit with the ClutchTamer, many racers using the unit have their slicks up to 20 psi or more. In the end, you get a consistent dead-hook launch without a bog that’s quicker and far less likely to break parts,” Robbins said.
Sound like an interesting solution, right? So, you might be thinking that it is complex or difficult to adjust. That doesn’t seem to be the case. Once it is installed, the device can literally be dialed in by turning a knob.
“It’s pretty easy really. If you are dialing it in at the track, set the ’Tamer’s outer ‘delay’ adjustment to four turns or so, pick a launch rpm near your power peak, and make a hit,” he said. “Abort the hit if the clutch is obviously slipping too much, but if the hit was fair and the tires didn’t spin, add one turn clockwise to the ’Tamer’s inner ‘hit’ dial and make another hit. Keep adding one turn of hit per pass until the 60-foot times stop improving and fine-tune from there.”
Of course, there are some nuances to dialing in the adjustment. There is some trial and error involved, as well as some knowledge needed about how the clutch release affects the vehicle launch.
“Some aspects of ClutchTamer tuning can be counter-intuitive, like adding delay when a clutch appears to be slipping too much already. This is because low-delay settings allow the pedal to pass too quickly thru the sweet-spot zone, which leads to an initial hit setting that’s too soft,” Robbins said. “When you release the pedal, you want it to instantly hit deep within that sweet spot zone to get a nice crisp hit, but that crisp hit will require a lot of delay to keep it from leaving the zone prematurely.”
You might be wondering, as we were, if this device’s efficacy is limited to stick cars with modest power. Power is a pretty easy to come by these days, but adding the ’Tamer to your repertoire can help on these machines as well.
“Yes, in the same way that a looser, ‘less efficient’ torque converter can make an automatic car quicker. Controlled clutch slip does pretty much the same thing by effectively raising the engine’s average horsepower/rpm over the duration of the run,” Robbins explained. “A slipping clutch is a less efficient coupler, but the energy that’s absorbed by the clutch while it’s slipping is more than offset by a much larger horsepower gain. This is possible because the engine can operate at a higher average rpm where it’s much happier and makes more power.”
“There’s also no need for an extra deep first gear to help induce/control wheelspin, as ClutchTamer launches are basically dead hook,” Robbins added. “Much like an automatic car can respond to less first gear ratio as a way to help keep the tires stuck, a less aggressive first-gear ratio in a manual box also hits softer and has that same side benefit of more time spent in the gear with the most mechanical advantage. Softer hit, more duration. Less aggressive first-gear ratio also means a closer split, which translates to less rpm drop after the gear change. The net result is that average rpm and power production get bumped up a little during the gear change.”
In A Clutch
While it will help in high-powered environments, don’t expect the ’Tamer to be a one-size-fits-all solution. You still have to choose a proper clutch for your application that can both handle your car’s output and survive the heat generated from the slip necessary to launch it smoothly.
“Yes, there are limits, but you don’t need a special clutch to start enjoying some ClutchTamer benefits. Even a stock organic clutch can typically be slipped a little longer, which increases average horsepower and reduces bog,” Robbins said. “Ceramic friction material is a better choice for controlled slip than organic, due to its tolerance for higher operating temperatures. I typically stay away from Kevlar, which can be easily damaged. Carbon/Carbon has a really high temperature tolerance, but low overall mass means carbon reaches critical temp much quicker than you might think.”
Choosing the right clutch for your application is going to depend on a lot of variables, including output and rev range. But the apparent key to having one that works best with the ’Tamer is one that can withstand enough slip for your combination.
“Super lightweight clutches may have a high torque capacity, but their lack of thermal capacity causes them to reach their critical temp pretty quickly. That in turn, limits how far you can go with exploiting more clutch slip for bigger power gains,” Robbins added. “For the most potential for e.t. improvement, I generally prefer lightweight steel flywheels; steel or iron pressure rings; and sintered-iron friction material. Basically I like to have enough clutch to be able to slip for about 1.5 seconds WOT without reaching critical temps. If you have synchros, a puck-style iron disc is a good choice, as it can tolerate high temps while its lighter weight allows for higher-rpm shift points. My personal ride is face-plated, which allows me to get away with using a heavy, full-face, sintered-iron disc. That’s an advantage for some of the zero-prep surfaces that the car occasionally runs on, as the extra mass allows the option to launch in second gear if a surface is really bad.”
So if you have been searching for a consistent launch from your stick-shift racer, the combination of the right clutch and the adjustability of the ClutchTamer might just be the solution you are seeking.