ClutchTamer Tuning Guide

NOTE- It's important to understand that additional clutch torque capacity, beyond the capacity needed to hold the engine's torque, is what controls how fast a clutch pulls the engine down after a WOT launch. Some additional torque capacity is necessary, as you don't want the clutch slipping when it doesn't need to. But too much additional clutch torque capacity will cause the clutch to pull inertia out of the engine too quickly, resulting in either bogging the engine, spinning the tires, or hurting the drivetrain.

Lets say you have an overkill clutch that can hold 1000ft/lbs behind an engine that only makes 600. If you launch the car and allow that clutch to hit with it's full 1000ftlb capacity, it's going to instantly pull an additional 400ftlbs of inertia out of the rotating assy, which in turn causes the engine to lose rpm pretty quickly. Too much extra clutch torque capacity, the clutch either pulls the engine down too fast (bog), knocks the tires loose (spin), or breaks drivetrain parts. But if you dialed the initial hit of that 1000ftlb clutch all the way back to around 700ftlbs, it still holds all of the engine's 600ftlbs of torque, except now it only pulls engine rpm down at a much slower 100ftlb rate. Because the car is gaining speed while the clutch is pulling the engine down, the result of the slower pulldown rate is that the engine doesn't get pulled down as far.

The inclined line on the graph (right) represents the average overall acceleration rate of a 1.40 60'. We will use this graph to illustrate how the ClutchTamer's "initial hit" adjustment affects the clutch's ability to balance engine bog vs mph.

Line A- full clockwise inner adjustment. ClutchTamer has no effect on clutch pedal return. This represents our example's baseline, no ClutchTamer control of the clutch's initial hit at all. Let's say for this example that line "A" represents the 1000ftlb clutch in the example above, hitting with it's full 1000ftlbs of holding power. 1000ftlbs of holding power is going to pull that 600ftlb engine down at a very quick 400ftlb rate. The result is the engine gets pulled all the way down to about 1800rpm in about 0.325sec.
Even if the engine were still making 600ftlbs at 1800rpm, that's only 205hp thru the low point of the bog. Obviously that 60' is going to suck.

LINE B- several counter-clockwise turns added to it's inner dial. Now the ClutchTamer is starting to have some affect on the hit, that 1000ftlb clutch is only hitting with 900ftlbs. Now the clutch is not pulling the engine down as fast, which gives the car more time to accelerate before engine rpm sync's up with vehicle speed (that sync point is where the clutch actually stops slipping). The result would look more like line "B", as the slower pulldown rate raised the sync point to about 2800 at 20mph, where the engine is obviously going to make a lot more power.
Big improvement, but that's still only 320hp thru the low point of the bog.

LINE C- two additional counter-clockwise turns added to the inner dial. This adjustment had the effect of making that 1000ftlb clutch hit with 800ftlbs. Now the engine stays above 3700.
The engine is now up to about 420hp thru the low point of the bog.

LINE D- two additional counter-clockwise turns added to the inner dial. That 1000ftlb clutch is only hitting with around 700ftlbs, now the clutch is only pulling 100ftlbs of inertia out of the rotating assy at the hit. That extra slip time allows the engine to stay closer to it's sweet spot for HP production.
The engine is now up to about 550hp thru the low point of the bog.

This is a big help for turbo cars too as it enables an instant soft hit from high rpm, which helps them build/hold boost during launch.


Initial ClutchTamer Adjustment...

The ClutchTamer's inner "initial hit" adjustment controls the amount of initial clutch clamp pressure that is applied BEFORE the ClutchTamer reaches the "hit" point, basically how far clutch t-bearing pressure initially drops before delay takes over.

The following procedure should get you up and running quickly. As always, be sure to do your testing is a safe and legal location.

NOTE- It's very important to choose a delay setting BEFORE tuning initial hit. It may seem counter-intuitive at first, but higher delay settings actually produce a crisper initial hit setting. That's because low delay settings allow the pedal to pass too quickly thru the "sweet spot" hit zone. That will make an initial hit setting that's actually too soft appear like it's too harsh. When you release the pedal, you want it to instantly hit deep within that sweet spot zone. You want a nice crisp hit that's just short of spinning the tires, but that crisp hit will require a lot of delay to keep it from leaving that sweet spot zone prematurely.

Step 1- slowly turn the outer "delay" knob counter-clockwise until you feel a slight resistance. The point where you feel that resistance is the "0" delay setting.
If your goal is to protect drivetrain parts, begin your ClutchTamer dial-in process with an outer "delay" setting of 1-2 turns clockwise from "0". These lower delay settings produce a softer hit with slightly more slipping after the shifts. Low delay settings are preferred when you have a weak link in your drivetrain.
If your goal is a good 60', low ET, and quick reaction time, begin your ClutchTamer dial-in process with an outer "delay" setting of 3-5 turns clockwise from "0". These higher delay settings produce a quick reacting crisp hit that's just short of spinning the tires. High staging rpm will be necessary to produce best results.

Step 2- set the ClutchTamer's inner "initial hit" dial to a setting that stops the pedal at about it's midway point during a simulated launch with the engine "off".

Step 3- begin a series of short 3000rpm test hits from a standing start. These hits shouldn't last more than a second or so.
If the tires spin on the hit- adjust the inner "initial hit" dial a couple turns counter-clockwise, repeat the hit.
If the engine instantly bogs on the hit- adjust the inner "initial hit" dial a couple turns counter-clockwise, repeat the hit.
If the engine does not bog at all on the hit- adjust the inner "initial hit" dial a couple turns clockwise, repeat the hit.
At this point we are looking for a happy medium hit where the clutch causes the engine to bog a bit without causing tire spin.

Step 4- Now make test hits from 4500.
...If the clutch doesn't bog the engine a little, abort the run. Give the clutch a little time to cool, then turn the inner dial 1 click clockwise and repeat step 4.
...If the clutch either bogs the engine too much or the tires spin, abort the run. Give the clutch a little time to cool, then turn the inner dial 1 click counter-clockwise and repeat step 4.
...If everything feels good, continue the pass thru 2nd gear. If the shift seems too soft, add another 1/2 turn of "initial hit" (inner dial clockwise), then repeat step 4.

For a quick et and minimal reaction time, don't be afraid of launch rpm. Launch rpm is basically stored energy, and the engine has to make the energy that it takes to spin up that rotating assy. The higher you can spin it up prior to the start, the more power that will be available to accelerate the car when the clocks are running. The ClutchTamer is there to control that energy flow, we want the clutch hit to be aggressive enough to get things moving as quickly as possible, without breaking parts or spinning the tires.

When you are done, be sure to measure/record your initial hit setting and the conditions. This will help you build a library of clutch tunes to draw on in the future. The most common method for the hit setting is to measure the gap between the inner "Initial Hit" dial and the inner part of the dash bracket's slide bushing. A small dial caliper works great. The gap you are measuring can be seen in the center of the picture to the right.

NOTE- The above procedure will get you to about 90-95% of your potential. To get that last 5-10%, you will likely need some data. Timeslips from the track are very useful, but adding a data recorder can save a lot of trial/error testing.


Clutch Tuning With A Data Logger...

G-meter output is affected by pitch rotation, which basically means a 6k/1.75g launch with a big wheelie could actually be slower than a 5.5k/1.45g launch with a smaller wheelie. You will be able to compare runs with more accuracy if you first zero the runs to the first movement of the g-meter, then overlay the runs to compare the differences in both Erpm and DSrpm traces.

Most important for clutch tuning is the angle/shape of the Erpm trace as it is falling, as this is the ONLY part of the trace that is basically controlled by the clutch when the engine is at WOT. This is where you will be able to see area added "under the curve" to the rpm trace after the launch and after shifts, which are generally indicators of increases to power production which were made possible by adding/controlling clutch slip.

To verify overall gains from clutch tuning, compare the time it took from first movement of the G-meter to a selected DSrpm just before the finish line. These are points in the run where wheel spin is least likely, which in turn means they are points more likely to be accurate indicators of vehicle speed (this assumes of course that you are concentrating on clutch tuning, with no changes to gearing/tire size/air pressure). Basically you are looking for the quickest time overall from first movement of the G-meter, to a selected DSrpm just before the stripe.

You can also compare clutch performance during individual shifts on different runs by selecting a DSrpm just before that shift, as well as a DSrpm just before the next shift, then comparing the times between those two points.

If you plan to shift clutchless, adding even more delay has the diminishing affect of softening shift harshness. Some prefer to take it a step further and combine that added delay with an adjustable base pressure plate (without any added centrifugal assist). It basically gives them a direct way to adjust the clutch's breakaway torque, which affects the harshness of a clutchless shift. Choosing a non-adjustable PP can also get you there and will generally cost less money, but you will probably need to add some shims under the PP to get the wheelspeed spikes after those clutchless shifts under control.


Please Read These Important Notes-

2-STEP / LINE-LOCK SWITCHES MUST NOT RELEASE FROM TOP OF CLUTCH PEDAL TRAVEL!!! With the ClutchTamer operating properly, your clutch pedal will not return to the top of it's travel until several seconds after the clutch pedal is released. Depending on your settings, it may not return to the top of it's travel until after your run is complete! If you use an oem style upper clutch pedal switch to release the 2-step and/or line-lock, the result at minimum will be a several second delay of when the pedal contacts the clutch switch. Late release of the 2-step will likely only cause a performance issue, but late release of the line-lock will cause a HUGE SAFETY ISSUE! Please make sure that your line-lock is not releasing AFTER the clutch hits!

ALWAYS RELEASE THE CLUTCH PEDAL FROM THE STOP WHEN CLUTCH TUNING or LAUNCHING !!! Before you install or test your ClutchTamer, it's very important that you install a clutch pedal stop and verify it's proper adjustment. By proper adjustment, we mean a setting that allows enough clutch dis-engagement to achieve clean hi-rpm shifts, also enough dis-engagement to be able to put the transmission into gear without grinding when the clutch is warm. Using a pedal stop helps ensure a consistent release point, which in turn helps ensure that you get repeatable results. If for some reason you have to change your pedal stop height after you begin the setup process (maybe you find the clutch isn't releasing cleanly which causes a shifting problem), you will need to go back to Step 1 and do the setup process all over again.

DO NOT "PRE-LOAD" YOUR CLUTCH BEFORE LAUNCH!!! It is important to release the clutch from a properly adjusted pedal stop. Many import racers "pre-load" their clutches in an attempt to minimize parts breakage, DO NOT do this when using the ClutchTamer. Pre-loading is basically releasing the clutch pedal to a point where the clutch starts to drag before the green turns on, an attempt to take all the "slack" out of the drivetrain. Pre-loading while using the ClutchTamer will result in less pedal travel on the launch and more pedal travel during shifts, which will result in excessive clutch slip after shifts made using the clutch pedal.

LAUNCH RPM CAN AFFECT YOUR CLUTCH TUNEUP!!! Even without any sort of "centrifugal assist", a typical 10.5" diaphragm style pressure plate can gain around 350lbs of clamp pressure going from 4000rpm to 7000rpm. You can choose any launch rpm you want, but it's a good idea to keep launch rpm consistent if you want consistent results.

CONSIDERATIONS FOR CLUTCH TUNING WHEN USING A SINTERED IRON DISC- it is important to allow plenty of time between test hits for iron disc temperatures to normalize. Basically no "back to back to back" test hits without some cooling time in between. The reason is the fact that the iron friction material actually bites quite a bit harder as temperatures go up. If you have an iron clutch where the "Initial Hit" setting was tuned to a much higher than normal disc temp, that clutch will likely slip way too much during a typical launch. If the engine is running, 5 min of cooling time between hits is usually enough. A non-running engine will need 10-15 min between hits due to less air circulation.


Frequently Asked ClutchTamer Tuning Questions...

Is there a ballpark "initial hit" setting that I can use to get started?
No, there are just too many variables. Even two cars with identical engines and clutch setups, but with different pedal stop adjustments, will require different initial hit settings.

My clutch pedal doesn't have enough time to return all the way up before it's time to shift. Is this a problem?
That's normal, and more noticeable when the clutch has a lot more capacity than the engine. Basically it's because the target window between a "properly firm initial hit" and "clutch lockup" is very narrow, and we are using the ClutchTamer's delay function to widen that window. It's not a bad thing and actually speeds up your wot shifting, as it effectively shortens pedal travel. Because the pedal has not yet returned all the way back to the top, now your foot won't have to waste time pushing the pedal thru that deadband area when you reach your shift point.

Can I make the Clutchtamer active only on launch, with no slip after the shifts?
Generally if someone is experiencing too much slip after the shifts when using the ClutchTamer, it's because their "Initial Hit" setting is not yet aggressive enough (needs more clockwise adjustment to inner "Initial Hit" dial, also needs more clockwise adjustment to the outer "delay" knob).

That said, if one wants to experiment with "active only on launch, with no slip after the shifts" while using the ClutchTamer, they can simply set the pedal stop deeper- basically use the pedal stop for launch only, then just stab the pedal for shifts instead of bouncing it off the stop. A more precise alternative is to keep the pedal stop setting that's optimal for shifting and install a drop out spacer between the delay knob and dash bracket for launch. Gives you the same result but allows bouncing the pedal off the stop during shifts.

Here's a comparison of two nearly identical back-to-back ClutchTamer passes. Both feature zero wheelspin during launch (no wheelspin variable), and "clutchless" faceplate shifts (no human pedal actuation variable). Both of these runs share the exact same ClutchTamer "Initial Hit" setting.
...The blue pass has a lower than optimal ClutchTamer "Delay" setting, and bogs to 4622 rpm at .728 sec into the run.
...The yellow pass has an additional 1/2 turn of clockwise of "Delay" added.
The basic result of adding more clockwise "Delay" was a decaying amount of additional slip time to be added after each successive shift. That added slip time after launch raised bog rpm to 5202, which increased the engine's hp output thru the low point of the bog. That added power helped the car reach the top of 1st gear 0.089 sec quicker. That added slip time also slightly reduced wheelspeed spikes after each shift, which improved net power overall to the point where the yellow pass reached the same driveshaft rpm 0.502 seconds quicker at the top of high gear. Notice that the car gains rpm at exactly the same rates in each gear on both passes. All the improvements come on the parts of the graph where the engine is losing rpm, which are basically the only parts of the graph that are controlled by the clutch...

Here's a graph with just the engine/driveshaft ratio displayed, so you can better see the differences in clutch slip time...

As you can see, it didn't take much of an increase in slip time to make a huge difference in ET.

Can I use a ClutchTamer with a SoftLoc style clutch?
Yes, you can. The main benefit will be that you will no longer have to compromise your launch to keep your clutch from slipping in high gear.
...If you are shifting using the clutch pedal and your PP has plenty of spring, we recommend that you remove all your counterweights and maximize your base pressure. If your PP doesn't have enough base pressure available to lock up the clutch in high gear on it's own, we prefer to install stiffer springs to achieve high gear clutch lockup, but in a pinch you can add just enough counterweight to get the job done.
...If you are shifting clutchless, you will be able to raise your 2-step setting to gain a little performance in 1st gear, we also recommend higher delay settings as a way of adding a decaying amount of slip after each clutchless shift. Here's a graph showing the previous clutchless run vs a throwout bearing psi curve with a high ClutchTamer delay setting. As you can see, the ClutchTamer is still holding back some clutch clamp pressure after a single pedal release, for a longer period of time than it took to complete all three clutchless shifts...

By adding a little slip after the shifts you will gain a little power production as the engine will not get pulled down as far, but you will also be reducing the size of the wheelspeed spike after the clutchless shifts, which represents an efficiency gain. The ratios in the transmission that produced the above clutchless graph were 3.17/1.96/1.34/1.00. Rpm in 1st gear at the shift was 7530, and should have dropped to 4655 in 2nd gear due to the ratio change. Engine rpm actually only dropped to 5192, which is a 537rpm above what the gear calculator predicted. At the 2nd/3rd gearchange, that gain was 274rpm. On the 3rd/4th gearchange, that gain was 80rpm.


Congrats to Coyote Stock Winner and ClutchTamer user Charlie Booze Jr & his crew, shown here picking up a $3600 check at the NMRA/NMCA SuperBowl event!

If you have any questions, feel free to e-mail me