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| Chapter 8 |
| Clutch tuning in
professional race cars |
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(click on any image to enlarge)
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| Professional
billet drag racing clutch |
An attractive
run graph from a Pro Modified car |
The most
sophisticated drag racing clutch systems allow controlled slippage to get
maximum horsepower to the ground with minimum tire spin. These clutch
systems are fully adjustable for spring and centrifugal pressure, as well as
wear so that the system can be tuned for the car to meet the track conditions.
Adjusting the
clutch system requires the use of a data recording computer. Engine,
transmission, and driveshaft RPM graph overlays indicate the amount of clutch
slippage and tire spin on both the launch and subsequent gear changes that allow
us to make proper tuning decisions. Without a data recorder, any tuning
decision is merely a guess.
The most
important consideration is how the car will react to the clutch settings when
the car is launched. On the launch, you want to achieve optimum wheel
speed without excessive tire spin or clutch slippage. To accomplish this,
the launch RPM needs to be significantly lower than the shift RPM to provide
some initial slip while allowing the clutch to gradually applying additional
clamp pressure as engine accelerates to the shift point.
| TECH
TIP - LAUNCH RPM
Since centrifugal
assist is RPM sensitive, increasing or decreasing the launch RPM will
increase or decrease the clutch pressure at launch without any actual
adjustments being made. Additionally, increasing the launch RPM
increases the inertia applied to the rear tires from the stored energy
of the clutch system.
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Once the
vehicle leaves the line successfully, the performance of the clutch can be
evaluated on subsequent gear changes. If
the vehicle tends to have no slip on the gear change, spins, or if the tires
shake, reducing the counterweight will provide additional clutch slippage
reducing the spin or shake. Without
the data recorder, it is extremely difficult to determine exactly what is
happening at these points in the run. Examining
each successive gear change, we should see the slip time reduced until there is
very little clutch slippage in high gear.
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