Heat and the Track:
The more sun and heat the track is subjected to, the more slippery or "greasy" it becomes. Check out the track temp on the tuning interface to get an idea how much traction you can expect the surface to provide.
Any reading above 100 degrees indicates that the track is "going away".
A slippery race surface most often requires a higher "wing attack" for dragsters and a less aggressive clutch settings for both TF and FC. The higher angle on the dragster wing provides greater downforce to add traction. Softer clutch settings also reduce chance of smoking the tires on a "greasy" surface since they put the horsepower to the track more gradually. For a cooler racetrack, the inverse rule applies, to a point, an extremely low track temp say below 70 degrees is also a "greasy" surface.
Corrected Altitude:
Nhra crew chiefs look at all atmospheric conditions as well as racetrack altitude to make tuning choices. In the game, "Corrected Altitude" is a good number to monitor when tuning your racecar. This number is calculated from all the variables in the weather portion of your tuning interface along with the altitude of the race venue. You are given a reading in feet, that is a great indicator as to how your hotrod will perform.
As corrected altitude increases, tune your horsepower settings more aggressively.
Note: At Houston Raceway Park you may have a negative number for correted altitude as the track is near sea level versus Brandimere Speedway in Denver where you see a "mile-high" reading.
Clutch:
Primary Clutch-The "Primary Clutch" is used to control how aggressively the car leaves the starting line.
These settings only pertain to about the first second of the race. Settings are measured in grams. A higher clutch weight will cause the car to leave the starting line harder and will yield a better 60 ft. interval time if balanced properly with engine settings. However, if this setting is too high it will most certainly cause your hot rod to smoke the tires and lose traction.
Secondary Clutch-The "Secondary Clutch" is based on an air-timer system and progressively engages during the run until "full lock-up" or "1 to 1" status. The tuning interface is based on time in seconds. Shorter times in this setting yield a more aggressive set-up. If this setting is correct, the green "traction Bar" will be full green the entire run. A setting that engages the secondary clutch too quickly usually causes the rear tires to lose traction sometime after the first second of the run.
Engine:
Blower Overdrive- The supercharger, or blower, is measured by the percentage of the blower speed versus the crankshaft. Simply, a higher percentage increases pressure in the engine and makes more horsepower.
Thus, a higher setting is a more aggressive tune for this part of the engine. A blower setting that is too high may cause tire smoke since too many horses will overpower the track. Even worse, it can cause the engine to go Boom!
Cylinder Pressure- Increasing Pressure is another way that a crew chief may ultimately increase horsepower. The cylinder pressure slider measures compression ratio which guages the combustible area of the cylinder at the top of the power stroke.
Tuning Screen
Clutch - The clutch is probably the most important parameter of the whole car. The clutch has to slip a certain amount for a short period of time, and then has to lock-up. The clutch has two disks and one floater. The clutch plate has springs that compress the disks together and weights on the fingers to provide further force due to centrifugal effects. The combination of the spring preload, the centrifugal weights, and the coefficient of friction of the clutch plates determine a line of torque versus speed that the clutch will be locked or slipping.
Where this curve passes through the engines torque-speed characteristic determines the "engagement speed" and thus how much torque is passed to the rear tires. This engagement speed can be affected by the preload or centrifugal weights. The preload determines the zero-speed intercept and the weights determine the curvature of the clutch line.
The preload on the engagement springs is the major tuning factor. There is 219 lbf per revolution of the holding screws. The preload is adjusted by the number of turns on the adjusted screws.
The preload adjustment range is 150 to 1100 lbf.
Clutch Weights - As discussed in clutch preload, the weights determine the curvature of the clutch torque-speed curve. More weight increases the slope.
The clutch weight range is 9 to 80 grams additional weight to a reference weight of the fingers.
Engine Speed at Launch - The stage rev limiter holds the engine at a constant speed with the throttle wide open. This engine speed is critical, if it is not too high, the tires might slip, if it is too slow, then the engine could bog.
The stage rev limiter range is 5200 to 6800 rpm.
Final Drive Gear Ratio - The final gear ratio is used to set the engine speed (rpm) at a given vehicle (mph). The tire diameter grows with speed due to the soft sidewalls and tread, and you can buy tires of static circumference ranging from 99 to 103 inches with 1-1 being the standard. The longitudinal slip ratio of the tire also affects the engine speed at a given vehicle speed. Therefore, the tire characteristics must be considered in the selection of the final gear ratio. The final gear ratio might have been adjusted if the track had better or worse traction at the start so the final speed might be different.
First Gear Ratio- The gear ratio for the first gear is critical. If the gear ratio is too high numerically (lower speed ratio) the tires could spin. The overall speed reduction (which includes the first gear, the final drive gear ratio, and the tire diameter) has to be set to the traction ability of the track and tire on that day. Therefore, the first gear and the final gear ratio are selected together.
Typical gear ratios for the first gear are 2.71,2.66,2.61.
Anti Squat Suspension - The anti-squat suspension linkage in the rear can be adjusted to put an upward force into the car chassis and a downward force on the rear axle. This can effect change the weight transfer to the rear axle in a transient. Without anti-squat, the front wheels can lift off the ground easily. With too much ant-squat, the front tires won't lift at all, and therefore traction will be reduced.
The suspension adjustment determines two parameters: the length from the axle center line to the instant center of the suspension, and the height the instant center is above the ground.
Shift Light - The parameters of the shift light may be adjusted as a signal to the driver of the optimum time to shift gears. Different set ups will require different shift light settings.
Wheelie Bar Height - The wheelie bar height will affect the amount of wheelie the vehicle will have from the launch. To much wheelie will make the vehicle's front end lift too high of the ground. This may cause a drag in the aerodynamics causing the vehicle to slow down.
The wheelie bar height may be adjusted between 1 and 12 inches.
