By Chief Craig C. Clarke

One of the most dangerous conditions for a race car driver besides fire, is a stuck throttle or an engine run-away condition. In the past, the driver did not have any option but to hang on and try and stop the car by slamming on the brakes or attempting to kill the ignition.
Reaching for the power switch in a panic situation is not an easy thing to do; Not to mention if the throttle linkage becomes jammed, stuck or broken. Now, this situation can me managed automatically with the introduction of the ROUSH IGNITION INTERRUPTER SYSTEM. This is a multi-component system that reacts to the vehicle and driver when the throttle linkage breaks or sticks, and positively disables the ignition system on the vehicle.

In a recent personal interview at a race with Roush spokesman Robert Corn, he described the various components and their actions:

INTAKE MANIFOLD VACUUM SWITCH:
This is a pressure switch that is installed in the intake manifold, and works off the principal that the throttled engines power is proportional to the vacuum in the intake manifold. The Roush system is set so that the switch closes just before full power is achieved. It is recommended that this switch be screwed directly into the intake manifold spacer under the carburetor. This switch has a 1/8 NPT male thread on it for this purpose. This switch is normally closed and will open with vacuum. It is set to go closed when exposed to falling vacuum. For Winston Cup, Busch Restricted and Super Truck vehicles, the vacuum set point is 4Hg falling vacuum. For Busch Open engines, the vacuum set point is 6Hg falling vacuum.

BRAKE LINE PRESSURE SWITCH:
The brake line pressure switch is set into the front brake lines and set to close at a value that represents a high pedal effort such as in a panic brake situation. It is however, not set to activate under normal race braking situations. The preferred mounting location for this switch is in the junction block where the right and left front brake lines divide from the master cylinder front brake line feed. They suggest that this switch be securely attached to reinforce the mounting in the brake line block. This is a normally open switch that will close with 1100psi rising pressure.

BRAKE PEDAL POSITION SWITCH:
This is a travel indicator switch that is attached to the brake pedal and works as a backup to the Brake Line Pressure Switch. It activates the Roush Ignition Interrupter if the brake pedal linkage breaks and/or goes to the floor. Since every team and each car varies so much, they state that the individual team should develop their own mounting bracket for this particular switch. It is suggested that the mounting location for this travel switch should be to attach the switch arm to the brake pedal at the same point where the master cylinder push rod attaches to the pedal. The switch is self adjusting for stroke, so you need to be sure to make the pedal go through its complete travel. This should be done after the switch is mounted to the bracket. It is important to note that some vehicles have brake pedals that bottom out on the master cylinder. Therefore, the switch must be adjusted with the master cylinder push rod hooked up.

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