Here's an obvious statement for a racer: The throttle is your friend. It's a simple enough apparatus, a series of linkages from the gas pedal to the carburetor that allow you to control fuel flow to the engine from your comfy cockpit. But treat it nicely or it can turn on you faster than your buddy in high school when he discovered you were dating his sister. Few wrecks produce harder hits than a stuck throttle. To avoid that and help you attain throttle control so precise it feels like you are working the carburetor butterflies by telekinesis, we visited the No. 10 (Johnny Benson) and No. 36 (Kenny Schrader) Winston Cup shops to see how these pros did it.
Whether you are installing a universal throttle-linkage kit or fabricating your own, there are a couple important points to remember. First, make sure there are no extreme angles between the gas pedal, linkage, and carburetor at either the idle position or full throttle. You want a smooth pull from idle to full throttle so that there aren't any hang-ups on your way to full throttle or when you let off the gas to "whoa" up.
Also, to avoid a dreaded stuck throttle, make sure to build in some redundancy into your throttle return. This is simple enough: Use two throttle return springs. They can be softer than normal so that the total pull is not too great, but if one breaks you still have a second pulling back the power. A toe-pull on the gas pedal also isn't a bad idea.
Bart Bates, the shop foreman for the MB2 Motorsports team that fields Johnny Benson's Pontiacs, says his crew builds all their throttle linkages in-house. The rods are 3/8-inch solid hex rod made from T6061 aluminum. Once the rod is cut to length it is bent so that the greater length of the rod is horizontal with a slight upsweep at the end to the carburetor. Both ends are drilled and tapped, and then 1/4-inch aircraft-quality heim joints are attached. Bates recommends aircraft-quality heims because they rotate freely, do not kink, and the only maintenance required is an occasional shot with spray lubricant.
Inside or Outside?
If you are using a through-the-firewall gas pedal, connecting up the throttle linkage rod is a piece of cake. But if the gas pedal assembly sits completely on the driver's side of the firewall it can be a little more difficult. Bates has experience with both. Benson prefers a brand of pedal that goes through the firewall, while Schrader uses a brand that requires the throttle linkage to pass through the firewall and then connect to the pedal assembly.
MB2 and MBV Motorsports get...
MB2 and MBV Motorsports get their engines from Hendrick Motorsports butbuild their own throttle linkages. Shop foreman Bart Bates says thesimpler the equipment the better when it comes to assembling abulletproof throttle linkage system.
The linkage bar itself is...
The linkage bar itself is simply a 3/8-inch piece of solid hex rod madeout of T6061 aluminum. Aircraft quality heim joints are threaded intoeach end to attach to the working hardware.
To allow the spring clip to...
To allow the spring clip to rotate freely, Bates uses a two-piecebushing with flanged ends. It allows the bolt to be tightened down whilestill including some clearance for the spring clip to pivot. The entireassembly has been loosened in this shot so you can see.
The spring anchor is secured...
The spring anchor is secured with the intake manifold bolts. It hasmultiple holes for adjustability. The lower holes stretch the springfarther, providing the driver a stiffer pedal. Always use two throttlereturn springs. That way if one breaks you have a second still workingto pull the throttle closed.
Bates cautions that it's critical to place the hole in the firewall correctly. Depending on your setup, the throttle linkage will move up and down a little as the accelerator is pressed down, so you want to make sure the hole is sized large enough that the rod won't make contact with the side of the hole and create a potential sticking point.
But, holes in the firewall are potentially dangerous places for fire to move from the engine compartment to the driver's compartment. A rubber grommet is the standard hole plug when it comes to firewalls in racing, but it's not a particularly good solution in this instance because it can also make for a sticky throttle. The best solution Bates has found is to make a Kevlar(R) fabric boot to seal the hole and protect the driver.
At the Carb
The opposite end of the throttle rod connects both to the carburetor throttle control plate and the mechanism for the spring return. A two-piece bushing cradles the spring clip so the bolt connecting the throttle rod to the carburetor throttle control plate can be properly tightened down without cinching the spring clip. "To keep the clip rotating freely, some people will try only threading in the bolt part way and Loctite it in or something," Bates explains. "They always manage to back out when you do that. It's better to use some type of bushing to keep the clip rotating freely after the bolt is tightened down all the way."
Finally, once everything is in place, Bates calibrates the throttle linkage so that a secondary throttle stop on the gas pedal engages at the same time as the primary stop on the carburetor. The carburetor throttle stop comes from the engine builder calibrated to keep the butterflies from opening beyond 100 percent open throttle, so it isn't difficult to match to that. The redundant throttle stop on the gas pedal is just for an added bit of safety, Bates says.
After every race the throttle linkage is inspected along with every other part of the car. The maintenance required is to clean the pieces and occasionally put a little bit of lubricant on the heim joints. Bates says he has never had a linkage fail on its own. Just what every racer wants: simple and effective. CT
Johnny Benson's Valvoline...
Johnny Benson's Valvoline Pontiac uses a through-the-firewall gas pedal,which makes for a very simple connection to the carburetor.
Ken Schrader prefers a different...
Ken Schrader prefers a different gas pedal design for his M&Ms Pontiac,which is contained completely on the driver's side of the firewall. Thismeans a larger hole must be made in the firewall for the throttlelinkage to pass through. The MB2 team solved this opening problem bycreating a Kevlar(R) fabric boot.
If you aren't currently using...
If you aren't currently using a throttle stop on your carburetor, thinkabout something like this. It's simple and just about bulletproof. Thethrottle control plate butts up against a bolt that is threaded in orout to reach the correct height. An adjuster nut (and some Loctite)holds everything down tight.