ACCUFAB, INC. & THROTTLE BODY CUSTOM APPLICATIONS

Accufab, Inc. does not recommend our products to be used on any application other than what they are designed for.  We constitute such use as a Custom Application.  There is no warranty, expressed or implied, on an Accufab product when used in a custom application.

This article is for informational use only.  If you have decided to purchase our product for use on a custom application, please consider the following before installation. 

A throttle body is a simple device with only one moving part, which rotates about 90 degrees.  Under normal conditions, including racing, the throttle body will last a lifetime and NEVER fail.

However, listed below are a couple of non-warranty conditions where a throttle body will fail: 

1. A nitrous explosion behind the throttle body (usually in the intake manifold) can bend the blade and/or break the shaft. 
2. When a throttle body has been incorrectly mounted on an engine in which it wasn’t designed for (usually an engine cross mounted in the chassis).

In every case of a broken or bent shaft, it has been as a direct result of the 2 situations above and/or one or more from the following list.  This list contains six non-warranty situations where any throttle body may or will fail: 

1. If you have to change (increase) the diameter relationship between the attachment point of the linkage and the centerline of the shaft, you may break the shaft.
2. If you have any tension on the throttle cable greater than what is required to overcome the throttle body return spring (with the engine at it’s fully torqued position), you may break the shaft.
3. If you have to remove the built-in stop bracket for any reason, you may break the shaft.
4. If you have to bolt, weld or attach a secondary throttle bracket to the existing bracket, you may break the shaft.
5. If at any time there is not reasonable slack in the throttle cable, even at wide-open throttle, you may break the shaft.
6. If the throttle is pulled open at any angle other than perfectly in line with the throttle linkage, you may break the shaft.

First, let’s discuss the dynamics mentioned above.  On a Ford V8, and most other V8 engines, under hard acceleration the engine torques over to the right (passenger side).  This causes no problems, added tension to the throttle cable.  Also, each of our throttle bodies are designed around the exact requirements, geometry and range of motion of the throttle pedal for the correct application.  What this means is that at full throttle, when your foot is hard on the floor, the cable bracket attached to the throttle shaft on the throttle body is both fully open and not quite touching the built in “throttle stop” on the throttle body.  The cable is NOT under tension, and uses only enough force to overcome the return spring.

Now, let’s look at some of the things racers have done when adapting an Accufab throttle body to a custom application and specifically, to a cross mounted engine combination.

In some cases, in order to get the correct range of motion between the throttle pedal and fully open at the blade, the throttle body linkage geometry has been altered.  This takes the form of several things, including attaching a secondary cantilevered linkage to the original throttle body linkage.  Because the new linkage is extended further away from the bearing, more load is put on the shaft, and because the cable attachment points may be further out from the centerline of the shaft, this too can cause increased load on the shaft (sort of like using a crank handle on a Model T that is larger in diameter, to give you more twisting torque).

The next problem that we have seen is that some racers remove the built-in throttle stop on the Accufab linkage bracket.  Because of the design of the throttle blade (slightly elliptical) the blade will NOT be able to go over center, and if you try, it will usually result in breaking the shaft.  The built-in throttle stop is there to keep this from happening.  The throttle stop on the linkage is specifically designed to open the blade precisely 88 degrees, 2 degrees from perfectly vertical. 

Finally, the cross mounted engine torques forward under full power (yes, even with solid type engine mounts there is some flex), not to the side as is the case with an engine mounted front to rear.  When the racer is first setting up his adapted throttle body, he will want to insure that the throttle body gets to a fully open (wide open throttle) position, and typically has someone sit in the car pushing the gas pedal to the floor (with the engine off), while he insures that the blade opens all the way.  The problem is that engine torque is not taken into consideration.  As the engine torques forward, it can increase the tension on the throttle cable (like a bow string), and given the typical modifications done to the linkage on the throttle body, eventually, the shaft will break.  The cable or rod used to open the throttle MUST be in line with the linkage and not at any angle.  All modified applications, in most circumstances, will require a pedal stop, to insure that the throttle blade and the gas pedal reach wide open throttle at the same time.

Accufab does NOT have a problem with throttle shafts breaking, which is why virtually all serious racers that know what they are doing using an Accufab throttle body.  We have our throttle bodies mounted on engines, including single and dual turbo engines, making serious horsepower.  For instance:

Mike Moran’s 3000 HP twin turbo big block Chevy Pro Mod

Chuck Samuel’s 2500 HP single turbo Ford small block Pro 5.0

We have many Sport Compact Series, NHRA and NOPI, racers that rely on Accufab, too: 

Shaun Carlson, turbocharged Mopar Neon

Abel Ibarra, turbocharged Mazda 

The racers listed above and many others have taken the time to understand the dynamics involved with adapting our throttle body to their racing applications.  Furthermore, they have NEVER broken a throttle body shaft.  

These are the same throttle bodies available to everyone, all out racecars and street machines alike.  Accufab does not make separate throttle bodies exclusive to racing.  The shafts do not break, period, end of story. 

It’s not difficult to adapt a throttle body from one application to another as long as you understand the dynamics and geometry involved.  If you follow these guidelines, you should not have problems with breakage.