Introduction

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This HowTo will show you another modification to the throttle body.

Why Do This

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This modification is to reduce the amount of restriction from the shafts as much as possible without sacrificing durabuility. The overall increase in useable cross-sectional area is about 6%, about 2% in each bore. This could increase the airflow through the bores but not by much, considering the shafts are not a brick wall and are rouned smooth, they are not much of a restriction.

The Work

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If you take a look at both primary and secondary shafts, you will notice one side has been cut down and the other side is rounded. That rounded side is what is going to be modified. I removed about 3/32 of meterial.

1. Remove the throttle body from the engine and bring it to a clean work bench.

2. You need to remove the shafts from the TB and to do this you first need to remove the TB plates.

3. On the primary shaft, remove the 12mm nut on the front of the shaft where the throttle sensor(s) are and remove everything from the shaft, remembering the order. Its not to hard to figure out how it all goes back on.

4. Remove the 12mm nut on the back of the Secondary shaft and remove the washer, the usless metal piece which looks like its supposed to do something but really doesn't.

5. Look at the primary shaft on the back of the TB and remember how everything is looking. You do not need to remove the 12mm nut on the back of the shaft but you want to know where the spings attach.

Slowly slide the primary shaft out from the TB from the back. Make sure the linkage from the primary shaft to the secondary comes off the secondary shaft.

6. Put the shaft in a vise and use either a dremal or air grinder to start the modification. Then use a metal file to finish removing metal which will give a nice clean smooth look.
Be careful not to remove more then you need to. Try to keep atleast 1/16" of metal

Do not grind where the screws are. Leave as much thread as possible so the screws will not back out after installing them again. Thread locker will work good.

7. After you are done with the primary shaft, remove the secondary shaft by removing the rest of whats on the back of it and slide the shaft out through the front of the TB.

8. Do the same modification to the secondary shaft.

9. Reinstall both shafts, making sure everything goes back the way it should.

Make sure the throttle plates are positioned perfectly in the shaft when tightening the screws. The plate can be off a tiny bit and still look like they are closing off the bore. Hold the TB up to the light and try to see light through the secondary plates, you should see none. Same with the primary plate.

If when you put everything back together and start the car, the engine idles high, check the throttle plates. The secondary plates I had to re-adjust 3 times to get perfect.

See Also

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[FC Modification Manual]
[Porting 86-91 Intake Elbow]