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Basic TPI modifications
Sunday, October 17, 2021

Basic TPI Mods: by DEBBIES87

There are a few basic mods that should be done to any TPI car, I call these "entry-level" modifications.

1) Cut the air box open without letting air in the engine without going through the air filter & remove the additional plastic piece below the air box to get more air into the engine.

2) Modify the mass air sensor; remove the screens, & and if your brave cut down the fins.

3) Port the plenum (upper intake). There are two small ridges sticking up in the entry-behind the throttle body, remove these. The throttle body openings are already 52mm, so don't go crazy when porting.

4) While the plenum is off for porting, it is now a good time to get a adjustable fuel pressure regulator & a MAT sensor relocater kit. The Adj. FPR will aid in tuning, and the new MAT sensor will improve throttle response as well. The new LT1 style MAT sensor is placed in the air box instead of the plenum, this allows it to read cooler air and advance the timing accordingly.

5) Advance the base timing to 12-13 degrees. Note: the harmonic balancers on these cars tend to drift with age, adjust timing to where the car still starts good and doesn't detonate.

6) If legal in your area, gut the catalytic converter and remove the smog pump belt (85-87), or run a shorter serpentine belt to bypass the pump (88-92); you will need to remove the smog pump on the 88-92's to reroute the belt properly. Check local smog laws first.

7) On automatic cars, adjust T.V. cable (throttle valve cable), so that the car shifts out between 4200-4500 RPM under wide open throttle. TPI motor power drops off drastically after 4500-4700 RPM, they peak at about 4200-4400 RPM. No need to over-rev these motors.

8) Bypass fan relay to make fans come on manually, or install aftermarket relay to turn on fans sooner.

All together these mods should make the car perform like it should have from the factory, gains should be between .6-.9 tenths of a second from these modifications.


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