[Marv D]

Ditto:

The Swirl port heads of the late 80's to mid 90's were great at making torque from idle to about 3500rpm, then they were all done. And lets be honest,,, how often are you really above 3500RPM??? GM decided a work truck didn't need HP (= RPM capabilities) it needed TORQUE from idle to 3000RPM and the 'LO' motors at 190-210 HP (but 350+ # of torque in a low RPM range) did that well. It didn't need a very smart ECM to manage the TBI with just 2 injectors in a throttle body and the prom was flashed specifically for the motor / chassis / tune.

The batchfire 8 injectors of the 96-2000 Vortec motor and OBD II TOTALLY re-vamped engine management, heads and compression, cam and needed a much smarter brain.

Then came the LS with cam sync / sequential port injection and the ECM continues to get smarter and smarter.....


What I'm getting at is the OBD I computer of the 80's to 95 was BARELY one step above a carburetor,, and then ONLY in attempting to reduce emmissions and cut power output so efficiency was 'controlled' . When they put a rev limit in the ECM GM saw $ signs because it simply wouldn't rev high enough to blow up. So think of the engine management system for the TBI as a FIXED, un-tunable carb with a FIXED timing curve. You can't make significant changes in the way the engine responds to throttle (cam and compression) because the dumb box controlling things just does't understand what's happening when feedback gets out of range of it's 'expected' feedback.