jhthornley

I've got a lightly modded '95 Z28 (see sig).

I'm planning on LT and ORY soon.

I've read all kinds of posts in the last year (and several tutorials etc) about tuning... I understand that PCMForLess and MadZ28 can get 13?? rwhp extra out of a "stock" car... (assuming 91 octane all the time... which I run anyway).

I gather that w/ LTs I should "get a tune".

I'd like to "roll my own" w/ LT1edit, freescan etc and a cable.

My question is this... What specific changes to the stock tune do these guys do?

I would assume that if changes are made to try to chg the AFR to 12.5:1 instead of stoic (14.7:1) that mileage would decrease?

It is a DD. 1) If I tune for my current practically "stock" state, what should I be doing? 2) after I put LTs and ORY on , what should I tune for? 3) If I then go w/ 1.6 RRs?

Thanks for any/all feedback

John T

Injuneer

The PCM always uses the 14.7:1 target A/F ratio in closed loop. You don't change that. And you don't program it to run richer. The problem pops up when you put the throttle to the floor (or close to it, depending on RPM), and the PCM enters power enrichment (PE) mode. It calculates a new target A/F ratio, typically about 11.7:1 with the factory tune. That's way too rich for peak power and torque. The mail order guys simply use the PE tables to lean out the PE mode target A/F ratio closer to 13.0:1.

Does not affect fuel economy, since the closed loop target A/F ratio is still 14.7:1.