Hi there! I'm Matt

I have a 1986 Pontiac Firebird Trans Am. My factory 305 spun a bearing so I decided to reuse my fatory TPI system on a 358 (350 bored .040 over), but I usually do this stuff with my dad and he knows nothing about tuning EFI so this is new grounds for both of us. I'm using a $6E setup originally ballparked by Tuned Performance on the thirdgen forums. If there's anything that someone wants to let me know or offer any support about fuel trims and spark tables, don't hesitate to reach out. Lord knows I could use the help.

Welcome, great project to work with your Dad with. Tuned Performance dude seems pretty knowledgeable and should be able to work you through the kinks. Plenty of ways to make that better, keep in mind that TP knows that too :)

tpi is a fun challenge that will always feel fast but tends to lose an actual race
your fuel and spark looks totally bizarre after you're done if you do a good job
what i usually do is to find the midrange band where the tpi system is most effective and ram a bunch of extra spark advance and fuel in there then run a leaner tune with conservative spark on the high end after the mid peak.
the top end of tpi can be really restricted in flow especially with a 350ci so it takes extra care and attention to maximize power there

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Originally Posted by steveo

tpi is a fun challenge that will always feel fast but tends to lose an actual race
your fuel and spark looks totally bizarre after you're done if you do a good job
what i usually do is to find the midrange band where the tpi system is most effective and ram a bunch of extra spark advance and fuel in there then run a leaner tune with conservative spark on the high end after the mid peak.
the top end of tpi can be really restricted in flow especially with a 350ci so it takes extra care and attention to maximize power there

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It does not matter if you put tuned port on a destroked 283 or 267 the runner length resonates where it resonates. Unless you use something like the Lingenfelter/Accell Super Ram or siamese ported SLPs the TPI will not rev. Even the FIRST TPI is not rev happy.

I find that just the opposite is needed for tuning. The engine will want more spark where the TPI is not working its magic and less where it is around ~3,200. TPI can approach 120% VE near peak torque and that requires retarding the ignition timing in that area. Similarly I had to pull some timing out of my aluminum head L31 based engine where the VE is over 100% in the 4,000-4,800 rpm range. Once the cylinder filling drops off a bit it wants more timing.