Hey, anybody experimented TBI mods like performer manifold, ultimate tbi mods, chipp burning, headers, highflow cat and cat back before converting theyr 305ci tbi to TPI? Everithing keeping it emission legal!!! I have a 91trans-am Lo3 and the car looks nice and fast but does not give me what I expect from a 5L engine. Is TPI conversion the way to go?

I just swaped from tbi to tpi on my 91 z28. It wasent to hard but there were some technicals things that were hard to work out. I rebuilt the stock engine with flat tops, a crane cam emissions legal camshaft, a fullt ported stock tpi setup with an airfoil and k/n filter, hooker sumpercomp headers, catco converter and magnaflow exuast. I'm running almost a stock chip and the stock heads. It's does what i would expext it to do, plenty of get up an go plus it will easily bary the needle on my 140 speddo. I think its got about 325 horsepower but cant prove it.

Thank you for information. looks like TPI always will make 50-100hp over a TBI.

ROL

I built a 312 TBI that made 423 FWHP @ 6,300 on the engine Dyno.

The TPI system alone will do little to increase power over TBI. It's all the little stuff that TPI cars got to increase power over the TBI cars that really matters.

No, you don't. All 91 Trans Am's came with the LB9 standard, L98 optional. TBI was only offered on the base Firebird.

A TPI conversion will cost you at least $500 to do it right, and probably will run closer to $1,000 and you'll still have less then 200hp.

Get a set of TPI HO exhaust manifolds, matching Y-pipe and cat, and a 3" catback. Follow that up with some LB9 heads, and a L98 spec or better camshaft. At that point you'll be pretty much matched to the TPI. The Ultimate TBI mods won't hurt, but they aren't going to make as much difference as exhaust, heads, and cam.

Don't get me wrong, TBI is virtually pointless on all counts, but just swapping the intake isn't going to make up for 60hp. TBI is just a cheap fuel injection system that gets better emissions standards and is more tolerant of inclimate weather, etc.

Also, you NEED to upgrade your 2.73 gears. Swapping to 3.73's with a posi would help immensely and it'll be a modification that will result in performance you can feel.

Hey that is awsom! You guys and especially Drew just gave me the litle kick to procede with upgrading my lo3.

Drew, I have a stock 91trans-am, w6 performance suspension, rear drums, with posi with lo3. And if you want proof that they exist check out on autoscout.ch

Post a clear pic of the SPID and maybe I believe you. All the printed materials from Pontiac contradict you.

Edit: The only way it could be authentic is if it was built for export, since that would change things considerably. For domestic sale it never happened.

I can e-mail you pics.
I was thinking the same thing must be exports, because here the lo3 trans ams and some corvettes have the same ugly mirrors. I bougt the original ones + original park lights and put them on mine, and my brothers 92trans-am lo3.

I'd really like to see it, not because I doubt you as much as it would be neat to see how they were configured differently. If you can email me pics I can upload them and I'm sure there are other people that would find it interesting over on the history/restoration forum.

I would not be suprised about GM using the LB4/L03/L05 TBI motors for more exports than the TPI engine. GM put the LB4/LO3/L05 TBI motors in Mexican made trucks into the late 90s, even equiping them with Vortec heads around 96-97.

I know it is not entirely related, but I offer this as proof that GM does some weird things on Export models. I have even seen a Port Fuel injected 4.1L inline six. Thats right the old 250 got MPFI.

http://www.thirdgen.org/techboard/hi...ml#post3138870

started a new thread to keep this discussion on topic...

I love GM.