I'm looking at a 1991 Firebird (bone stock) and I'm already trying to figure out what I'd do to it. It has the LO3 TBI engine, but to be honest, I'm not a big fan of TBI at all. My current car has it (1990 Plymouth Sundance with 2.5L I-4 TBI), and I really don't think its all that genius of an idea.

Anyways, I was wondering how much power would be picked up by swapping to a TPI setup. I take it this would consist of a new ECM, new harness, and all of the associated TPI stuff (runners, injectors, throttle body, etc.). Is there anything else that would be needed? I mean, it sounds fairly easy to do and fairly cheap like ~$300 if I can find a ECM cheap enough.

What kind of gains would I be looking at over the stock 170HP and 255LB-FT?

Obviously, I realize a tune-up and the such would be done before all of this, I'm just trying to get an idea of waht kind of power difference there would be if I were to do this.

EDIT: I'd also then go with a CAI/Ram Air setup of some type, but I'm looking for what just the swap to TPI would bring...and then what would be the total effect with the CAI/Ram Air (haven't decided yet)..

 

I just realized this might have been somewhat of a stupid question considering the LB9 engine is basically a TPI variant of the L03 (same compression, etc.). So, would a TPI'd L03 be comparable to a LB9 (the low-output model)? How different is the L03 cam from the lower-output LB9 cam in 1991?

 

Swapping the TPI set up and retaining the stock LO3 heads and cam will only give you about 15 to 20 hp. It is not worth the money. I would much rather have a modded 305TBI than 305 TPI. The stock TPI stuff doesn't make high end power at all and you can easily do that with a TBI set up. The TPI cars had really good cams and really good heads (as far as stock equiptment goes) but the induction system is lame after 3500rpm. The TBI system is lame all around in its stock form but is cheap to mod and make fast.

 

Ah yes, forgot about that how it hold back the upper RPMs. I suppose the only really decent way for a CAI/Ram Air effect on a TBI unit then is to get either a new hood or cut a hole for one of those cheap ram-air hood bulge things. Obviously, I wouldn't want to keep the crappy stock intake..

How much power do these cars get from an improved intake (beyond an open element though, something like CAI or Ram Air)? Also, how exhaust-restricted are these engines? They come with a 2.5" exhaust stock, correct?

 

I believe the stock LO3 exhaust was actually 2 1/4" (correct me if I'm wrong). The exhaust on that car is by far the biggest restriction. Headers and a full 3" exhaust should be done on it; some have gained about 30 horsepower just from exhaust, that's pretty solid gains.

The TPI swap is definitely not worth it. I'd say the only time you need an induction swap from TBI to something else is when you have a built up motor that TBI can no longer support. At that point TPI would be a bad swap too because its still very restrictive especially high RPM. Go aftermarket then.

Basically, my thoughts are keep TPI cars TPI cars and keep TBI cars TBI cars after you've exceeded stock induction limitations then go with a stealth ram or super ram or something comparable.

 

Aw and I just passed up a great deal on a 3" mandrel bent exhaust system. I figured it'd be overkill for a 305...guess I was wrong, lol. Oh well, I don't even have the car yet, I'm just trying to get an idea whether its worth it to buy a TBI one, but they seem decent enough..

 

It's not worth it. Someone on this site did the swap a while ago, and he picked up hardly anything at all.

Like the others have said, it's not the induction system that makes these engines suck. It's the package underneath them. . . broomsticks for cams, crap swirlport heads, tiny exhaust. . .

I went with the TBI for insurance purposes. It's not considered a performance model, which saves me $1,000 a year or something like that, plus, it's cheaper to mod.

 

Aight sounds good enough. I'll stick with the stock TBI unit if I end up getting the car. My uncle has a 70's sbc 350 with forged 10:1 pistons that I'd want to get together by, say, next summer, if I end up getting a Thirdgen this summer. Thanks for the help guys!

 

Honestly, I wouldnt go past 2.5'' for a 5.0L 305c.i. If so, you might be facing some serious back-pressure issues and a possible loss of power rather than gain. 3'' is usually reserved for Big Blocks, ***** extention trucks, and ricers. Just my .02

 

Actually this couldn't be farther from the truth. Any small block chevy, even as meesy as the 305TBI, will see gains from a 3"
exhaust. You never want back pressure EVER. I suggest you do more research on exhaust.

 

Theres nothing wrong with a 3 in exaust on one of these cars. The only place where you can really get into trouble is using headers with too large of a dia. primaries. The slow moving exaust pulses will reduce scavanging and cost torque. Its not the back pressure that causes problems...

 

I sit corrected.

 

Yeah, I ended up being able to get teh exhaust system anyways. Made by SLP, 3" mandrel-bent cat-back to the dual 2.5" (i think?) tailpipes on the driver's side. Got it used for $125. Amazing how I spent $125 on parts for a car I don't even have yet...can you say addiction? Obsessive compulsiveness maybe?