MadOTC

In the next week or so i'm probably going to be buying 3rd gen and it looks like the one im getting has the TBI 305 engine in it. I've been reading up on what can be done to that engine to get more power out of it and I've pretty much decided on the setup im going to put together. I'm looking at getting a set of the L31 Vortec heads, a Vortec manifold to go with the heads, an LT1 cam, and probably a Holley TBI unit. I've read in a few places that you need to mill these heads because they are 64cc and will cause compression loss if you install them stock. Does anyone know if this is really necessary? Will these heads cause a significant compression and power loss if they arent shaved first? Also, after these mods are installed what do i need to do to the TBI computer to make the engine run right? Last on my long list of questions, I was wondering if I would be better off using a 4 barrel carb intake with an adapter, or sticking with a stock vortec intake? Lots of questions at this point. Any suggestions short of an engine swap I cant afford are welcome.

Damon

Not sure which Vortec TBI intake you are referring to so I'll steer clear of that one.

The main thing that needs to be addressed with the TBI, aside from hardware, is chip tuning. These motors are notorious for not responding well to mods without chip reprogramming, at least beyond the usual external bolt-ons. Getting a chip custom burned on a dyno AFTER you do all the hardware mods is going to be important- and it's not cheap.

Yes, you compression will drop considerably if you just bolt on the Vortecs. Not only do they have larger (62-64cc chambers) but the head gasket you are likely to use to bolt them on is probably going to be thicker than stock, lowering compression even further. Mill the heads down to 58-60cc and use a GMPP .028" compressed thickness composite head gasket and you'll stay close to stock compression ratio (about 9:1).

You MUST also address the exhaust on a TBI car. The stock exhaust is VERY restrictive. Exh manifolds are not good and they have the smaller 2" outlets (TPI cars use 2-1/4" outlets). The y-pipe uses 2" down pipes going into a very small 2-1/4" y-pipe and then it stays a single 2-1/4" pipe all the way through the cat and back to the muffler. A COMPLETE exhaust system for a same-year TPI car (including headers, y-pipe, 3" diameter cat and muffler) is actually a very nice improvement in power even on a dead-stock stock motor. On a modified motor it's mandatory in my book.

Damon

Another thing- might want to talk to some of the guys over on Thirdgen.org about TBI performance and chip burning to match the mods. There are several very knowlegable people over there that have worked very hard on their TBI cars to go fast but be unique (not a carb or TPI).

ChrisUlrich

A 88Z with suspension work, mild cam, and lt's... where do you think the car will land with a 1/4 time and dyno numbers?

What size torque converter would you guys suggest?

njspder

what kind of ET are you shooting for? you cna easily get an LO3 into the mid to low 13's without much trouble if that is what you desire.
the stock cam is a joke, the lt1 is an excellant choice for a replacemnt. don't worry so much about the heads as the factory intake is a much larger restriction. i would go for a holley street dominator tbi. it is equiped with 2inch bores so it is ready for a big block/holley replacement tb and it hs a bit more plenum volume than the edelbrock offerings so it will deliver a little more top end power.
chip tunign is key for any major swap on parts. get a proper chip done from real data logging. don't settle for a mail order ship, they are never optimized for your combo.
above all else make sure you take care of teh chassis. get yourself a posi adn some 4.10's and the car will fly. get a good torque arm, control arms, and control arm relo's to get it to the ground.

later
tim

Alvin@pcmforless.com

We have seen really really nice gains with just a plain jane stock Lt1 camshaft, nice catback and headers. We also have many different TBI setups in our library that have known to help quite a bit.