305 tbi mods?

[njmadman]

wondering what i can do to get some power out of a 305 tbi? I would like to to do an ls1 conversion eventually but funding is very limited right now.

[Danimal]

Lucky you! I’ve already done this once. There is a ton of stuff you can do without spending a lot of money! Lets start with the exhaust side. Any of the cat-backs are good and mostly the same. Don’t waste money on headers. Sure they work. But they cost, and are a pain in the a** to install. Head to the junkyard and find a set of 350 exhaust manifolds. They have a ¼ inch larger outlet. GALE BANKS use to make a great pre-cat pipe for the F car. I had one on my 89 firebird. If they still make it get the one for the year car you got the manifolds off of. You can have the cat modified for 3” in 3” out or just buy a new one from JC Whitney. All of that installed should be 30 to 35 ponies. Because the 305 exhaust parts are such crap, and are not much better than V6. Now the intake side. The factory TBI is only good for 525 CFM. Holly makes a replacement TBI that makes 670 CFM. I found in an off road magazine. I called their support line and asked the tech. “the 305 pickup motor and the 305 in my firebird are the same so why would it not work” He said he couldn’t figure out why either so one came in the mail shortly after that. Now head down to the local GM parts counter. And order the duel snorkel air cleaner off of the 80’s model Monty Carlo SS. Even though it had a 4bbl carb. They use the same standard 4 ½ inch opening on the TBI as the all the carbs ever made. Holly also makes a performer intake manifold for the TBI engine. So the last thing is the cam. I used a L98 cam with new factory lifters. But you have a lot more cam choices now then I did in 90. Also I have to keep the California smog nazi’s happy. My car had a rear with an open diff 2.73 gears and drum brakes. All that swaps out with a rear from a donor possi car. It tales 7 bolts two cables and the brake line. I found a Camero a year older than mine with the same miles on it that someone parked on a fire hydrant. 3.42 possi with disks. The firebird stated life in the 16.4 second range at the local track. When I traded it for the 96 TA it would run in the low 14’s all day. It would be great, except for the duel snorkel air cleaner you can’t tell it from stock. Guys would give me crap in the pits. “Why run a TBI stocker”. I would say I’m just there for the fun. Run a 14.2 or 14.3 and watch them stare at me. You could get deeper in the motor with heads pistons and the like. You would probably see low 13’s. Send me an e-mail if you need more. I’ve already gone on to much here.

[wako29]

www.thirdgen.org will help you mucho better

[Detroit_Bird]

It might be too soon for this mod, but....

If you need extra flow (Read: a cam, etc.) and are on the cheap then check out a Rochester unit off a late 80's early 90's Big block pickup- they bolt right up and flow around 650 CFM. A buddy of mine managed to get a TBI powered RS down to high 12's with some coaxing (including a 350 block) while using a stock big block throttle body.

[njmadman]

the 350 manifolds will bolt right up to the stock heads?

[Danimal]

I would like to point out that the above mods were done in the late 80's early 90's. So most late 3rd gens were in the 14.7 range, if they were lucky running showroom stock.

[Detroit_Bird]

Yes- 350 manifolds should bolt right up to 305 heads- In fact you can put 305 heads on a 350 (but not vice versa as the 350's valves will hit the 305's smaller bore). My friend who got his into the 12's did so with a 350 block, and ported L98 heads I think, and a moderate cam. I'm sorry if I made it sound like he did it with 305 heads on a 350- not that it's not possible, but 305 heads, even ported can't support much past 300 hp, and you need close to 400 to run what he was. Really cheap buildup though- a lot of junkyard parts used (rebuilt of course). TBI is a solid system and if you can find a good tuner in your area you should be set. If you want the details of my friends buildup I can get them to you-

[njmadman]

thanks for your help