Thread: 350 w/ 305 heads and TBI intake... help!

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Hello everyone, let me explain...

I have a 1991 firebird formula that came stock w/ a 305 HO matched with a 700R4 tranny, like most have. I threw a rod through my oil pan making a pretty peek hole in it...

Well, i found a 350 4-bolt main that is a little older... stamped 350 insted of 5.7 and is that light blue that they painted them back in the late 70's. I pulled the heads off of the 350 and swapped them for the stock 305 heads and intake(TBI) that i had from the origional engine along w/ the distrib and coil.

after it was all said and done... primed and timed(4º adv.)... i got her started. She fell on her face when i stepped on the gas... timing was off... i thought. We advanced the timing to 14º, it ran better... idled high around 1800rpm and still loses power when i get on it.

also... i find myself priming it with gas manually from a gas can...


so, i'm looking to get rid of the ECM and go carburated. i have a set of vortec heads for a 350 and a holly 650. would it help if i swap them in? please help!!! I'm really in a bind w/o a vehicle... anything would be a big help. thanks for your time!!!

The original 350 heads were probably 76cc chambers. The 305 heads are probably around 58-60cc. That's quite a jump in compression.

I'll bet your ECM is all kinds of confused.

I would use the Vortec heads, but you'll need a Vortec style intake. You'll also need to swap out the distributor. Then, just disconnect the computer.

Thanks for your help!
Yeah, i was told that with that head/block configuration that i had a 10:1 ratio.

I have another distributer and carb! You confirmed what we had in mind to do... it's always a good idea to ask around.

thanks again!

Theres a problem with the TBI on a 350 theory. When you hit the gas, the computer is still only sending enough fuel to make the proper mixture for a 305. Thats why its falling "flat on its face". The reason it still keeps running is due to the fact that the 02 sensor is registering a lean burn. Want to get your power back? Get a programmable ECM and re-curve your injector timing

friend did the same thing with his truck I argued with him until I was blue in the face. It ran but it didn't run right. I put the 416 heads on my 79 350 block and It figured out to be 10.47:1. with premium unleaded gas and octane boost I don't have any problems. Mine's carbed though