I was wondering if there is any difference in the 305 and 350 ECM (89 model to be exact), or is the prom itself the only difference. I have a line on a low mileage IROC and am wanting to build if for my girl. I am going to retain the EFI on this one and it will get a cam, heads, stealth ram, bigger injectors, headers, exhaust...etc. It has a 305 in it right now, I know it will need tuned anyway so does it really matter what computer I use?
Thanks

 

I'm almost positive you'll need a 350 knock sensor, and an adjustable regulator if you use the 305 injectors. I think the computers were the same also, until 1990, when it went to Speed Density. I ran a stock 305, SD set up on my 350 for many years before upgrading to bigger "stuff". It ran sweet, and I got excellent mileage.

 

ECM same, prom different.

On a stock 350 vs 305, the car will run with the 305 ecm, and even drive. the 02 will correct any fuel needed. This is a temp fix though.

The fact is no matter what fp/inj size you have, the ECM is gonna get it to 14.7 or as close as it can anyway.. to actually get the inj size/fuel pressure/pulse width right you have to force open loop, and tune to a wideband o2.

-- Joe

 

Thanks guys, I was pretty sure that the prom was the only difference, but wanted to make sure. A good buddy of mine has a 87 IROC with the 350, but this thing has had absolutely no tuning with it being bored .030, 10.5:1 compression, edelbrock heads, stealth ram, bigger injectors, full exhaust, ...etc. The car has went 12.30 and is in full street trim. He said he just drives it for a while and the computer does all the tuning he needs. I guess that you would need to do some fine tuning with chip, but his runs great and gets good mileage.

 

Drop in to the Prom board sometime. Take a look around. I'm sure you'll find out that there is a LOT to be tuned on even a stock setup!

The MAF setups (which means before 90) will work better without any chip changes. The spark advance is off more than the fueling when dealing with MAF (from what I see) although there are gains to be had in recalibrating the MAF tables.

It's all pretty in depth, and somewhat overwhelming, but very worth learning. I'm just getting into all this myself, so don't take my word for it, go look at the PROM board!