I have an '86 IROC with a tired 305 with a cam lobe going down. I played with the idea of changing cams but would really hate to put money in a motor that is showing its age.

Sooo...I have a 350 that I bought a number of years ago for another car that has since been pulled and is sitting in my shop. It only has some 5000 miles on it so it seems I should try to use it if possible. The couple of questions I have follows:

• Is an '86 305 a one piece rear seal or two? (as it concerns the next question)
• This is an older block (late '70's I think) 350. Will it have any problems with oil pan clearance, fly wheel, etc?
• The cam in the 350 is (from my best memory) .222@.050'' with a 112 lobe seperation and .480'' lift. Other than a prom change is there anything that I need to look out for?
• The heads are the small valve truck heads from the late '70's and they have been ported some. I have been told they will pull great through low and mid rpm. Will they work good with TPI as it does also?

I have changed the injectors to 22lb from a 2003 Mustang GT and rebuilt the rest of the TPI system. It works well.

It is an auto tranny with the factory stall and a 323 posi rear end. Any suggestions would be wonderful.

 

I'll answer what I can.
86 305 should be a two piece rear main seal.
There shouldn't be any problems with clearance, just swap the 305 stuff over.

As far as the TPI stuff, since the cam and heads are not 350 TPI stuff some the values will be off, but it should run okay. The computer can compensate for things fairly well. If you want every last ounce of power out of it you'll need to do some custom tuning.

I am suprised that it is running well at all w/ the 22lb Mustang injectors as stock was 19lbs, so your computer is doing some serious compensation in that area.

 

An '86 305 has a one-piece rear main seal. Most likely you'll need to get a 153-tooth flexplate/flywheel to put on your 350 and maintain the 305 starter. This mostly becomes an issue with headers.

The PROM doesn't need to be changed (it's a mass air flow system), but the 350 PROMs from '87-'88 will run a 350 slightly better than an '86-'88 305 PROM will (mostly timing curves). However, you should get 350 knock sensor & module, as the 305 pieces have been known to cause problems with 350's.

The computer hasn't been doing much compensating for 22 lb injectors. Just cycle a little less based on O2 feedback. It probably ran slightly rich in open loop operation.

 

I looked in my shop manual last night and the 305 is a one piece seal. I've been told that one is internally balaced and the other is externally balanced. This causes the flywheels to be different. And on top of that the IROC's had lighter flywheels than other apps. Is this true and what would be the fix? Just the proper tooth count on an old style wheel?

Also, will the cam set up in the older motor (id tag said v7812fb) cause too low vacuum?

I would definitely change the chip but the advice on the knock sensor I haven't heard before. Does that old of a block have a place for a knosk sensor? I don't remember seeing one.

Thanks for the help so far. Trying to make sure I've accounted for everything before I start this project.

 

Don't get caught up in this internal- vs. external-balance thing. It's one-piece or two-piece rear main seal, that's the difference. It's true that the one-piece rear main seal crank flexplates/flywheels have a balance weight, but that's just to take the place of the counterbalance that was built into the two-piece rear main seal cranks. Internal- vs. external-balance involves 3.75" stroke cranks, and gets the harmonic damper sucked into the picture.

A 1955 265 cid SBC has the "provision" for the knock sensor. It was called a water jacket drain back then, the factory just took advantage of its presence when they started adding a knock sensor.

I don't know what that cam is, but I would start by assuming a new cam that is designed for EFI is the right thing to do. Modern profiles are highly superior to old school grinds in every way, especially when you're talking about TPI applications.