My 305 is starting to push oil through the exhaust so I think its time to do something different, this is my daily driver, nothing special done to it. The only modifications are Bosch Design 3 injectors, no cat converter, and flowmaster. I was thinking of building a late model 350 shortbock, preferably roller cam, and having my heads on my 305 rebuilt and putting them and my tpi stuff back on the 350. If I do this what else will I have to change, im assuming something with my ecm, but not sure of what else. I'm needing to this in a cost saving fashion, but I am open to suggestions.

 

Why are you wanting to reuse the 305 heads? The 305 heads are smaller bore and will shroud the larger bore of the 350 block. And generally the 305 heads have smaller valves and runners. I don't see an advantage of reusing them if you buy a complete 350 long block. JMHO

 

What stock heads should I be looking for that will work with my TPI lower intake. Will my injectors I just put in about 3 weeks ago be good enough for a stock 350.

 

350 tpi heads should work. if u can find a decent set

 

Are all of the 350 TPI heads the same as far as bolt angle.

 

you will need to swap the ecm, knock sensor something else but i cant put my finger on it you can find this at your junkyard

 

So since my car is a 1985 TPI will I have to update to a 165ecm to get one for a 350

 

you will need to upgrade cause all the setting are for a 305 not a 350 it requires different setting

 

Not true. They have smaller chambers, but not smaller "bore" - they don't "shroud" 350 cylinders (305 cylinders do slightly shroud the valves, however).

The ports (what you called "runners") are identical. With 1.94" intake valves, they'll flow just like 350 TPI heads.

1.94" intake valves aren't too big of a deal to install, but even if you can't afford that expense, the 305 heads still have advantages to them:
1 - You have them.
2 - You can raise compression with them.
3 - The 305 heads you have are better than 90% of the factory 350 heads out there (such as any truck 350 before 1996, which is what the majority of 350's are).
4 - On otherwise equal SBC's, with same cam, valves, CR, etc., the one with the smaller chambers and dished pistons will outrun the one with larger chambers and flat tops.

 

If I build a 2 piece rear main 350 with dish pistons and a very similar camshaft to what is in my car now and put my 305 tpi heads on it will I have to change my injectors or mess with my ECM.

 

The 305 injectors will be fine until the upper power levels. Raising the fuel pressure will compensate for that, but reduces injector life.

The ECM will be fine with a 350. It's a mass air flow system, not nearly as sensitive as a speed density (MAP) system to displacement change. The '85 ECM is nothing to write home about, though.

350 knock sensor and module will be in order as well.

 

The only reason I was going to do a 350 was because I figured it was pretty much the same money to build a 305 or 350 bottom end and why not get 50 more cubic inches.

By module do you mean the EST module by the brake booster.

 

I agree with your motivation.

Yes, the knock sensor module aka EST module is on the firewall over by the brake booster.

 

Manily I would buy a long block to minimize down time. You can swap one long block for another when the time cames.

As for the head debate, I had an 84' Monte Carlo SS years ago. I put the heads off of it on a 350, it ran OK. When I tore it down about a year later, there was a ring on the bottom of the cylinder heads where the combustion chamber was physically smaller than the 4" bore of the 350. It hung over the bore at least an 1/8". In college I worked in a shop that built engines for circle track cars. I saw many sets of 305 heads that had the chambers matched to a 350 head gasket to make the chambers match the bore.

As mentioned before, you do not need a different ECM. Get a knock sensor for an 85' Corvette.

 

Just out of curiosity what kind of power gain would I see just changing out the short block with a 350 of the same specs as my 305.

 

The most noticeable gain will be the TQ increase. 35-50 ft. lbs right off the bat. When I swapped out the stock LB9 in my 86' for an 87' L98 - the TQ increase was the first thing I noticed. IIRC - the 86' LB9 is weaker then your 85'... 85' had a better camshaft. But, in my case the LB9 was 190HP/285TQ IIRC, and the 87' L98 was 225HP/330 TQ. Nothing but an engine swap I went from 15.20's w/ the 305 to 14.60's w/ the 350. I used the stock chip & injectors from the 87' L98 vs my stock 305 stuff. I didn't know about the different knock sensors then and was still running my stock 305 sensor. Doubt it hurt me very much though given the gains.

 

Ok, last dumb question, if I do a later model 1 piece rear main block the only additional piece I would need would be a different flywheel correct.

 

Flexplate for automatic tranny, yes.

The intake manifold bolt angle for the center two bolts on each side also went from 90 degrees like all the rest to 72 degrees in 1987. Only affects the heads.

Well, also went to center bolt valve covers in '87.

 

Right, but I am going to keep my existing heads, and if I use flat top pistons instead of dish pistons will that change my compression enough to have to mess with the ecm and injectors.

 

Won't affect the ECM. But, CR will be a bit high for pump gas and street driving. 9.5:1 is a pretty good target for street CR. That will take about 18-20cc dish/valve relief pistons depending upon deck height and gasket thickness (should shoot for .040" total).

 

Any suggestion on a camshaft for this setup.