The Stovebolt Site Forums The Shop Area Engine Shop 350 heads on 305 engine

Can it be done? I have a good 305 block and good 350 heads. Can you but this together and will it run right.

First issue might be that the compression ratio would drop a LOT, since the 350 heads are sized for 350 cubic inches of displacement versus 305. That is a BIG difference, that would drop the compression into the anemic range.

You would have to mill the head a LOT to get that amount of dispplacement difference compensated. I don't know fi you could do that without other problems, like interference between pistons and valves.

I don't know what other issues might be encountered, but I would think the compression ratio loss would be a disqaulifier all by itself.


Jim G

It depends on which head we're talking about. A lot of them will work. Give us some casting numbers.

I don't know of any 305 heads that weren't also used on 350s not sure but heads with 2.02 valves may hit the edge of the cylider but for the most part small block Chevy heads are small block Chevy heads here is a list of casting numbers for you.
http://www.mortec.com/castnum.htm

Lots of differences in small block Chevy heads. Especially between 305 and 350 heads. Some were open chamber, some were closed. Some may have had 2.02 valves, others 1.94.

A friend of mine put a pair of 305 heads on a 350 once, and I didn't know it until I couldn't help him get it to run correctly.

It would grunt while trying to start and clatter going down the road if you timed it according to specs. If you timed it so it would start, it wouldn't pull itself hardly.

Didn't help that he installed mismatched heads too.

I agree with Grant. Some will interchange depending on the cc volume. There are a several listed on mortec that are shared by 305's & 350's. Not too likely you have a regular set of heads with 2.02 valves.
Fred

If the 350 heads have the larger intake valves (194 or 202) they will not work.

The heads I have are 1978 truck heads with the 194s. I can get a set of 1976 heavy duty truck heads with small valves (3927185). I was thinking these might work. Just still wondering about CCs and compression. Buddy of mine was saying it might drop compression to 7 or 7.5.

I just looked on the site that heavyhauler sent me and they say the 1976 heavy duty (3927185) heads are 307,327,350 heads 70cc heads. these should work on a 305. Sound right?

JUST A NOTE,

I swapped in a 350 to replace the 305 in a 86 Monte carlo. The bolt pattern for the exhaust manifold is different by one bolt of a larger distance on the end of the head of the 305. I could not use the original exhaust manifolds of the 305 and had to go to headers. Just thought you may be able to use that information.

Dave

you will lose a point or so compression with those heads. It's common for the saturday night roundy rounders to put 305 heads on their 350s, because you will get a bit over 10 to 1 CR with a stock dished piston for cheap and if they win their competitors cam buy their engine and all that rules stuff. That's why the above post had so much problem cranking the 350 over...