307 heads on a 350

[olds1985]

What would the pros/cons of putting 5a 307 heads on a olds 350?? I've read that it wouldnt be a good choice but i want to hear your guys opions

 

[bill]

What would the pros/cons of putting 5a 307 heads on a olds 350?? I've read that it wouldnt be a good choice but i want to hear your guys opions

5A 3317 64cc
1981 - 1985 307. Used on the regular hydralic lifters engines. This head is preferred for 307 performance use because there are port matching problems between aftermarket intakes and exhaust headers with the 7A heads. 5a heads are rumored to flow slightly better. The 5a ports are larger than the 7A's, so this makes sense. So, if you switch from 7A to 5A heads you should get the intake and exhaust manifolds from the donor engine. Rotator style spring retainers were used on the intake and exhaust springs.
and this from 442.com
http://442.com/oldsfaq/ofe350.htm#E350 350CIDEngineDetail

 

[DoubleV]

The 5A heads barely flow well enough for a 307 let alone anything bigger. Unless you're building a very low RPM truck engine perhaps ( and even then....), the 5A heads have nothing to offer over any other 350 head ( the 3A heads suck though ). Even with the right build, the #8 heads can be a good choice.

 

[beeterolds]

How high are do you plan on revving it? If you open up the valve sizes and do some home porting, (remove the AIR injection bumps and tubes) clean up the valve guide area and port match the gaskets I bet they would make a hot set of heads for the street.. but youll be limited for air flow capacity over 5000 thats for sure..

I look at it this way.. I used 1972 350 heads on a 403, with the comp XE262 cam the motor effortlessly pulled like a motherf*cker to 5200 where I shifted it..

Ok my point.. the 403 should have come from the factory with big block heads.. It flowed more than enough air.. But if my motor allowed my car to run 13.30s @ 106 with "good" early 350 heads think what early 307 heads will do for a "street" 350...after they see a little attention first..

I went from a 2.00 intake to a 1.875.. throttle response was nuts.. but it was no race motor.. just a stout stop light to stop light killer.. I foresee similar results on a smaller scale... even if you left the heads stock...youll see a small bump in compression and with the smaller port design it will be a torquey motor with good throttle response..

 

[DoubleV]

Ok my point.. the 403 should have come from the factory with big block heads.. It flowed more than enough air.. But if my motor allowed my car to run 13.30s @ 106 with "good" early 350 heads think what early 307 heads will do for a "street" 350...after they see a little attention first..

I don't think 307 heads on a 350 is the same as 350 heads on a 403. I have read multiple times from people alot more knowledgable than myself that even a fully ported set of 5A heads don't equal the flow of stock early 350 heads. If that's the case, I don't think porting 5A's destined for a 350 build would be a wise choice.

So yeah, 5A heads would work, but you'd just be leaving power on the table. To go through the effort and expence of rebuilding an engine, I wouldn't want to saddle it with restricting heads when better ones are available for cheap.