Not too familiar with the 350 heads so which ones are best to worst?

 

68-72, 5, 6, and 7a’s are all about equal
and good.

 

The 3A are the worst. Big 75cc chamber, crack prone and the horrible "A" head exhaust port and a tiny 1.5" exhaust valve. The 8 heads just need a bowl hog on the exhaust side, already has 1.625" valve. After that they flow the same as the early heads. They work best with flat top pistons due their large 77 to 78CC(79CC factory spec) chamber.

 

Number 8's aren't anything to brag about either. #4's are good heads also.

 

The #8 flow the same as early heads IF the lip is removed under the exhaust valve in the bowl. Any of the later #A heads need many hours with the grinder.

 

Some of the earlier heads CC under 64 cc's I cc'd a set of #4's and they came in at 61 cc's

 

Which is why the #4 heads are desirable. A 39 degree CBA and smaller chamber. They would give right around 9 to 1 on 73 to 80 350's.

 

Do you actually have any data to back this or just heresay?

 

The only flow numbers I saw were for 7A heads, talking 135/120, horrible. The Mid Am numbers are inflated but were the same for the 4A heads that J+S flowed. Stock the 8 heads have very similar numbers to the 4A heads. Pull an exhaust valve on a 8 head and see what I mean about the lip. He said the #8 were a much better starting point than the 4A head. You would have to be blind, the 4A's exhaust is bad but looks better the 5A heads eyeballing it. Pretty sure the now absent Smitty said the same thing about the 8 heads as well and did flow tests.

 

You talking about the 80's 307 7A heads? That would make more sense...

Anybody wanna start a Go Fund Me campaign for Mark to flow bench Oldsmobile heads with fresh valve jobs and 2.00/1.62 valves?? ha

Flow bench is nice BUT, in the case of LS engines, the lowest flowing cylinder head which came on all the trucks up until '07 (862/706) actually made the most power, unported, on 5.3 AND 6.0 engines.

 

We flowed 7a’s, maybe this will help.
https://classicoldsmobile.com/forums...rmation-72789/

 

Just shows that the 4A intake port is decent, looks better and flows slightly better than the 8 and probably even the early 350 heads. The problem is the exhaust port, very constipated and a tiny 1.5" valve. Yes, I meant the 7A 307 heads, flow numbers I saw posted were beyond horrible. The Pontiac 301 heads are also that bad according to the flow numbers.