Tried searching this and didn’t have any luck. Anybody tried putting 5A heads on a 350? I’ve read around and seen people saying they don’t flow very good but nobody seemed to have tried it.

They have a smaller chamber and larger ports than later 350 heads so I’m wondering how they could be worse than say the 8 heads I have already. Couldn’t find anything on valve size and they look a little smaller but if I can get em cheap enough that could be easily fixed.

 

Valve sizes are 1.75/1.50. It'll be GREAT until about 3000 RPM..ha. Largest valve you can put in them is 1.875/1.625 which is the size of the intake valve on most of the non-performance 350s back in the day. Where are you located? There's a set of #3 heads that would be a better fit on eBay right now for $150 in Michigan.

https://www.ebay.com/itm/1966-Oldsmo...Condition=3000

 

I have a fresh set of #8 heads with low miles. (Sat for a few years) but they came from a running engine i recently had on my engone run stand. 100 plus shipping. That should leave you some cash to deck the block and mill these heads. Or buy some pistons. Just putting it out there.

 

I put stock 5A heads on a stock 76 350 short block. It was in a truck application, so they worked great. I also used the 204/214 cam, shorty headers and 2.25" dual exhaust. You will only have 8.5 to 1 using .040" head gaskets, stock pistons sit .025 to .030" below deck, so only a .5 compression gain. My 94 Z71, idle to the 4200 rpm shift points would out perform the LS trucks I drove with the same 4L60E trans and 3.73 gears. The LS trucks actually had slightly shorter tires, 245 vs 265 so they actually had a gearing advantage. If I would got the 454 TBI working the way it should; it would have killed stock 6L LS trucks. Above 4000 rpm is a different story, the LS was designed for rpms. Remember I believe the 5A heads are only like 155cc intake runners and unless some .011" shim gaskets are purchased from Smitty, you will gain very little compression and gain no flow. Those #8 heads with a bowl hog will outflow the 5A heads without a doubt, they match early 330-350 heads just doing that.

 

Good stuff from experience. So I probably need to stay away from the 5A’s. But man. Those ports are so much bigger I was sure they would do better.

help me out here I’m pretty new to this, what are you talking about when you say bowl hog? And .011 gaskets?? I can get around 9.5:1 if I run those with some flat tops and just leave the heads and deck alone. Might be the way to go, if those will seal and not have to constantly replace them. Anyone got experience with those shims/gaskets?

 

If you go flat top, just run regular, cheap Felpro head gaskets. The bowl hog is a cutter to open the bowl a machine shop uses. There is a lip right under the exhaust valve. Add a W31 1.995/2" or a 2.07" intake valve and leave the stock 1.625" exhaust valve.

 

So I think I’m going to just run the #8’s I already have. They’re in pretty good shape but I’m thinking about milling them down to get a little more compression. I know I’ve seen a page where someone showed how much you need to take off to go down 1cc for the different heads but I can’t find it to save my life.
Anybody remember where that is?

Also I’m interested in those .011” head gaskets. Who knows about them? Worth it or not?

 

Jmullins, check the casting # on those 5A heads. If they have 397 742A stamped on them they would be from a '69 350 which will be the same as the desireable #5
heads. Have them on my stock '69 Cutlass. Apparently, just a rarer version of the #5's ?

 

No such luck. They’re full of smog ports and have small valves... thanks for the input though! I’ll look closer at the next set of 5A’s I come across

 

The difference is 5A vs 5A. The former are the 307 heads, and the latter are the 350 heads. The latter don't show up all that often though.