Would stock 71 #5 heads be a good swap for my 1973 350 with #8 heads? Can I just swsp heads to raise compression?

I see a stock set available locally.

 

Well, the #8 heads have 79 cc combustion chambers and the earlier heads have around 68 cc chambers. But aftermarket head gaskets are thicker than the factory gaskets, so the compression increase from the headv swap is not as much as you would anticipate.

FYI, #5 heads are 1968-1969 vintage and #7 were used in 1971.

 

The 2 sets of of #8 heads I measured were around 77 to 78cc. My fully rebuilt #6 heads, were 62 to 64-65, one was nicked in storage, so it was cut twice. So it would put them around 68cc stock, like most find, do a 10cc difference. Plug in these numbers into a compression calculator, 68cc head CC, 14cc piston dish .025" below deck, 4.057" bore size, 3.385" stroke, a .040" thick head gasket with a 4.250" gasket bore size. Standard replacement Felpro head gaskets puts you at 8.5 to 1 from the factory 8 to 1 with .017 factory shim head gaskets. You gain .5 in compression and a better flowing as cast exhaust port. A bowl hog on the exhaust side makes the #8 and #5 about equal for flow, there is a restrictive lip under the exhaust valve on the #8's. Now mill the #6 heads to around 62cc and get .027" heads gaskets, no problem with the factory piston to deck and you will have 9 to 1 compression. I did it with the now discontinued .028" Rocket Racing head gaskets, it ran great with a 214/214 cam till it went flat. Seriously consider even the generic 204/214 cam if you do this swap, your motor probably needs the timing set replaced anyways. Good luck.

 

Here is the link to the calculator I use.
https://uempistons.com/p-27-compress...alculator.html

 

Awesome. Yes these are #7 heads. I grabbed them as they were cheap and local. Two concepts that almost never coincide . visual inspection suggests low mileage excellent condition but we'll see what machine shop says. . Very little ventured.

 

Always a good thing. I paid $400 for a fully rebuilt set of #6 heads with the guides machined with new positive seals, 2.07" intake valves with both intake and exhaust bowls opened with a cutter and upgraded springs. I checked the center exhaust guide clearances, many have had valves stick on those guides, mine were around .003. I believe .0026" is the bare minimum or sticking can occur. Near free makes the rebuilding cost much easier to swallow .

 

YES but depending on the piston in your engine it could be a flat top all the way to a way below deck with a big dish so results may vary.. 7.5:1 up to 10:1