What non-350 heads would fit on a 77-80 olds 350. Could I take #8 heads from a 403 or #5A heads from. 307 and stick them on a 77-80 olds 350. This is purely hypothetical, but I want to know more about these and information is scarce.

What non-350 heads would fit on a 77-80 350 Olds? And what would be the ramifications of doing such? Do any of the heads need modifications to fit?

I ask because I have heard of people swapping heads between the 3 Main small block olds engines and am curious about it myself.

 

The #8 heads were used on 1973-1976 350 engines. The 403 used 4A heads, from what I recall.

In answer to your question, the heads from all Olds second generation V-8 engines (260, 307, 330, 350, 400, 403, 425, and 455) are interchangeable, as in they will bolt to the block. The alignment dowels and head bolts are different size for the later (1977-newer) engines. The combustion chamber volume and intake port sizes are also different between many of the different heads, so that needs to be taken into account.

 

To my knowledge Pontiac was the only one that made a 3 main V8 in the last 50 years.

 

The 5A heads will bolt right on but you will lose some intake flow with the smaller 1.75" intake valve and smaller port. You gain a bit of compression with the smaller chambers. The 4A heads will bolt on you gain a 2" intake valve but you will loose a point of compression, not good. My 4A measured 86cc.

 

Of note, the largest valve you can stick into a 5A head is 1.875 so, not terrible considering that's all that was in all of the small valve 350 heads.

As previously noted, all 65-88 Olds V8 heads will bolt physically to the block HOWEVER, any head to 1976 (2, 3, 4, 5, 6, 7, 7a, 8) will need the bolt holes drilled out to 17/32 to accommodate your 1/2" head bolts.

Number 2 and early #3 heads have a 3/8 rocker stud instead of the pedestal mount rockers. Easy if you're doing a stud mount rocker.

Number 2, 3, and early #4 if they were on a 45* block will need the pushrod holes wallowed out at the top. Easy fix with a Harbor Freight tapered drill bit.

Easiest pickup for any sort of gain is #3 (pedestal mount) or #4 with the smallest chambers followed by 5, 6, 7, and 7a.

If you are not using a steel shim head gasket and just an aftermarket Fel Pro or similar brand head gasket, keep in mind they're compressed thickness is .024" thicker than the factory so you'll want to cut the cylinder head that much to benefit from the smaller chamber.