283 with 350 Heads

[Normmus]

This is not in my squarebody but in a project jeep that I am working on. A previous owner SBC swapped it with a 283. I just finished doing the valve cover gaskets and while the valve covers were off I took note of the head casting numbers which are 3986336X. Googling that casting number it seems that these heads are from a 1971 350 with 2.02-inch intake valves and 1.60-inch exhaust valves, and a 76cc volume. It seems to me that this would lower the compression ratio so not sure why someone would do this swap, are there advantages such as more flow? The jeep runs decently.

 

[bucket]

Seems to be an uncommon casting number that was used in '71. Hard to find info, but comparable to the 487 head. Could have 2.02 or 1.94 valves. Could be screw-in studs, or pressed studs.

It was probably somebody's hot rodded 283 back in the day. It will be low compression unless pop up pistons were used.

 

[Normmus]

Unless the pistons are domed the compression ratio is probably down from around 9.5:1 to below 8:1 since 283 heads are 58cc and these are 76cc, according to a compression ratio calculator.
I believe the 'X' after the cylinder head casting number indicates the 2.02 valves.

 

[bucket]

Unless the pistons are domed the compression ratio is probably down from around 9.5:1 to below 8:1 since 283 heads are 58cc and these are 76cc, according to a compression ratio calculator.
I believe the 'X' after the cylinder head casting number indicates the 2.02 valves.

The "X" is a mystery to me. I once had a set of '71 487X heads and they were 1.94 valves.

 

[Ricko1966]

2.02 valves won't clear the 283 bore with out machine work. This is all very suspicious.