olds 350 block w/ 403 heads

[shortyb]

i am the new owner of an 86 cutlass salon 442. i was told the 307 was switched out for a 350. after researching the castings # on the block and heads i found out it has a 350 block (casting # 557752-3b) with 403 heads (casting # 4A). is this bad/good, or gonna cause problems? any input would be helpful.

 

[dan2286]

I think it really depends on what is in the rest of the engine. How does it run right now?

 

[shortyb]

it runs good. i haven't really been able to drive it around as the speedo doesn't work at the moment.

 

[88hurstolds]

403 heads are low compression heads, you might also have a late 350 block with windowed mains and a cast crank, the 77-80 350s aren't good for performance.
I would leave the motor as is and just drive it, if you want to do any performace upgrades go with a 68-72 motor that have Nodular cranks, solid main webs and higher comp #5, 6 or 7 heads. 73-76's are also good motors to, just swap in some early heads.

 

[jae]

Yes, you have a later 350 block, 77 - 80 vintage, with the windowed mains. The solid main blocks are the pre-77 castings, having numbers like 395558-2 (and -5 I believe) and 381917-2 (note the 381917 is also used on 330 blocks but should say -1A).

Though the main webs are windowed you should still be able to produce some decent power with the block, depending on the internals. As others stated, I would go with the earlier heads, concentrating on the #5 up to #7-subscript A heads - these are the same as the #7 but have the hardened seats for unleaded fuel. I'm guessing the eariler 330 heads may work too. Again, it's going to be based on the internals, intake and exhaust to get the most out of it.