455 heads on 350?

[Pghstarsky]

Will 455 heads fit directly onto a 350 block? I dont think they will but I overheard someone talking about how it would work. Thanks

[falconsfan]

ive read some threads stating you can but it changes the compression ratio if youre using stock 350 pistons?
Maybe someone with "the know" will post as I have a chance to pickup some 455 heads for my 350 and would like to know the answer as well.

[captjim]

They physically bolt on, but will seriously lower the CR over the older 350 heads. And you can get the same size valves in a SBO head. Also, you will have intake issues, I believe you will need to port match an RPM, but not positive about that.

[joe_padavano]

Originally Posted by Pghstarsky

Will 455 heads fit directly onto a 350 block? I dont think they will but I overheard someone talking about how it would work. Thanks

Yes, all Olds heads are the same size and bolt pattern. 77-up small blocks use 1/2" head bolts vs. 7/16" on 76-older blocks. You can drill early heads for the larger bolts.

As others have noted, big block heads have 80cc chambers vs. 64-ish chambers on 70-earlier SBO heads. The BBO heads also have larger ports that a street-driven 350 will be hard-pressed to use. The Performer RPM and some factory intakes are the only ones with enough meat to port-match to the BBO ports. Failing to do this matching will negate any flow benefits. As others have noted, simply maching the SBO heads for the big block valves is a much cheaper way out (and is what the factory did on the W-31).

[Pghstarsky]

Interesting, thank you so much for your prompt response.