[ScottU]

Did any of the OEM 455 pistons have only 2 valve reliefs or did they all come with 4?

Any variance of valve relief cc from 1970 to 1975?

[Steve Barcak]

no Pontiac 455 pistons were produced with 2 as you asked. if you find any, it would be aftermarket. The 455SD had what is called a trough.
When you ask about valve relief cc, as best I know they are all the same BUT, remember, starting in 1975, Pontiac dropped compression to 7.6 and they did that by changing piston design on the edge of the top of the piston, above the ring land. they used a 45 cut instead of a 90 and this lowered compression further. Many Pontiac people are not aware of this. Hope this helps you. I have also seen aftermarket replacement forgings like this and have a set for a 400 in my stash

[ScottU]

Hi Steve,

Thanks for replying.

Yes the SD piston had a trough with the two valve reliefs combined into one large D shaped pocket.

All other OEM 455 pistons I have seen have 4 valve relief as well. The reason I ask is NHRA lists different CC volumes for valve reliefs for different year 455 pistons. They list the 1971, 455 HO rated at 335 hp as having -3.10cc valve relief. No idea where this number came from. I have a 1975 piston that looks to be only 1.0 cc with a valve pocket depth of roughly 0.060.

Anyone have a 1971 455 HO OEM piston?

Thanks, Scott