what's the compression ratio on a 1975 400 sbc (882 heads)
does the cam change anything? (xe274h)
and how much would 72cc heads change it.. or 64 cc (more common)?
thanks

 

Pretty low. I recall it being spec'ed around 8.2:1 from the factory. 72cc heads won't make much difference. 64cc will raise it close to 9:1.

The cam won't change the mechanical compression ratio but it will lower the "dynamic" compression ratio. The bigger the cam the lower the cylinder pressure. At 8.2:1 the fairly large XE274 will be pretty doggy below 3000-3500 RPMs, even in a 400.