budgdawg

I've got a '66 425 with B heads i plan to use in my '67 Cutlass. I have a '69 455 with C head also, but i'm going to use the 425 b/c of the internals. Since i have both sets of heads, i was wondering if there was a performance or flow difference. I know I'd have to enlarge the pushrod holes on the C b/c of the *45 cam bank, but that wouln't be really necessary if they are the same performace wise. Both came out of 88's from each year. Opinions?

442Harv

If it were me I would use the B. Being they both need to be rebuilt,The C will not flow that much better than the B. Then you can sell the C if you want, and they will be easier to sell than the B heads.

64Rocket

Use all the guts from the 425 in the 455 block. That way you can get any cam real easy. "B" heads "C" heads not a noticeable difference. Do port work and you will be better off.
take .020 off the block and .020 off the heads and that makes up for the fel-pro .040 head gasket.
Gene

507OLDS

Use either pair.No difference.

Run to Rund

Good tip above on using the later block. The 66 425 uses the old 45 degree ifter angle and needs a specially ground camshaft. The 455 F block uses the common 39 degree and you can use off-the-shelf cams. you can put 425 piston and rods into a 455 block, but would have to grind reliefs in the 425 block to put 455 stuff in it.