[68bird400HO]

Originally Posted by bird72

Here is a question for you HO guys..... presently in my 72 F400 is an incorrect 71 455, added 4 bolt, with 96 heads, big valve D Port with 9.5 to 1 comp, RAIV cam and headers now.

I have an HO top end, heads, intake and exhaust I will build in a couple of years and use on my 4 bolt 71 bottom end. My first reaction is decam it a notch to a RAIII type pattern.... But I am not sure on that, the 455's seem to like big cams better than 400's and be streetable. So may stay RAIV...

My question: what would you HO guys expect in power change from what I have now? (say I keep RAIV cam) and go to the round port, and factory exhaust, ditch the headers..... Same carb. I wonder what effect the 1 point comp drop will have, but the added round port flow will negate and maybe add a bunch, so this will be an interesting experiment....

I would sell the roundport heads and port/polish the 96s. I think that is the easiest/least expensive way to have the compression and the flow. Then pick up some 2 1/2" RARE reproduction D-port manifolds if you want to lose the headers.