deadeyejedi

have a quick question regarding a 1976 455 .i know its referred to as a smog motor but, i do have a set of 70 455 heads(i believe d heads ) i could put on it along with some headers .would that make a noticable difference in horsepower ?or will i also have to change pistons to get the extra horses im looking for ?was hoping for 350 + hp without breaking the bank .doable?thanks

Fun71

All BBO heads have about the same combustion chamber volume, so a head change won't do much to increase the compression ratio. You would need new pistons to accomplish that since the factory '73-'76 engines used huge dog dish sized piston dishes.

Regular BBO heads had 2.00" intake valves and the high performance versions had 2.071" valves, so that may make a slight difference. The real difference between the '73-'76 J heads and the others is the port passages - the J heads are more restrictive than the earlier ones so they don't flow as well.

FYI, if you really have a set of D heads you could sell them for enough money to build a new performance engine, and maybe have money left over.

Olds64

If you already have the parts then use them. My dad; Oldsguy, had a 76 98 coupe with a 455 and J heads on it years ago. It was one of the best Oldsmobiles I've ever driven.

joe_padavano

OK, first, D heads were only used on 1968-69 W-30 and H/O motors. If those are what you really have, sell them to a restorer and use the $4K you get to buy a set of E-brock heads and a bunch of other parts.

In any case, simply changing heads isn't going to produce a dramatic increase in performance. Every single BBO head (except the D heads) has about 80cc chambers (D heads have 72cc chambers). You won't notice this difference in CR on the street. While the J heads have small valves and small-ish ports, for street use in a heavy car that isn't all that bad. Your bigger problems are cam, carb, and advance curve. Fix those first for improved performance. Different heads with big valves will help, but only after you fix the other problems noted above.

deadeyejedi

ok not d heads confimed . carb cam and maybe aftermarket distributor wouldnt be bad on the wallet .