73aussie455

Not sure where to put this.. here will do

I've found 2 pairs of heads for my '73 smog Delta to replace the J units, no mean feat finding any here in oz..

One pair is the C heads from a 455 (394548) and the others are B heads from a '65 425 (383821).

Am I correct in thinking the C units will go straight on and easily out flow the J's?
The exhaust manifolds from the J heads should also bolt straight up to the C heads?
I found an old edelbrock dual plane performer intake manifold to sit the original 4bbl 800cfm Qjet carby on.

I am ditching the single pipe and going to a dual 2.5" exhaust with free flowing cans at the same time, is it simply a matter of blanking off the crossover on the R/H exhaust manifold on this model?

I dont want a race car, just get the thing breathing and rumbling like it's suppose to..

Hopefully I'm on the right track and the old girl wakes up and comes to life! Cheers

joe_padavano

Either set will bolt on and outflow the J heads. Either set could have come from a motor with a 45 deg lifter bank angle, so you have to check pushrod clearance as you may need to open the pushrod holes slightly.

All Olds heads have the same exhaust flange bolt pattern, so yes.

On the 1971-76 family of full size cars, Olds actually used dedicated dual exhaust manifolds on the BBO cars (and yes, I know there were no factory dual exhaust cars after the 1974 model year). The W/Z manifolds used on the A-body cars work on the full size. You can get repros. Capping the current manifolds works, it just won't be very efficient and you'll need to have a custom pipe bent for the driver's side.

73aussie455

Thanks Joe. Does either the B or C heads have an advantage over the other? valve size, etc?

joe_padavano

Either casting could have come with large or small valves. The only way to know is to measure the intake valves. Otherwise, on your stock motor with low compression and mild cam in a heavy car, the difference between the two will be negligible.

oldstata

Hey joe, I have read about the 73-76 blocks having non dished pistons and that they lowered compressen through the heads.
I have not seen this I was wondering if this could be a factor here ?

joe_padavano

I don't know where you read this, but it is not correct. All BBO heads have about 80cc chambers except the 68-69 D heads, which have about 72cc chambers. Note that these are the blueprint numbers, not the as-cast numbers. The latter will typically be a few cc larger.

And if you've ever seen the pistons on a 73-76 BBO, there's a chance you'll mistake them for soup bowls.

oldstata

Joe , I thought I read it on olds FAQ but I can't seem to find it again so I am unsure where I have read it .
I didn't nesseraly believe it just didn't know if it was true

Thanks for clearing that up

Seff

The FAQ states that SBO heads from '73 onwards have larger chambers, and those same engines have flat(ish) pistons. So a 64-72 head on a 73+ engine would help compression. I think that's what you got mixed up.

oldstata

Thanks this seems like what I was thinking so I mixed up SBO with BBO