350TurBRO

I have a '69 f85 with a 350 sbo in it and I've heard that you can easily swap 455 heads onto it and get great power gains with no problems. Is this true/ does anyone have those heads?

coppercutlass

You need a lot of work to actually see gains. Its all relative to your build.

67 Cutlass Freak

This has been done a lot, but more often ends in failure. There's a lot that needs to be considered.
1) You need to get the compression back up since the combustion chamber is considerably larger. You could mill the heads, deck the block, get dome pistons or stroke the engine. If you intend on running this on pump gas, I would keep your compression ratio under 10.5:1
2) The head bolt holes all line up perfectly but two dowel pin hole need to be opened up slightly.
3) Another problem you will encounter is the intake manifold port mismatch. Currently there's only two intake manifolds in production that have enough material to match port the roof. You will need an Edelbrock RPM Performer or the Victor. The difference in the ports is approximately .250".


You need to do some serious research if you really want to go forward with this swap. And don't even think about wanting good gas mileage also. I'm going to point you toward some threads that talk about this. The first one is "Home Porting Techniques" This thread is really long, but it has a ton of good info-
https://classicoldsmobile.com/forums...echniques.html


http://realoldspower.prophpbb.com/topic5563.html


http://realoldspower.prophpbb.com/topic5512.html

brownbomber77

Yes, they physically fit. Without a lot of machining, the combustion chamber will be huge. Don't do it. You'll probably hear the same thing from everyone else on here.

70cutty

With an otherwise stock engine there will not be any great gains.

Smitty275

There are things that have to be accounted for when swapping the BBO heads onto a SBO. It is not just a direct swap and instant power gain on the 350 engines. At a minimum you need to cut the heads to reduce the chambers so they are at least within a couple of cc. Then you'll have to cut the intake so it fits.
The swap to a BBO head is much more favored if your starting from scratch with the short block and new set of pistons to help make up the compression difference.

joe_padavano

In fact, if you simply bolt them on without raising compression and port-matching the intake, there will be a power LOSS.

You can install the larger big block valves in small block heads, as the valve center-to-center spacing is the same on both.

joe_padavano

And once again, you'll get better answers if you don't ask the exact same question in two different sub-forums. If everyone sees the previous answers, you are more likely to get correct info. I've merged your two identical threads.

oldsmobiledave

You heard wrong.

olds 307 and 403

I would get Procomps from Smitty if you want to go that route. But an electric fuel pump, adjustable valve train and milling would be necessary. You could do what the factory did, add bigger 2"/1.625" valves with bowl porting. Also put in a better cam, the factory did that too along with better springs.

88jetstar

Do you have a link?

olds 307 and 403

Just PM Smitty275 on here, I am sure he will give you all the options.