76Supreme350

Trying to get the best out of these heads for my 76 350. I pulled them off what I believe to be a 70 cutlass 350. First thing I'm wondering is the cc's. I read it was 64 but also saw someone saying that source is wrong and it's actually 68-69 cc's. Can anyone else confirm this?

Next is valve size. I understand if it was a w-31 it would have the larger valves, I THOUGHT I ordered the large valves from my work and was going to have a machine shop enlarge the heads for the bigger valves. I compared the new valves with the heads by pushing them up against the seat and they seemed to be the same size. Can anyone help me figure out how and where to measure exactly with a dial caliper so I can figure out what size I have? And also the sizes that were available for the #6 heads?

And lastly, for these heads do I have to fill the heat crossovers and fill in around the exhaust ports like someone told me? Or is that for the later smog motor heads? I want these heads done right because this motor is going to be in for a while and I want to make sure I get the most out of them while they are out.

Sorry for the long read, thanks for reading through.

defiant1

Just had my #6 heads redone.

Yes combustion chamber size is more like 68/69 cc. I had .015 milled off of mine so I believe I am more around the 66/67 cc mark. I will be measuring them this weekend before install.

I installed 2.00 intake valves and stock 1.562 exhaust valves. I bought new valves from Valveguy (I think that's his name off of ebay). Had multi-angle valve seat jobs done on both. Intake: 35/45/60/70 Exhaust: 39/45/60

One thing to keep in mind if you order new springs/valves, etc. The #6 heads have a deeper spring seat than earlier heads. There is a .125 difference so keep that in mind when ordering parts. I had an issue with installed spring height due to this fact.

Exhaust crossover: Some say leave it alone - necessary for hot air choke intake to operate carb properly. Especially in cold weather operation. I am using an electric choke and blocked off the hot air port on my Edelbrock 3711 intake manifold.
I could not find anyone locally that was willing to fill the crossover in the heads as I was not comfortable doing it. So I cut 2 pieces out of my old turkey tray (it is .020 thick) and molded that to fit in the opening of the crossover port. I am leery of filling this opening with anything other than recommended aluminum. I have heard of using aluminum foil, silicone, etc. but have not heard of a easy full proof method that does not run the risk of burning out.

I am going to use Mr Gasket intake manifold gaskets that have the crossover port open blocked as well. I am hoping the turkey tray pieces I cut will prevent the gasket from burning out.

Hope the above info helps.

d1

76Supreme350

I'm not concerned with the heat crossovers because it will be strictly a weekend car. Also, the gasket thing was another problem I was having. I ordered the mr gasket set that doesn't use the valley pan. I heard this was the best thing to do. Is this true? Others have said to cut the valley pan out and throw it back in just floating around under the manifold but that seems odd to me. The help is greatly appreciated, thank you.

defiant1

I have heard using the middle section of the turkey tray as well to keep the oil off the bottom of the intake. Not sure of performance or oil circulation issues will arise if you don't use the turkey tray.

I also am not sure on how it would mount either. Good question.

joe_padavano

Keep in mind that the chamber volume information for Olds heads is the blueprint value. The as-cast heads tend to run a few CCs larger. I believe this was done on purpose to ensure that even after doing a valve job and surfacing the heads, the CR would not be raised above the factory-designated level.

76Supreme350

Thats good to know. I guess ill just have to mill off a little more than planned haha

64Rocket

The gasket will burn through at the cross over port with in a mile or so. The .020 piece of valley pan will take a little longer, but will burn through sometime.
If you wanted to block the cross over, you should have used a block of steel or aluminum about an inch thick and ground on it until you molded it to fit the opening in the intake.
Just my thoughts.
Gene

70Post

Run some type of turkey tray or splash shield setup to keep the PCV valve isolated from direct oil splash...that is if your PCV valve is going to be mounted on the intake. Had a buddy with a Buick leave that out and he wondered why his motor used a quart of oil on a 70 mile round trip on the highway (older Buick V8s have the factory PCV in the intake behind the carb).

Even if you run the PCV in the valve cover it's still not a bad idea to run some type of tray to keep hot oil off the bottom of the intake.

defiant1

Can you just lay the bottom portion of the tray in there or does it need to be affixed somehow?

Railguy

What ever you mill off the heads you should mill off the intake as well.I used stainless on my cross over block off ,not sure how aluminum would hold up exhaust gases are pretty hot there.
I have an aluminum intake if you look in the carb opening right in the middle theres a threaded hole going in to the exhaust cross-over never found any one who could tell me what its for.Any ideas?
railguy