BBC heads: open vs closed chamber

[StockerChevy]

BBC 291 Stock Cylinder head @ 28" 2.19 int valve/ 1.88 exh valve.

Long Intake.. Exh
.100.. 90.6.. 60.1
.200.. 154.0.. 114.9
.300.. 222.1.. 144.2
.350.. 250.2.. 158.5
.400.. 268.9.. 168.0
.450 .. 287.2.. 174.3
.500 .. 302.3.. 180.6
.550 .. 315.7.. 185.4
.600 .. 326.8.. 187.8


Short Intake.. Exh
.100.. 73.5.. 57.9
.200.. 138.5.. 114.1
.300.. 201.3.. 145.0
.350.. 229.5.. 158.5
.400.. 248.7 .. 164.8
.450.. 260.6.. 175.9
.500.. 271.7.. 177.5
.550 .. 278.3.. 185.4
.600.. 282.8.. 190.1

I don't know what length of pipe was on the exhuast port for the measurements!

Jim

[falcongeorge]

Not to step on this thread, but what are the opinions of the 3964290, oval port, closed chamber heads? I'm running them on my car.

Thanks
Bruce

I think they do pretty well myself. I like a closed chamber oval port head with larger valves on a 454 with flat top or small dome pistons. The closed chamber head there seems to be less prone to detonation, especially when run with about 0.042" total deck clearance.

Those heads flow about the same as the "049" and "781" open chamber castings, and respond to work as well. Do a search here for those two casting numbers and you'll see how well the open chamber works. I think the added compression and reduced detonation from the closed chamber makes it even better.

It's hard to get good compression for the street with open chamber heads without a good sized dome, and I think the open chamber tends to aggravate the tendency to detonate you get with a large bore. I think having to put a big dome in the open chamber head makes that worse.

Since Chevrolet went to a small chamber on the Vortec 454 head, I guess they felt the same way (although the Vortec 454 head isn't really a closed chamber head). I could be way off base, I suppose, but what I'm saying has been my experience over the years.

I will say that I'm not at all interested in getting rid of any of my collection of closed chamber oval port heads (3-4 pair, and always looking to pick up another pair). If I were building a 454 or 496 for a street car, or for a heavy duty truck (dooley to tow a trailer), I'd be leaning strongly towards oval port closed chamber heads with 2.19 intake valves, and maybe even bigger exhaust valves, up to 1.84 or 1.88. Now, if I didn't have the old iron heads, I'd look at the Edelbrocks, the only reason I don't look at the Edelbrocks, is I have the castings, and I can put valve seats and big valves in myself. If that were not so, I'd look seriously at a set of Edelbrocks.

To answer another question, I do not like the "closed chamber" with the big relief behind the exhaust valve. I prefer the true closed chamber.

Theres already alot of guys on this thread that have a lot more expertise than me, but this reflects my experience too. I have had good success using closed chamber heads and grinding the chamber to relieve the valves, angle milling the snot out of them, then progressively grinding on the domes after the engine is together, by looking at the tops of the pistons. Street motors in 12.7/1 range on chevron 94 with tight squish, big cams & a relatively small dome. Are you allowed to cut on the chambers in your class?