Information needed on 3964291 bb heads

[Bob W.]

A friend has a set of these head they are cast f 6 69 -f 17 69 . They are square port open chamber . I don't think they were used on any corvettes. His cousin bought then in the mid 70s .


Thanks Bob

[Joe L.]

Re: Information needed on 3964291 bb heads

A friend has a set of these head they are cast f 6 69 -f 17 69 . They are square port open chamber . I don't think they were used on any corvettes. His cousin bought then in the mid 70s .


Thanks Bob

Bob-------


The 3964291 cylinder heads were released about mid 1969. So, these heads dated as you mentioned must have been about the first ones ever produced. I don't think they were ever used in PRODUCTION for any Corvette application. However, they were used for other non-Corvette SHP applications. They may have been used for some late 1969 non-Corvette SHP applications but they are, primarily, a 1970 cylinder head. They were used for 1970 L-78 and LS-6 applications in Chevelles and Camaros. They were also used for quite a few years to SERVICE most 1965-70 SHP big block applications, Corvette and otherwise. Contrary to what some folks believe, these were NOT open chamber cylinder heads. No open chamber, cast iron cylinder heads were ever used on any PRODUCTION Chevrolet big block. Such heads were scheduled to be used on 1971 LS-6 Chevelles but no such cars were ever actually produced.

[Bob W.]

Re: Information needed on 3964291 bb heads

Joe
These heads were bought at motion performance in NY. When they are put next to a closed chamber head they are different. So maybe motion modified the stock head in some way.

Thanks B0b

[Joe L.]

Re: Information needed on 3964291 bb heads

Joe
These heads were bought at motion performance in NY. When they are put next to a closed chamber head they are different. So maybe motion modified the stock head in some way.

Thanks B0b

Bob------


Most of the combustion chamber of these and other big block heads is as-cast. The only real machining in the combustion chamber is the un-shrouding cut for the intake valve. The primary difference between the 3964291 and earlier rectangular port big block cast iron heads is the increase in size of the exhaust valve from 1.72" to 1.88". Some folks might think that this makes the 3964291 an "open chamber" head but it does not. The combustion chamber volume of the 3964291 head (109 cc) is only slightly larger than the earlier rectangular port heads (107 cc) and that's mostly due to the exhaust valve size increase. Open chamber big block heads have a combustion chamber volume of about 118 cc and a differently configured combustion chamber. I've never heard of anyone converting a closed chamber to an open chamber.

The 3964291 heads were machined for either gasketed or tapered seat spark plugs. Which of these are the heads you referred to?

[Bob W.]

Re: Information needed on 3964291 bb heads

Joe
Iam not sure at this time about your question i will have to ask my friend and reply back.

Thanks again Bob

[Patrick B.]

Re: Information needed on 3964291 bb heads

The 69 Corvette production extended well into the ordinary 1970 model year, so June cast 291 heads were used on late 69 L-71 Corvettes. There were no 1970 Corvettes with SHP big blocks thus no 291 heads on 70 Corvettes.