[Tom Vaught]

Man, I missed the lack of the 1 in the 76 deal for sure, John.

Was trying to finish the post before dinner, LOL!

Sorry for the 64 INFO in the 65 thread.

Tom Vaught

[gto_ron]

Tom, John

I've been following this thread and the info is valuable. Tom, if the flow is about the same for most of the cast iron heads mentioned does that mean the larger valve sizes in the later heads(670 etc.) didn't really increase horsepower as one would expect?

thanks again for the info, I'm always learning

Ron
64 convertible

[John V.]

Tom and a lot of other guys on this Board can answer the flow question a lot better than me but here's my

The early heads were limited to a valve combo of 1.92/1.66. Some used even smaller valves, but I believe the GTO Heads along with heads like the 76 & 092 all had the same valve size.

The production of power difference was likely related to the chamber vol., cam selection, rocker arm ratio, and rpm potential.

The later 2.11/1.77 big valve heads likely benefitted from the larger valve sizes which was made possible by the revised valve inclination angle that began in '67 with the 670 head (most '67 heads remained close chamber with the old valve inclination angle, not til the release of the late '67 061 followed by the '68 heads did the first open chamber heads appear which all had the new valve inclination angle).

Perhaps they had higher power potential, but if they were limited to the same static compression, same cams, same rocker ratios, and same rpm limitations as used with the earlier heads, they likely did not take advantage of the potential the increased valve sizes could offer.

I think what I am trying to say is that air flow was not the limiting factor for stock engines.

The topic has always been too technical for my grasp and this is my basic understanding of it.

It would be interesting if somebody could explain how the bigger valves were useful to a stock engine (if they were) and then how they help with power potential in a non-stock build.

[Ken K]

Originally Posted by gto_ron

Tom, John

I've been following this thread and the info is valuable. Tom, if the flow is about the same for most of the cast iron heads mentioned does that mean the larger valve sizes in the later heads(670 etc.) didn't really increase horsepower as one would expect?

thanks again for the info, I'm always learning

Ron
64 convertible

There is a noticeable difference in performance switching to big valve heads. The big valve heads also have guide plates. The pushrod hole on the 1965 heads is smaller, it keeps the pushrod in place. Chevy small block heads of the same era used the small pushrod hole. Later model Chevy heads opened up the pushrod hole like the big valve Pontiac heads.