GM Intake throttle bore - 1966 L-36

[Keith B.]

Just confirming 66 427/390 GM2 3866948 cast iron oval port intake...............has 1 9/16 throttle bore size?

Wanting to box up my 575 CFM Holley and tuck it away in favor or of HR 780 series QuickFuel technology carb but I believe they and many of them have 1 11/16 throttle bore blades................thx Keith

[Keith B.]

Re: GM Intake throttle bore - 1966 L-36

Nobody here can confirm that a 66 427/390 GM2 3866948 cast iron oval port intake...............has 1 9/16 throttle bore size? My car is in storage and not accessible now. Appreciate your help..

[Joe C.]

Re: GM Intake throttle bore - 1966 L-36

Nobody here can confirm that a 66 427/390 GM2 3866948 cast iron oval port intake...............has 1 9/16 throttle bore size? My car is in storage and not accessible now. Appreciate your help..

Call these folks:

http://www.castheads.com/

Not only will they answer your question, but they specialize in modifying it for high performance use. I see from another forum that you don't want to replace it. These manifolds are a dime a dozen, so I wouldn't worry about decreasing its value. Open the ports and open the plenum as well as increase the bore size to 1 11/16 and install your QF 780 carb. The smarter, cheaper and easier thing would be to install a Performer from Edelbrock and paint it orange if that makes you feel better.