'72 454 Engine Intake Selection

[Jim H.]

I'm running a '72 Corvette 454 GM #289 block, freshly bored and stroked to 496 w/'69 Corvette 427/435 GM #291 heads (2.19/1.88 valves, 109.037 cc closed combustion chamber, square port) in my NOM '66 427. My carb is a correct '66 Holley 427 4BBL. The car will not be judged in this configuration so NCRS correctness is not a factor for now. (This engine runs great and has been dyno'd at 514hp/604 ft lbs at the crank.)

However, I think I made a mistake in selecting a '71 Corvette 454/425 GM#3663569 LS6 aluminum intake I had on the shelf for this engine and would appreciate your advice. It seems to me that the height limitations of the '70's Corvettes necessitated a short stacking of the intake runners (like the 569) which have no vertical travel and are virtually lateral from the base of the carbs to the heads. With more intake-to-hood height available in my '66, I may get more air flow and velocity w/a taller hi po intake. But which intake to select - '66 L36 3866948, L72 3885069, or other? I'm not concerned about the intake material (i.e., aluminum v. cast iron). And if the difference will be nominal, I'll drop this. But if I've waste the vertical space available underhood and strangled the engine with this intake, pls let me know.

Joe Lucia - any thought on Corvette/Chevy interchange possibilities for this?

Thanks much.

JCH

[Duke W.]

Re: '72 454 Engine Intake Selection

The '66 L-72 manifold would be a better choice than the LS6 manifold, but not a huge difference in power, and there are likely aftermarket manifolds of very similar design to the L-72 manifold that are probably less expensive. The L-36 manifold would be a poor choice as it is designed to mate with oval port heads.

As a general rule the taller the manifold the greater the runner flow efficiency, but the limit is hood clearance, which is why the LS-6 could not use the L-72 manifold.

Duke

[Joe L.]

Re: '72 454 Engine Intake Selection

I'm running a '72 Corvette 454 GM #289 block, freshly bored and stroked to 496 w/'69 Corvette 427/435 GM #291 heads (2.19/1.88 valves, 109.037 cc closed combustion chamber, square port) in my NOM '66 427. My carb is a correct '66 Holley 427 4BBL. The car will not be judged in this configuration so NCRS correctness is not a factor for now. (This engine runs great and has been dyno'd at 514hp/604 ft lbs at the crank.)

However, I think I made a mistake in selecting a '71 Corvette 454/425 GM#3663569 LS6 aluminum intake I had on the shelf for this engine and would appreciate your advice. It seems to me that the height limitations of the '70's Corvettes necessitated a short stacking of the intake runners (like the 569) which have no vertical travel and are virtually lateral from the base of the carbs to the heads. With more intake-to-hood height available in my '66, I may get more air flow and velocity w/a taller hi po intake. But which intake to select - '66 L36 3866948, L72 3885069, or other? I'm not concerned about the intake material (i.e., aluminum v. cast iron). And if the difference will be nominal, I'll drop this. But if I've waste the vertical space available underhood and strangled the engine with this intake, pls let me know.

Joe Lucia - any thought on Corvette/Chevy interchange possibilities for this?

Thanks much.

JCH

Jim------


As far as GM manifolds, there are really only a few that would "fit the bill". These include the 3866963 (expensive), 3885069, 3919878, 3933163, and 3933198. Actually, any of these usually fetch a pretty big price if they're in good shape. Many have repairs, though, or post-factory machining. There is also a currently available GM manifold that will be, performance-wise, just about the equal or better of any of the aforementioned. This is GM #19131359. You can buy this manifold for about 300 bucks and it will be BRAND NEW. This is a rectangular port, dual plane manifold for square bore (Holley) carb applications.

I do not recommend a single plane manifold for any street application.

One other caveat: if you are using a stock C2 small block hood, none of the above-referenced manifolds may fit under the hood.

[Jim H.]

Re: '72 454 Engine Intake Selection

Duke and Joe, thank you for your comments. I have a line on a unused 3933163 that will fit the bill nicely, offered by an NCRS member. While never used on the Corvette (which is no problem in this application), it ran on a wide range of 427/425 Chevys including the COPO Camaros and Chevelles. Mission accomplished. This car has a correct 66 big block hood. Thanks for the caution on the single plane manifold. Made that mistake in my youth. JCH

[Jim H.]

Re: '72 454 Engine Intake Selection

Joe,

I was thumbing through my well-worn Chevrolet and Corvette By the Numbers this morning and discovered that the 3933163 you recommended and I've purchased for my 66 427 is identical (except for minor changes) to the 3885069 used on the 66/67 427/425, 67 427/430 L88, and 68 427/430 L88 and a third the price. Perfect. Thanks again.