Quick Tech: Holley’s New Two-Piece Cathedral-Port Intake

You don’t need us to tell you the LS engine market has the needle almost pegged. But we can tell you that Holley has just helped move more air through all four barrels with a new, LS Gen III, cathedral-port race manifold using two-piece, split-manifold technology (part No. 300-256, street price around $450). The manifold literally is a two-piece affair split lengthwise, right down the center. This allows porting professionals unequalled access to every corner in the manifold for massaging.

This has been a common technique for pure competition engines for years and Holley now offers this same high-rpm horsepower potential for cathedral-port engines. The manifold suggests a 2,500 to 7,000 rpm range but this package is really aimed at making peak power with 5.3L to 6.2L (and above) engines at 6,000 to 7,000 rpm. The manifold seals with an O-ring around the plenum split using shouldered bolts to create a leak-free seal. The intake ports also seal to the heads with supplied O-rings.

The manifold is designed around a 4150, standard carburetor mounting flange that will accommodate up to 1.750-inch throttle bores (which is 1,000 cfm territory) and the carb pad height is plenty tall at 3.28 inches. The runners start huge in the plenum and taper from 3.5 to 2.9 square inches at the flange exit and this convergence helps torque, which is a good thing. This manifold will also be available for use with multipoint EFI. Or it could easily be fitted with a throttle body injector.

This manifold would also lend itself to an aggressive turbo package with either a blow-through carburetor or a Holley Sniper blow-through throttle body. The manifold would allow porting that would certainly benefit the power numbers. Of course, porting would be especially beneficial to a normally aspirated package while still maintaining inlet airspeed through the more conservative cathedral-port heads compared to the rectangle-port versions.

If your goals include pushing a set of big-port cathedral heads to the limit on the drag strip, this new 2-piece Holley manifold looks like a killer path to righteous horsepower.

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