Holley Hi-Ram vs. LS6 Manifold: Dyno Test


Holley Hi-Ram vs. LS6 Manifold: Dyno Test


When it comes to LS intake manifolds, which one would you choose: a factory-LS6 style intake or a Holley Hi-Ram? We decided to compare them to see which comes out on top. For this test, we used a Dorman version of the LS6 manifold, instead of the increasingly scarce original factory unit. The Dorman version shares the same composite construction, and it's essentially identical to the factory piece, making it a valid substitute performance wise.

To illustrate the difference in power and effective rpm of the Dorman LS6 and Holley Hi-Ram intakes, we first needed a suitable test motor. We started with a junkyard SBE 6.0L LY6. This was given increased ring gap to accommodate plans for boost at a later point. Then it was equipped with a healthy cam from Brian Tooley Racing. The BTR cam has a 641/595 lift split, a 237/252-duration split, and 114-degree LSA. The BTR cam was teamed with a set of Gen X, TFS 225 heads, Hooker 1-7/8-inch headers, and a Holley HP ECU controlling 80-pound Accel injectors.

Worth noting, the LS6 and Holley Hi-Ram aren't really aimed at the same application, but should instead be chosen to optimize the power curve for the desired outcome. Intakes are best thought of as RPM specific, meaning the design is most effective within a given rpm range rather than at one specific rpm. Generally speaking, long-runner intakes favor power production at lower engine speeds, while shorter runners are optimized for power production at higher engine speeds. The terms higher and lower are subjective here, as the long runner LS6 intake made peak power at 6,800 rpm, but there was a distinct difference in the power curves offered by the two intake designs.

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Our test motor started out life as a junkyard LY6, meaning a VVT 6.0L equipped with LS3-style rectangular-port heads and a matching intake.

Because our SBE LY6 would eventually see some serious boost (1543-hp at 29 psi), we took the liberty of adding ring gap to the factory pistons.

To really find out how much power these intakes were worth, we needed a suitable cam profile. We chose a cam from Brian Tooley Racing with a 641/595 lift split, a 237/252-duration split, and 114-degree LSA.

The original VVT cam and timing gear were replaced by this 3-bolt cam gear to allow installation of the non-VVT cam from BTR.

Knowing the 6.0L required plenty of airflow for our cathedral-port intake test, we replaced the factory rectangular-port LY6 heads with a set of CNC-ported Gen X 225 heads from Trick Flow Specialties. These CNC-ported TFS cathedral-port heads made more power than the stock rectangular-port heads.

Working with the BTR cam was a set of dual springs, factory rockers, and hardened pushrods. The TFS heads required longer than stock pushrods and some trimming of the factory rocker stands.

The exhaust system consisted of a set of Hooker stainless steel 1 7/8-inch swap headers feeding 18-inch collector extensions with a 3.0-inch OD.

For our test, the modified 6.0L was first equipped with a Dorman LS6 intake, 80-pound injectors, and billet-aluminum fuel rails.

The Dorman LS6 intake was fed by a billet-aluminum throttle body from Accufab. The 80-mm throttle body matched the opening in the factory LS6 intake.

To dial in the air/fuel mixture and timing, we relied on a Holley HP management system. The timing curves weren't changed between the two intakes.

Run on the dyno first with the Dorman LS6 intake, the modified 6.0L produced 546 hp at 6,800 rpm and 483 lb-ft of torque at 5,200 rpm.

Next up on the modified 6.0L LS was the Holley Hi-Ram. The slightly shorter runner length on the Hi Ram is designed to enhance top-end power production.

The Holley Hi-Ram was equipped to accept a number of different upper lids, but we chose the single-throttle-body unit fed with a 105-mm Holley throttle body.

In preparation for the installation of the Hi-Ram, we installed intake studs into the TFS heads. Note that the studs are directional, with the shorter threaded section going into the heads.

On the dyno, the long-runner LS6 offered more torque down low, but the Hi-Ram increased peak power by 43 hp.

With the Dorman LS6, our BTR-cammed and TFS-headed 6.0L produced 546 hp at 6,800 rpm and 483 lb-ft of torque at 5,200 rpm. After installation of the Holley Hi-Ram, torque was down slightly, to 472 lb-ft at 6,100 rpm, but peak power output jumped to 589 hp at 7,100 rpm.