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Holley Performance Products


Holley Performance Products

Holley® has been the undisputed leader in fuel systems for over 100 years.

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Having run hundreds of LS intake tests, including no less than 20 different cathedral-port intakes in one sitting, trust us when we say that intake testing on a LS usually goes one of two ways. Comparing an aftermarket intake to one of the factory intakes usually results in either limited gains, or a big trade off. Truth be told, the GM engineers did a pretty good job on the factory manifolds, especially the truck intake. The early LS1 left a little to be desired, but all the other factory offerings, including the most common, the early truck intake, perform very well. The fact that they did such a good job on the factory intakes means they can be difficult to improve upon. Sure, you can add a short-runner intake and improve the high-rpm power (remember, intakes are optimized for a specific rpm range), but the gains in top-end power almost always come with a loss in torque production elsewhere. Sometimes the tradeoff can be for most of the power curve, which is to say it’s not a very desirable (or effective) tradeoff. Knowing this, we were naturally a tad skeptical about our test on the Sniper Dual Plenum.

Don’t get us wrong, it was difficult to be skeptical after seeing the Sniper Dual Plenum in person, as there was no denying the appeal of the dual throttle body, cross-ram design. Much more than the LR4/LM7/LQ9 truck manifold, the Dual Plenum just screamed "look at me". Heck, pop the hood (or deck lid) of a fancy Ferrari, Lambo or other super exotic, and the chances are good that they employed this super sexy design. Not only is the Dual Plenum a knockout-looking package, but the design provides ample airflow from the use of dual throttle bodies. Sure, one 90-mm throttle body probably flows enough to support the desired power level, but having twice as much flow is always better, right? Truth be told, the power potential of the Dual Plenum design had less to do with the extra flow offered by having dual throttle bodies as it did the runner length. Extra airflow is most effective at higher engine speeds, where additional airflow becomes necessary. The added power production at lower engine speeds, and through most of the usable rev range, comes from runner length. The Dual Plenum design offered ample runner length, which promised prodigious torque production. It is with this power production in mind that we set a test between the factory truck intake and the Sniper Dual Plenum.

Knowing a stock 5.3L just wasn’t sufficient to test the Sniper EFI Dual Plenum, we cammed up a bigger 6.0L. To help with power production, the LY6 received a Comp 54-469-11 camshaft. The healthy stick featured a .617/.624 lift split, a 231/247-degree duration split and 113-degree LSA. Further aiding head flow was a set of TFS Gen X 225 cylinder heads. The cathedral-port Gen X heads offered impressive flow numbers, more than enough for the Sniper intake to handle.

To properly test our two induction systems, we first needed a test motor. Lucky for us, we had a suitable 6.0L ready for action. Having already pumped out 1,543 horsepower in twin turbo form, the stock-bottom-end (SBE) 6.0L was still sporting the TFS Gen X 225 heads. The CNC-ported (cathedral-port) heads were combined with a Comp 54-469-11 cam that offered some healthy specs. The Comp stick featured a .617/.624 lift split, a 231/247-degree duration split and 113-degree LSA. Other components employed on our 6.0L test motor included stock rockers, Fast coil packs and a Holley Dominator management system. Both intakes were run with Holley 83-pound injectors, as boost was in the cards later for this test motor. Both intakes were also run with a set of 1 7/8-inch Hooker long-tube headers. First up on the dyno, the early truck intake produced 524 horsepower at 6,600 rpm and 480 lb-ft of torque at 5,000 rpm. Having run the truck intake, we were anxious to install and test the Holley EFI Dual Plenum.

The design (and manufacturing) of the Dual Plenum was interesting, as the pair of (intersecting) four-cylinder intakes required assembly prior to finish welding. Having designed and built x-ram prototype intakes in the past, it was interesting that the Sniper design did not feature a communication channel between the two plenums. After installation of the Sniper intake, we connected the map signal using a t-fitting and a vacuum source from both independent plenums. The Dual Plenum intake flanges featured O-ring receiver grooves for sealing. Naturally the supplied fuel rails were designed to accept the Holley injectors (though others will work). For you guys thinking twin turbos, each plenum featured multiple threaded ports to connect vacuum/boost lines. Holley designed the Dual Plenum to accept a pair of 92-mm (DBW) throttle bodies. For our test, we configured the Dual Plenum with a pair of manual throttle bodies, complete with (fully rigged) cable actuation. Once WOT was confirmed, we set our sights on running the Dual Plenum in anger, and it pumped out the promised, prodigious torque. The peak numbers checked in at 536 horsepower (at 6,300 rpm) and 491 lb-ft of torque (at 5,100 rpm), but what was most impressive was the extra 35-40 lb-ft of torque offered in the 3000-4000 rpm range.

To see just how much power and torque the Dual Plenum had to offer, we first equipped the 6.0L with our old standby intake, an early truck unit that was designed to accept a stock (pre-2003) manual throttle body.

We dialed in the air-fuel ratio (12.8:1) and timing curves (29 total degrees) of both intake manifolds using a Holley Dominator ECU. To ensure plenty of exhaust flow, a set of Hooker long-tube 1 7/8 headers feeding 18-inch collector extensions were employed. And while it wasn't a big concern for a naturally-aspirated combination, we liked having the Accel ceramic-boot plug wires all the same.

Equipped with the truck intake and tuned to perfection, the warmed-over 6.0L LY6 produced peak numbers of 524 hp (at 6,600 rpm) and 480 lb-ft of torque (at 5,000 rpm).

After running the truck intake, it was removed and replaced with the Sniper EFI Dual Plenum. Fun fact: the intersecting cross ram design requires finish welding the intake after merging the two halves together.

Bolting the intake on was easy enough, but take note of where we combined the MAP signal from both of the individual plenums (the red vacuum hose and T-fittings).

The openings in the dual throttle body flanges on the Sniper intake were designed to accept 92-mm throttle bodies.

Because we employed a pair of manual throttle bodies, we had to rig up our own “Drive By Wire” throttle assembly. Joining the cables allowed us to use the single dyno (Morse) throttle cable.

To ensure adequate and consistent fuel delivery, both LS manifolds were run with Holley 83-pound injectors.

No doubt it looks cool, and many will purchase it based on its looks alone, but the Sniper EFI Dual Plenum simply made more power. The LS truck intake is a popular choice for two reasons: it works and it's already on the engine when you pull it at the yard in most cases. The truck intake offered up 524 horsepower and 480 ft-lbs of torque. But the Dual Plenum worked the dyno to the tune of 536 horsepower and 491 ft-lbs. The long runners improved low-speed torque (look between 3,000 and 4,200 RPM), where many intake swaps lose ground in the name of higher-RPM horsepower gains.



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