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5.3L LS Small Block Build - Twice As Nice: Part 5

Modern Mouse, Part 5: Getting Carbs

By Richard Holdener, Photography by Richard Holdener

Naturally the single-plane intake was run with another Holley carburetor: in this case a 750 HP equipped with Percy's external Adjust-a-Jet system. The external adjustment screw eliminated the need for bowl removal to facilitate jet changes to dial in the air/fuel mixture.

Loyal readers of Super Chevy should be familiar with our test rodent, but a brief rundown will be provided for those who just tuned in. What started out as a bone-stock 5.3L eventually evolved into a TFS-headed 383 stroker thanks to a 3.902-inch bore and 4.0-inch stroke combination from Procomp Electronics, Probe Racing, and L&R Automotive. The stroker kit kicked up the displacement from 324 cubic inches (5.3L) to a full 383 inches (6.27L). The GenX 215 heads from Trick Flow Specialties combined with an Xtreme Energy cam from Comp Cams and a Fast LSXR intake to push the power output well over 500 hp.

Running nitrous back in Part 2 produced over 600 hp, and we even managed to coax over 800 hp with the help of a Whipple 2.9L twin-screw supercharger. Modern Mouse had since lost the supercharger, but was still sporting the GenX 215 heads and Comp cam. Obviously, the FAST LSXR intake would give way to the dual-quad counterpart from Holley, but not before establishing a baseline with the single-plane Victor Jr. intake.

The 383 stroker was first equipped with the Edelbrock Victor Jr. intake. The intake was combined with a Holley 750 HP carburetor and run using an MSD LS ignition system (PN 6010). Designed as a plug-'n'-play system, the MSD ignition offered map-based, programmable timing curves and direct connection to the factory cam, coil, and crank sensors. All that was necessary was to hook up power and ground and your carbureted LS was up and running—what could be easier? Run on an engine dyno, Modern Mouse was equipped with a Meziere electric water pump and a set of 1-3/4-inch headers feeding Magnaflow mufflers. After testing a few different timing levels (30 degrees worked best) and minor tuning to the air/fuel curve via the Percy's external Adjust-a-Jet system, we were rewarded with peak numbers of 527 hp at 6,000 rpm and 484 lb-ft of torque at 5,100 rpm. Indicating the high-rpm nature of the single-plane intake was the fact that torque production exceeded 460 lb-ft from 4,400 rpm to 6,000 rpm.

Having successfully converted Modern Mouse to carburetion, it was time to see if the dual-quad was indeed "twice as nice" as the single-plane. Off came the Victor Jr. and on went the Holley dual-quad intake. Manifold swaps were a breeze on the LS motor, as the swap involved disturbing neither a distributor nor any water passage.

The dual-quad intake was teamed with a pair of vacuum-secondary, 4160 carbs rated at 390 cfm each. The pair of 390s (780 cfm) nearly equaled the flow rating of the 750 Holley employed on the Victor Jr. It is possible to install larger carbs on the dual-quad intake, but the twin 390s performed admirably on the 383 stroker.

After a single jet change, we were rewarded with peak power numbers of 526 hp at (a slightly higher) 6,200 rpm and (more importantly) 490 lb-ft of torque at (a lower) 4,700 rpm. Not only did the dual-quads match the top-end power of the single-plane setup, but it offered more peak and average torque production.

Below 5,000 rpm, the dual-quad easily outpowered the single-plane, with gains exceeding 50 lb-ft near 3,200 rpm. Not very often do you get to combine form and function in one exciting package, but if this test is any indication, we should be seeing a lot more LS motors roaming the streets with these new dual-quad Holley systems.

13. Dual-Quads Vs. Single Four-Barrel
The typical comparison between a single-plane and dual-plane intake involves a trade-off. Generally speaking, the single-plane offers more power at the top of the rev range, but the dual-plane provides considerably more torque at lower (and medium) engine speeds. This usually involves a choice of where you are most concerned about power production. In this case, the dual-quad Holley eliminated the need to choose, as it offered every bit as much peak power as the single-plane Victor Jr. but considerably more low-speed and mid-range torque. Dual-quad intakes are often more about looks than performance, but this Holley dual-quad LS intake offered both. Measured peak to peak, the dual-quad was up by just 6 lb-ft (490 lb-ft versus 484 lb-ft), but down near 3,000 rpm the dual-quad offered an additional 50 lb-ft of torque. The difference in the curves despite relatively similar peak numbers is why we go to the trouble of including a complete power graph (or numbers).

SOURCES
Edelbrock (Carbs)
800-416-8628
http://www.edelbrock.com
Holley/Hooker
1801 Russellville Road
Bowling Green
KY  42101
270-782-2900
www.holley.com
Trick Flow Specialties
1248 Southeast Avenue
Tallmadge
OH  44278
330-630-1555
www.trickflow.com
L&R Automotive
13731 Bora Drive
Sante Fe Springs
CA  90670
562-802-0443
www.lnrengine.com
Comp Cams/Fast
3406 Democrat Road
Memphis
TN  38118
800-999-0853
www.compcams.com
By Richard Holdener
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