LS3 vs Speedmaster IR on a Modified LS3 (Horsepower)
Stock LS3 Intake: 575 hp @ 6,500 rpm
Speedmaster IR LS3 Intake: 605 hp @ 6,800 rpm
Largest Gain: 36 hp @ 6,800 rpm
With the exception of a slight dip in power near 4,500 rpm, the Speedmaster IR induction system improved the power output through the RPM range. There was a bump in power near 5,000 rpm and then a serious jump past 5,500 rpm. This intake would show even greater power gains on a larger or wilder application.
Stock LS3 vs Speedmaster IR on a Modified LS3 (Torque)
Stock LS3 Intake: 517 ft-lbs @ 5,500 rpm
Speedmaster IR LS3 Intake: 533 ft-lbs @ 5,000 rpm
Largest Gain: 22 ft-lbs @ 5,000 rpm
The torque curve shows the sign wave in power created by the IR intake from Speedmaster. The new induction system lost out in torque from 4,200 to 4,700 rpm, but bettered the stock LS3 intake everywhere else. A resonance wave at 5,000 rpm really bolstered torque production.
Test 5: Stock LS3 vs Speedmaster Fabricated Intake on a Mild LS3
A number of sources offer these fabricated intakes, but Speedmaster supplied this particular test piece for the LS3 application. Once again I was looking at a substantial change in runner length, to say nothing of plenum volume and throttle opening. Where the stock LS3 intake was designed to accept a 90-mm throttle body, the Speedmaster fabricated intake featured a 102-mm opening.
Various sources offer fabricated intake in different configurations, both with and without radiused air horns for the runners. If you plan to run one, make sure you select the one with air horns because the smooth air entry is worth 10 to 12 hp over the non-radiused version (at this power level).
The overall look of the intake combined with the cost make it a desirable commodity, but look over the dyno results before making your choice, especially for a mild street application. The intake certainly has its place, but like other short-runner intakes, there is a trade-off in low-speed (and mid-range) torque on all but the largest and wildest combos, which includes turbo and blower applications.
This test was run on an engine that clearly favored the long-runner, factory intake. The Gandrud LS3 crate engine was simply augmented with a mild 224 Crane cam (.624/.590 lift, 224/232 duration, 113 LSA), a set of long-tube 1¾-inch Quick Time Performance (QTP) headers with extensions, and mufflers. The test mule also featured a Holley 90-mm throttle body (stock intake), stock LS3 injectors (raised fuel pressure), and Holley HP management system. Run with the stock LS3 intake, the mild LS3 produced 538 hp at 6,300 rpm, and 504 ft-lbs of torque at 4,800 rpm.
After installation of the fabricated intake, the peak power jumped to 556 hp at (a higher) 6,800 rpm, but peak torque dropped to 485 ft-lbs of torque at 5,200 rpm. The stock intake offered improved power up to 6,050 rpm, where the fabricated began to pull away. This intake works much better on high-RPM or larger (and wilder) applications than on this mild LS3.
The factory LS3 intake is impressive, offering a good combination of power and torque production on most mild and modified LS3 applications.
Run with a mild cam, headers, and the stock intake, the LS3 produced peak numbers of 538 hp and 504 ft-lbs of torque.
Stock LS3 vs Speedmaster Fabricated Intake on a Mild LS3 (Horsepower)
Stock LS3 Intake: 538 hp @ 6,300 rpm
Speedmaster Fabricated Intake: 556 hp @ 6,800 rpm
Largest Gain: 32 hp @ 6,800 rpm
The Speedmaster fabricated intake offered impressive peak power gains, increasing the power output of the mild LS3 from 538 to 556 hp. It is important to note that the peak power occurred 500 rpm higher (from 6,300 to 6,800 rpm). This was a surefire indication of the high-RPM nature of the intake design.
Stock LS3 vs Speedmaster Fabricated Intake on a Mild LS3 (Torque)
Stock LS3 Intake: 504 ft-lbs @ 4,800 rpm
Speedmaster Fabricated Intake: 485 ft-lbs @ 5,200 rpm
Largest Gain: 40 ft-lbs @ 4,500 rpm
The torque curve is even more telling because the long-runner, stock LS3 intake offered considerably more torque up to 6,000 rpm. As trick as they look, the short-runner intake designs are best left to high-RPM and/or large-displacement applications. The shorter runners lost as much as 40 ft-lbs of torque at 4,500 rpm.
Test 6: FAST Adjustable LSXR Intake on a Mild LS3
Perhaps the best illustration of the effect of runner length comes from this test on the (then new) FAST LSXR adjustable intake. Recognizing that changes in runner length alter the effective operating range of the intake manifold, FAST designed the new intake to allow installation of different runner configurations. Using bolt-in runs, users can swap out runner lengths to tune the intake to different engine combinations and/or applications (think street/strip).
One thing I also tested but did not show in this book was to combine different lengths (four short and four long or four medium), not unlike a single-plane, carbureted intake. For this test, I simply ran the intake on a cam-only LS3 with the different available runner lengths. As should be evident by now from the results of the previous tests in this chapter, shorter runner lengths increased peak power but traded low-speed torque.
The test engine was a crate LS3 from Gandrud Chevrolet augmented with a cam from Brian Tooley Racing (BTR).
