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). The grind featured a .615/.595 lift split, a 229/244-degree duration split, and 113-degree (+4) LSA. The cam was combined with a dual-spring upgrade to replace the factory LS3 springs. Other components used on the test engine included a FAST management system and injectors, Hooker long-tube headers, and a Meziere electric water pump.
Running 5 quarts of Lucas oil and the longest of the three runner configurations, the LS3 produced 562 hp at 6,400 rpm and 512 ft-lbs of torque at 5,200 rpm. Installation of the medium-length runners increased peak power to 568 hp at 6,800 rpm, but torque dropped to 490 ft-lbs at 5,300 rpm. The final test involved installation of the shortest runners that resulted in 577 hp at 7,100 rpm, but torque dropped further still to 478 ft-lbs at 5,300 rpm. Each successive decrease in runner length resulted in increase peak power but a drop in torque (in this case, below 6,500 rpm).
The adjustable intake offered three bolt-in runner lengths to dial in the power curve to a specific combination.
The LSXR adjustable intake looked just like the original, but under the lid was a surprise.
FAST Adjustable LSXR Intake on a Mild LS3 (Horsepower)
FAST LSXR Long Runner: 562 hp @ 6,400 rpm
FAST LSXR Medium Runner: 568 hp @ 7,000 rpm
FAST LSXR Short Runner: 577 hp @ 7,100 rpm
Largest Gain: 20 hp @ 6,700 rpm
Looking at the numbers, you might be tempted to pick the intake combination that offered the highest peak power. Unfortunately, we do not live by peak power alone. While the middle and shorter runner offered higher peak power numbers, there was a trade-off in power elsewhere in the curve. Only above 6,500 rpm and below 3,400 rpm did the middle or shorter runners offer more power.
FAST Adjustable LSXR Intake on a Mild LS3 (Torque)
FAST LSXR Long Runner: 512 ft-lbs @ 5,200 rpm
FAST LSXR Medium Runner: 490 ft-lbs @ 5,300 rpm
FAST LSXR Short Runner: 478 ft-lbs @ 5,300 rpm
Largest Gain: 45 ft-lbs 4,400 rpm
The results of this test on the mild (cam-only) LS3 clearly show the effects of changes in runner length. The trick LSXR adjustable intake allowed me to show the drop (or increase) in torque at lower engine speeds offered by shortening or lengthening the runners. The shortest runner offered the lowest peak torque, followed by the middle runners. The longest runners offered the highest peak (and average) torque production.
Test 7: Stock vs Kenne Bell 102-mm Throttle Body on a KB SC LS3
About the only thing better than a modified LS engine is a supercharged one. Nothing adds zing to an LS like some boost from a Kenne Bell twin-screw supercharger. While twin-screw kits are efficient and powerful, boost is only the beginning. The reality is that superchargers are only as good as their induction system.
Nothing chokes off the power potential of a supercharger faster than a restrictive