Largest Gain: 37 ft-lbs @ 4,300 rpm
Much like the previous test run on the Holley Hi-Ram versus the stock LS3 intake, the long-runner FAST LSXR offered considerably more torque up to 5,850 rpm. The FAST offered torque gains as high as 37 ft-lbs lower in the rev range, but the high-RPM single-plane pulled away strong past 5,900 rpm.
Test 3: Stock LS7 vs MSD Atomic for LS7, Modified LS7
This was one of those instances where an intake manifold swap did not trade low-speed torque for top-end power. In fact, this intake improved power through the entire curve, so you know it was the right choice for the engine combination.
Assembled by Cool Performance Machine, the 427 LS7 test engine was created by sleeving an LS3 block. The 4.130-inch bore received a complete Manley stroker assembly that included flat-top pistons, H-beam rods, and a Platinum-series (4.0-inch) stroker crank. Also included in the mix were Total Seal rings, a custom CMP cam (.644 lift and a 246/254-degree duration split), and an adjustable cam sprocket. In true LS7 fashion, the stroker featured an Aviad dry-sump oiling system. Feeding the over-bore LS7 was a set of CNC-ported CMP Brodix SI LS7 heads (395-cfm). Lucas 5W-20 synthetic oil, a Holley Dominator management system and Kooks long-tube headers were included in the mix. The build list also featured an ATI dampener, Meziere electric water pump, and FAST 102-mm throttle body.
It was easy and fast to swap intakes on the LS7. The factory LS7 intake offered good power but nothing compared to the MSD Atomic.
This test involved running the stock LS7 composite intake against the MSD Atomic AirForce LS7 intake, which is also available for cathedral-port heads. Equipped with the stock LS7 intake, the modified LS7 produced 642 hp at 6,800 rpm and 554 ft-lbs of torque at 5,400 rpm. Torque production exceeded 540 ft-lbs for a 1,100-rpm spread (from 4,750 to 5,850 rpm). Since both intakes offered long(ish) runners, I was eager to see how well the MSD compared to the stock LS7.
After installation of the Atomic intake, I was immediately rewarded with both extra torque and horsepower. The peak numbers jumped to 684 hp and 586 ft-lbs of torque. The MSD intake offered nearly 20 ft-lbs below 3,500 rpm but as much as 40 ft-lbs elsewhere. The gains became serious after the tach passed 4,500 rpm. As much as I liked the extra 42 hp (peak-to-peak gain), I also liked the fact that the MSD improved the power output everywhere on this modified LS7.
Equipped with the stock LS7 intake, the CMP-modified LS7 produced 642 hp and 554 ft-lbs of torque. Both intakes were run with a FAST throttle body.
Stock LS7 vs MSD Atomic for LS7, Modified LS7 (Horsepower)
Stock LS7 Intake: 642 hp @ 6,800 rpm
MSD Atomic LS7 Intake: 684 hp @ 6,900 rpm
Largest Gain: 52 hp @ 6,000 rpm
The MSD Atomic intake started well and then became excellent as the tach zoomed past 4,500 rpm. Even down low, the Atomic offered improved power, but the intake really came alive after passing 4,500 rpm. Compared to the stock LS7 intake, the MSD increased the peak output by 42 hp but offered as much as 52 hp elsewhere in the curve.
Stock LS7 vs MSD Atomic for LS7, Modified LS7 (Torque)
Stock LS7 Intake: 554 ft-lbs @ 5,400 rpm
MSD Atomic LS7 Intake: 586 ft-lbs @ 5,100 rpm
Largest Gain: 40 ft-lbs @ 5,000 rpm
As much as I love an extra 42 hp, I love extra torque through the entire rev range even more. As this chapter illustrates, top-end gains are often accompanied by losses in low-speed (and mid-range) torque. This was not the case on the Atomic intake test. The MSD AirForce intake improved torque production through the tested rev range and improved torque output by as much as 54 ft-lbs.
Test 4: Stock LS3 vs Speedmaster IR on a Modified LS3
More than just a change in runner length, this test involved a comparison between a conventional long-runner factory intake and an individual-runner (IR) intake from Speedmaster. The IR intake differed from the factory not only in the length of the runners (although they were different), but also in the lack of a common plenum. Each of the runners on the stock LS3 intake was connected to a common plenum fed by a single throttle body. By comparison, the Speedmaster intake featured no common plenum and eight individual throttle bodies, which measured 50 mm.
Some might be quick to point out that the IR system offered better airflow from the increased surface area of the eight throttle blades. However, the change in runner length, combined with the lack of a common plenum and, therefore, the absence of Helmholtz resonance are what really produced the power differences. (You know this because of the lack of vacuum present in the stock intake at wide-open throttle, or WOT.)
Let’s face it: Nothing is sexier than an individual-runner (IR) intake on an LS engine. This unit from Speedmaster offered impressive power gains to go along with its good looks.
This test was a comparison between the stock LS3 intake and the Speedmaster IR manifold. The test engine was a crate LS3 upgraded with a Comp (PN 281LRRHR13) cam (.617/.624 lift split, 231/247 duration split, 113 LSA) and CNC-ported, TFS Gen X 255 heads. The LS3 crate engine from Gandrud Chevrolet was run with Kooks headers, a Holley HP management system, and Meziere electric water pump. Run on the dyno with the stock LS3 intake, the modified LS3 produced 575 hp at 6,500 rpm and 517 ft-lbs of torque at 5,500 rpm. As always, the long-runner, factory intake offered an impressive torque curve.
After installation of the Speedmaster IR intake, the peak power numbers jumped to 605 hp at 6,800 rpm and 533 ft-lbs of torque at 5,000 rpm. I liked the fact that both peak horsepower and torque were up, but also that the peak torque occurred lower in the rev range with the IR intake. With the exception of a small area near 4,500 rpm, the IR intake equaled or bettered the factory intake through the entire rev range.
The Speedmaster IR intake offered anodized fuel rails, full-radiused air horns, and individual ports to combine the MAP sensor readings.
Stock
