In part one of our Great Crate Update, we subjected a GM Performance Parts LS2 crate motor to a series of performance modifications, including a Comp Xtreme Energy cam, a FAST LSX intake, and two different sets of roller rockers. The LS2 had first been configured for engine-dyno use with a FAST XFI engine-management system, a Meziereelectric water pump, and an open set of Hooker long-tube headers. Additionally, the LS2 intake was equipped with a 90mm FAST throttle body, which replaced the factory drive-by-wire unit. This allowed us to manually operate the throttle for testing.
The GMPP LS2 impressed us by thumping out 467 hp and 457 lb-ft of torque. After adding the FAST intake and Xtreme Energy cam, peak horsepower just topped the 500 mark, with peak torque up to 487 lb-ft. The Ford guys have to resort to supercharging to produce those kinds of numbers.
For this session, we decided to try a second cam profile, along with every Gen III/IV intake we could get our hands on. The first test involved replacing the Xtreme Energy XR265HR cam from Comp (0.522/0.529-inch lift, 212/214-degree duration, 114-degree lobe-separation angle) with a slightly hotter Crane Z-series (0.551/0.551-inch, 216/224-degree, 115 LSA). Oddly enough, the motor produced almost exactly the same power with the Crane cam as it had withthe Comp. Looks like we'll have to step things up considerably for our next cam swap.
Undaunted, we began our intake comparison. Equipped with the factory LS2 intake, the GMPP LS2 produced 485 hp at 6,000 rpm and 469 lb-ft of torque at 4,700 rpm. With our baseline numbers established, we removed the LS2 manifold to make way for the first of two carbureted units. First on the list was the Edelbrock Performer RPM LS1, teamed with aBarry Grant Race Demon carb. Generally speaking, for motors making peak power at or below 6,000 rpm, a dual-plane design like the Performer RPM is tough to beat for average power production. After jetting and timing changes to optimize the power curve, the Performer RPM-equipped LS2produced peak readings of 473 hp and 473 lb-ft. The carbureted intake bettered the factory LS2 manifold up to 4,500 rpm but fell off slightly thereafter.
Next up was the Edelbrock Victor Jr. For hot small-blocks with cam timing designed to run effectively beyond 6,000 rpm, a single-plane intake like the Victor is usually a good choice. Oftentimes the trade-off is a drop in low-speed torque production. The Victor Jr. was run with the same Barry Grant carb and jetting, and timing sweeps wereperformed to optimize the power production on the 91-octane pump gas. True to form, the Victor Jr. equaled the power output of the factory LS2 intake from 5,000 to 6,500 rpm but lost out below that point. Compared with the dual-plane Performer RPM, the Victor Jr. offered more peak power but less low-speed torque. It's interesting to note that neitherof the carbureted intakes made more peak power than the factory LS2 manifold (though the Victor Jr. did match it).
The dual-plane intake might be a better choice for a primarily street-driven Vette, since the vast majority of driving is done in the lower rev ranges. The dual-plane intake would offer better fuel economy, too, but the drawback would be a loss in peak power compared with thesingle-planer. In the end, it just depends on where you want your power.
With the carbureted intake testing out of the way, it was time for us to convert the LS2 back to EFI. The first EFI intake to be tested was an old-style LS1 manifold. While no self-respecting LS2 owner would perform such a downgrade, we wanted to see just how much better the LS2 was thanits predecessor. Would the larger 90mm throttle opening pay dividends against the 78mm version used on the older manifold? As it turned out, the LS1 intake wasn't that far off. As expected, it made less peak power than the LS2 (476 hp versus 485 hp), but the power curves were virtuallyidentical from 3,000 rpm to 5,500 rpm. From 5,500 rpm to 6,500 rpm, the LS2 intake offered as much as 10 additional horsepower, but the LS1 unit actually produced an additional 2 lb-ft of peak torque (471 versus 469 lb-ft).
After running the LS1 intake, we were curious to see how a factory LS6 manifold would perform. As in the previous test, the manifold was equipped with a 78mm throttle body. Despite the 12mm handicap in throttle opening, the LS6 intake easily outperformed the larger LS2 unit, producing peak numbers of 489 hp and 481 lb-ft of torque. The LS6offered serious power gains from 4,500 rpm to 5,700 rpm but offered smaller gains as low as 3,800 rpm. We suspect that the smaller throttle opening was responsible for the drop in power past 6,000 rpm, but even out to 6,500 rpm, the LS6 outperformed the LS2 by at least a few horses.
Once we were finished with the factory offerings (we didn't bother to run the truck manifold, which will produce less peak power than the LS1 but more low-speed torque), we moved on to the aftermarket. Since FAST offers its Wilson-designed LSX manifold with two different throttle-opening sizes, we decided to follow up last month's test of a 90mm version by evaluating the 78mm version for this issue.
As with the previous manifolds, the air/fuel was dialed in to 13.0:1 and the timing kept constant at 28 degrees (more did not help). Equipped with the 78mm FAST intake, the LS2 peaked at 499 hp and 487 lb-ft of torque, just missing the 501 hp and 487 lb-ft produced in our last test by the larger 90mm version. The 78mm unit actually produced better power up to 3,700 rpm, but the two manifolds performed nearly identically from there on up. Compared with the factory LS2 intake, both of the LSX manifolds offered as much as 22 hp and 22 lb-ft, and they bettered the power output from 3,000 rpm all the way through 6,500 rpm. We suspect these power gains would only improve with the addition of a larger cam and CNC-ported heads.
Check back with us next issue, as we introduce our LS2 crate motor to the exciting world of forced induction.
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