In the September issue, we strapped a stock LS2 crate engine to our engine dyno and coaxed 472 horsepower and 505 lb-ft. of torque out of it (see "Great Crate" Sept. '06). Impressive numbers, but as the saying goes, there's no such thing as too much power. What we wanted to know is how easy it would be to get more power out of the engine with some relatively simple bolt-ons. Our test engine was already fitted with stepped race headers, so the exhaling was as good as it was going to get. Now we needed to get more atmosphere into the mill.
The LS2 is shipped from GM rated at 400 hp at 6,000 rpm and an equal amount of torque at 4,400 rpm. The redline is 6,500 rpm, but it's all done building power by 6,000 rpm. Remember that this is an engine designed for an emission-compliant production car, so the camshaft is pretty conservative, and the heads, while excellent in many regards, are designed to flow enough to support this camshaft. The factory LS2 also runs a 65cc combustion chamber and a stout 10.9:1 compression ratio. Our tests would all be done on 91 octane, so we didn't want to jack up the compression. That brought us back to helping the LS2 increase its capacity to inhale. Dyno Time
We decided to swap three of the most common parts: the intake, the heads and, most importantly, the camshaft. The Superflow dyno at Westech performance would be the location of testing and we would use the SAE J-607 correction factor commonly referred to as STP. This corrects the data to 60 degrees Fahrenheit and 29.22 inches of Hg barometric pressure. Just like before, we would employ a cable-actuated FAST 90mm throttle body, since our dyno doesn't have provisions for the LS2's standard 90mm fly-by-wire air valve. To control the engine, we would also revisit FAST's XFI computer and adaptor harnesses.
The goals for the engine were to end up with a streetable combination that would kick butt at the track, yet still be a blast to drive on the street. We weren't going for the biggest peak numbers possible, but a good compromise that would be durable, have excellent low-end response, and not fall apart at the top end. Check out the photos and captions to see how it all unfolded.
Go With The Flow
The LS2 crate engine ships with some pretty good heads that, with port work, can flow some respectable numbers. Nevertheless, we decided to go with AFR's new 205cc Mongoose street heads. AFR states that the flow performance is 300 cfm at .600 lift (about 70 cfm over a stock LS1 head) and that the heads feature 2.020-inch intake and 1.600-inch exhaust valves with ductile iron interlocking valve seats. The AFR heads weigh a bit more than the stockers, but that weight is in the right place with a .75-inch thick deck, reinforced rocker stud bosses, and thick-wall runners. If you run over .600 lift, or rev over 6,600 rpm, AFR recommends that you upgrade to their 8019 dual springs to help lessen the chance of valve float. The standard AFR 8017 springs are also a dual design but with less seat (and over-the-nose pressure). Our COMP cam is almost right at .600, so we decided to spend $99 and get the better springs. This way we are set if we want to try an even bigger cam in the future. As pictured, the assembled AFR heads with the upgraded springs run $2,373.
ON THE DYNO
STOCK GM LS2 CRATE MOTOR
1.875-INCH HEADERS
Dyno Results
LS2 CRATE ENGINE
AFR 205 HEADS, FAST INTAKE, 1.875-INCH LONG-TUBE HEADERS, STOCK CAM
Dyno Results
LS2 CRATE ENGINE
AFR 205 HEADS, FAST 90MM INTAKE, 1 7/8-INCH LONG-TUBE HEADERS, COMP CAMSHAFT
