LS2 Engine Modification - Power Play

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.

The head bolts from the factory are called torque-to-yield. This means they stretch when torqued down and can't be reused. We took this opportunity to install a set of stronger ARP head studs (PN 234-4316). The nice thing about studs over bolts is that it makes future head swaps easier and over time saves wear and tear on the threaded holes in the block.	The factory rockers on the LS family of engines are very well engineered. Along with a semi-roller design, they also benefit from being very lightweight. We know of engines making way more power than ours running the factory stuff, so we saw no reason to change them. We ditched the easily bent stock pushrods for some hardened ones from COMP.	We thought the AFR heads required a gasketed spark plug, so we switched to Denso Iridium IQ22 plugs. Later, we found out that the AFR heads are machined for both types. Live and learn. You should note that the gaps on the factory Delco plugs were set all over the place and were more than likely costing us a few horsepower on the baseline pulls.
After doing a head swap, it's necessary to change the oil and filter since it's almost impossible to keep water from getting into the oil during the swap. Normally, we would run 10w30 oil, but we were out, so we used some 5w20.	The FAST intake was originally designed for the Gen III LS1 and LS6 engines. Since GM loves to change stuff around for no apparent reason, the LS2 fuel rails do not line up with the hold-down holes on the FAST intake (or LS1/LS6 intakes). Luckily, FAST is working on an adaptor kit to make it all work. Here, you can see prototypes of the offset spacers.	The FAST intake has many advantages over the offerings from GM. Out of the box, it is worth 15 to 20 hp over the stock intake, however, its strongest feature is the provision to customize the intake. The three-piece design (the lower black section is actually two parts) makes porting and blending the intake a breeze. In addition, the intake has provisions to install burst panels and integrated nitrous injector ports.
Another change GM made to the LS2 was to the fuel injectors. The injector on the bottom is from a 2000 LS1 engine, and the one on the top is the 33-pound injector that comes with the LS2. The LS2 injector is quite a bit shorter compared to the other style. Also, the lower O-ring is thicker and the injector requires a different style plug from the wiring harness. If you plan on upgrading injectors, it's important to keep this in mind.	As you can see, the AFR heads and FAST intake really helped the LS2 inhale. With a gain of 41 hp and an increase in torque of 39 lb-ft, only the limitations of the stock cam were holding back the engine. Still, for such a mild cam, 503 hp and 489 lb-ft of torque isn't too shabby. Timing was set at 29 degrees.	With more power left on the table, we turned to a bigger cam for inspiration. We could've slapped in the biggest possible cam to get high numbers, but what good would that be in real life? After talking with Tony Mamo at AFR and the technical wizards at COMP, we came up with a great compromise between power and street manners. The specs are 230/232 degrees duration at .050 and valve lift is .591 for intake and .595 for exhaust. We also went with a lobe separation of 114 degrees and had two degrees of advance ground in.