With bolt-ons including Stainless Works headers, our 2005 GTO project previously made 375.9 hp and 372.7 lb-ft on SLP's Superflow dyno. Then Stainless Works bolted up its new 3-inch exhaust system at its Chagrin Falls, Ohio headquarters. As an added benefit to the well-designed and great-sounding system, the baseline dyno numbers, 356.1hp/356.5 lb-ft on GMR Speed's Dynojet, went up to 368.1/376.4, a solid gain.
Our time with this 2005 GTO was winding down, and I left Ohio and headed west for Chicago, where this Goat had a heads/cam appointment at Speed Inc. Speed Inc, based in Schaumburg, Illinois, and led by President Tom Izzo, has earned an excellent reputation with LT and LS owners. The key to any performance shop is having all of your bases covered; Speed Inc's staff is highly experienced in all aspects of late-model GM performance: heads/cams, blowers, turbo systems, high-end tuning, race car building-the guys up front know what they're talking about, and the techs out back know what they're doing. Needless to say, our LS2 Goat would be in good hands.
As we'd done a nitrous system and a host of bolt-ons to the 364-inch mill, it was time to give it some serious power. We'd done some forced induction on previous project GTOs, and as car owner Bruce Corcoran was a fan of the big-cam sound from classic Goats, this project would be a bumpy-cammed, high-rpm screamer.
We've had good luck with AFR's 205cc LS1 castings in the past, picking up nearly 40 horses at the wheels on an LS1 with no other changes. As such, after a good conversation with AFR's Tony Mamo regarding the 205s on an LS2, a set of AFR heads was given the nod for this build. I disclosed this head choice to Tom Izzo, who went to work choosing a camshaft to complement the AFR castings. It had to be a drivable stick, as this GTO spends 95 percent of its time on the road. But it also had to make good power over the factory cam. With those parameters in mind, Izzo chose a 234 duration, .598/.576, 114 LSA grind.
When I arrived in Schaumburg, all of the hard parts were ready. We let the car cool down overnight and when I showed up bright and early the next morning, Speed Inc Tech Dan Marks was ready to tear into the LS2. Follow along on our heads/cam swap and see how much power it gave us
But what happened next took the cake: our safety consciousness bit us in the collective ass when we learned that the 2004-only loop we'd modded for use with our ride had contacted the larger BMR driveshaft, unbalancing the shaft to the point where on the nitrous dyno pull, the bad vibrations cracked the M6's tailshaft housing! With the housing peeing trans fluid, our test was over. Speed Inc graciously replaced the housing with a new one, but we were unable to get a follow-up nitrous test done. Still, the heads/cam swap netted us over 60 rear-wheel horses and nearly 25 ft-lbs of torque naturally aspirated, and this is an easy 500-rwhp GTO with a tuned 75-shot. And best of all: with all of the extra power, she still idles and drives smooth. We have a couple more tricks up our sleeves before this project is done--stay tuned.