For our needs, we decided that it was all about power, or at least enough about power that we chose to turbocharge the 5.7L stroker rather than add a blower. This stroker is every bit as suited to a supercharger as a turbo, and who knows, maybe a blower test is in the cards, but for now, its all about the turbo. For the do-it-yourselfer out there, a turbo kit can be as simple as plumbing all the exhaust to the turbo. For a single turbo system, this means joining the exhaust from each bank into some sort of Y-pipe. We have used the stock truck manifolds before with great success, but for this application and turbo kit from HP Performance, we ran the SRT8 exhaust manifolds. The factory manifolds offered exceptional heat retention, making them ideal for turbo applications. The kit from HP Performance was designed for a 300, but they also offer a similar system for Hemi-powered trucks. Wanting to try a pair of different turbos, we elected to first attach an affordable turbo from CXRacing to the hot side of the turbo kit. Do the cost-effective turbos really work? That was one of the questions we hoped to answer.
In addition to the 76mm turbo, CXRacing also supplied an air-to-water intercooler. The kit from HP Performance included an air-to-water, but (like the turbo) we wanted to check the cost-effective turbo components while we had the motor on the dyno. The turbo kit from HP Performance was originally supplied with a 38mm wastegate, but we elected to take this opportunity to upgrade to a 45mm HyperGate from Turbo Smart. The new HyperGate not only offered additional flow for better boost control, the new wastegate also featured a revolutionary new locking collar mechanism that made spring changes a snap. The compact design eased installation in tight (read late-model) engine compartments. Turbo Smart also supplied one of their manual wastegate controllers to allow us to dial up the boost above the minimum wastegate setting of 6 psi. Tuned to perfection using the XFI/XIM management system from Fast, the turbo stroker pumped out 672 hp and 635 lb-ft of torque at 5.7 psi. Adding 150 hp to our stroker was impressive, but we were just getting started.
After success at the lower boost levels, we cranked it up to nearly 9 psi. The increase in boost elevated the entire power curve, pushing the peak numbers to 765 hp and 764 lb-ft of torque. Things were starting to get serious, but we feared the smaller turbo from CXRacing was running out of steam. To cure this problem, we stepped up to an 80mm unit from Comp Turbo. The larger turbo was installed and run through the same air-to-water intercooler. We meticulously tuned the combination and increased the boost until we reached more than 15 psi. Subjecting the motor to an additional atmosphere of pressure resulted in a serious jump in power. The turbo Hemi stroker produced 1,015 hp and 867 lb-ft of torque. Nothing short of an all-out race truck is going to require any more power, but the combination does illustrate what happens when you add boost to an already potent stroker Hemi. To say we were excited about the turbo stroker Hemi would be an understatement—we were PSIched!