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GM Performance Parts LS3 Engine Build Part 3 - Late Crate Update

Want A Crazy, 900HP Street Car? Check Out The...

By Richard Holdener, Photography by Richard Holdener

The big-chamber Procomp LS3 heads were installed using new Fel-Pro MLS head gaskets and ARP heads studs. With the stroker now boost ready, we installed the turbo kit from HP Performance in Roswell, New Mexico. The kit was originally designed for use in a '10 Camaro, but we had to perform a few minor adjustments to tubing position to facilitate installation on the engine dyno. In the end, the turbo kit looked like a cross between the kits offered for the '10 Camaro and a late-model LS-powered Chevy truck. This had no effect on power or performance; it just made our life easier during testing. The intercooled turbo kit featured a Y-pipe designed to channel the exhaust from both sides of the motor to a single turbo mounted adjacent to (and slightly ahead of) the passenger-side cylinder head. The Y-pipe also featured a mount for the 45mm wastegate from Turbo Smart and a (very useful) oxygen sensor bung. Like the remainder of the kit, the Y-pipe was treated with a thermal barrier coating and featured V-band clamps to secure together sections of tubing for a leak-free seal. The Y-pipe was designed to bolt to the factory LS3 exhaust manifolds, but we employed a set of shorty headers from JBA. Also coated, the JBA headers looked right at home and obviously offered improved flow over the factory manifolds. Mounted to the Y-pipe using a T4 flange was a custom 67mm HPQ turbo from Precision Turbo. Capable of supporting 750 hp, the 67mm turbo featured Precision's unique, CEA (Competition Engineered Aerodynamics) forged-aluminum compressor wheel. The impressive turbo from Precision offered exceptional boost response. We employed a manual boost controlled from Turbo XS to regulate the boost beyond the wastegate spring setting.

Bolting on the turbo system was no more difficult than a typical header swap, but we made sure to drill and weld a fitting onto the steel Moroso oil pan to serve as an oil drain prior to installation. We ran a section of braided line equipped with -10 fittings from the oil drain on the bottom of the turbo to the oil pan. The oil feed for the turbo came from the fitting located just below the oil filter. The ultraefficient air-to-air intercooler was plumbed in line between the turbo and FAST LSXR intake. A dedicated fan was used to supply cool air to the intercooler during testing. Knowing the turbo kit offered plenty of potential, we installed a set of 60-pound injectors. The stock 42-pounders were obviously inadequate for our turbocharged stroker application. As we would soon find out, so were the 60-pounders. The idea was to run the small 67mm turbo on pump gas, then switch over to the larger 80mm turbo and run race fuel to see some big power numbers. Prior to running the motor under boost, we tuned the combination with the Procomp heads to see just how much power the drop in compression was worth. It lowered the peak power numbers from 608 hp and 570 lb-ft to 577 hp and 551 lb-ft of torque. These numbers were close to the general rule of 3 to 4 percent drop per point of compression.

By Richard Holdener
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