505CI, 1,073HP, Twin Turbo Pontiac
Jeff Hutchens, Springfield, MO
In the world of serious horsepower, Pontiac isn't usually the first name dropped in the average bench racing session. That's unfortunate because there is plenty of Pontiac power to be had for anyone who wants it. When Jeff Hutchens brought his '67 GTO to Muscle Car Restorations (MCR) in Chippewa Falls, Wisconsin, for a complete restoration, he told the company he wanted a car that could run with the high-dollar exotics but still retain the factory GTO look. Because of Butler Performance's strong reputation for producing Pontiac power, MCR commissioned the staff to come up with a twin turbo Pontiac combination that would provide some serious yet still streetable performance.
Assembly, break-in, and initial tuning were accomplished at Wheeler Dyno Service in Blaine, Minnesota, while the final chassis tune and traction control were done by HiTech Motorsports of Elk River, Minnesota, back at MCR's Mustang chassis dyno.
With 17.7 pounds of boost and a tank of C16, the twin turbo Pontiac engine made 1,073 hp at just 5,800 rpm and 1,079 pounds of torque at only 4,500. Using 13.4 pounds of boost (pump gas), it still made a tire-wasting 920 hp. It also idles relatively smoothly and quietly with just a hint that there's something special inside. Off boost, it drives around like a stocker, but get on it and, well, you can just imagine.
With a 70mm Turbonetics unit perched on either side of Jeff's 505 Pontiac, he gets the quick spool up of a smaller turbo and enough capacity to flow big on the top end. Evolution 35mm mechanical wastegates control the boost.
B. Exhaust And Intake
MCR crafted a pair of stainless steel 2-inch primary turbo headers with 3-inch collectors and a full 3-inch stainless exhaust system. It also did a good job fitting a Bell air-to-air intercooler to a 70mm Accufab throttle body and plenum. The scream of a Turbonetics Godzilla blow-off valve may startle the unsuspecting as it relieves excess pressure when the throttle closes quickly after a boost session. Since the hood was to remain factory stock, the engine setback was adjusted so the throttle body would be directly under and therefore fit into the GTO hood bulge.
Butler Performance's IA II block is a very solid foundation to build on. This one is spinning 4.350-inch Ross pistons through a 4.250-inch stroke with 6.700-inch Scat rods. The blocks ship dry deck, so Wheeler needed to drill the holes for the water passages. Oil drain-back holes must also be drilled in the lifter valley to run the block wet-sump, and main bearing oil passages were notched to join with the cam bearing oil passages. A seemingly mild Comp Cams hydraulic roller with 0.541 lift with 258/248 duration keeps the driveability in the low end.
The heads are Edelbrock Performers with 2.110/1.660 valves that were port-matched to a Victor manifold. Since this thing will rarely, if ever, see the other side of 6,000 rpm, Comp Cams' 1.5:1 aluminum roller rockers will work just fine with a set of Smith Bros. 0.040-inch restrictor pushrods. Compression is a turbo-friendly 7.96:1. Wheeler likes to run Cometic MLS (multilayer steel) head gaskets because he thinks they will handle the boost potential of the turbos but seal the water passages better than a copper gasket with O-rings.
Twin Turbo Pontiac - Engine Management
Very precise control over fuel and timing at every rpm and load level makes it possible to generate more than 1,000 hp and still be your-grandmother-could-drive-it docile while cruising. A FAST XFI ECU controls the 83-lb/hr injectors and manages the spark from an MSD dual-sync distributor, which allows the FAST box to run the injectors sequentially and set the fuel and timing (on a cylinder-by-cylinder basis, if necessary) for every rpm and load range possible. The FAST software also contains an Intelligent Traction Control feature that helps Jeff make the best use of every pound of torque. And TCI Automotive's universal transmission controller works in step with the FAST unit to tightly control the Bowler-built GM 4L85E transmission's shift points.