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500hp 6.5L Diesel Race Engine

Revenge Of The GM IDI

Text By: Bill Heath, Jason Thompson, Photography by Bill Heath

500 Hp!
In the January '09 issue of Diesel Power we showed you Heath Diesel's 6.5L-powered Chevy pickup ("This 6.5L Chevy Runs 153 mph"), which could outrun most Corvettes. The article highlighted the truck's Bonneville land speed racing buildup, but there was so much reader interest in the motor, Bill Heath agreed to let us publish his GM indirect-injection (IDI) engine building secrets. While these modifications may not be for everyone (or every truck), they should help readers looking to narrow the gap between '82 to '99 GM diesels and '01 to '11 Duramax trucks.

A Near-Stock Combination
Heath Diesel's land speed race engine wasn't stock by any means, but it did use a lot of factory engine components. Heath's buildup began with a Scat Enterprises cast-steel 6.5L crankshaft bolted into the block with a Heath Diesel main stud kit.

Based on Heath Diesel's experience, the 6.2L piston design is thought to be superior to that of the 6.5L piston. The 6.2L part is heavier, features a more robust wristpin boss, a heavier crown, and a lower placement of the rings. These are differences that play a role in the more extreme applications such as land speed racing.

Engine Block
Heath Diesel cleaned the 6.2L block using a three-step process that included hot tanking, sandblasting, and acid etching. Then engine block filler was poured into the coolant passages with the main bearing caps torqued in place. Heath added the filler until it was 5/8 inch below the engine's deck surface. This improved the structure, while still allowing the necessary coolant circulation between the block and the cylinder heads. As soon as the first side was poured, Heath Diesel worked fast to install a cylinder head with a used gasket and the fasteners used in the final assembly. When the first side of the engine had firmed up, Heath Diesel rotated the block and filled the other side. The engine was then allowed to sit for more than 60 days to allow the block filler to fully cure.

Machine Work and Rotating Assembly
The block was delivered to Joe's Grinding in Yakima, Washington, for the necessary machine work. Owner Rich Eims thoroughly examined the block and checked the main bearing housing bores and alignment. He also made sure the decks were square and parallel to the crankshaft centerline. The block was bored and honed with the main bearing caps in place and a BJH deck plate was installed with a used head gasket torqued in place. Mahle recommended that its 6.2L pistons (PN 027481) were fitted to the individual cylinders with a skirt clearance of 0.0025 inch. Because Heath's engine operates at higher combustion temperatures and engine speeds, it was decided the clearance should be set at 0.0033 inch. To help achieve this finished clearance, Tech Line PowerKote DFL-1 coating was applied to the piston skirts to help fill in the irregularities of the cylinder walls.

Bored Not Honed
Heath Diesel believes reconditioning the connecting rods is critical when building a quality 6.2L or 6.5L. After checking for any cracks, the rods were outfitted with new bolts and properly resized on both ends. An important part of this process was to ensure the proper finishing and accurate sizing of the wristpin bushing bore. After fitting each connecting rod with a new wristpin, the pin bushings were finish-sized to the correct internal dimension and the bore centerline was made perfectly parallel.

For best performance and durability, the pin bushings were bored to dimension-not honed. Heath Diesel is convinced that these pin bushings cannot be successfully honed to size (the accepted automotive practice) because the honing stones will load with the relatively soft material and cause a coarse and deeply scratched load-bearing surface-one that will imbed hone-stone material. These gouges cause point-contact-welding and lubrication breakdown failure between the pin and bushing. The diameter of the bushing is then too large to provide the necessary contact surface area.

By Bill Heath, Jason Thompson
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