Pontiac Sprint Six Engine - The Last Page

Fans of Pontiac's Overhead Cam Six, which was built between 1966 and 1969, frequently lament the missed opportunities with the sophisticated powerplant. The four-barrel Sprint version was the first high-performance six since the Hudson Hornet of the '50s. It was dropped after the '69 model year due to production costs and packaging problems-the engine was too tall to clear the hood of the '70-1/2 Firebird without a bubble. Had the engine lived just a few more years, it could have been installed in the Ventura to make for a nice budget-performance car in the Sprint tradition that would have been perfect for the OPEC-beleaguered '70s.

Before the plug was pulled on the program, Pontiac built a few experimental versions with a special OHC Hemi cylinder head. They reportedly made 325 hp, though they never had a chance to call any engine bay their home.

Quenton Olson and Brent Hougestol of Primatech Motorsports International have embarked on a new chapter of Cammer development. More than 35 years after the last example was built, their company has developed a new line of high-performance parts for the OHC-6 that is truly bringing the engine into the 21st century. From intake manifolds, headers, cams, and stroker kits, to head porting and forced induction kits, PMI is doing its best to support John DeLorean's innovative brainchild.

To that end, PMI is in the process of taking the experimental OHC Hemi concept to the next level. It is building a DOHC cylinder head, based on the late-model GM 3.4-liter Twin Dual cam V-6. It is the company's most ambitious and highly advanced engineering and development project to date. Born of a desire to improve the breathing performance of the cylinder head, the DOHC is intended to be a high-performance, aluminum, bolt-on head assembly. Depending on the success of the project, it may well become a commercially available unit.

"We have gone as far as mocking up the head on a cylinder block to plan the timing gear/belt arrangement and to decide which water jacket holes need to be closed up before we heat treat the head," Olson says. "I want to make sure we give proper credit to the welder, Gary Gunther of Gary Gunther Welding in Sun Valley, California. He has done an amazing job on this project."

The DOHC head begins as two separate 3.4-liter DOHC heads (GM's LQ-1). Each head is cleaned, stripped, and machined to become a perfectly matched set. Water-jacket passages are closed off between the heads and then opened later during subsequent machining operations. The heads are welded together end to end while installed on a fixture to maintain proper alignment.

During the process, the head bolt hole bosses are remachined for proper position for the Pontiac OHC block. Two "common" bolt bosses are welded closed, plunge-cut on the mill, then sealed and rebored though several weld-machine-weld-machine steps.

The cam carrier (stock items from the LQ-1 motor) goes through a similar process of joining end to end, but are not welded, and have no water jackets to seal. A 24-valve DOHC head for the OHC block is the result. Custom cam drive gearing is installed, as well as custom-built camshafts. Designed and built to be a high-rpm, high-horsepower screamer, these heads should only be used on "built" short-blocks, where reconditioned rods and forged pistons have been installed. We will update this story as it develops. In the meantime, log on to www.primatechmotorsports.com.