Mopar's new "Hemi" head

Sonny Leonard's Chevy "Hemi"

"My motors would make as much or more power as the Fords in cooler air, but in hot weather the Fords and Chryslers had a horsepower edge," Sonny admitted.

In order to make his new engine a better air pump he knew that he would have to have a more efficient head. What he ended up with was a cylinder head that combined the best properties of the wedge combustion chamber with intake and exhaust valves that were placed directly in front of the intake and exhaust runners. Placing the valves where he did in the head provides not only a better path for the intake charge but also a more efficient way to move burnt fuel/air gases out of the combustion chamber.

CadCam design of Sonny's combustion chamber

The valves in his new cylinder head aren't shrouded and the spark plug hole has been positioned in the chamber to encourage more and better flame travel. Better flame travel means more efficient burning of the fuel-air mixture and results in more horsepower and torque.

To ensure plenty of air volume and flow, the head can have intake valves as big as 2.700 inches in diameter and exhaust valves as big as two inches. According to Sonny, with a good porting job, a .900-inch lift cam and a 2.550-inch intake valve, the port will flow 590 cfm. The exhaust port will flow 390 cfm with a 1.960 valve.

"In testing we found that this engine will make more horsepower at 20 cfm less airflow that a comparable sized engine with our five-inch bore center heads on them," Sonny said.

This is more than just a high-horsepower engine. This engine will live longer and has a broader horsepower curve than the wedge-headed engines. The Ford Hemi head has 10 9/16 studs. Sonny's head has 22 1/2-inch studs necked down to 7/16" studs for better load distribution. This will help keep the head gaskets from pushing out of shape when a racer adds massive amounts of nitrous or runs a supercharger with 50 lbs of boost.

The rest of the components that Sonny uses to build this engine are the same track-tested components he uses in all of his engines: Sonny Bryant crankshaft, Bill Miller rods, Federal Mogul rings, Venolia pistons, and Manley valves.

While Sonny allowed us to take photos of cylinder heads, blocks and rotating assembly components, he was unwilling to reveal the exact info such as bore, stroke, rod length, and other proprietary information.