Pontiac 400 Poncho Engine Build - A 650HP Hard-Core Pontiac Stroker

Flow Numbers
These flow numbers were generated on Westech's SuperFlow 600 bench using a 4.175-inch bore size at 28 inches of water test depression. While Mitchell's cam only lifts the valve to 0.675 inch, note how these heads continue to deliver flow improvements up to a staggering 1 inch of valve lift. These are as-cast flow numbers. Porting could easily push the intakes above 400 cfm.

Buttoning up the engine was a complete set of 1.60/1.65:1-ratio T&D shaft rockers actuating Manley mechanical roller valvesprings and retainers.

Buttoning up the engine was a complete set of 1.60/1.65:1-ratio T&D shaft rockers actuatin

The Test
The final assembly included adding the necessary Roland CV-1 single-plane intake manifold along with a 2-inch phenolic spacer topped off with a Holley Ultra Dominator 1,050-cfm three-circuit carburetor. Even though the motor was only 434 inches, the CV-1 heads seem to prefer a larger 2-inch primary header. Bolting up this completed package on Westech's dyno, Mitchell and Westech's Steve Brulé performed some quick jetting and timing exercises and then cranked out an impressive 650 hp at 7,000 rpm. On the other end of the curve, peak torque occurred at 5,500 rpm with 549 lb-ft, which outlined a wide powerband of 1,500 rpm. And there was no race gas here-this was on little more than California-conservative 91-octane. Mitchell says the owner was initially going to stuff this beast into an original '65 GTO but reconsidered, and it now occupies the engine compartment in a '69 Firebird. Just for fun, we plugged the power curve into a simulated 3,000-pound Firebird with a TH400, a 28-inch-tall tire, and a 4.10:1 gear using the Quarter Pro software. The sim reported a 9.90 at 135 mph, which should make any Pontiac owner proud. We certainly do live in the golden age of horsepower.

The final top-end pieces included the requisite CV-1 Roland single-plane intake that Mitchell merely cleaned up internally along with a Holley 1050 three-circuit Ultra Dominator carburetor that required very little tuning to make 650 hp. Ignition was handled by an MSD billet distributor and BOP Engineering composite gear.

The final top-end pieces included the requisite CV-1 Roland single-plane intake that Mitch