Dyno Testing The TPI Chevy Small-Block Engine - Third-Gen Torture Test

Four Induction Systems And Two Cams Dyno-Tested On A Vortec-Headed 355 For Tpi Fans

By Ray T. Bohacz

Photography by Ray T. Bohacz

As the clich goes, the only constant in life is change. For 1982, Pontiac saw a big one. With corporate-wide restructuring, GM decided that V-8 engines of Pontiac design would no longer be produced. The majority of GM eight-cylinder applications would be from Chevrolet, but were identified for marketing as a "corporate V-8."

Though it was an excellent engine for its time, there's no way around the fact that the F-body corporate V-8 was a Chevrolet small-block. This posed a problem beyond the obvious disappointment for traditional Pontiac fans. A pure Pontiac engine shared little DNA with the SBC aside from the valvetrain design, and both took decidedly different approaches to making more power. The Pontiac engine was not as exhaust-port deficient as most engines in the '60s and '70s, and the extremely high numerical rod-to-stroke ratio meant that camshaft theory and other speed logics were unique to the brand.

Additionally, when the TPI Chevy small-block arrived for the '85 model year, it was an unknown entity. Never before had GM produced an intake manifold with such a long runner (24 inches from the plenum to the seat of the intake valve) as this induction system enjoyed. Not only did the electronic fuel injection require a learning curve for hot rodders, but the camshaft and cylinder-head-port theories used since the SBC was born in 1955 no longer applied.

An accurate dyno cell is required...

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As a result, the early efforts of tuners were often disasters. A TPI engine would be modified with a carburetor mentality, and the outcome would be a poor-running, surging, stalling car that made less power than stock. Now almost 25 years after the first TPI hit the Pontiac showrooms, making power with a tuned-port design remains a mystery to some enthusiasts and engine builders.

There's good news, however. As time marched on, so did technology. Today there are many more sophisticated components for the TPI engine, such as camshafts and induction systems, that were not around 10 years ago. HPP feels it's time to revisit some of the modifications that are available for the Third-Generation Firebird enthusiast who chooses to keep his car fuel injected.

To perform this in-depth test, the crew at RaceKrafters Automotive Machine in Lancaster, Pennsylvania, was contacted. Owners Bob and Craig Wise are knowledgeable engine builders, and theirs is one of the few shops that knows how to make big power with either a traditional Pontiac or a GM corporate engine.

The Test Engine
To reap accurate results, RaceKrafters built a dedicated test engine. It's a 355 small-block (+0.030-inch 350 with a 4.030-inch bore) with a 6.0-inch-long connecting rod instead of the standard 5.7-inch length. In theory, the longer connecting rod will add octane tolerance, improve torque, and make the corporate powerplant more Pontiac-like in operating characteristics.

For the cylinder head, they chose the cast-iron GM Vortec design, which was treated to a full bowl blending and competition valve job. This cylinder head is an excellent design, with good flow characteristics and a very quick burn rate. It flows 278 and 210 cfm at 28 inches of water. These features allow for a 10.95:1 compression ratio on 92-octane pump gas for better performance.

The rest of the engine is basically stock GM with nothing special but excellent and high-quality machine work, blueprinting, and assembly. It's an engine that an average HPP reader can build for his Firebird at a reasonable cost.