Upon teardown, the engine looked fantastic with the exception of one head gasket that failed. The cause was determined to be that it was actually the wrong set for the application. Its bore size was just a little too large, and it went by undetected. No other damage was present, and the engine has been buttoned back up with the correct Cometic head gaskets and is ready for more testing.
As it stood though, the results were very impressive. In fact, the engine made nearly 37 hp more than the blower was rated for. Max power came in at 862.9 at 5,300 rpm, with 890.5 lb-ft of torque at 4,800 rpm. For a stock-block combination, this was very impressive.
From his past experiences, Steve concluded that if a larger carburetor was used and properly dialed-in, 1,000 hp was well within reach. Even so, an 850-plus-horsepower Pontiac street engine with docile street manners is a very enticing combination. No doubt that the '64 GTO it is going in will be a speedy little unit!
Conclusion
One of the things you might be saying to yourself is, "Wait a minute, aren't Pontiac blocks only good for 700 hp before they split down the middle?" How is it possible that an unfilled, two-bolt block can go more than 150 horses above what conventional wisdom says is impossible?
It's not so much how much horsepower one makes, as it is how that power is made. Back in the '60s, Arnie "The Farmer" Beswick was arguably the leading Pontiac horsepower maker, and his method of making it was in lockstep with the technology of the day. He used GMC superchargers, high-overdrive ratios. and large percentages of nitromethane.
While the combinations would make ridiculous amounts of power, they were not very durable. The combination of high rpm, heavily overdriven, low-efficiency blowers, and explosion-prone fuels would split the block at the 700hp to 800hp range.
Blower drives had the additional problem of adding length to the crankshaft, which would introduce flexing, especially at high rpm. Forged or not, the cranks would fail, if the thrust against the block didn't split it first or a blower didn't lift off the engine. Nitrous combinations are also very rough on bottom-end parts and are failure prone in many 700-plus-horse Pontiac combinations.
By reducing detonation, rpm, and blower drive stress, a stock-block Pontiac engine can make well over 700 hp without splitting the block, throwing rods, or tearing apart a crank. Marty Palbykin's twin-turbo 400 Pontiac made over 1,600 hp using a garden-variety '67 400 block. Granted, it had a Ram Air V forged crank and four-bolt mains, but the block had coolant circulating through it and it did live for a full race season.
It can be done, even if conventional wisdom says otherwise.
Comparing the normally aspirated...
Comparing the normally aspirated and supercharged horsepower and torque curves tells a fascinating story. One atmosphere of boost will just about double your horsepower.
One of the most interesting...
One of the most interesting aspects of this engine is how simple it really is. The '68 400 block still retains its two-bolt mains, though they are augmented with ARP main studs. Butler Performance supplied the 4.21-inch-stroke forged crankshaft. It has 3-inch mains with 2.20-inch rod journals to use big-block Chevy-style rods.
The piston and rod combination...
The piston and rod combination came from Butler Performance and is a Ross forging for a standard 455 bore size. It swings on an Eagle H-beam rod with a 6.800-inch center-to-center length and a 2.20 journal, a standard Big-Block Chevy size. The pistons were treated to a special Luhn Performance coating that is heat resistant and provides additional lubrication.