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Pistons for offshore racing

pistonsOne benefit to building a maximum 510-cubic inch big block Chevrolet engine for American Power Boat Association (APBA) offshore racing, is the cooling. Because cold water constantly throbs through the block and cylinder head, there is very little fall-off in performance and very little micro welding in the ring lands to deal with.

According to Stewart Van Dyne II and Stewart Van Dyne III (Tres) of Van Dyne Engineering in Huntington Beach, California, "We tend to like pistons with longer pins and thicker walled pins because they help keep the pistons alive."

Primarily utilising products from local purveyor CP Pistons in Irvine, California, the Van Dyne operation specifies 2618 material weighing 670 grams and goes with three ring lands, with radial gas ports, double pin oilers and wire locks.

"The off-shore pistons get a bigger beating than any of the pistons in our other [big block] engines because, even though they are on and off the throttle a lot, they are on it a lot! The pistons have a tendency to get soft, losing their strength and they end up ripping the wrist pins out of the bottom of the piston."

pistons off-shore-piston-1

Because they are limited to 12:1 compression in the Super Cat class, the company's client Craig Ferguson of nearby Garden Grove, who has campaigned The Renegade to two World championships and 11 APBA Western Division titles, ends up with fairly traditional piston specifications.

"We may run a different shape [dome] but it's not that critical because the dome is not too tall. We normally don't use coatings because we haven't seen much value in it, or seen them live longer, or better, because of the coatings. We have done the skirts with black moly coating, but it doesn't seem appropriate for the application as the CP skirts always look perfect," both father and son agreed.

The engineers specify a high deck block, one that is about 0.400 thousandths taller than the standard deck. The engines come out a bit under the maximum allowed size at 3.750 stroke and 4.600 bore. Using a 7.000-inch rod, this also helps piston life, giving a 1.866 rod/stroke ratio. These engines make about 830 horsepower.

pistons off-shore-piston-2

The American Power Boat Association races last about an hour with three practice sessions of 20 minutes each the day before the event. This run time allows the pistons to go for four races - sometimes five - before being removed and replaced with new stock, according to the Van Dyne operation.

It's rare that they see much wear, particularly with the current imposed rev limit of 7600 rpm, but they'd rather replace the units than have their client's engine develop problems.

The approximately 10 hours run time on the pistons has become nearly a full season's racing for Ferguson, who has backed off his competition in 2009 with the economic downturn. "The fields are a bit shorter than they had been but Craig seems to win nearly every race he enters."

Fig. 1 & 2 - Pistons life is extended by the cold water that runs through the block and head

Words and photos by Anne Proffit

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