High grade valve springs for offshore racing
Van Dyne Engineering of Huntington Beach, California keeps it local when looking for valve springs to fit their big block Chevrolet engines used for offshore racing.
Building for the American Power Boat Association's (APBA) Super Cat two-time World champion and 11-time Western Division titleholder 36-foot The Renegade, driven by Garden Grove's Craig Ferguson, Stewart Van Dyne II and Stewart Van Dyne III (Tres) specify Tool Room valve spring material by Isky Racing Cams from nearby Gardena, CA.
Because they have to use a spec head and manifolds on their near-510 cubic inch Chevy that makes around 830 horsepower, the engines are limited to 7600 rpm to keep speeds under 140 mph, the Van Dyne's fit a double spring with flat insert damper.
"These springs hold their own over the rebuild schedule of four races, running without any problems. The springs usually go down about 10 pounds from where they started and we normally replace them when we rebuild the engine," father and son agreed.
"The only time we ever broke a valve spring is when we had a driveline failure, but that doesn't occur very often," they said. "Actually, that happened before we had a rev limit. If you have a failure like that, it causes the engine to hit really high rpms" in excess of the decreed redline.
In this series, it's not possible to port and polish and the carburetor size and compression ratio (12:1) are fixed. "There was a time when they didn't have rev limiters and they ran to 8500 rpm the whole race without missing a beat," they reminisced. "Everything was perfect; ran like a champ. We would check the valve lash after the races and a couple of valves would change about a thousandth or so. Everybody was happy!"
The Isky Tool Room valve springs feature full-spectrum harmonic vibration control to suppress surge and avoid harmonic convergence. These springs are the "RAD" style, which is a special process that makes them nearly bullet-proof. They have endured Gold Stripe test certification through a 1000-mile certification test for each batch.
The springs have an outside diameter of 1.625-inches and inside diameter of 0.770-inch on the inner spring. The seat pressure is 250 pounds at 2.020 inches installed height and 675 pounds at 1.270 inches when new. "We actually shorten the installed height a little and bump the pressure up a bit." These valve springs are used on hardcore roller tappet engines. With these spring pressures, the builders recommend using a roller bearing camshaft.
According to Richard Iskenderian at Isky Racing Cams, this heat-treated super high-grade spring uses a super-clean high tensile chrome silicon material. The manufacturer uses a special process in constructing this spring that helps it hold pressure better, last longer and manage breakage better. It is, he told me, best suited for higher rpm applications.
The Renegade races about four times per year in contests of one hour duration. There are customarily three 20-minute practice sessions the day before each race, giving the valve springs a life span of about 10 hours on the water. They are replaced at each rebuild but could be returned to service a second time if needed.
Fig. 1 - The Isky Racing Cams Tool Room valve spring is strong enough to last on the water.
Words and photo by Anne Proffit