Pushrods on the water
"Any time we need a 3/8-inch diameter pushrod with a 0.120 wall, we go to Manley Performance Products of Lakewood, New Jersey," state Stewart Van Dyne II and Stewart Van Dyne III (Tres) of Van Dyne Engineering in Huntington Beach, California.
Pushrod sizing is important for the 830-horsepower, 510-cubic-inch big block Chevrolet (with spec heads and manifold) that the Van Dyne father-and-son combo prepare for the American Power Boat Association (APBA) Super Cat used by two-time World champion Craig Ferguson's 36-foot Skater Catamaran "The Renegade" of nearby Garden Grove.
"The length and diameter of the pushrods we use depends on the cylinder head, valve length, rocker arms, tappet length and base circle of the cam lobe," they told me. "The diameter is also controlled by the position of the pushrod cup in the tappets and the pushrod cup in the rocker arm." To meet the challenge of keeping the intake ports out of the way, "When possible, we run offset rockers and offset tappets to help the problem.
We try to get the biggest pushrod that will fit the application," the Van Dyne's agree.
The pushrods chosen for this application are of one-piece 4130 chrome moly tubing with 0.120 wall and swedged ends made of 4130. These pushrods are heat-treated and black oxide coated. The swedged formed ends have exact radii for low friction and long life in the cups on the tappet and rocker arm, the Van Dyne's said. The pushrods normally last a full season of running on the water and are not affected by any difference in water condition.
With a 7600 rpm redline dictated by the American Power Boat Association (boats had been running in excess of 140 mph with the previous 8600 rpm redline), "We wanted to keep the RPMs up to come off the corners better. But we had to go to more aggressive cam profiles to pick up the torque at a little lower rpm, to jump off the corner harder and still run down the straights hard," they said.
When the Van Dyne Engineering brain trust went to the 0.120 wall pushrod, it added some weight to the mix. The 3/8-inch diameter, 8.2-inch long 0.120 wall Manley pushrod weighs 96.5 grams, compared to the same length, 3/8-inch diameter 0.080-wall unit, that weighs 73.5 grams. Another example is an 8.2-inch long, 5/16-inch diameter 0.080 wall pushrod Van Dyne currently uses that weighs 61.5 grams.
"The difference in weight on these pushrods really doesn't change what we do. It has been found that the weight on the pushrod side of the rocker arm isn't quite as critical as on the valve side. It doesn't matter what it weighs; if it's a short fuse that won't let you run as hard as you need to," they told me.
In addition to its work building championship APBA engines, Van Dyne Engineering manufactures the Offenhauser "Offy" engines, prepares stock blocks for racing purpose and has its own line of racing water pumps.
Fig. 1 - The larger, 3/8-inch diameter 0.120 wall 8.2-inch long Manley pushrod works best in the big block Chevrolet used in American Power BoatAssociation Super Cat racing.
Words and photo by Anne Proffit