PRI 2015: Diamond Pistons’ 5.3 Bore-Space Piston For Nitrous Combos

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“Any of the guys with the 5.3 bore-space nitrous engines in classes like Pro Mod and PDRA Pro Nitrous have always considered pistons as throwaway items, because they’re so abusive to the parts,” says Diamond Pistons‘ Mike Panetta. “We’ve always made these out of billet, but the issue with those is the price. These guys are price-driven; some guys make one pass and some guys make 30 passes on them, it depends what they are doing with the tuneup.”

In response to these concerns, Diamond has developed a forging that’s based around the billet design that they already have confidence in, but is available at reduced cost when compared to the billet jewelry.

In this application, thin piston rings are not ideal, so Diamond has outfitted the slugs with a .043-inch, .043-inch, 3/16-inch ring stack to handle the immense heat created when the squeeze is activated. The piston is also designed to use a pin button with a support rail for the oil ring.

“A traditional support rail is .030-inch thick, but for these pistons we do a .045-inch thick rail because there’s so much side load that it was bending the support rails, pinching the oil rings, and creating oiling issues,” says Panetta. “We’ve designed skirt profiles to work with the bigger strokes — some of these guys are running over a six-inch stroke — and the piston speed is so high because the rods are so short, we’ve tailored a skirt profile that works very well.”

Traditionally, a piston’s top ring land is tapered 1.7 degrees toward the piston crown, but in this application Diamond has designed the pistons with a 2-degree taper for both the top and second ring land because they see so much heat. The extra taper leaves the piston some room to grow without growing into the cylinder walls.

On the underside, the piston has struts built into the lower areas of the corners to help provide some support to the pin area.

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Jason Reiss

Jason draws on over 15 years of experience in the automotive publishing industry, and collaborates with many of the industry's movers and shakers to create compelling technical articles and high-quality race coverage.
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