Horsepower comes in all shapes, sizes, and cylinder counts. But for the import inclined, making big power inevitably requires more robust engineering. Unlike a big V8 that spreads the loads over 8 pistons, a high-strung 4 cylinder needs extreme cylinder pressure and rpm to make the number. It's an Everest-sloped challenge, but one that has no shortage of willing contenders and checkered flags on the summit.
Turbos, nitrous, and superchargers do a "too-easy" job of providing the necessary power boost to run the number. However, getting that horsepower through the engine, transmission, and chassis is the black magic that separates first and second place. Diamond Pistons has long been a supporter of import racing and stood at the front line as FWD-class e.t.s saw 12s, 10s... and now times as quick as 7s in the 1/4 mile! As e.t.s continue to drop, they've used their considerable engineering experience to build pistons able to take unending racing abuse.
Building a piston to live with over 1,000hp in a 4-cylinder application—a bare minimum in today's racing environment—takes considerable skill. It also, historically, required a custom-made piston that took several iterations of development and testing to get right. The latter is no longer the case. Diamond's new Rebel Series pistons are the first shelf-stock Honda pistons ready for quadruple-digit power—and they have quite the racing pedigree.
Following in the lineage of the LS2k program (a shelf-stock piston for LS engine applications ready for 2,000hp), the Rebel series combines years of race-derived knowledge and a host of high-end features and packages it into a shelf-stock design. This cuts down on lead time tremendously for engine builders and racers alike.
"This is the first high-horsepower Honda product to market that's sold as a shelf part like this," said Dan Fonz, Sales and Technical Support Specialist at Diamond. "The pistons themselves are spec'd for 1,000-plus horsepower and include Tool Steel pins with a total seal ring pack. That's a steel top ring, steel napier second and a 2.8mm oil ring. We wanted to use high-quality components that could deliver right out of the box."
In addition to the high-end Total Seal ring pack, Rebel series pistons play host to several racing derived features such as lateral gas ports, to increase ring seal, and oil retention grooves which keep a reserve of oil just under the oil ring to help the piston effortlessly glide in and out of the bore at high rpm.
"These are built to the hilt as far as what Diamond can offer in a forging," said Fonz. "You've got to get the oil out of the hole when you're turning RPM like these guys do. That oil retention groove helps keep oil on the skirts and helps it glide in and out of the bore. It's a feature you see a lot on Pro Mod pistons but we went ahead and added it onto these. And, those lateral gas ports combined with the steel top rings are going to help seal with 40-50 pounds of boost."
- Dedicated Forging (stronger than billet)
- Lateral Gas Ports
- .220in Thick Crown
- .160in Thick Skirt
- Total Seal Stainless Steel Top Ring, Steel Napier second ring and 2.8mm oil ring
- Oil Retention Groove
- Trend Tool Steel Wrist Pins
- Forced Pin Oiling
- Wrist Pin Buttons
- Center balanced
WHAT MAKES THE REBEL SO STRONG?
The Rebel series draws from Diamond's experience in all forms of motorsports, but one of the main takeaways from previous drag racing endeavors was to put adequate material in the right places for the desired power level. "We spent the time to put the thicknesses in the right places, we 3D radiused everything," said Fonz. "It's a premium part and you know that when you pull it out of the box. First and foremost, the top ring lands are as thick as possible to be able to take the heat," "The material has to be thick and sturdy there and support that top ring and make sure there's no collapse. With the RPM and the boost levels these guys run you absolutely need that-it's crucial."
The full round forging design is also a key to the Rebel's rigid design. "You see full round in a lot of higher horsepower stuff—anything full-on drag race, Pro Mod, Top Fuel—all of those guys are running full round. When you combine that with a Tool Steel pins and pin buttons, there's no movement, or travel. A lock isn't going to fall out if there's any type of stress."
A full round forging rigidly bolsters the circumference of the piston, and also features a wider pin to help spread out the load of high cylinder pressure. That skirt shape, combined with the strength of the Rebel's dedicated 2618 aluminum forging and Tool Steel wrist pin are major factors in its quadruple-digit horsepower carrying capacity. But another detail that makes it ideally suited to high-revving Honda applications is full center balancing.
"Having a piston that's heavier on one side than the other, it's always going try to rock over in the bore," said Fonz. "When the piston is center balanced it goes up and down the bore easier, from a harmonics standpoint alone. At the 10,000-plus rpm these guys are turning, it's essential."
WHO'S IT FOR?
The Rebel Series will be available for both K- and B-series Honda engines in a range of compression ratios and compression heights-all designed for extreme horsepower applications. "We've had great success with the B series," said Fonz. "The B gets a lot of love. We've been thinking it was going to die off for 10 years, but it hasn't. People are still building them—there's a lot of great combinations out there. But there is going to be a demand for high-horsepower K-series engines. It's where the market is going to end up swinging, so we wanted to be prepared for when that happens. We're really shooting for the sport front-wheel drive community—teams that are looking to make all the horsepower they can to be competitive."
Despite the Rebel's race derived design, it is 100 percent compatible with high-horsepower street cars, as well. "There're a lot of guys out there, especially in the K series market, getting into that 700-800hp range where they maybe need something a little bit more," said Fonz. "This is the piston for that. The parts really speak for themselves. When someone picks up one of these pistons and they look at the bottom side of it, and the structure and design, they can immediately tell this is a fully engineered and properly machined part ready to make power."