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Top Fuel piston secrets

pistonsWhen it comes to prepping pistons for their NHRA Top Fuel rail, Don Schumacher Racing’s Antron Brown-driven team relies on co-tuner Rob Wendland. This year, the team led the ‘regular season’ of 18 races and finished third in the point standings, 49 behind six-time consecutive champion (and teammate) Tony Schumacher.

Wendland said the team uses a variety of pistons, depending on the nature of the circuit. Their primary choice is a hard anodized JE piston, “Because they provide excellent customer service. It’s also part of the combination that was on this car when we came over here. You hate to change a system that already works,” he said.

Trying different combinations during a race weekend – there are only four in-season test sessions allowed over the 24-event campaign – Wendland may want to “raise a piston or lower a piston’s compression,” so with one-week turnaround that is easier to do when they’re on extended road trips. Raising or lowering a piston is the tuner's way of increasing or decreasing compression in a particular cylinder. Such changes are slight, but a cylinder that burns consistently ‘hot’ might become normal with a little less compression by lowering the piston in that hole.

One of the biggest challenges is dealing with dish on the top of the piston. “After a run, depending on the dome thickness that you run, you may see conditions change. Given the tremendous amount of dome heat on the top of the piston, and compression [combustion pressure is concentrated on the dome of the piston, which is hollow underneath] and cylinder pressure, it’s almost trying to knock that piston through its dome [that is, the surface area of the piston exposed to the heat and pressure of the spark and combustion of the fuel mixture]. Then add the heat and it can really knock it through.”

“The problem is,” Wendland continued, “when you develop this piston so thick on top, it doesn’t dish. You then have a heavy top-ended piston, so you have all that weight above the pin height and that sometimes causes the piston to rock. If you get the piston rocking too much, you see a lot of wear on the sides of the piston – and that turns into scuff, which is a nitro tuner’s worst nightmare!

“Once you have scuff, the piston loses ring seal and then you lose compression, blower, fuel – all those things that can cause failure. It’s a fine line. We don’t run a thick belt, like some of our competitors, because of the weight issue,” Wendland told me.

The Matco Tools team’s pistons can last as few as half a 1000-foot run or as many as four passes down the dragstrip. They weigh about 2000 grams and are made of forged aluminium. “Antron can step on the throttle and have the wrong kind of oil and ruin the piston,” Wendland said. How do you ruin the piston with the wrong kind of oil? “If the rings don’t seal well, then it allows that oil to go by and it loses ring seal. Then the piston tightens up and does nothing, and you can do that at the step of the throttle.”

By using Valvoline’s nitro oil with the proper amount of ‘slickum’* put into the product, that determines the ring seal. “Too much ring seal is never a bad thing; too little ring seal is a very bad thing,” he laughed. “We’re experimenting with different types of oil to combat those problems and keep our pistons (and corollary items) happy.

The Matco Tools team is also experimenting with different forms of hard anodizing – using only one thousandths thickness – but Wendland acknowledges, “What it boils down to at the end of the day with our piston wear is tune-up and oil.”

(*‘Slickum’ is slang for ‘ingredients’ or ‘additives’ as it pertains to the new technology in racing oil for nitro cars. Racing oil has to lubricate revolving parts like crank bearings, rod bearings and cam bearings but new technology ingredients are helping increase ring seal in nitro engines. The heavy liquid volume of nitro, compared to the mostly air over fuel ratio of a gasoline or methanol engine, can wash past piston rings and scuff cylinder walls causing reduced ring seal.)


Words and photo by Anne Proffit.

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