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Valve Spring Failures

valve-springsAs the NHRA Full Throttle Drag Racing Series 24-race season wound to a close in early November, the Matco Tools Top Fuel team with driver Antron Brown, a group that had changed ownership twice over the off-season, did so again when it was sold to Don Schumacher Racing just before the penultimate round on The Strip at Las Vegas Motor Speedway.

That change will likely result in changes to parts distribution, as DSR campaigns two other T/F dragsters for [now] six-time consecutive champion Tony Schumacher and 2009 fourth placed contestant Cory McClenathan – Brown finished third in the title chase.

“There is a bunch of testing going on with a smaller diameter spring – like a small block Chevy – and they are having excellent luck with them,” noted Rob Wendland, co-tuner for Brown’s rail. “Our understanding is that DSR are doing a lot of valve spring testing in December so we might see changes.”

The Matco Tools team currently uses a titanium double spring with Teflon insert from Michigan-based PSI. “The Teflon insert keeps the inner spring a little straighter without having it touch the outer spring. Our springs go through a crazy heat cycle as it is, and that Teflon piece is what keeps the two apart,” he told me.

“These springs go through a frequency when they’re running and this frequency can be destructive – there are destructive and good frequency ranges, so you want to be in the ‘good’ frequency range, depending on the spring and how its ground, how it’s heat treated and the materials used in manufacturing that determine the frequency,” Wendland said.

Valve control is what determines the choice of spring. “We want our valve control to take place between 6500-8500 rpm, so we use our Spintron to help us determine that frequency. If you find a product that works well, you darn sure want to know what the frequency is for that spring so that you can build maybe a better spring at that same frequency. These harmonics do change, depending on the rpm changes.”

Wendland explained that some tuners have tried foam filling the driveshaft to have an effect on valvetrain harmonics, or putting weight in varying places on the driveshaft. “Even tuning the exhaust a little bit differently can change harmonics or frequencies,” he said. “It’s all about finding the motor’s happy place and that’s where you want the spring to activate. That is how we get longevity and better control on the valve. When the frequency is off, then it doesn’t have valve control.

Valve springs, like every component in a Top Fuel engine, are checked and replaced as necessary. On the Matco Tools dragster, valve springs can last as few as 12 runs down the 1000-foot dragstrip or as many as 30 passes.

Breakage occurs through heat cycles and poor harmonics. “This spring had a failure in the inner spring. One of the good things about a titanium spring is that, when it loses an inner, it still has a lot of force on the outer spring, which has a bigger, heavier wire diameter.”

This failure occurred when the team was simply turning the motor over – not during a qualifying or elimination pass – it “just went ‘bing’! It’s nice to detect this before it happens on the track. That is why we’re doing so much valve spring development here at Don Schumacher Racing.

Words and photo by Anne Proffit.

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