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Valve spring progress

valve-springsNitromethane-fed engines have different ways of destroying their valve springs. There are challenges, as there are in every type of motor racing, to help valve springs survive the sub-four-second damage realities these springs face.

Jim Oberhofer, responsible for the Top Fuel Kalitta Motorsports rail run by Doug Kalitta on the NHRA Full Throttle Racing Series' 24-race tour, explains what the challenges are for a nitro motor. “We don't have high lift camshafts and high engine RPMs to worry about – like a Pro Stock engine. Our biggest challenges are overcoming blower boost, fuel volume and heat.”

Oberhofer likes to run a PAC 1350 Triple Spring on both the intake and exhaust sides, “while some teams prefer to use a titanium spring,” he related. “On the intake side, we will use a brand new PAC triple spring. We'll set it at about 550 PSI. We normally like to run a new spring on the intake side and break it in for about 10 runs. Then it goes to the exhaust side,” he said.

Oberhofer finds the “normal service life for a PAC triple valve spring around here is about 25-30 runs, which is significantly better than the five runs we used to get about 10 years ago.” While they do tend to wear out a lot faster on the exhaust side, the effect of beginning the usage on the intake side allows the Kalitta group to gain more runs from each spring.

In the early 1990s, most drag racing teams used a double spring with a dampener. “We would set them at about 275 pounds. When we started going to bigger fuel pumps better blowers, better flowing heads and bigger camshafts, the need for a better spring with more PSI became apparent. In 1993 we made the switch to a triple spring. When we first went to the triple spring, we would set them at 325 pounds on both intake and exhaust sides.

“We used to just flat wear springs out in 2001-2002,” Oberhofer continued. “There has been an evolution of the triple spring (since they began using it) and we are just on the latest version, which has been the best so far.”

These days the team will install the intake springs at 550 pounds and, after five runs or so they might lose 5-10 pounds of pressure. “Sometimes we might keep a spring on the intake side for up to 15 runs,” Oberhofer allowed. “It just depends on how much pressure they lose.”

Of course it is important to keep high PSI springs on the intake side because “the intake valve is always fighting against high blower boost and the high amounts of fuel volume we put in a nitro engine. It is important to have a very good and very reliable valve spring – otherwise, you could have a misfire in the manifold, which will lead to an engine explosion,” he explained.

On the exhaust side, Oberhofer runs a triple steel spring installed at about 425 PSI. “We change them every run because the exhaust valve spring sees extreme heat and, with that it will lose about 5-15 pounds of pressure at its installed height on each run. This is significantly better than the old springs we used to run that would lose about 30-40 PSI per run.”

Written by Anne Proffit.

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