Keeping valve springs alive on a budget
In the destructive world of NHRA Full Throttle Drag Racing Series Funny Car competition, few parts take more of a beating than valve springs. "What kills them is going up and down 8000 times a minute uncompressed, as close as we can get them," says Jim Dunn, who runs his eponymous Funny Car race team from a small workshop in South Gate, California.
Dunn is pretty much of a throwback to the earlier days of straight-line competition, a man who prefers not to use computers in his diagnoses but rather to let his innate knowledge dictate the manner in which he attacks tune-ups for a 1000 ft catapult down the dragstrip in an 8000 hp nitromethane-burning Funny Car.
Jim Dunn Racing's Flopper, sponsored by dog-food producer Canidae, uses valve springs produced by Noel Manton of Manton Engineering in Lake Elsinore, California. Collaborating with Manton over a period of about 15 years, his choice is a tool steel triple spring. "We have to have triple springs to get the spring tension we want on the seat," Dunn says.
When initially installed, the valve spring - produced by pushrod manufacturer Terry Manton's father Noel - has about 550-600 lb of spring pressure. "They'll lose about 25-30 lb on the first run and then go down each run by 'X' amount, from the heat and vibration." The valve spring is not terribly dependent on Dunn's tune-up. "It doesn't kill them that much," he says.
Because he's running on a budget that would leave many amateur drag racing competitors in shock - Dunn operated his professional team on less than $1 million over the 23-race 2010 season - he has to be very careful where the money is spent. To be on the side of safety, he and his volunteer crew examine valve springs after every run to make sure the seat pressure isn't below his specified number.
Dunn says he gets somewhat less than the 20-run figure quoted by much of his competition, which has more money to spend on the spring and its ancillaries. And he has developed his own way to get his valve springs to last longer in his high-compression engine, which he runs at a standard 6.9:1 level, the upper reaches of the class.
"When they come down to 425 [lb], we'll put a 60 thousandth shim under it and that brings it up past 500 lb. When they come back down to 425 again we'll take them out because they'll bind up," he says.
Dunn's four crew members will check both intake and exhaust valve springs with every pass down the racetrack. "We'll probably go through one or two each pass and it's not bad at all," he says. Using the same size and spring pressure for both sides of the engine, Dunn says that about 90% of his competitors run the same type of spring he does.
"The rich guys run titanium on the intakes, and they cost about four times as much as the steel," he says. "What's bad about the titanium springs - for a guy on a budget like me - is that they don't go away. Titanium has a memory so they'll keep coming [back] up. After about 20-25 runs, though, they'll disintegrate and [the resulting failure] goes all through your motor and you get a 'big one'. Now, with our springs, you measure them and they're shorter because they start collapsing." It's his best opportunity to keep an eye on wear.
Valve sprigs don't break very often, Dunn says. "I think I've broken one in the past five years - and that was this year! It was the first one I ever broke in the centre, but of course, those [flat] ends will break off." But that means nothing in the scheme of things to Dunn.
When he has used a valve spring to the fullest extent, Dunn says, "I'll take them out and give them to the Bonneville guys. Heck, they run 350 lb of seat pressure, so we take out the shims and those guys have a new set of valve springs."
Fig. 1 - Manton Engineering triple valve spring, as used in Jim Dunn Racing's Funny Car (Photo: Anne Proffit)
Written by Anne Proffit