NASCAR have acted to try and reduce the speeds at which cars can run at Daytona International Speedway, ahead of Sunday's Daytona 500.

Officials announced modifications to the front grille opening and the introduction of a pressure-relief valve to radiators on Sunday; both modifications are intended to make it more difficult for cars to keep their water temperatures under control while drafting.

These measures were followed up on Wednesday with a reduction to the size of the carburetor restrictor plate itself, reducing it by 1/64th of an inch to 57/64th, equivalent to taking 10-12 horsepower away from the engine and a move that will probably mean cars will have to return to sub-9000 RPM running.

During last weekend's exhibition Budweiser Shootout, speeds in excess of 206mph were seen at some points as the cars adopted a new two-car drafting style of racing on the newly repaved Daytona surface, where the old surface had been too bumpy to allow such prolonged drafting through corners in the past. It was Bill Elliott's record lap time of 210.364mph in 1987 that spurred NASCAR to introduce restrictor plate racing for the first time at Daytona and Talladega events because of safety concerns, and seeing speeds getting close to that mark again in 2011 has resulted in NASCAR once more jumping into action to bring speeds under control.

The emphasis on safety is particularly prominent this year since the 2011 Daytona 500 marks the tenth anniversary of the death of Dale Earnhardt, which will be marked by a moment of silence on the third lap of this year's event and the painting of Earnhardt's #3 into the grass infield area overnight before the start of the Great American Race.

Some changes were expected after last Saturday's Shootout when teams saw the speed data, but they had been expecting a change to the restrictor plate. Instead, NASCAR initially announced a change to rule book section 20-7.3 "whereby, no matter the shape of the grille, per manufacturer identity, it would have an aluminium plate behind with a rectangular opening with a 50-square-inch maximum opening for cooling." The bulletin also mandated set-diameter hoses to and from the tank and a pressure-relief valve supplied by NASCAR and set to 33 PSI.

"What that's going to do is drive the cars to where they're probably not going to be able to push as long," Earnhardt-Childress Racing Engines president Richie Gilmore said. "In two or three laps they'll have to get out and get some air, or they'll start pushing water [out through the safety valve.]"

The exact nature of the new requirements did catch teams by surprise and there was a steady stream of technical personnel heading up to speak to NASCAR's top officials on Sunday for clarifications.

Teams had already been instructed to remove an auxiliary engine-cooling hose that had been introduced by some of the teams, in an attempt to limit the time they could spend in two-car drafts. "Some teams didn't have it but some did, and we asked them to take it off to cut down on some of the cool air the engine gets," NASCAR spokesman Kerry Tharp said. "It wasn't intended to reduce horsepower; it was something we tried to see if it would curtail the length of those two-car hook-ups." However, the cool 40F evening conditions at Daytona on Saturday for the Shootout had meant the teams were able to manage the water temperature and still continue to push the draft, with or without the extra hose: Jamie McMurray gave Kurt Busch a race-winning push to the chequered flag lasting over 12 laps, despite not being one of those car with the auxiliary hose.

"It was so cool [during the Shootout], when the car [water temperature] would get 275 degrees, you could peek the nose out and my car would go back down to 230 in a straightaway," McMurray said. "If it's 40 degrees hotter on Thursday it's not going to do that."

Having had two days to return to their respective bases and make the necessary changes, teams will now have a chance to run and assess the latest modifications during the next practice session later today (Wednesday) to make sure that there aren't consequences that will affect the cars' ability to make it to the full race distance without boiling dry, with NASCAR also keeping a careful eye on how things go in case further changes are required.

Even though practice on Wednesday was rained out in the morning, NASCAR decided to introduce the change to the restrictor plate size after all with immediate effect starting with today's practice sessions, which most teams had been fully expecting and had planned for. "I wouldn't be surprised from the speeds that I've seen that we could have a plate change, so we are preparing as if that might come," Ford engine builder Doug Yates had said earlier in the week.

"If you look at what creates speed, the plate would be fine as it is," Sprint Cup director John Darby had said, explaining: "If drivers never pushed each other, we'd be putting bigger plates on the cars; so that's part of what we want to watch - how the cooling system changes and what the reaction to it is, and we may not have to change the plate. That's what we've got to watch on Wednesday.

"I think we can agree, for both the competitors and NASCAR, that 206[mph] was probably a little bit too on the extreme side."



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