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NASCAR Cup Series manufacturers have a technical decision to make on Friday after practice and before qualifying on Saturday afternoon.
Autódromo Hermanos Rodríguez in Mexico City features by far the highest elevation that the division races at. It sits at 7100’ and the next highest is Las Vegas Motor Speedway at 1100’.
As a result of the resulting thinner air, NASCAR has allowed for an optional hood louver to be used the rest of the weekend. Chevrolet, Ford and Toyota will have to make the decision for each of its cars – no mix and matching.
The reason for all of this was explained by Joe Gibbs Racing (Toyota) competition director Chris Gabehart.
“Think about the amount of air density you’re passing across the radiator and into the engine,” Gabehart said. “It uses those molecules of air to do the work. Up here, you’re going the same speed, so you don’t get any more speed to get more air, but the air is a lot thinner.
“So now I just have less air to do the cooling or to feed the engine horsepower — all those things. So, the only way to get more out of it is to get the whole system to pass more air across the radiator.”
In other words, the alternative hood louver will allow more air to cool the engine but with a downforce loss as explained by Hyak Motorsports (Chevrolet) competition director Mike Kelley.
“If we try the wide-open louvers, you have to run a wide open blocker plate,” Kelley said. “You couldn’t run a blocker plate and open up the louvers. So, there’s a little downforce loss (and) drag gain if we do it but it’s the right way for us to go right now because the temperature is going to be too high the other way.
“So we have to give up a little efficiency on our car I think all the Chevrolet teams tried it and the OEMs landed on a spec before start of second practice, and I think that’s where we’re going to end up racing — louvers out blocker plate out.”
For what it’s worth, Hendrick Motorsports vice president of competition Chad Knaus said they were still going back and forth after practice.
“It probably looks that way but we haven’t circled up 100 percent yet to make that decision,” Knaus said.
On the other hand, it seems like Ford teams don’t think they need the open louvers according to RFK Racing No. 17 crew chief Scott Graves.
“I think our take was that we were okay,” Graves said. “Temperature wise, I don’t see a need to make the change but I don’t know at a higher level than me. I think the top level guys from each team are going to get together and talk about it with the Ford guys and make a decision.”
Toyota seems to be committed to running the opening as well.
“Yeah, just with the high altitude, just not a lot of air to help these fire breathing dragons cool off.”
