Penske Downforce Mods - '69 Cars

[naparsei]

This was posted on Facebook. The claim was that the modification was part of a ducting system which prevented/limited front end lift at 170 mph. I am inclined to think the purpose is different, or that if the benefit is there, it would happen at much lower speeds. Any thoughts?

[ss jim]

Probably to relieve pressure from inside vehicle, which would cause lift. I think NASCAR did something along those lines. Jim

[maroman]

What shows here is the wedge shape of the front fenders. They would almost act like a spoiler themselves. I've not seen the cars from this angle before.

[Steve Holmes]

Donohue said in his book it was to let hot air our from under the hood, and to help cool the rear tires. The downforce theory is interesting. Air trapped beneath the hood probably would have had the effect of lifting the nose at high speeds, but my limited understanding is that the front chin spoiler plus hood cowl scoop would have helped both press the nose into the ground and release trapped air. Maybe the concept of the ducting system was also to release air as well as engine bay heat.

The Penske team were originally planning to fit front tires to their '69 cars that were at least as big as the back tires, hence the heavily flared fenders. But in testing they couldn't get the cars to handle right, so reverted back to smaller front tires.

[Jon Mello]

Donohue, in his usual understated way, says the larger wheel well openings and holes drilled through the fender wells and doors weren't of critical importance, but of course they wouldn't have done it if they thought there was minimal benefit. He described the modifications as being a benefit to allow a little more air out of the engine compartment and a little more cool air being directed toward the rear tires and brakes. The drooped noses on the cars in '69 probably had more aerodynamic benefit than the drilled holes provided.


Photo by Ron Lathrop

[firstgenaddict]

The Grand Sport corvettes had a problem with front end lift due to trapped air in the engine compartment which is why they went to the Louvered hoods.

[1109RWHP]

I would imagine a ton of garbage would go through there during a race especially if it was raining.

[Jon Mello]

The first race of '69 at Michigan was a very rainy, muddy mess. I had not previously considered how much crud would have gone through those holes into other parts of the car(s).

[Swede70]

Greetings,

Note too the very large front flares, evidence of Penske/Donohue ambitions to run larger tires up front for the use of power steering.  A race failure of such a system trimmed back ambitions especially in the face of early-season Bud Moore Engineering/BOSS 302 form, hence these went away before too long. 

Mike K.

[kgu]

They might have had close fitting sheet metal covers for conditions like rain, or maybe some duct tape.

[Jon Mello]

In the case of the Michigan Wolverine Trans-Am in '69, the rain did not start until the cars were on the track and the green flag fell. There would have been no opportunity to block the holes at that stage, although I assume they knew rain was in the forecast.