Timed runs - windows up or down?

coloradoporsche · 07:46 AM

Hello,

I am taking my 79SC to some DEs on tracks that are anywhere from about 1-3 miles in length. The longest of which is Pueblo Motorsports Park here in Colorado with a 1/2 mile straightaway. I'm pretty sure most cars are over 100mph on that one.

I notice most cars do their timed runs with windows down, but a few put the windows up.

Is there a significant aerodynamic gain with windows up, and do you need to be on a big, fast track for it to matter?

Thanks,

Martin

cstreit · cstreit's Garage

Usually you don't have a choice. Safety regulations dictate windows down for most competetive events. I suppose if you can have them up, aero is better, but I'd still leave them down for a quick exit if necessary.

Jack Olsen · 08-23-2005, 12:04 PM

Up is faster -- right up until the point you get a black flag for having your windows up. Like Chris says, you drive on a track with your windows down for a few different safety reasons. The biggest is being able to get out of the car if it's on fire after a crash.

coloradoporsche · 08-23-2005, 12:48 PM

OK...just to clarify:

The PCA rulebook for the clubs in Colorado states that windows can be either all the way up or all the way down for timed runs only at DEs.

That is, we do some timed runs at the end of a DE with only 2-3 cars on the track at one time. Some guys choose to go with windows up, and I was wondering if anyone can quantify how much of an impact this might have, big or small.

Walt Fricke · 08-23-2005, 01:19 PM

Quantify I can't, but with the rise in gas prices the energy folks are saying run with your air conditioner off and your windows closed (a bad combination in the heat, but that's what they are saying).

I think that I have seen assertions that even Targas and cabs with top off/down are better off with windows up.

So it shoud be quantifiable.

So where the rules permit, I run with closed windows. Since the only place I have run where they permit it is on timed runs, and under those circumstances a wreck needing extraction is rare, one where the doors won't open even rarer, and fires even rarer yet, that part doesn't worry me. I drive around on the street with my windows up all the time, just like everyone else.

Walt Fricke (no such option in the open car, though).

widebody911 · widebody911's Garage

I wonder if window nets would make an aero difference. I seem to get less window noise with mine.

Walt Fricke · 08-23-2005, 02:58 PM

I've seen suggestions that the flat web window nets are better than the thin mesh ones for aero. Also that running one on the right (or non-driver's side for those living where drivers sit on the wrong side) as well as the left is advantagous. Don't recall any quantification, though.

Walt

Jack Olsen · 08-23-2005, 03:48 PM

Coloradoporsche, if you are just starting to do DE's, then the effect your windows will have on your laptimes is easy to quantify: it will be zero.

It will take several visits, during which you will see wildly different lap times as the result of the normal novice learning curve, before things as subtle as aero will play an important factor in what you're doing.

When you're starting out, even the model of car you're driving hardly makes a difference at all. There are just too many new skills that have to be developed first.

If you're an experienced DE driver, then it will make a slight difference -- a few tenths, depending on the car and the track. But it will probably come in conjuction with lots of other little aero tricks, like folding mirrors back and taping up body panel seams.