1/4 mile times with T-Tops off

[fasterthanu]

Anyone ever g-tech their cars 1/4 mile times with the t-tops off and the windows down? Just curious what the difference in times would be vs. having tops on and windows up. I figure you are definently losing aerodynamics and creating drag... My cars ac went bad, havent fixed yet, and with 94 degrees, didn't want to run with tops on and windows up on the expressway.. Just curious...

 

[69MyWay]

I am obviously no engineer, but I don't imagine the difference if any will be that much in simply the 1/4 mile.

I guess that would be a fun experiment, but you would have to run a butt load of base runs stacked against the t top off runs.

I hope your a/c is a simple problem to fix.

 

[Hijinx]

At the speeds most of us will reach in the quarter mile, it would probably make little difference. The nose of your Vette is punching the hole and by the time the air gets over the windshield its already getting pretty turbulant.

Now, if you plan to do hard quarter mile passes at the top end of what one of these vehicles is capable of, then your into issues. At that point you want the air as clean as possible as it passes over the roof so that a rear spoiler will keep the back end pressed down. The windows are less of an issue as you need to worry more about the air going over the car, and not around it.

Watch a few windtunnel videos and you will see how messed up air gets after it goes over the roof of a car. You really have to channel it to get it to press the back end down well. Two big holes up there at high speed will act like a suction.

My two cents on aerodynamics, but what do I know, I'm 6'5" and my head almost sticks out the top. Talk about your drag coeficients!

 

[Bob Chadwick]

I gathered research and put together a study for the federal government back in the late 70's on the affects of open windows v. a/c. In the early model a/c's (60's to very early 70's as I recall) you used more horsepower and gas, which really was the basis of the study I was doing, with the a/c on at highway speed. On the later a/c's, they didn't use as much horsepower as having the windows open.

Bob

 

[inferno-vette]

Bobchad, that's a very interesting study.

Of course it's better to use a/c on highway but driving around town, going from stop to stop, I bet the a/c gets a grater toll than the open windows factor, the speed isn't that high and the engine is contantly changing rpms wich of course is going to need more fuel to get those rpms if the a/c is on.

I think this subject is worth the time to check out and learn from experiences.
Paul

 

[Rowdy1]

Check The Rules

I'm NOT positive, but you may not be able to run that way. I don't have the NHRA rules but I'm "pretty" sure you have to run with the windows up and unless you have a roll bar, you have to have a top if you run under certain times. I'm sure someone in here can give you more info

 

[fasterthanu]

I know you MUST have the windows closed and tops on at the tracks, tried it before =P Too hot out here for me to do comparison runs with and without tops on and windows open. Been told by a couple heavy duty racers in the 60's now own machine shops that there is 7/10s of a second difference. Curious to find out...

 

[Bob Chadwick]

Paul,

That was another component of the study. As I recall, under 45mph or so the open windows used less horsepower on the older units. There was also a limit on the newer units as well but I don't recall the actual speed.

Bob