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11-18-2009, 01:17 PM

#31

d_ames117

2nd Gear Member

Join Date: Jun 2007

Posts: 368

Quote:

Originally Posted by FastDEW

In the case of the OP, the calcs would be correct. Drag will limit your ability to reach redline in top gear if you do not have enough HP to overcome the drag.

However in the OP he made it to redline, this means that he had enough HP to overcome the drag. So at redline, given the gears, he would have been going 174mph. Drag is not part of the equation here because mechanically, unless he was slipping, the car was turning the RPM's with the gears and tire size to be going 174mph.

Damn fast!

My point exactly.

11-18-2009, 02:53 PM

#32

Norm Peterson

6th Gear Member

Join Date: Feb 2007

Location: state of confusion

Posts: 7,635

Quote:

Originally Posted by trigger06

the Cd doesnt change. it is determined by the shape, frontal area, and smoothness of the surface of the car. The drag force does change based on speed.

Actually, Cd does change slightly with speed, due to changes in rake caused by unequal aero lift, front vs rear. Mostly it's a small effect, unless you're about to flip over like Ryan Newman did at Talladega a couple of weeks ago and are putting a lot of the car's underside into the wind.

******CORRECTION*******
I didn't change one of the variables in the earlier analysis. So I re-ran it (it's a spreadsheet solution that only takes a few seconds)

173 mph at 6150 rpm. Slightly past the 6000 rpm indicated redline, but still drag-limited assuming that the torque curve stretches out smoothly but dropping slightly to a 6250 rpm redline/fuel cut.

(trap speed went up a tiny bit to 119 mph)

Norm

Last edited by Norm Peterson; 11-18-2009 at 03:01 PM.