Drag racing question
Safety Car
Joined: Sep 2002
Posts: 4,030
Likes: 6
From: Maryland
Originally Posted by Nathan Plemons
What would happen if....
You launched your car in 4th gear and just left it there through the entire run? What would your MPH be at the end of the track? Would it be the same as your MPH if you raced normally?
Thoughts?
.
You launched your car in 4th gear and just left it there through the entire run? What would your MPH be at the end of the track? Would it be the same as your MPH if you raced normally?
Thoughts?
.
This is an easy one. For constant acceleration travel, from a standing start, Vf^2=2*a*x
where x=1/4 mi (distance traveled), a=the constant acceleration level
If you are in 4th gear you will not be able to use the leverage of the lower gears to accelerate your car nearly as fast. So your Vf will be wwway low compared to normal.
Vf is a perfect indication of A. A depends on your vehicle weight, the gears, and the motor.
Safety Car
Joined: Sep 2003
Posts: 3,599
Likes: 24
From: Orange County NY
St. Jude Donor '10-'11-'12-'13
Originally Posted by CentralCoaster
Don't think about the long ET giving you more time to accelerate. Slower acceleration will use more length of track to get to a certain mph.
The track is a fixed length.
Your motor doesn't make constant power across the powerband, and that's why the mph will be lower. Because your rate of acceleration will be lower in the rpms below the powerband.
The track is a fixed length.
Your motor doesn't make constant power across the powerband, and that's why the mph will be lower. Because your rate of acceleration will be lower in the rpms below the powerband.
I don't think the 1:1 final drive ratio will allow the engine to accelerate the car at nearly the same rate over the 1320 foot distance, resulting in a much lower MPH at the end of the track.As someone mentioned earlier, a heavier car would be affected more.
But what do I know - my car hasn't been doing ANY accelerating lately. I just enjoy seeing Nathan and Jesse agree!
Racer
Joined: Mar 2005
Posts: 399
Likes: 2
From: Newtown PA
My brother-in-law owns an 03 Cobra with some mods (pulley, headers, exhaust, air intake, chip). With the stock gears 3:42s?, he typically runs on DRs 12.1x's at about 119-120 and dynoed at about 470 rwhp and about 485 rwtq.
In the middle of last summer he installed 4:10s. With everything else the same, he ran a bunch of 11.9x's at only 112-114.
He then brought the car to a shop for some tuning and another pulley change. The baseline dyno test before the new pulley and the tune indicated a drop in rwhp to about 430 and a drop in rwtq to about 450 just with the gear swap. After the new pulley and tune, the rwhp was about 450 and rwtq was about 480. The car ran a 11.70 at 116 after this.
In the middle of last summer he installed 4:10s. With everything else the same, he ran a bunch of 11.9x's at only 112-114.
He then brought the car to a shop for some tuning and another pulley change. The baseline dyno test before the new pulley and the tune indicated a drop in rwhp to about 430 and a drop in rwtq to about 450 just with the gear swap. After the new pulley and tune, the rwhp was about 450 and rwtq was about 480. The car ran a 11.70 at 116 after this.
