Acceleration, drag, engine power..applied formulas to 993TT
12-10-2006, 04:14 PM
#1
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Acceleration, drag, engine power..applied formulas to 993TT
Maybe we can throw a few formulas in this thread left and right in case someone has the bug to play with some numbers... 
Many questions were raised recently about the correlation of engine power, long G (acceleration), aero drag, weight, etc..
Many questions were raised recently about the correlation of engine power, long G (acceleration), aero drag, weight, etc..
Last edited by Jean; 07-26-2007 at 04:45 PM.
12-10-2006, 07:57 PM
#2
for effective gear ratios and speed or power calcs I prefer to start w/ the manufacturers published revs per mile # instead of the tire OD. This gives a much better indication of the dynamic loaded radius of the tire i.e what the real efect of the tire in use is.
Dynamic loaded diameter = 20168.11439/revs per mile
Of course if you need Dynamic loaded radiusdivide the above by 2
Dynamic loaded diameter = 20168.11439/revs per mile
Of course if you need Dynamic loaded radiusdivide the above by 2
12-11-2006, 06:41 AM
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Bill, great insight, I agree that is a great way to look at it. The only downside being that seldom any of the cars doing these runs are on stock tires. I typically reduce 1-2% to the calculated tire OD, gear ratio and speed number based on my datalogger data.
I thought this was the simplest and practical way to approach it!
Originally Posted by AVoyvoda
Gee... Jean, you get all these formulas from the books you take to the beach? Waaay above my head.
I thought this was the simplest and practical way to approach it!
12-11-2006, 07:29 AM
#5
The torque (tau) at the wheels will change during acceleration. Interpolating wouldn't be suitable, so you need to sample values of the torque to its function of RPM. Probably by taking values from the torque/RPM-curve and run it in something Matlab, Fortran or perhaps Excel.
12-11-2006, 08:50 AM
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Right Rassel,
Of course this needs to be built into a spreadsheet sampling all RPMs and gears... This is just the formula for one datapoint. It is quite interesting to see a dyno sheet being extrapolated into acceleration by gear and RPM.
Jean
Of course this needs to be built into a spreadsheet sampling all RPMs and gears... This is just the formula for one datapoint. It is quite interesting to see a dyno sheet being extrapolated into acceleration by gear and RPM.
Jean
12-11-2006, 08:58 AM
#7
Originally Posted by Jean
Bill, great insight, I agree that is a great way to look at it. The only downside being that seldom any of the cars doing these runs are on stock tires. I typically reduce 1-2% to the calculated tire OD, gear ratio and speed number based on my datalogger data.
I thought this was the simplest and practical way to approach it!
I thought this was the simplest and practical way to approach it!