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Discussion Starter #1 (Edited)
Dyno-time sellers beware. In the April R&T is a simple formula for calculating horsepower from 1/4 mile trap speed and vehicle weight.

it is: HP=(mph/234) cubed, times weight.

I have seen reported M5 trap speeds of 117 mph.

117/234 cubed, times 4000 equals...

drum roll......


500.
 

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Dyno-time sellers beware. In the April R&T is a simple formula for calculating horsepower from 1/4 mile trap speed and vehicle weight.

it is: HP=(mph/2343) cubed, times weight.

I have seen reported M5 trap speeds of 117 mph.

117/234 cubed, times 4000 equals...

drum roll......


500.
To confirm its (mph/234)^3 * weight?
Your first formula has a typo???

The calculation is a long known formula. I have an old slide rule some where that shows that.
 

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Remember, you should use the 'test weight', not the curb weight of the car. For my car, best trapspeed is 116.3 mph on a lousy traction track, with a test weight of 4280 lb. That gives:

525 HP

Which is probably low given the mods I have. With a better track, I should be able to hit around 118, which would give

549 HP.:M5thumbs:
 

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S3 Horsepower Calculation(s)

My 4250 lb (E39 M5 S3 + driver) turning 11.7 @122 mph in the 1/4 mile is making:
1. hp = weight*(speed/234)^3 (Road & Track formula)
602 HP at the crank.
2. The online calculator** at Fast Math, using a 122 mph 1/4 mile trap speed
711 HP at the crank and
602 HP at the rear wheels


3. The online calculator** at Fast Math, using an 11.7 ET
619 HP at the crank and
524 HP at the rear wheels


**Black Box

The Road & Track and Fast Math ET calculations most closely approximate the 621 HP rating of the Dinan E39 S3 motor.

Ray




 

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My 4,810 lb (CL65 + driver) turning 11.403 @121.59 mph in the 1/4 mile is making:

1. hp = weight*(speed/234)^3 (Road & Track formula)
675 HP at the crank.

2. The online calculator** at Fast Math, using a 121.59mph 1/4 mile trap speed
796 HP at the crank and
675 HP at the rear wheels


3. The online calculator** at Fast Math, using an 11.403 ET
641 HP at the crank and
757 HP at the rear wheels

4. Drag Times Horsepower Calculator:
Horsepower Calculator from 1/4 mile ET and Trap Speed - DragTimes.com

Flywheel HP: 658hp
 
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