mistral150

Does anyone know the formula to calculate HP given weight of car, and elapsed time from 0 to a given speed at WOT?
Thanks

aforeign

<ul><li><a href="http://www.rconcepts.com/beard/dragnet/drag/weather.html">Detailed HP</a></li></ul>

mistral150

Thanks

dannyboy

aren't there other factors such as gearing that come into play?

aforeign

Though using a calculation (as opposed to a dyno)leads to some errors. Those errors can be minimized by using longer runs. ie. don't use this formula with 0-60 times, 1/4 times is the shortest you should use, standing miles would be even better.
-chris

mister pepper

While horsepower is work / time, your speed at the end of the quarter mile cannot give you an accurate horsepower amount. Horsepower is measured at only one point in the dyno plot, where the car is run throughout most of it's rev range three or more times to finish the quarter mile. Not to mention this is done over several gears. The formula you referenced above is certainly a curve-fit approximation based on several quarter mile results from cars with known horsepower ratings. (Or at least I would hope it is.) As such it should only be used in conjunction with quarter mile speeds and not 0-60 or 0-100 or anything else.
If you don't believe me then explain how a manual and a tip can have the same horsepower and run different times at the track. There's a lot more involved in running the quarter mile than just horsepower.

mistral150

to accelerate my heavyweight A4 from one speed to another. This will obviously be less than the rated HP since while gears are being shifted there is little power available and the engine is not always delivering max HP. There is also dynamic drag to consider.
But there must be a formaula.....
assuming the total work against drag is more or less constant up to say 100 Km/h, there should be a formula that uses car weight, and et to some speed (say 100Km/h)..
Still looking but thanks for you comments.

towrig

check out this website.<ul><li><a href="http://www.race-technology.com">http://www.race-technology.com</a</li></ul>

aforeign

Ok, I re-read your post, and I see where we are off, The problem is still going to be the basic HP formula is based on work over time. In the this equation work is distance (1/4 mile) This is how the G-tec works, BTW. FIY Drag increases at the cubed root of speed so drag is not constant at all. This explains why it takes A LOT more power to go 150 V. 140 V. 130 etc..
I am sure there is a calculation to figure out your specifice question, but it will have to be at least a two parter. I forwarded your question to an Engineer friend of mine, I will let you know

mistral150

I agree about the drag, but was looking to simplifiy the equation a little. So if I measure the time (et) to get to say 100Km/hr, then the final speed is the same from run to run. Now if I take longer to get to 100Km/h then more energy will be spent on drag but I suspect the difference will be small.

Anyway, using the VWTool I can plot time and speed and get so so (+/- 1/4 sec) measurements without going to the strip.

I want to thank you for sending this off to an engineer. They usually are good at making assumptions that simlefy the math.

Thanks
Barry