HP from 1/4-mile trap speed
Thread Starter
MBWorld Fanatic!
Joined: Nov 2001
Posts: 2,465
Likes: 0
From: SF Bay Area
2002 C230 K
HP from 1/4-mile trap speed
I tried to post this as a follow up to a different thread, but since the site wouldn't let me it gets to be its very own thread now.
Hopefully of interest is this formula that calculates (roughly) the horsepower of a car from its trap speed in the quarter mile. Think of it as a poor man's dyno.
HP=(mph/234)^3 x weight (in lbs)
The only caveat is to be accurate you need to know the exact weight of the car, including driver, mods/options, etc. Using Road and Tracks results in the 1/4-mile (88.9 mph) and MB's published weight for the coupe (3305, plus an estimate 200 lbs for driver, gas and equipment [I think I recall reading once that the equipment R&T uses weighs about 35 lbs] for a total weight of 3505) gives a result of 192.2 hp, so the formula appears to be surprisingly accurate. This is assuming that the curb weight quoted by MB doesn't include driver and gas weights; I know MB does its performance tests with driver, luggage and half tank of gas, but I don't know if they include these things in the car's weight.
Should at least give you guys modifying your rides an idea of how much HP the mods have given you (at the least some before/after comparison).
Enjoy, BT
Hopefully of interest is this formula that calculates (roughly) the horsepower of a car from its trap speed in the quarter mile. Think of it as a poor man's dyno.
HP=(mph/234)^3 x weight (in lbs)
The only caveat is to be accurate you need to know the exact weight of the car, including driver, mods/options, etc. Using Road and Tracks results in the 1/4-mile (88.9 mph) and MB's published weight for the coupe (3305, plus an estimate 200 lbs for driver, gas and equipment [I think I recall reading once that the equipment R&T uses weighs about 35 lbs] for a total weight of 3505) gives a result of 192.2 hp, so the formula appears to be surprisingly accurate. This is assuming that the curb weight quoted by MB doesn't include driver and gas weights; I know MB does its performance tests with driver, luggage and half tank of gas, but I don't know if they include these things in the car's weight.
Should at least give you guys modifying your rides an idea of how much HP the mods have given you (at the least some before/after comparison).
Enjoy, BT
Almost a Member!
Joined: Dec 2001
Posts: 56
Likes: 0
Trench:
That formula works out to about 250HP vs 260HP advertised for my stock 95 Impala SS. (even closer if I use an instantanous "G-Tech" rather than an averaged "Time slip" end speed)
I am surprised that there is not as much discussion on the W203 Forum about using the G-Tech-Pro; but then again, I have one but have never had it in my C320. I hope
it is due to my priorities and not a sign of old age.
At any rate, I'm impressed with your formula.
That formula works out to about 250HP vs 260HP advertised for my stock 95 Impala SS. (even closer if I use an instantanous "G-Tech" rather than an averaged "Time slip" end speed)
I am surprised that there is not as much discussion on the W203 Forum about using the G-Tech-Pro; but then again, I have one but have never had it in my C320. I hope
it is due to my priorities and not a sign of old age.
At any rate, I'm impressed with your formula.
Thread Starter
MBWorld Fanatic!
Joined: Nov 2001
Posts: 2,465
Likes: 0
From: SF Bay Area
2002 C230 K
I checked out C32life page once and I noticed the G-tech was quite popular there. I've always considered getting one as it's not particularly expensive, but for some reason never have. I guess if I had another car I added modifications to (as it's too late to do this with my Acura - unless I wanted to put the stock pieces back on for some runs ). It seems like a handy way to see how each mod affected performance.
Regarding your Impala, did you include your weight in the calculation, usually the weight of a grown man (180-200 lbs) throws the calculation off by about 10 hp.
Cheers, BT
). It seems like a handy way to see how each mod affected performance.Regarding your Impala, did you include your weight in the calculation, usually the weight of a grown man (180-200 lbs) throws the calculation off by about 10 hp.
Cheers, BT
Almost a Member!
Joined: Dec 2001
Posts: 56
Likes: 0
BT:
I was figuring 150# driver, using end speeds, and calculated/ advertised HP. I'm sad to say that real world HP for mine (and I'm not alone) is more in the 230-240 HP range. I thought that I would never sell it, but I will be putting it on the market in a few days. 
I was figuring 150# driver, using end speeds, and calculated/ advertised HP. I'm sad to say that real world HP for mine (and I'm not alone) is more in the 230-240 HP range.
I thought that I would never sell it, but I will be putting it on the market in a few days.
Admin Alumni
Joined: Nov 2001
Posts: 8,143
Likes: 19
See Garage
For the EXCEL Spreadsheet oriented, the Power User formula for this is:
=POWER((NX/234),3)*NY
...where NX references a cell with the 1/4 mile trap speed (in mph), and where NY references a cell with the vehicle weight (in lbs).
Yes, you can also get there with:
=(NX/234)*(NX/234)*(NX/234)*NY
...but the Power User way is just a bit more elegate and economical...
=POWER((NX/234),3)*NY
...where NX references a cell with the 1/4 mile trap speed (in mph), and where NY references a cell with the vehicle weight (in lbs).
Yes, you can also get there with:
=(NX/234)*(NX/234)*(NX/234)*NY
...but the Power User way is just a bit more elegate and economical...
Last edited by MB-BOB; Jan 11, 2002 at 09:47 AM.
Newbie
Joined: Dec 2001
Posts: 11
Likes: 0
From: SE U.S.
'02 C32 Obs Black Chrcl/Blue
Horsepower is a function of torque, which is the real component you should be concerned with.
The SAE formula for horsepower is:
HP= (torque x engine rpm's)/5252
More horsepower does not necessarily equate to a more powerful engine...but measuring torque over a spectrum of engine rev will show you the power band of your engine. Your max torque is NEVER at your peak horsepower point
If you want impressive numbers take note of this:
The C32 produces 295 lb-ft of torque from 2200rpm through the redline of 6220rpm and peaks at 332lb-ft @4400rpm...vrooooom.
The SAE formula for horsepower is:
HP= (torque x engine rpm's)/5252
More horsepower does not necessarily equate to a more powerful engine...but measuring torque over a spectrum of engine rev will show you the power band of your engine. Your max torque is NEVER at your peak horsepower point
If you want impressive numbers take note of this:
The C32 produces 295 lb-ft of torque from 2200rpm through the redline of 6220rpm and peaks at 332lb-ft @4400rpm...vrooooom.
