DIY_EFI Digest Monday, September 27 1999 Volume 04 : Number 549 In this issue: Re: Calculating HP with G See the end of the digest for information on subscribing to the DIY_EFI or DIY_EFI-Digest mailing lists. ---------------------------------------------------------------------- Date: Mon, 27 Sep 1999 11:36:26 -0700 From: Will McGonegal Subject: Re: Calculating HP with G > Just wondering how to calculate HP(torque?) with g . Don't confuse up your Horsepower and torque. If you measure Horsepower at the wheels and want engine torque and can't simultaneously measure engine speed, you have to know the radius of your drive wheels and the gear ratio from the engine to the wheels (torque multiplication-speed reduction). The Horsepower remains the same through the system (assuming no loses!). If you calculate wheel horsepower and you know the equivalent engine RPM to vehicle speed then you can determine the effective engine torque.G is a measurement of acceleration. 1 G of acceleration is 9.80665 meters/(second squared). Power = Force * velocity = Mass * acceleration * velocity. If you're accelerating at 0.1 G in a 3000 lb car going through 25 mph........ 0.1 G is 0.1 * 9.80665 = 0.980665 m/s2 3000 lbs = 3000 / 2.2046 kg = 1360.8 kg 25 mph = 25 * 0.44704 m/s = 11.176 m/s Power = 1360.8 [kg] * 0.980665 [m/ss] * 11.176 [m/s] = 14 914.248 Watts 14 914.248 / 745.69 [Watt / Hp] = 20 Hp Simplified...... Horsepower = Mass [lbs] * Acceleration [G] * Speed [mph] / 375.0 (the 375 factor comes from 3600 [seconds/hour] / 5280 [feet/mile] * 550 [ft.lbs/sec per horsepower] Now if you happened to know that the engine was reving at 2000 rpm when the vehicle was traveling 25 mph....... Engine torque (assuming no drivetrain losses (HA!)) = 20 [Hp] * 5252.1131 / 2000 [rpm] = 52.5 ft-lbs. (the 5252.1131 factor comes from 550 [ft.lbs/sec] * 60 [seconds/minute] / ( 2 * pi [3.1415....] ) ) Will McGonegal Project Engineer/Dynamometer Developer Environment Canada ------------------------------ End of DIY_EFI Digest V4 #549 ***************************** To subscribe to DIY_EFI-Digest, send the command: subscribe diy_efi-digest in the body of a message to "Majordomo@xxx. A non-digest (direct mail) version of this list is also available; to subscribe to that instead, replace "diy_efi-digest" in the command above with "diy_efi".