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#11
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AChevyFan wrote:
> That's a great algrebra lesson but I am assuming that I have neither HP nor > Torque to calculate so that doesn't help me. > Ah, then your only choice is either a dyno session or one of these accelerometers. With the accelerometer you can compute torque at rear axle but it also takes a lot of algebra. Knowing the rear axle ratio you can convert rear axle torque to transmission torque, and ultimately to engine torque, though that is a bit iffy with an automatic (fine to do with manual box, however). |
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#12
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I've seen formulas to calculate - or estimate - hp from acceleration data.
If I had nothing and wanted to do better than a guess, I would probably get one of those G-force accelerometer gadgets. "Don Stauffer in Minneapolis" > wrote in message ... > AChevyFan wrote: > >> That's a great algrebra lesson but I am assuming that I have neither HP >> nor >> Torque to calculate so that doesn't help me. >> > Ah, then your only choice is either a dyno session or one of these > accelerometers. With the accelerometer you can compute torque at rear > axle but it also takes a lot of algebra. Knowing the rear axle ratio you > can convert rear axle torque to transmission torque, and ultimately to > engine torque, though that is a bit iffy with an automatic (fine to do > with manual box, however). |
#13
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AChevyFan wrote:
> What is the calculation for torque? > I know the Horsepower is: > > HP = Torque(lb-ft) * RPM/5252 > > But how do I get Torque? Not sure what you're asking here. Typically, torque is MEASURED, not calculated. Horsepower is computed from measured torque. If you have a horsepower curve and you want to back-derive torque, just solve for Torque in your equation above: (HP*5252)/RPM |
#14
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AChevyFan wrote:
> That's a great algrebra lesson but I am assuming that I have neither HP nor > Torque to calculate so that doesn't help me. OK then... what DO you have? You have to know something to start the calculation. And any calculation that depends on knowing cylinder pressure will have to be converted to BMEP, and you'll have to know the engine's geometry as well (bore and stroke). Calculations like that aren't very precise unless you have a full-blown computer model akin to "Desktop Dyno." |
#15
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Actually, its first-year "Physics for Engineering Students," regardless
of engineering discipline (even us EEs had to take basic physics and mechanics. Kathy and Erich Coiner wrote: > Get a mechanical engineering degree with emphasis on thermodynamics. > You will learn this in your 4th year thermodynamics classes. > > Erich > > "AChevyFan" > wrote in message > ... > >>What is the calculation for torque? >>I know the Horsepower is: >> >>HP = Torque(lb-ft) * RPM/5252 >> >>But how do I get Torque? >> >> > > > |
#16
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Brian wrote:
> I've seen formulas to calculate - or estimate - hp from acceleration data. > If I had nothing and wanted to do better than a guess, I would probably get > one of those G-force accelerometer gadgets. > > If you carefully plot acceleration versus speed, yeah, you can do it. If you use an average, like a 0-60 time, you will get an AVERAGE torque, not a peak one, or a torque vs rpm. Further, 0-60 is too high, because at speeds above about 35-50 mph, air resistance is using a considerable torque. It would not be just a function of mass of car. So you'd have to compute acceleration vs speed up to 30, at several data points. This is getting a bit hard to measure accurately by a stopwatch and speedometer, which is why actual accelerometer is good. I have seen some for a little over a hundred bucks. |
#17
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Using vehicle acceleration to measure hp is useless. We've done it
with airplanes on takeoff, and we get a horsepower figure of about one-fifth of what we know the engine is giving us. Any movement thru air represents drag, any rolling wheels represent drag, and the losses through the drivetrain are significant. Further, unless the engine is operating at the desired RPMs (redline or max torque) it's all irrelevant. The most accurate measurements use an engine brake and torquemeters. Torque x RPM x 6.28 divided by 33,000 equals hp. Dan |
#18
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In late model cars you maybe able to capture the needed data from the
ODII port. The rolling and air drag losses can be calculated. Afar as the drive train losses you ignore this and what you have is very close to what you would get from a chassis dyno. Stan wrote: > > Using vehicle acceleration to measure hp is useless. We've done it > with airplanes on takeoff, and we get a horsepower figure of about > one-fifth of what we know the engine is giving us. Any movement thru > air represents drag, any rolling wheels represent drag, and the losses > through the drivetrain are significant. Further, unless the engine is > operating at the desired RPMs (redline or max torque) it's all > irrelevant. > The most accurate measurements use an engine brake and > torquemeters. Torque x RPM x 6.28 divided by 33,000 equals hp. > > Dan |
#19
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#20
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Steve > wrote in message ... > wrote: > > > Using vehicle acceleration to measure hp is useless. We've done it > > with airplanes on takeoff, and we get a horsepower figure of about > > one-fifth of what we know the engine is giving us. > > I know several people who have taken their car to the strip, weighed it, > and used trap speed to compute horsepower, and THEN gone to a chassis > dyno and checked the power that way. They've all said that the numbers > are amazingly close- usually within 10-15%, and nothing like the 1/5 > you're talking about. 10-15% ?? Struth. With my vehicle performance simulation software (details on the website) I can get within a couple of percent of true bhp if the vehicle performance and weights, gearing etc are known accurately. -- Dave Baker - Puma Race Engines (www.pumaracing.co.uk) |
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