instantaneous hp
instantaneous hp
(OP)
I'm looking to get some opinions on a home project idea. We are wondering if it is possibile to measure instantaneous hp on a car.
Our current thoughts include using the drag force, mass, and friction to determine the total resistive force on the car. Then using the speed and engine revs calculating hp.
I have done a bit of research online and have not found much so I'm wondering if anyone has done this before. Any thoughts on our current idea?
We could get a dyno reading, have a computer find the engine speed and look up the hp from a programmed curve (found using a dyno) probably. Of course, we don't have a dyno so we're looking for our ways.
Cheers
Our current thoughts include using the drag force, mass, and friction to determine the total resistive force on the car. Then using the speed and engine revs calculating hp.
I have done a bit of research online and have not found much so I'm wondering if anyone has done this before. Any thoughts on our current idea?
We could get a dyno reading, have a computer find the engine speed and look up the hp from a programmed curve (found using a dyno) probably. Of course, we don't have a dyno so we're looking for our ways.
Cheers





RE: instantaneous hp
You could probably get within 10% percent by getting instantaneous fuel rate from the ECM and taking the ratio over peak HP rate (from a quick run down the highway), then multiplying by advertised peak HP.
RE: instantaneous hp
However, neither of these is especially easy, your approach of modelling the instantaneous performance of the car is pretty good, but you'll have to factor in gradients and wind, which will ruin the accuracy.
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: instantaneous hp
Normally when people want engine power, they want just the engine power, not the net output at the wheels. So your not necessarily measuring the same thing other people are, so can't directly compare numbers.
I don't know how you'd accurately measure drag force or friction, either. You can measure the rate of deceleration with the car coasting, and get the sum of aerodynamic drag + friction, but you won't get an accurate number necessarily.
We did this for a lab in college (measuring drag by deceleration, that is). One problem is wind. You can do the test in two different directions to cancel out wind exactly parallel to path of travel, but can't account for effect of crosswind that way.
RE: instantaneous hp
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: instantaneous hp
The operating principle was simple enough; it put displacement transducers across the engine mounts. Because engine mounts are not linear, you'd need to lock the crank and apply a range of known torques, including large ones, to calibrate such a system. Today's microprocessors could take care of display and any calculations needed, but the transducers would still be a little pricey.
Accelerometer- based systems sold today are potentially as accurate, easier to install, and much cheaper.
Mike Halloran
Pembroke Pines, FL, USA
RE: instantaneous hp
Maybe I am missing something but several companies make accelerometers for cars. The ones made by G-tech have built in programs that calculate torque and hp based on the weight of the car and the engine rpm. They sense rpm through the electrical feed even on CI engines. You do have to add hp due to wind and drag but their web page has some approx. formulae. Hope this helps.
RE: instantaneous hp
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: instantaneous hp
RE: instantaneous hp
I was looking for a way to measure the HP output. The friend of mine who i'm 'working' with on this actually has done up a pretty basic accelerometer. I'm not sure how good it -- or how bad it is -- but as Ivymike pointed out, we were worried it wouldn't work at constant speed.
Actually, what we want to use this the most for is for a long distance commute, on highways...with constant speed.
RE: instantaneous hp
Wind could be reasonably estimated by looking at the difference between the vehicle's speedometer and a pitot tube airspeed indicator.
Since I'm pitching aircraft stuff, grade could be estimated using the vehicle's odometer against a variometer.
Bearing drag is a function of speed and load. You should be able to get an approximation formula from one of the bearing companies.
Is there a real need for this, or is it just to see if you can?
RE: instantaneous hp
RE: instantaneous hp
RE: instantaneous hp
RE: instantaneous hp
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: instantaneous hp
What sort of calipers are you referring to? Some sort of vernier caliper or am I overlooking something basic to the autoworld?
RE: instantaneous hp
using engine speed, fuel consumption, maybe boost, and an efficiency table to figure out how much power the engine is producing
My problem with that is the efficiency table. Either constructing one or finding one. Besides that, i don't see how it wouldn't work.
Which reminds me, i should mention the car has a turbo which may make things even more difficult
RE: instantaneous hp
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: instantaneous hp
MS
RE: instantaneous hp
AW
RE: instantaneous hp
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: instantaneous hp
Any ideas how they do it?
(Not cheaply I'd imagine....)
"I love deadlines. I love the whooshing noise they make as they go past." Douglas Adams
RE: instantaneous hp
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: instantaneous hp
you would have to have a very sensitive and accurate instrement. there is a engine load percentage that is calculated by the ecu and can be read using a obd2 scan tool (at least on my car which was obd2).
if you are talking about geting an on-the-road acceleration number than I cant think of a better way than an accelarometer.(or using that math junk)
I am by no means an expert, I could be totally wrong and usually am.
RE: instantaneous hp