28 replies to this topic

[Alonsofan007]

i've been hearing a lot lately that horsepower can be estimated using gps data in f1, trying to understand how that is possible ? any ideas ?

[Alonsofan007]

cool, thats great info n link, thanks

[Lee Nicolle]

Really just look at the car and lap time. About as accurate.

And most confuse horsepower with torque. A short twisty track uses torque to go fast,,until said torque burns the tyres up! Fast flowing circuit HP is the key

[RogerGraham]

Err.. no.  Lap time is dependent on many factors, and it's not possible to separate out bhp from the other factors using just laptime measurements.

 

Power can be far better isolated by tracking acceleration in a straight line (using GPS, if no other methods are available).

 

As for the bhp/torque thing...

[Ross Stonefeld]

I love a good power/torque thread. Eventually we'll move on to China/airplanes/driving style and the real learning will begin.

[GreenMachine]

PII, come back, all is forgiven ....

[Lee Nicolle]

Err.. no.  Lap time is dependent on many factors, and it's not possible to separate out bhp from the other factors using just laptime measurements.

 

Power can be far better isolated by tracking acceleration in a straight line (using GPS, if no other methods are available).

 

As for the bhp/torque thing...

Sure lap times are dependent on many things. I did say LOOK at the car and lap times. Probably more accurate than GPS. A fat high car with a big engine may do the same time as a small nimble one with  small engine. but the lap time is the thing,, fat car has more power [and torque], nimble car has better braking and handling.

I might know,, I have done this crap for well over 40 years!

[Joe Bosworth]

I definetely won't buy into any discussion of whether torque or horsepower is more important to lap time/performance as the two factors are completely interchangeable.

 

However several years ago I developed a programme to forecast lap times for a known track configuration and vehice performmance factors.  I used HP curve as one of the inputs as it was much easier to write the programme from the HP data rather than torque data. 

 

For what it is worth, a reasonable approximation of the change in lap time for a given track with changes to power to weight ratio can be calculated based quarter mile acceleration time.  For instance if you know that vehicle "X" turns 12.5 second quarters and 90 second lap times for a given track then the 90/12.5 ratio will hold pretty closely for other vehicles.  

 

Amazingly to some, you will find that quarter mile times for most all vehicles will hold quite closely to the equation that time in seconds equalls 516 times kw of running weight divided by HP all raised to the .333 power.

 

Play with those relationships to your heart's delight.

 

Regards

[Alonsofan007]

i got this link http://www.engineeri...ion-d_1309.html which has formulas to calculate power. i see that post is removed now

 

 

this is what i got, not sure how to take aero into account,i suspect for these calculations they are considering aero/drag effect  negligible.

 

dt = time of acceleration (s)
a = acceleration (m/s^2)
l = distance moved (m)
m = mass of car (kg)

Power = (m x a x l)/dt
 

Edited by Alonsofan007, 27 July 2015 - 22:33.

[Joe Bosworth]

Fan 007

 

Use the same flat road with no wind that you use for measuring acceleration HP.  Bring the car up to thge max speed that you find in acceleration. Place the car in nuetral or put in the clutch and use negative g measure and distance to calculate the sum of aero drag and friction.  You will run out of space before you getting very slow but you can use math and/or eyeball extrpolation to extend the aero/friction curve into the lower ranges of speed.

 

Rear wheel HP will be very closely calculated by adding the acceleration and deacceleration derived HPs.  Flywheel HP will be very close to rear wheel HP divided by .75.

 

With care and multiple runs or use of a g-meter that records you can plot HP and Torque curves.

 

Regards 

[johnnycomelately1]

i have tried a g meter (app on an iphone) on a motorbike for tuning via a powercommander, same bit of road etc, it works to a degree.

dyno to finish off though.

it was a curiosity

[Kelpiecross]

Instead of using a g meter you can time the decay in speed over a short mph range - this will give the deceleration rate. You then use F=ma and the weight of the car to calculate the force needed - horsepower is then speed times the force. If you are doing the calculation in Imperial measure you have to be careful with the units used.

You can also do useful things by fitting a vacuum meter to the car - at a particular speed (or going up a hill etc.) you can note the manifold vacuum and the later load the engine to this vacuum on a dyno to get the HP.

[Greg Locock]

I first got into coastdown testing to estimate aero and rolling resistance 30 years ago. At the time we never got a really good grip on it, partly due to lousy fitting software, and partly due to lousy technique, and partly because it wasn't actually that important. Then for the solar car I had the luxury of an oval, a lot more time, and a need to get accurate results. The only way I could get a good handle on the results was by recording speed vs time, starting from 6 positions on the oval, and modelling both gradient (of the nominally flat track) and wind, because one side of the track runs against a line of trees. The advantage of using a closed circuit is that any error in gravitational potential energy is eliminated over one complete circuit.

[johnnycomelately1]

Instead of using a g meter you can time the decay in speed over a short mph range - this will give the deceleration rate. You then use F=ma and the weight of the car to calculate the force needed - horsepower is then speed times the force. If you are doing the calculation in Imperial measure you have to be careful with the units used.

You can also do useful things by fitting a vacuum meter to the car - at a particular speed (or going up a hill etc.) you can note the manifold vacuum and the later load the engine to this vacuum on a dyno to get the HP.

i think i'd beat you to the finish line, red dog

[Joe Bosworth]

A few comments on posts above.  My comments are based on my evolution of methodology over several years.

 

I have had near no luck gathering data with a g-meter on a motor cycle.  Bikes pitch too far and this pitch corrupts cheapy g-meter efforts such as those on a phone.

 

By all means speed degradation can be used to get good drag data in deacceleration and HP data in acceleration.

 

Care must be used to eliminate elevation change corruption and the affect of head/tail winds for all efforts using a g-meter, speed time, speed distance and/or distance time calculations. Greg's comments apply.

 

I regularly tried to make sense out of the information that a vacuum meter could give going as far back as the 1950s.  Save your time and effort.  I haven't pulled my old meter out of the tool box in the last many decades.

 

Likewise my early efforts of using an un-damped g-meter only provided the barest of useful data.  That is useful as being repeatable and believeable.

 

In the 1970s I got very good data using all of the speed, time, distance methods but found greatest hapiness with distance/time data.  I was lucky to have a great section of road to use. I worked at Hannibal Ohio and lived in New Martinsville WV.  Between the two is a highway running between the Ohio River on one side of the road and a quite high hill on the other.  No cross roads and free of E - W winds.  Just made sure that a couple of nearby flags showed no N - S winds on days that I got data.  The road ran quite close to river for a couple of miles for which a long length of safety rail stopped any yobbos from driving into the river while under the influence or whatever. It was quite easy to get a good measurement of the rail length and the road was as level as the water in the river.  I could get new data almost every day going to or coming back from work if I so wished.  

 

I have never left my daily driver in a stock condition going back to to my first in 1950.  That one was a 1940 Ford sedan with a Mercury engine, lowered with sway bars, split exhaust, Stromberg 97 carbs, lightened flywheel and you get the idea.  In the early/mid 1970s I was racing formula Ford, Driving a TR4 and towing with a two liter Ford Pinto.  

 

Anyway, to cut the story down I breathed on the TR4 for 127 RWHP and the Pinto to 140 RWHP using the above measuring methods.  All readings were sensitive to changes being made and were repeatable.  Both correlated with quarter mile drag times/speeds.

 

So, by all means, a good GPS can be used if you can find the right section of road to apply it on.  Your biggest problem might be in writing the programmes to use with your data collected.  You need a decent appreciation of physics and care in the use of compatable units of measurement.

 

Over about the last 15 years or so I have found it far easier to use G-meters.  There are several relatively inexpensive and easily available.. There are several more not so cheap but even better.  There are also several high speed GPSs, not so cheap, but that built in HP software.

 

Oned of my sons is now using one of my devices to coach some HP out of his Ford XR6 Turbo.  Without spending big bucks he has had a flash reading of 415 Hp and over 400 HP available every day.   Just as doing dyno work there is a risk of blowing things up as you get to close to the line with some things like ignition timing.  I have always  pulled tuning back about 1 to 1.5% from peak measured for safety on a daily driver.

 

Unless you wish to burn lots of money on rear wheel dyno time you can get similar results using these methods.

 

Regards 

[johnnycomelately1]

A few comments on posts above.  My comments are based on my evolution of methodology over several years.

 

I have had near no luck gathering data with a g-meter on a motor cycle.  Bikes pitch too far and this pitch corrupts cheapy g-meter efforts such as those on a phone.

 

By all means speed degradation can be used to get good drag data in deacceleration and HP data in acceleration.

 

Care must be used to eliminate elevation change corruption and the affect of head/tail winds for all efforts using a g-meter, speed time, speed distance and/or distance time calculations. Greg's comments apply.

 

I regularly tried to make sense out of the information that a vacuum meter could give going as far back as the 1950s.  Save your time and effort.  I haven't pulled my old meter out of the tool box in the last many decades.

 

Likewise my early efforts of using an un-damped g-meter only provided the barest of useful data.  That is useful as being repeatable and believeable.

 

In the 1970s I got very good data using all of the speed, time, distance methods but found greatest hapiness with distance/time data.  I was lucky to have a great section of road to use. I worked at Hannibal Ohio and lived in New Martinsville WV.  Between the two is a highway running between the Ohio River on one side of the road and a quite high hill on the other.  No cross roads and free of E - W winds.  Just made sure that a couple of nearby flags showed no N - S winds on days that I got data.  The road ran quite close to river for a couple of miles for which a long length of safety rail stopped any yobbos from driving into the river while under the influence or whatever. It was quite easy to get a good measurement of the rail length and the road was as level as the water in the river.  I could get new data almost every day going to or coming back from work if I so wished.  

 

I have never left my daily driver in a stock condition going back to to my first in 1950.  That one was a 1940 Ford sedan with a Mercury engine, lowered with sway bars, split exhaust, Stromberg 97 carbs, lightened flywheel and you get the idea.  In the early/mid 1970s I was racing formula Ford, Driving a TR4 and towing with a two liter Ford Pinto.  

 

Anyway, to cut the story down I breathed on the TR4 for 127 RWHP and the Pinto to 140 RWHP using the above measuring methods.  All readings were sensitive to changes being made and were repeatable.  Both correlated with quarter mile drag times/speeds.

 

So, by all means, a good GPS can be used if you can find the right section of road to apply it on.  Your biggest problem might be in writing the programmes to use with your data collected.  You need a decent appreciation of physics and care in the use of compatable units of measurement.

 

Over about the last 15 years or so I have found it far easier to use G-meters.  There are several relatively inexpensive and easily available.. There are several more not so cheap but even better.  There are also several high speed GPSs, not so cheap, but that built in HP software.

 

Oned of my sons is now using one of my devices to coach some HP out of his Ford XR6 Turbo.  Without spending big bucks he has had a flash reading of 415 Hp and over 400 HP available every day.   Just as doing dyno work there is a risk of blowing things up as you get to close to the line with some things like ignition timing.  I have always  pulled tuning back about 1 to 1.5% from peak measured for safety on a daily driver.

 

Unless you wish to burn lots of money on rear wheel dyno time you can get similar results using these methods.

 

Regards 

on a bike, its in a straight line, there is no pitch unless a roo jumps out

the g meters produce a pretty little graph which is surprisingly accurate in a relative sense, which is what you need for tuning

anyway all interesting reading

[gruntguru]

On a motorcyle there is a lot of pitch when accelerating or braking, due to a high CG and short wheelbase.

[Greg Locock]

and springy things

[Kelpiecross]

i think i'd beat you to the finish line, red dog ;)

Black dog I'll have you know.

[johnnycomelately1]

Black dog I'll have you know.

[johnnycomelately1]

On a motorcyle there is a lot of pitch when accelerating or braking, due to a high CG and short wheelbase.

you accelerate, read the pretty graph, change the tune, do it again.

any acceleration "pitch" is relatively consistent and does not affect the purposes of this really unsophistkated method.

[Greg Locock]

is that really more accurate than graphing speed or rpm vs time?

[Joe Bosworth]

Greg

 

If you are aiming the query above at me I can share my experince.

 

It all depends on accuracy and repeatability that you are after.

 

All of the methods that i discussed can give good results as the physics are constant only the units in the derived equations change.

 

I really like distance vs time.  Distances can be measured to an accuracy of about 2:1000 with an easily calibrated bicycle speedo.  Mark you test distance once with paint blobs and you have that fixed.  The stop watch doesn't lie, (sometimes the finger or thumb does).

 

There is no physics that relate to RPM so you haave to convert RPM to speed.  I find that starting a run from different RPM ranges gives insights so yes I use RPM/speed to set specific starting points for some regimes but when all is done you need to calibrate the speedo.  A known distance/time is used for that as well so we are back to distance/time preference.  And that way you don't bring in wheel rvs per unit distance changes with temperature and air pressures.

 

And Johnny, if you don't mind pitch type errors you are free to ignore.  But in my experience bikes typically have one or more relatively flat spots that can change the pitch and a lot of the tuning is aimed at smoothing the flat spots.  I have a lot of cycle power/torque vs revs curves that illustrate.  While tuning my own bikes I have oftern introduced some real whopper torque holes that need to be worked out.  It all depends on what you are doing.  I find that repeatability of data from run to run is important, you might find otherwise.

 

Regards

[johnnycomelately1]

is that really more accurate than graphing speed or rpm vs time?

i only related to accuracy when i said a dyno to finish off a proper tune.

it was a curiosity as someone said it was being done.

i think it was the porsche g force meter.

it has very fine scales on the graph and it worked, was repeatable and showed the bigger fuel and ignition changes, amazing really.

combined with the ease of power commander tuning it was a worthwhile exercise and i didnt get booked

[johnnycomelately1]

Greg

 

If you are aiming the query above at me I can share my experince.

 

It all depends on accuracy and repeatability that you are after.

 

All of the methods that i discussed can give good results as the physics are constant only the units in the derived equations change.

 

I really like distance vs time.  Distances can be measured to an accuracy of about 2:1000 with an easily calibrated bicycle speedo.  Mark you test distance once with paint blobs and you have that fixed.  The stop watch doesn't lie, (sometimes the finger or thumb does).

 

There is no physics that relate to RPM so you haave to convert RPM to speed.  I find that starting a run from different RPM ranges gives insights so yes I use RPM/speed to set specific starting points for some regimes but when all is done you need to calibrate the speedo.  A known distance/time is used for that as well so we are back to distance/time preference.  And that way you don't bring in wheel rvs per unit distance changes with temperature and air pressures.

 

And Johnny, if you don't mind pitch type errors you are free to ignore.  But in my experience bikes typically have one or more relatively flat spots that can change the pitch and a lot of the tuning is aimed at smoothing the flat spots.  I have a lot of cycle power/torque vs revs curves that illustrate.  While tuning my own bikes I have oftern introduced some real whopper torque holes that need to be worked out.  It all depends on what you are doing.  I find that repeatability of data from run to run is important, you might find otherwise.

 

Regards

when i hesitated on acceleration for one reason or another it shows on the graph, as you would expect.

same as a bad flatspot for sure , but as for the tiny amount of pitch which happens but then stays while accelerating inducing a misleading graph, i cant see it.

interesting we both mentioned repeatability, a good indicator.

[Greg Locock]

No Joe, I was asking johnny why he liked using an accelerometer in preference to speed or rpm vs time, or I suppose, distance.

[gruntguru]

A two axis accelerometer (x and z) with some smart processing could eliminate any pitch to give a corrected value for horizontal acceleration (the vertical component of the total acceleration vector must always be 1G)

[johnnycomelately1]

No Joe, I was asking johnny why he liked using an accelerometer in preference to speed or rpm vs time, or I suppose, distance.

greg,

i guess one reason would be that elapsed time doesnt show, say, a flatspot because it is total time, whereas a graph shows the progression with all its problems or lack of.

[Brandnelson]

Ive had good luck datalogging time vs rpm for tuning purposes. I cant see gps giving any more usuable information on the state of tune. In my case I use a desolate stretch of desert highway. All runs in the same direction, in 4th or 1:1 gear, and giving time on the return route for coolant, oil, and intake air temps to return to a "normal" value. Its certainly good enough to set fueling and ignition timing and see any holes in the powerband. Plus its free and always available, unlike the chassis dyno. From there I have a excel spreadsheet that can fairly accurately predict hp once vehicle weight, gearing, cd, and tire size are inputed and manipulated to align with a control test made on a chassis dyno. Only downside I see is if one gets greedy for hp and pops the motor on a desolate stretch of highway outside of town! Yes it happened, once..