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Disingenuous Minion
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Discussion Starter #1
Has anyone tried one of the "street dyno" programs on a Lotus?

There is a very old (1998 or so) posting on a Porsche site (Pelican Technical Article: Street Dyno) of someone using a voltage divider to record a sound file off a plug wire then processing it with a software tool to estimate dyno results using car mass and controlled runs in 2nd and 3rd gear on the street.

I found this more recent program for motorcycles: GSF_Dyno - Street Dynamometer Software

The Auto Enginuity OBD-II reader has this function too, but my OBD-II port isn't hooked up any more (EFI X2 installed).

Any experience with these? Recommendations?

Thanks,
 

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It is only the cars acceleration that matters.
So wheel size etc to get engine HP is only good for talking points.
If you are only using this for getting the HP it look like it would do the trick.
But for tuning it is doubtful.

A regular dyno is good (better) for holding the car one RPM and getting the lambda and advance set for steady-state.

The harder part is any dynamic tuning.
Which is often done in-situ.
This is where tuning like this is done, and also for cars that may change with speed (.e.g LeMans where the aero can influence the air pressure for the intake).

If you are thinking that you can forego steady-state dyno tuning as a DIY on the road, you may be disappointed.
If you think that you can tune for partial throttle and dynamic conditions with this you may also be disappointed as you will probably need Lambda and a way to tell what the advance is needed, as well as if there is detonation. So while it is good on theory you already have the RPM on the OBD Bus. And you need the throttle position, MAP, etc to have any comprehensive understanding of what is happening.

But yes it will give you a HP number.
 

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Disingenuous Minion
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Discussion Starter #3
It is only the cars acceleration that matters.
So wheel size etc to get engine HP is only good for talking points.
If you are only using this for getting the HP it look like it would do the trick.
But for tuning it is doubtful.

A regular dyno is good (better) for holding the car one RPM and getting the lambda and advance set for steady-state.

The harder part is any dynamic tuning.
Which is often done in-situ.
This is where tuning like this is done, and also for cars that may change with speed (.e.g LeMans where the aero can influence the air pressure for the intake).

If you are thinking that you can forego steady-state dyno tuning as a DIY on the road, you may be disappointed.
If you think that you can tune for partial throttle and dynamic conditions with this you may also be disappointed as you will probably need Lambda and a way to tell what the advance is needed, as well as if there is detonation. So while it is good on theory you already have the RPM on the OBD Bus. And you need the throttle position, MAP, etc to have any comprehensive understanding of what is happening.

But yes it will give you a HP number.
Thanks. I have lambda, throttle position, MAP, RPM, etc from the EFI nEditor... Just trying to learn more about the affect of making small changes on the base map without scheduling (and paying for) dyno time.

Have you used any of these programs, or others?
 

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Thanks. I have lambda, throttle position, MAP, RPM, etc from the EFI nEditor... Just trying to learn more about the affect of making small changes on the base map without scheduling (and paying for) dyno time.

Have you used any of these programs, or others?
No I have not... I have always just "rolled my own" so to speak.
If you have RPM, then you only need to know which gear you are in to know MPH.
Then if you know MATLAB or Octave it is easy.
I would suggest Excel if you like that, but I do not use it.

There is a balance between good measurements and safety.
It is better using 5th or 6th for the measurements as it slows up the rate and gives less noise.
But that may not be practical unless you are at the Isle of Man, or Germany.

If you want corrected HP (which I think you DO NOT want), then you need more math. Wheel/tire rotation inertia, drag, etc.
You will need the vehicle mass if you want power, otherwise just use acceleration, which is analogous to torque (without the gear ratio, tire diameter etc which may over-complicate things). You only want more torque, so want more acceleration. But temperature and air pressure can change power as well as drag, so unless you compensate for that you may get mislead.


Below is what the drag looks like:

The top curve is the measured "coast down test" (I think in green). The red is the modeled coast down using wheel inertia, tire drag, and aerodynamic drag, and I took into account the wind speed and the slight elevation changes on that section of road (race track).
I also ran the car the other direction and go the same fit between the curves using the same solved for drag coefficients.
The solved value for the Aero was pretty close to advertised cDA of 0.41 (or 0.43... but I cannot remember exactly but I think it was 0.41)

The lower curve has the labels in the wrong place for the X and Y axis (swap them). It is the HP required on the Y-Axis for the speed shown on the X axis.



If you do not need HP it is easy.
If you do, then either look up the equations or I will give them to you.
But I would ignor drag and just look at the acceleration... That is all you are trying to affect, so why go through extra steps, unless you have a fondness for the math.

Just difference the RPM a small time step before and a small time step after some time.
Then divide by the 2* "the time step" (which is called a derivative).
That number is all you are trying to make larger.
 

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Disingenuous Minion
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Discussion Starter #5
You do seem to know what you are talking about! Thank you for your info. I am travelling in Asia on business right now and have limited time, but will do some research and come back to you when I get home this weekend.

John
 

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You do seem to know what you are talking about! Thank you for your info. I am travelling in Asia on business right now and have limited time, but will do some research and come back to you when I get home this weekend.

John
Where in Asia?
I was living in San Pedro a whole back, so we are somewhat local!



You do seem to know what you are talking about!
...
Yeah sometimes...
 

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Coast-down for a calculation base was brilliant, it encompasses all losses which must be overcome when the car is under power (versus wheel horsepower, not crank horsepower). The amount of energy bleed (rate) at a specific speed, is the amount of energy required to sustain that speed, and acceleration past that speed only has acceleration of mass to be added in to the calculations. Good work!
 

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You can make very coarse changes to a map and see the results fairly well by street tuning and looking at acceleration data.

However there is simply no way you will see fine changes you make on the street. Any torque you add or remove from a small change is in the mud. Way to many variables besides your small change to actually be able to see over things like elevation, wind speed, other cars, etc.

So yes if you are looking to get a decent base map street tuning may work. To fine tune something put it on a dyno.
 

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Coast-down for a calculation base was brilliant, it encompasses all losses which must be overcome when the car is under power (versus wheel horsepower, not crank horsepower). The amount of energy bleed (rate) at a specific speed, is the amount of energy required to sustain that speed, and acceleration past that speed only has acceleration of mass to be added in to the calculations. Good work!
Thanks Addertooth.
It also gave me a chance to have my daughter (the mathematician) on some MATLAB on that data analysis.
So it is "all good".

Working in the altitude part too a couple of hours, but really was worthwhile.

One could make a good cruise control if they wanted to using the pitch angle (or road slope) along with needed HP versus HP(torque)-at-an-PRM-TP.

Of course I am really doing this to do DIY-dyno, so I can get the street tune pat of the map worked out.
 
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