Realtime Hp readout

[Blu302]

I don't have great gobs of cash or spare time to spend on dyno time, so i was wondering if there was someway to "calculate/measure" RWHP from G-force sensor or torque sensors? I looked at driveshaft mounted torque sensors and 20+ Hrs on the dyno would still be cheaper. Would it be possible to measure torque from engine mount displacement because i'm looking for shock loading as well as steady-state running. feel free to shoot me down on my hair-brained ideas .
Any help appreciated

[Holmz]

This is on my list of things to do.
You will need:
1) Some measure of the losses
- Aerodynamic
- Rolling resistance

Then the mass of the vehicle
Also the mass of the rotating stuff wheels/tyres/brake rotors. Probably an estimate using the wheel and tyre weights will be pretty good as a start.

Then use the G-Force or derive the acceleration from the wheel speed or GPS (differentiated).

I need to fiigure out where to put in the masses and and the loss coefficients to have them accessible from i2.
Should be easy, but I do not know how.
Then probably the easiest way is a .dll to do the math.

One could also much of this for a cruise control or to calculate brake energy.

[Blu302]

Would coasting at different speeds and measuring the negative G-force give approximate total losses?(aero and driveline drag combined)

[Holmz]

Would coasting at different speeds and measuring the negative G-force give approximate total losses?(aero and driveline drag combined)

Of course... Because F=MA
And aero usually dominates - or at least it does when you go fast enough.

So you can either differentiate the speed to get A , or measure A directly.
It is probably easier to differentiate speed, as the chassis pitching under acceleration or the road going up or down will change the acceleration longitudinally. The best would be some combination (averaging) of the two approaches.

The wheels make the mass seem heavier than the vehicle mass as measured on a scale.

The driveline losses would have little to do with coasting, but do suck out power between the engine and the road. Really if you want to improve acceleration then the driveline losses do not matter a whole lot. The wheel HP is the only thing that matters in the end, so working back to the engine seems to be only good for bragging rights.

If you want to do HP in real-time or in i2 post facto then you probably need to take into account the fact that the road is not always flat, so you might need GPS or some other way to sense going up and down hills.

[Blu302]

I currently have a 3-axis G force meter wired to the ECU(+/-4G) if that helps

[Holmz]

I currently have a 3-axis G force meter wired to the ECU(+/-4G) if that helps

Imagine that you are moving at a constant speed. the longitudional G is zero. Imagine that speed being the maximum speed that the vehicle goes.
Based upon G-force you get zero HP, which is unlikely.
So you need to know the vehicle's speed, and the drag losses (e.g. aero, rolling).

Take a look at these...
I went up to speed, then chucked it into neutral and coasted for about a minute and a half till I was moving pretty slow.
exported the data from I2 as a csv file, and used only the coast section.
Then fitted coefficients to make a model of the car being dragged down by aero and rolling resistance match the observed speed.
On the top graph the purple is the speed coasting down over time, the green is the speed assuming aero resistance, and rolling resistance. Again - I estimated the coefficients for the aero and rolling resistance, which are what where used for the green curve.

The bottom graph is the HP to move constantly at a given speed using the coefficients that were estimated.
I think it is pretty close as the max speed that can be attained is about 10% below the advertised HP, but the max speed was using the speedo which is probably ~5% too high.

http://www.flickr.com/photos/32230177@N06/5980682021/

The second set is a repeat of the process.
http://www.flickr.com/photos/32230177@N06/5980682971/

I have some more coast down runs uphill and down hill, but will need to get around to those. And there are good reasons to coast up and down hills.
So for a constant speed you need to get the right HP. This I view as step #1, unless you are not aero or rolling resistance limited, so maybe OK for a drag car at low speed - but unlikely in my world..

I currently have a 3-axis G force meter wired to the ECU(+/-4G) if that helps

If the chassis does not move then the G-force would give you wheel torque and you use RPM and gear to give you engine torque, and then HP. But you still need speed to estimate the gear that you are in.

Now imagine a motorcycle on the rear wheel at a constant speed. The longitudional G will be high, but you are not accelerating. I think I have figured out a way around that, but have not done the math to prove it yet.

There are more nuances, but we probably need to start with this.

If you chase up how to get the math done in the ECU or ACL, then I will take a crack at it.
There should be tech note somewhere.
Also you will need to dig up the tech notes to get that "math Channel" to a display (e.g. dash).

Doing the math in I2 is probably easier, and looking HP while driving may not be worthwhile, so doing it post facto is where see more value.
Looking at the HP in-situ, I would think that looking at torque rather than HP would at least be flatter and easier to glance at a number that doesn't scroll around like a petrol bowser.

[Holmz]

Imagine the motorcycle on the rear wheel.
Long-G =0.707
Vertical G = +/- 0.707 (depends on the sign)

So the total-G (ignoring the lateral) =
(LG^2 +CVG^2)^0.5 = total G
So if the road is flat, or you are not going over bumps etc)... Then the longitudinal acceleration = (Total-G - 1G)^0.5

It all can go pear shaped if the sensor has some misalignment about the roll axis as you will get values in lateral the go too high.
Should work for drag racing, or HP in a straight line though.