gregturek

I'm replacing my MXL Pista with an MXL2 and looking forward to using the math channels.

Has anyone looked at using a fuel level sensor and math channel techniques similar to those in the Corner Vmin and Straight Vmax discussion to estimate gallons/lap, or miles/gallon?

I was thinking about something like = (fuel (@fiinish) - fuel(@start))/(@finish-@start) with the appropriate conversions, where @start and @finish is similar to the turn1/turn2/etc. math channels. (Sorry for the math channel shorthand)

Also, is there a list and description of math channel functions in RS3?

Thanks!
Greg

Matt Romanowski

That should work, but it will only be by the lap. But then you could export the channel report and take the average of the averages or pull out green flag mileage, yellow flag mileage, etc.

Most times fuel consumption is done by the ECU based on the injector flow rates and duty cycle plus a fudge factor.

RS3 is only for setup of the MXL2, MXS, MXG, Evo4s, and Evo5 units. All analysis is still done in RS2 Analysis.

ProCoach

You'd need to calculate this for each track and it would vary according to lap times (percentage WOT over the lap). Never tried to do it without calculating consumption data, first.

Hopefully, RS3 Analysis may add more flexible and powerful features, similar to MoTeC i2 and Dash Manager, which allows this computation now, without segment data or building a spreadsheet.

Matt Romanowski

All fuel mileage is done by track, so this would be no different. In the end, I don't think a fuel sender is going to have enough precision to give a good result. It's difficult doing it with injector flow rates.

We normally just pump out after the session and that gives us very good results.

ProCoach

The ICM fuel level sender (specifically for AiM loggers) after being set up as a custom sensor for some BMW's works very well. The extensive MoTeC database for Cup cars and now GT4 CS cars is quite accurate.

ProCoach

Here are the current options for ICM's fuel level sensor. Their second gen has a microprocessor for more accurate and stable readings. It's about $175.

Frank 993 C4S

The math channel is easy to do but from a purely practical application perspective, I have never gotten this to work given the unreliability of the stock fuel level sensor for the 987.1 Cayman. I ended up weighing the car before and after a session to determine the actual fuel consumption and found out that the scale set-up used at most PCA Club Races is totally unreliable to do this as well. I then resorted back to the "go out with a full tank and then top it back off after you return" methodology as the only true reliable way to calculate fuel consumption.

Given that I am absolutely fanatical about carrying around as little weight as possible for a race I would love to figure out a truly reliable way to make this work. I took note of the better sensors now available.

Matt Romanowski

Please note the Iron Canyon device does not make the stock sensor more accurate, it only provides a voltage conversion from the resistance measurement. It could probably get pretty close, but I'm not sure I would trust he stock tank measurement without verifying it with pump outs.

If you want accurate measurements of consumption, then you have to find a way to pump your tank dry after each session. Then you can measure what you put in and take out, divide that by the miles you ran, and have a real number. You still have to control for drives to the grid, pace laps, etc. And remember to go by weight not volume.

If you have an aftermarket ECU, you can calculate fuel burn by injector size and duty cycle, but that is not most people.

ProCoach

Actually, the V2 ICM conditions the output to reduce the variations, IIRC.

The directions to calibrate the initial custom sensor curve from the ICM involve starting with an empty (I mean, REALLY empty) tank, going through progressive addition of specific quantities of fuel and notating the sensor value. Once the curve is set, there is no reason to continually pump down to know what you have. But that's not specific to consumption.

Most pro teams do what Matt has described. Measure weight of fuel added from empty before session, measure weight of fuel removed at end of session, divide by miles run. Add the positive fudge factor (for pace and cool down laps) and you're set.

gregturek

Thanks Matt/Peter,

I understood that is would per lap on a per track basis, but if I setup the Vmin/Vmax it shoud be relatively easy to add it. I should have added that it is an older car, 944S2 in SP3, with the AIM sensor.

We have the ability to drain the tank with the fuel pump to get every last drop that would get picked up, so our plan is to add a gallon at a time and take a reading to setup the custom sensor.

A concern I have is will the sensor be precise enough using less than a half gallon per lap, and how much smoothing will be needed to get the noise out of the data. By taking the average I'm hoping it will be useful, so when the team asks me how much fuel I want for a 14 lap race, I'll have a better answer than "i don't know, 10 gallons?". And know with some confidence if I can make it to the end of a 90 minute enduro.

It would be cool if I could do it in the dash.


Greg

mglobe

Before you jump too far down the rabbit hole, you may want to look at your fuel level vs distance. Mine varied a fair amount with changes in lateral loading. In simpler terms, the gas sloshes around a lot.

gregturek

Yep, that was my concern, especially with a stock fuel tank. I was hoping looking at the fuel level on the straights (Start/Finish) with an appropriate amount of smoothing would help. Averaging over the whole session could also even things out.

Greg

ProCoach

Bigger sample, better info.

The V2 ICM has improved this issue substantially, AFAIK.

Viperbob1

The Iron Canyon works great. Have it running in a few cars. Very simple reliable and accurate. Just took reading at full and move sensor to empty and built simple curve for a sensor in AIM. Now we show gallons left on display. seems dead accuarate.

ProCoach

And the V2 is even better!