Request for Data from TheHolyCow

[monroe74]

Just chiming in late on this very interesting discussion.

Originally Posted by theholycow

I stand by this statement:
"At 2000rpm and 20% throttle it will use the same amount of fuel regardless of gear."

I think you're getting right to the heart of the matter with that statement, but I think confusion is invited because your phrasing is ambiguous.

When you say the "same amount of fuel," I think you're leaving it unclear as to whether you mean 'same amount of fuel per unit of time' as compared with saying 'same amount of fuel per unit of distance.' The former is true. The latter is not.

In other words, "2000rpm and 20% throttle" will always use the same number of gallons per hour, regardless of gear (and vehicle speed). But if I change gear (while maintaining 2000rpm and 20% throttle), vehicle speed will change. Since I am changing MPH while holding GPH constant, MPG is going to change.

Originally Posted by theholycow

It does offer additional functionality (logging), though, and I think I may be able to combine it with real fuel injector pulse width data.

I agree with you that logging could potentially be very helpful, although I'm still trying to figure out the best approach to that. I also think you have a very good idea about integrating injector data somehow, so I look forward to hearing more about that.

[dosco]

Originally Posted by monroe74

In other words, "2000rpm and 20% throttle" will always use the same number of gallons per hour, regardless of gear (and vehicle speed). But if I change gear (while maintaining 2000rpm and 20% throttle), vehicle speed will change. Since I am changing MPH while holding GPH constant, MPG is going to change.

That's the root of what I want to know.

If I'm driving in my development at 20 mph in low gear at 2000 rpm, I'm burning the same volume per unit of time as I am if I'm driving at 60 mph at 2000 rpm in top gear.

[theholycow]

Originally Posted by dosco

That's the root of what I want to know.

If I'm driving in my development at 20 mph in low gear at 2000 rpm, I'm burning the same volume per unit of time as I am if I'm driving at 60 mph at 2000 rpm in top gear.

No, because throttle position will be different.

This morning I actually was thinking about this thread a little as I accelerated, going from gear to gear at WOT. As I entered each gear at the same RPM and same throttle angle, I watched the meter, and it used the same fuel rate.

I'm still waiting for my ELM327 to arrive from China. The PCMCIA USB card I ordered arrived but doesn't work in the laptop I planned to use; I need to try it in another to find out if it's bad or if the laptop is bad.

[dosco]

Originally Posted by theholycow

No, because throttle position will be different.

Sure. According the the BSFC charts, I should be burning *more* fuel. Thus the question. You should see it in your data, assuming you can correlate duty cycle, throttle angle, and rpm at the same time.

I would think, though, that one could do it "by the seat of your pants" to get a feel for what's happening.