Theoretical Max

[trebuchet03]

Originally Posted by bikin' Ed

Wouldn't infinity be your theoretical max mpg? i.e. going down hill during EOC. Trying to factor in grade, road surface, weight of vehicle (how much fuel, how many passengers, cargo) air speed, wind speed and angle and whatever else I missed, how can hope to get even a formula for max mpg?

Maybe theoretical wasn't an optimal term to use to avoid confusion. Perhaps practical max? The term theoretical is used to find the maximum possible performance of a system (always less than 100%). It's not so much a formula in this case, as much as it is a method to test.

Passengers and cargo wouldn't matter - the maximum possible will be without things you don't carry around all the time. Adding these things will reduce current efficiency further away from the practical/theoretical max.

[tasdrouille]

Originally Posted by trebuchet03

But, it makes me want to create an FE map -> throttle v. mpg v. speed

You just need an OBDII interpreter ala elm327 and software to do the logging.

[trebuchet03]

Originally Posted by tasdrouille

You just need an OBDII interpreter ala elm327 and software to do the logging.

I've got two OBD -> ISO IC's in the mail at the moment The 327 is nice, but it's about $30 more :/ Eventually, I'll upgrade to be compatible with everything I think I've got the programming skills to do that though (or, I might just do it manually )

[roflwaffle]

Originally Posted by trebuchet03

Not so much - I want to know FEmax @ Xcondition. Whatever that condition is.

A BSFC map w/ a (reasonable) range of loads corresponding to whatever gear you're in... Like the BSFC map on the bottom of pg. 37, except w/ road load as a swept area w/ high and low bounds, right?

[cfg83]

trebuchet03 -

Here's my SGI numbers for my car :

TPS: 0
MPH: ~25
MPG: 62.5
RPM: ~850
Road: Asphalt on the flat

Engine Size: 1.9 liters
Gear: 5th

I have my own custom Elmscan data software, but the MPG algorithm would not "map" properly to what the SG is reporting. Maybe I will do a datalog session for "relative" MPG comparison.

CarloSW2

[tasdrouille]

Well... if you only do top gear and you stay in closed loop, all you really need to log is MAF and RPM. There are quite a lot of ELM327 based interfaces available for less than 30 bucks shipped on ebay. If you want to buy such an interface, I can recommend vendor alpha-bid. He's a bit more expensive than others shipping straight from China, but I bought 2 times from him and I had good service both times.

[MetroMPG]

I'm not entirely sure if the Suzuki 1.0L will idle along in top gear without lugging madly. If this helps...



The green line was with the stock transmission, orange/yellow is with the taller final drive. Both are flat road, cruise control, bi-directional averages, and pre-XFi cam (and pre-Kammback). No TPS info though, sorry.

[tasdrouille]

I guess we should determine what lugging is exactly. What I read lead me to believe lugging is a condition when you can't gain rpm while at full throttle.

[trebuchet03]

Originally Posted by roflwaffle

A BSFC map w/ a (reasonable) range of loads corresponding to whatever gear you're in... Like the BSFC map on the bottom of pg. 37, except w/ road load as a swept area w/ high and low bounds, right?

Doh! I never really considered BSFC.... I guess - as this has morphed a bit... I want to come up with a method to create something similar to BSFC.

So thinking out loud... I think I was hoping for a horizontal asymptote starting off low, going high, then going back low.

I need to put more thought into what it is exactly I'm trying to find....Or maybe... I don't know exactly what to call throttle v mpg v velocity, but I still think it will be somehow useful. Especially if I can make a way to determine it quickly (ie, car shopping )

[MetroMPG]

I don't know the technical definition of lugging; this non-tech definition matches what I thought it was though: engine jerking/shuddering. The kind that makes you go, "oooohhh, that can't be good..."

Treb: sounds like you may be after a metric that I wish government agencies would provide: just show me the fuel consumption across a range of constant speeds in top gear. Forget trying to simulate an entire trip to grandma's house for freaking sake!

EDIT: deleted some other rambling. Need to get some sleep. :P