Convert Boost Gauge to MPG gauge???
08-13-2005 | 04:21 PM
#16
Racer
Joined: Mar 2003
Posts: 418
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From: Bellevue, Washington
Originally Posted by Porsche-O-Phile
Incidentally the MPG gauge on the n/a cars (at least on my early n/a) is INTENDED to be both a fuel rate gauge and an MPG gauge (it has both scales), although this is obviously ridiculous - for example, you can't be doing "60mpg" when your speed is zero - your miles per gallon is also zero, since you're not moving. I think therefore that the rightmost "peg" is actually zero, but has a limit approaching that of infinity from the left (anybody that's taken calculus will understand what I'm talking about)
IIRC the "0.5 g/h" indication corresponds to roughly the "30mpg" position, which only going to be true in one gear (probably fifth, although I've not calculated it out). I think you could fairly easily (and accurately) convert the stock boost gauge on the turbo to a fuel FLOW gauge, but not an MPG gauge - there's no way for it to compensate for vehicle speed, which obviously impacts this value quite dramatically.
IIRC the "0.5 g/h" indication corresponds to roughly the "30mpg" position, which only going to be true in one gear (probably fifth, although I've not calculated it out). I think you could fairly easily (and accurately) convert the stock boost gauge on the turbo to a fuel FLOW gauge, but not an MPG gauge - there's no way for it to compensate for vehicle speed, which obviously impacts this value quite dramatically.
Also, the N/A guage reads flow rate below a certain speed (12 mph or something like that) and above that speed the computer that drives it switches over to a mpg signal. That's why there are the two scales. If you're above that baseline threshold speed, then it will read accurate mpg for any gear as long as all the electronics are functioning correctly.
08-13-2005 | 05:45 PM
#18
Racer
Joined: Mar 2003
Posts: 418
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From: Bellevue, Washington
Originally Posted by Porsche-O-Phile
Interesting and good to know. . . I've never heard that before and I don't think it's in the manual, but I'll double-check. . .
What seems to happen fairly regularly is that the speed signal gets lost just from the contacts corroding slightly with age and the guage reads in gallons per hour all the time because it thinks the car is sitting still.
Aaron
