What's the instant economy of your car during a hard acceleration?

[MercenaryForHire]

Originally posted by: dman
Hmmm... I would think that at higher speeds the MPG would go up at full throttle... (not necessarilly above the 'avg' but up from 0mph acceleration...) because you are covering more ground per unit of time, while there can only be so much gas being fed to the engine at any given time.

Also, in college, one of my professors explained that gasoline engines were most efficient at full throttle, and I think it was along those same lines (max power / output also factored in).

Anyway, my cars don't have readouts, so no idea here.

IIRC, fuel consumption/RPM graphs tend to be a U shape. Higher at low RPMs, dropping down to the Econo-Max point where an automatic transmission will try to stay in, and it climbs rapidly after that.

That being said, I made a road trip at felony speeds in my old 93 Civic, and still got near 40mpg.

- M4H

 

[AStar617]

For years I've loved BMW's ability to monitor instant fuel economy via an analog VDO gauge. :thumbsup: Much better than the old Benz "Economy" needle that swings across an increasingly red field... no grades, no digits. Funny that both makers use VDO but their implementations differ so much... I prefer the BMW's.

A little off topic but interesting: one of the features of the M50 (2.5L straight six) engine in my 525i is the ability for fuel feed to cutoff temporarily if the engine management computer detects that the torque of the rear wheels is sufficient to keep the motor running (i.e., when coasting down a notable decline or down from a high speed). Maybe newer cars have this but it was pretty kickass in '92 This is done obviously for added fuel efficiency... but because of this, the analog economy gauge actually has a "infinity" readout (any speed, with zero fuel to the engine). If you look at this huge, horribly blurry dash pic from when I hit 200k, it's the bottom portion of the speedo on the right ("MPG"), and specifically the black mark on the white field on the left end, rather than the white marks on the otherwise black field. Cool stuff.

But getting back on topic... unfortunately I'm driving the truck for the season so I don't have any numbers to contribute...

 

[malbojah]

I still mainstain a healthy 25 mpg at WFO

 

[no0b]

2

 

[Evadman]

It stays at zero until about 30 mph, and it changes to 1.

 

[jagec]

Originally posted by: AStar617
A little off topic but interesting: one of the features of the M50 (2.5L straight six) engine in my 525i is the ability for fuel feed to cutoff temporarily if the engine management computer detects that the torque of the rear wheels is sufficient to keep the motor running (i.e., when coasting down a notable decline or down from a high speed). Maybe newer cars have this but it was pretty kickass in '92

My 1990 Volkswagen Golf has that

Originally posted by: dman
Hmmm... I would think that at higher speeds the MPG would go up at full throttle... (not necessarilly above the 'avg' but up from 0mph acceleration...) because you are covering more ground per unit of time, while there can only be so much gas being fed to the engine at any given time.

Also, in college, one of my professors explained that gasoline engines were most efficient at full throttle, and I think it was along those same lines (max power / output also factored in).

Anyway, my cars don't have readouts, so no idea here.

well, it get complicated. Obviously fuel economy readouts mean nada if you're not at steady state (IE, not accelerating). That's because a lot of the fuel being dumped into the engine is going into increasing your kinetic energy, rather than just keeping the car going. If the engine was so weak that it had to be floored and a little short of the redline in order to maintain a constant speed, then it WOULD be at its most efficient operating point (MPG-wise). In short, the engine may be able to output the MOST power per gallon per hour at full throttle, making it most "efficient" at that point, but in a real driving situation, what matters is how many gallons per hour it takes to output a given power, which is always less than the maximum the engine can produce.