Ted B. wrote:
> "N8N" > wrote in message
> oups.com...
> >
> > Ted B. wrote:
> >> Over the years I've owned my current ride, I have observed that it is
> >> most
> >> fuel-efficient at 3500RPM, where 42MPG is easily attainable. I have also
> >> observed that, at 3000 RPM or less, the mileage on my vehicle drops to
> >> 35MPG
> >> or lower. My experience with my current vehicle is similar to several
> >> other
> >> vehicles I've owned. In every case, I've found that the best fuel
> >> economy
> >> is achieved somewhere above 70MPH. In the case of my current vehicle,
> >> 3500RPM in top gear equates to about 78MPH. Now I'm sure someone will
> >> state
> >> the obvious, which is how do I know that my tachometer and speedometer
> >> are
> >> accurate? I don't. But the bottom line is, in top gear, I can achieve
> >> BETTER fuel economy at slightly higher than normal highway speeds.
> >> Actually, the better fuel economy is due to slightly higher engine RPM,
> >> and
> >> the higher ground speed is COINCIDENTAL.
> >
> > <snip>
> >
> > just curious Ted, what do the power/torque curves look like for your
> > particular engine, and/or what engine is it? Do you have access to a
> > full BSFC map for your engine? Would be interesting to see.
> >
> > thanks,
> >
> > nate
> >
>
> Y'know, I've searched online to find exactly that information on my engine,
> or any similar engine. I've had no luck finding it, so far. I know I've
> got the brochure for my car in my house somewhere. I'm going to pull it out
> and see if I can get a hardcopy of the power/torque curves. IF so, I should
> be able to post specific information on what the curves look like for my
> particular engine. I didn't mean to focus on my engine in particular. I
> just thought it was REALLY INTERESTING to learn that Otto Cycle engines
> achieve maximum fuel efficiency near 40% of redline. (especially as that
> agrees EXACTLY with the performance I have observed over many years of
> driving vehicles with Otto Cycle engines) Knowing THAT particular data
> point makes it a little easier to pick a new car when you are car shopping.
> But only if the car has a tachometer. If it doesn't have a tachometer, then
> you have no idea what ground speed the engine was made to be most efficient
> at. That is, without running many hundreds of miles of tests first.
>
> Best I can come up with at the moment is that the engine in my current car
> is a Mitsubishi "4g64" 2.4L inline 4. -Dave

Really I was just curious if there was anything magical about 40% or
redline, or if that happened to coincide with the torque peak, which
I've always heard was a good approximation of where the BSFC map is
most favorable even under part throttle conditions. Having a nasty
Real Job(tm) I can't be looking for that info just at the moment

nate