Yet another gas mileage thread...

[waynehoc]

Just curious to hear people's thoughts on this one - is there, for our 3A-C's, or for any engine for that matter, a gas mileage 'sweet spot rpm' that will consistently yield the best gas mileage in steady driving? I've read all the hints and stuff re getting good gas mileage, based on driving habits, type of gas, engine mods, etc., and I don't recall any mention of this.

It occured to me that each engine, based on its design, should perform best, mileage-wise, at a certain rpm. I.e., if on a longish trip, or stretch of road, for mileage purposes only, other things aside for now, is it best to keep rpms at, say 2000, 2500, 3000, or is it just best to keep rpms as low as possible without lugging the engine?

Maybe I'm out to lunch on this, but interested in everyone's comments, ideas, etc., looking at the 3A-C from a gas mileage point of view, assuming all other things to be equal. This assumes a stock engine, as obviously any mods will change the picture somewhat.

Wayne

[Typrus]

A certain Swedish company recommends shifting by 3000 and cruising no higher than 2500 in gas engines. Doing that versus my norm will yield improvement.

[Gasoline Fumes]

or is it just best to keep rpms as low as possible without lugging the engine?

I think that's probably the one. Engines do have a specific RPM (usually around the torque peak) where they make the most power per unit of fuel, but I think you'll see lower fuel consumption at lower RPM. The only way to know for sure is to do your own testing.

[dcn]

If I crused at 2500 I couldn't go faster than 80Km/H..
I get about 34 or so (Canadian), maybe that's 30-ish.

[Typrus]

Ever wonder why 55 is highlighted in the 83/4? 55mph= roughly 2500RPM. Probably something to that eh?
Aerodynamically, most cars are most efficient around 55mph. So, my guess would be that back in the early 80's, seeing as speed limits were darn low back then (55 in some places) they tuned the RPM sweet-spot to be near that speed?

Random theory.

[Gasoline Fumes]

Ever wonder why 55 is highlighted in the 83/4?

Because it was the national speed limit. A lot of USDM cars had it.

[Typrus]

I know that, but the point that it may have been tuned for optimal RPM at that speed still stands.

[waynehoc]

Good point Typrus. 55mph = 88.7 kph, and most of our freeways here in the Lower Mainland (B.C.) are posted for 90kph speed limit, although some I've been on are posted as high as 110 kph. In my '87 2WD wagon (with 3.58:1 diff) 2500rpm = very close to 90kph.