mpg improvement with another diff?

[///m42 sport]

Another gas mileage thread.  Just curious what which diff is the best for cruising on the highway and getting the best gas mileage.

[monko141]

I've put 3.73's in both of mine and they make highway driving much more bearable but they only added maybe 2 mpg.

[lbreevesii]

To a point- lower the better.  3.73 is the easiest choice.

[1991 E30 M42]

I'm running a 373 and get 34mpg on trips

[DesktopDave]

I get mid-30s too, I've seen 38mpg tanks with my 3.73.  City mileage was unchanged...still too low.

[tjts1]

Some guy is running a 2.79 on rev. Madness. 3.64 was enough for me.

[dvmotorsports]

I'm running a 373 and get 34mpg on trips

I get mid-30s too, I've seen 38mpg tanks with my 3.73.  City mileage was unchanged...still too low.

Weak. I got near this with my 4.10. Makes me wonder why.

[DesktopDave]

Weak. I got near this with my 4.10. Makes me wonder why.

IIRC it was 38 mpg at an average of 72mph...but we typically have a 10% alcohol mix here.  Keeps fuel mileage down, that's for sure.

[gearheadE30]

I used to get about 38 averaging around 70 mph and the 4.10. With the turbo, I get around 30 if I don't use the go pedal too much.

[///m42 sport]

how are you guys doing more than 30 mpg with 4.10?  Obviously there are alot of factors involved but I could barely get 28 mpg driving at 65mph with tires inflated to 35psi all around.

Are you guys measuring fill-up to fill-up and miles calculate by gps rather than the odometer? Also with shorter tires, it throws the odometer off.

[DesktopDave]

I found my mileage results are pretty close to the GPS reading.  Less than a 5% difference with stock 185/65 14's despite the taller diff.  It works out because the speedo reads a little over 70mph at 75mph.  I can psych myself out of speeding tickets that way...

That is a really good point about GPS verification though.  I usually check every car once or twice then just compensate for my final calculations.  Many members run larger circumference tires, so the stock diff will throw off the speedo by a fairly substantial amount.

[gearheadE30]

I found my mileage results are pretty close to the GPS reading.  Less than a 5% difference with stock 185/65 14's despite the taller diff.

The diff has a different speed impulse sensor, so it will compensate for itself.

I run based on the odo, but I have stock circumference tires and GPS verified the speedo and the odo, just because I was curious. the difference was also around 5%. The few trips that I got almost 40 mpg, I was running 70mph average, 35psi in the tires, used engine braking (the injectors don't fire on overrun) and probly spent a third of the trips drafting semis. Upping speed to 75mph with no drafting still netted 33 to 35 mpg though...

[KenC]

I got 31 on a full tank trip recently with my 4.10 and 3k on a rebuild, and a lot of that was mountainous driving. About half the trip was above 3,000ft though too so that made up for a lot. I usually get 25-26 combined with a heavy foot.

I'm installing a 4.45LSD next week .

[dvmotorsports]

I'm installing a 4.45LSD next week .

Did you buy this from the member here who was selling? If so, you should know that i'm very jealous.

[romkasponka]

BMW E36 M44 2,93 medium size LSD (was 3,3 small open )

6,5 litre /100km in highway if you driving 90-100km/h, 1 litre less than was before.
8,5-9 liters/100km in town, 0,5 lire less than it was before.