m20b25 getting 25/30 mpg. possible?

[Julien]

I have a 325ic recently converted to 5 speed. I kept the 4.10 rear end and you guessed it, it gets crappy MPG (per OBC). i drove from asheville to charlotte yesterday (2 hour drive somewhat moutainous with cruise on 80mph) with the a/c on and i got 22mpg. The motor is in good running health (AFAIK) all maintnance done etc.

My question is, for long road trips, is there a way to make the m20b25 guzzle less? Maybe something as far out as running an ETA ECU on it? This conversation is really to throw ideas out there to see what can be done to the m20b25 to run a bit cheaper. I know a/c off and 70mph would have me at 23-24 mpg.

I get roughly 15 in town and 22 on the HWY. That is rediculous. I know i come from two economic euroboxes (euro 318is and 324td) which get extremely good mileage and are still fun to drive, but a 2.5l motor getting 22mpg at cruising speed?

What is stopping the fuel efficiency, the rear end? the flow problems of the m20? maybe the fact that the car is a rag top? My heavy foot? (even though 80mpg should be a joke on this motor) what kind of mileage does a m50 get in similar conditions?

I'm sure many other e30 owners are asking themselves these questions.


Thanks for the input.
Julien

[StereoInstaller1]

I get about 28 in my coupe, no A/C, about 70 MPH, 3.73 diff.

Around town? Fuhgeddaboutit, like 18. Love the roar through 1st, 2nd, 3rd...

Luke

[nando]

something is wrong with your car.. you should not be getting 15mpg in any situation.

[BavarianBimmer]

last week I've had 25.3 calculated (9.3l/100km) mainly HWY 80mph and local roads at 40/45mph

and with my supershort 4.45 diff

[X2theZ3]

something is wrong with your car.. you should not be getting 15mpg in any situation.

I disagree.

15 should be about right with a 4.10 City ONLY, maybe a little higher.
The list was 18/22 for an I engine so depending how you drive I suppose. I don't understand how people always claim a lot more than 22 mpg? Was that listing super conservative or something. Since I can remember, I never got more than that when I had my I.

Btw, to the OP, I got about 19mpg combined with my 4.10LSD; sometimes worse. If you want better mpg, you need to swap in a 3.73.

last week I've had 25.3 calculated (9.3l/100km) mainly HWY 80mph and local roads at 40/45mph

and with my supershort 4.45 diff

You're engine has a higher r (compression ratio); i'm not sure how much that makes a difference in mpg on the m20. Also, you get better fuel there?

[IS]

I average 19mpg combined freeway/city. Sadly, it's mostly freeway - but that's the result of a lead foot.

m20b25 / 3.73 lsd

[equate975]

I must of had an amazing car... my 325i got 24 city and 28 highway. All bone stock.

Only thing I could suggest would be putting a 3.73 diff in.

[X2theZ3]

I must of had an amazing car... my 325i got 24 city and 28 highway. All bone stock.

Only thing I could suggest would be putting a 3.73 diff in.

amazing something. I would have killed for 24 city...

[equate975]

Heh yeah, although Im in a "small" city compared to you CA guys, only about 100,000 people here, 2nd biggest in MN (unless you considier the twin cities 2 cities)

Not really a huge amount of stop go, traffic only gets "bad" at rush hour, and it can easily be avoided.

[nando]

I had a 4.10 in an auto, with a cam % injectors, and i've never seen less than 19mpg (all city driving).

I got 26 on the freeway, and 21 with mixed freeway/city driving.

maybe if you have a lead foot..

[MarkH]

I have a 325i with an auto and a 4.10 LSD and never get below 22-23 mixed and frequently see 27-28 on long highway drives.

[BavarianBimmer]

You're engine has a higher r (compression ratio); i'm not sure how much that makes a difference in mpg on the m20. Also, you get better fuel there?

I don't know if we got better fuel here
Mostly I fill up in an Shell gas station with 98 RON

Once I've tried 93 RON China market place fuel (we use that at my work,and is not available in Europe for road use) and that turned out in a noticeable power lost and a bad idle

[Avus E30]

well I dont know if I am a rarity but with a 2.93, m20b25, and a moderately heavy foot I can get 34 mpg on the highway and I average about 24-26 mpg in the city

[bimmerphile]

I usually put around 14 gal into the tank with around 350-375mi on the clock, which works out at around 26mpg.