Improving fuel economy

[silversleeper]

I just bought a bike to get better MPG. I am curious about trying to run some seafoam through this thing... would be fun I would imagine.

[kylebes1]

my m42 gets 33 mpg average. I've been driving about 500 miles per week and it sure has helped.

My 318is is stock ride height with fresh plugs, K&N panel filter, fuel filter, wires, o2 sensor and MarkD chip.

I plan to lower it and swap in a 3.73LSD... Skinny hard compound tires are a must for fuel economy.

I also can say driving 65 is good for 2 mpg average as compared to driving 85...

[BMWDriver]

how accurate is the little MPG guage on the cluster?

i try to keep it between the 25 and 40mpg when im on the highway, this results in 65 -80mph on the highway, back roads i try to take it easy from stops but the eta is so slow to begin with.. this has resulted in an average speed on 35 mph and an average mpg of 29 from the OBC. (my odometer gears need to be replaced so i cant really check the old fashioned way) im also running bottle caps with 185/65 tires everythings pretty much stock 86 325e 4 door 5 speed 200k+ mi

[nando]

it should be close as long as nothing in your fuel system has been messed with - it basically takes the injector pulsewidth from the ECU, calculates that VS vehicle speed and derives MPG.

[CorvallisBMW]

how accurate is the little MPG guage on the cluster?

mine is very close, to within +/- 1 mpg when I calculate it at fill-ups

[BMWDriver]

well i drove three or four tanks keeping it around 65 mph, rafting tractor trailers taking it our of gear on hills and basically tooling around like gramps and managed to get the OBC to read average mpg of 31.5, it was cool to see the range break 400 and get through my 350 miles of weekly commuting on one tank but for the extra 3-5 bucks a week i drive a bit faster and im still getting around 29 mpg..


has anyone taken the eta to a higher level of economy? i have been wondering what would happen if you put an eta head an "i" block or running an underdrive pully (are these available?) or running megasquirt to really tune the engie for possibly better economy? different injector or fuel pressure regulator, head work for better economy? then when i get bored with that i could build a stroke and already have the fuel management.

on a side note even driving "slow" i love the way the e30 has go-cart like handling.

[dashboardmonkey]

DAMN!

I am lucky to see 250 miles on a tank of gas.

Doesnt your car see redline every time you shift from first to second?

Andy

[stegosaurus]

I've been taking records of my mileage and blah blah... nice to see some other people care about saving some money too. Last fill up I got 35.7 in the m42 with new oil, lowered, and some steady driving. Just had the timing system done, wondering if that's going to see some improvement as well.

[hahmeta]

i'm in the same boat StereoInstaller, I get 250mi avg from a tank in los angeles. commute is 25mi 50/50 surface and freeway and either way it's a lot of stop and go. got an 89 325i bone stock.

i'm going to change the injectors and maybe m30 afm. anyone think it'll make a noticeable difference?

by the way, how big is the gas tank on these?

[moatilliatta]

im lucky to get 230 in my ix, it needs a good tune though I believe. m30 afm is dookie. ive got 15mpg last fill up, but that week, i was taking all back roads full throttle - full brakes. And just driving the back roads even if i had no place to go.

gas at 1.50.. minus well...

[napabavarian]

Drive down hill more often, uphill less often.

[sandlock]

glad someone made this thread because i'm wondering the same about the gas needle vs the mpg needle. i don't think i have the full OBC, just the 6 button clock/temp panel, so i can't use it to calculate. i'm on my first full tank with the trip set to zero, driving about 108 miles both ways all highway. i'm struggling to be in the 25mpg range, but i currently have a 4.10LSD. so the main question is, it would appear i get better mpg needle action (25+) around the peak torque of the rev range 3600rpm or so. but isn't it strange you wouldn't get better mileage below 3k, like 2500 or so like every other car that has no MPG needle?

[nando]

it all has to do with VE - the reason you get better economy is because the VE at that part of the engine's operating range is much higher than at low RPM. it is a mistake to assume lower RPM always equals better economy, because it depends on where the VE of the engine is tuned for.

the eta for example is tuned for low-RPM VE, while the B25 is tuned for higher RPM VE (between 3500-5000, basically the fattest part of it's torque curve). More modern engines with broader torque curves have higher VE over a wider band (thanks to things like VANOS), which is part of why they get better fuel economy - you're almost always in a high VE area of the torque curve.

[jlevie]

I find it interesting and slightly disturbing that nowhere in this thread has anyone suggested that the first step in better fuel economy should be making the engine run the way it is supposed to. At the least that means correctly adjusted valves, good plugs and ignition wires, no intake leaks, O2 sensor with less than 100k on it and a properly operating fuel system. It could also mean replacement of the AFM, cleaning & blueprinting the injectors (or new injectors), a valve job, new catalytic converters, or even an engine rebuild.

[nando]

i would assume that, but I think that's pretty much the rare case in E30 circles these days. It's more like 200,000 mile bone stock motor where half the sensors are bad, fix symptoms like hard starting and lack of power with 19# injectors and M30 AFM, then wonder why it makes 127whp..