I have a 1989 BMW 325i that I am not really trying to hypermile.
But. . . I do need to save gas money, as I don't have steady income.
I initially wanted a drift car to take to the local track, so I was just looking for a diff to use so I could get the stock 3.70 diff welded up solid. I traded my MP3 CD stereo with remote, and the power antenna for a 2.93 diff from a 325e (economy?).
I usually run near empty because there is no gas money, but I measure by the stock fuel consumption gauge. I figure that for the same rear tires I get accurate enough results to compare.
With the 3.70 gears I made 19-21MPG at freeway speeds of 58-68, with the 2.93 gears I hover around 25mpg on the gauge.
I removed the A/C. including the front electric fan and condenser, which had a cast metal(!!) surround and weighed almost as much as the compressor.
I also removed, and weighed, 55lbs of tar in two 1/2" thick sheets that covered the floor of the trunk. I think it is there to keep the rear end of the car down, it is quite squirrelly and I am un-intentionally squealing the tires even with the 2.93 gears. (currently running some 185/65-14 tires in the rear.)
In town I try to get into 4th as soon as possible (it is 1:1 in this transmission, no gear losses.) I usually idle along between 1,000-1,500 and am getting closer to the 40 mark than the 25 mark (there are no marks between those two.)
On some back roads I can go along at about 40mph in 5th and get almost 40mpg on the gauge. Dangerous with a lot of traffic because everyone wants to go 58-60 outside of town.
I wish I had the 4cyl, but the modern M42 motor car was only produced from 1989-91 is a rare and expensive car (compared to the $200 that was payed for this car, whole.) I would consider an engine swap from the e36 next-gen 318i, as that is the same motor.
I have some tire options for free, I can go to a taller tire with some 15" wheels I have, I have some Honda mini-van tires, and some much bigger tires from a Ford Crown Victoria. I think they are 215s or wider, would the extra width make them inefficient due to friction?
I would love to try some 155/80-13 wheels and tires on this car, but with the inline 6 motor that would probably be downright dangerous. I could probably lighten it up a lot with a 4cyl and still have the same level of performance, or greater due to the un-sprung weight reduction. Some people claim to be around 2,000 lbs on the car with extensive weight reductions. I know the 4cyl diff is lighter, but I don't know if 2.93 or better gears are readily available for it.
I know the M3 used a different higher trunk, and the rear window had a shallower angle to it for improved aero, would that show noticeable gains? Could I do it for less than $50 out of plexiglass, making a double rear window and putting spacers on the trunk to lift it?
Glad to be here, I just searched for my Ninja 250 on these forums and was pleased to find several people near 100MPG, that will probably be my main transport if I can afford the $500 back-fees on it any time soon, or bring them down to something more reasonable with a bill of sale stating the price I paid for it ($300, no bodywork, no tires, no airbox, etc).
