1989 6 cylinder BMW 26 mpg highway

[nubie]

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).

[DamageX]

looks pretty fine for a $200 car. I wouldn`t be surprised if your actual MPG is better than what it says on the gauge. I don`t think 13" wheels will fit on the front of the e30 3-series. If you have the 14"x6" wheels maybe you could find 175/70 tires, but 185/65 are probably a better compromise between traction/handling and economy.

[nubie]

Originally Posted by DamageX

looks pretty fine for a $200 car. I wouldn`t be surprised if your actual MPG is better than what it says on the gauge.

Interesting, I think the speed is accurate, I check by setting the computer to chime when I hit a certain speed (Will set in 1mph increments up to 120+ I think), then setting the cruise control and running by a radar speed sign.

That leaves the calculations for the injection pulse width suspect, or the accuracy of the analog guage. I am afraid I don't have the proper harness for the in-dash computer, so it isn't displaying the average MPG currently.

Originally Posted by DamageX

I don`t think 13" wheels will fit on the front of the e30 3-series.

True, I haven't looked into smaller front brakes, although a 4 cylinder car may be a better place to start. I don't understand why un-sprung weight is such a hard concept to grasp for the majority of the population. I live 45 minutes from what could be called a city, and half the cars/trucks in town are on some kind of chrome monstrosities.

Originally Posted by DamageX

If you have the 14"x6" wheels maybe you could find 175/70 tires,

That is a good idea . . .

Originally Posted by DamageX

but 185/65 are probably a better compromise between traction/handling and economy.

I agree, I would love 185/65-14 all the way around, I like the look of the ones I have now. I probably would be fine with those in the front, but I would like some 195/60 in the rear, but on a 6.5 inch wide rim so the tire sidewall looks the same front and rear. 195 is the stock tire width, I am not sure of the aspect off-hand, just that it is around 2 inches taller than the 185/65-14s.


Modifications I would love:

Pedal power or electric hybrid for stop and go or "fast-food" drive thru. I was stuck in Taco Bell today for a while and wound up restarting the car two or three times.

Honda S2000 or Miata drivetrain (I have seen a 2.0 block from some kind of SUV that is supposed to bolt up to the Miata head/transmission with a little work.) Lighter, plenty of power, even from the stock Miata, if I lighten the car up. Installing a Miata engine would be a good place to start I think.

Urethane rear subframe and trailing arm bushings ($160 shipped on eBay, I keep watching the auction every re-list). I think the rear suspension isn't what it could be, I get squeaking and some odd rear steering, I think one or both of the subframe bushings are torn out. I packed them with strips of timing belt and put a half a hockey puck on top of them, they move around less, but it still can't be good.

Lose the power steering, cuts a lot of weight and complexity. If I am feeling masochistic I can put in an e36 rack with a quicker ratio for better steering feel. Go with 175 or 185 tires in the front paired with a light 4cyl and I am sure it will be livable.

Get rid of the oil cooler, I am not sure what it is doing to help, but then the dog days of summer aren't here yet. Maybe replace it with a water/oil intercooler I have from a VW. Changing to a 4cyl would let me get rid of it no problem.

Mini Alternator with low output. I already have HID headlights, supposedly once lit they draw 35w apiece. Or switch to a battery drain system and only charge at home, with the alternator for emergency backup?

Clean up the front end with covers for the vents and radiators. Maybe even movable air dams.

Keep air out from under the car, some folks run a lower lip from a Volvo, looks dumb but available for $x instead of $xxx.

I have a B/W security camera I picked up for $1, and a in-car screen I bought for $10 I believe, it has a mirrored option so I could use it as my mirror and ditch the side mirrors. I already took out the powered antenna and used a plastic hole plug from the hardware store to cover the hole, I think they are $0.45 or something less than a dollar.

This car has a rain drip rail along both sides of the windshield, I think you can fill it in with a plastic or rubber piece and get cleaner airflow. This is something the first VW GTi was purported to use in Europe/The UK.

The hood has a fairly big panel gap on each side, there is an M3 weatherstrip that fills the gap for better airflow.

I am not averse to moon covers or wheel fairings.

A titanium exhaust is out of the budget, but I think a single exhaust instead of Dual is lighter. Obviously that isn't legal without an engine swap, the catalytic converter is a OEM only California required item with dual in and dual out.

[320touring]

Hey welcome, and congratulations on driving the right sort of car

looking through your thread so far a few things spring to mind..

1. The Eta diff (2.93) is too long to work correctly with the m40/m42 4cylinder engines- Ideal ratio for them would be about 3.64 if you didnt mind losing some accelleration

2. If you used an m42 out of an early (pre 1996) e36 (92 onward) the gearbox has a 1:1 5th so would work with the 2.93.

3. The ideal setup for a 2.93 diff would be to build a 2.7 stroker m20 engine- Basically use the 525e (eta) bottom end with a 2.0 m20 head. This would give you approx 180BHP, and a torque curve that starts at 1000rpm- and levels off at max torque from 1700-6000rpm. Essentially build a torque monster to pull that diff. Several folk I know of manage 35+ UK MPG with "Spirited" driving using this setup.

4. 13" wheels will not clear standard e30 Discs/calipers on the car. Minimum wheel size is 14". Car came as standard with 195/65/r14 on the 14" bottle top alloys. I'd suggest fitting 195/50/15- gives a smaller rotating mass, better steering feel and cheap tyres

5. Oil cooler removal on the m20 is simple- just fit the oil filter adapter from a 2.0 m20- It doesnt have the takeoff for the cooler pipes. Cooler itself is a couple of bolts in the front valance and 2x 24mm fittings at the oil filter.

6. if you're doing the rear beam- Please fit Genuine BMW (Lemfroder) bushes. They last better than anything else,a dn its such a pig of a job to do..

7. The e30's biggest issue is its cD of 0.36 compared to the e36's cD of 0.30, so time invested in cleaning up the aero should pay off hansomely- especially if pulsing and gliding at higher speeds

8. I'm happy to source and ship any bits you may need- e.g. m42 engines/2.0 m20 heads/oil filter bits etc, as as far as I can see you dint get either of these cars over there?

keep up the good work though- more folks shourld drive these rather than 3.8v6 FWD trash that seems to be the marketplace norm over in the US!

Neil

[nubie]

Originally Posted by 320touring

Hey welcome, and congratulations on driving the right sort of car

looking through your thread so far a few things spring to mind..

1. The Eta diff (2.93) is too long to work correctly with the m40/m42 4cylinder engines- Ideal ratio for them would be about 3.64 if you didnt mind losing some accelleration

2. If you used an m42 out of an early (pre 1996) e36 (92 onward) the gearbox has a 1:1 5th so would work with the 2.93.

3. The ideal setup for a 2.93 diff would be to build a 2.7 stroker m20 engine- Basically use the 525e (eta) bottom end with a 2.0 m20 head. This would give you approx 180BHP, and a torque curve that starts at 1000rpm- and levels off at max torque from 1700-6000rpm. Essentially build a torque monster to pull that diff. Several folk I know of manage 35+ UK MPG with "Spirited" driving using this setup.

4. 13" wheels will not clear standard e30 Discs/calipers on the car. Minimum wheel size is 14". Car came as standard with 195/65/r14 on the 14" bottle top alloys. I'd suggest fitting 195/50/15- gives a smaller rotating mass, better steering feel and cheap tyres

5. Oil cooler removal on the m20 is simple- just fit the oil filter adapter from a 2.0 m20- It doesnt have the takeoff for the cooler pipes. Cooler itself is a couple of bolts in the front valance and 2x 24mm fittings at the oil filter.

6. if you're doing the rear beam- Please fit Genuine BMW (Lemfroder) bushes. They last better than anything else,a dn its such a pig of a job to do..

7. The e30's biggest issue is its cD of 0.36 compared to the e36's cD of 0.30, so time invested in cleaning up the aero should pay off hansomely- especially if pulsing and gliding at higher speeds

8. I'm happy to source and ship any bits you may need- e.g. m42 engines/2.0 m20 heads/oil filter bits etc, as as far as I can see you dint get either of these cars over there?

keep up the good work though- more folks shourld drive these rather than 3.8v6 FWD trash that seems to be the marketplace norm over in the US!

Neil

1. / 2. Thanks, I was aware of that. I do have the 3.73 diff, which would be better than the 4.10 that the 4cyl cars come with. Although I am not happy with the medium case diff on a car that only needs a small case, adds weight.

3/5. We have 325e popular here, no oil cooler, although if the block is machined to accept the oil filter, I can probably just use my VW fitting if the thread is the same (I have a lot of water-cooled VW parts). There is a 520i, perhaps the same 2.0 engine you mention.

4. I can almost get 13" wheels them on the rear with no modification, a tiny bit of clearance grinding to the corner of the caliper. I would love 13" bottlecaps on the car. I don't mind modification, I did find a thread with a guy running a special 13" (for racing?), and all he needed to do was grind a little for steering joint clearance. As for brakes, I can have the rotors turned down and move the calipers in, or use smaller calipers. I would probably run a 14" with 175/60, or a 185/50 if I can find them. I think 175/65 is $43 apiece, it is really difficult to cross-shop different tire sizes online.

6. I was planning on Urethane bushings from $66 a pair, I don't want any shimmy back there if I am going drifting. I need a lathe, I could make a dozen rear bushings from urethane for the same cost as one set of pre-made ones.

8. The M42 came in maybe a 1991 only with the 318iS, but being rare and good cars I can't find them for $600 or less like the 325i and 325e. For a couple years there wasn't a 318i at all here.

I don't have any money for a m42 swap, especially not with parts shipped from overseas. If a complete M42 car lands in my lap for $400 - $500 I might consider it. I should spend my money on the Ninja 250 to really save on gas.

I have an Audi 80 2.0 8v motor that would probably work great, I don't have the longitudinal engine mounts or exhaust, but I think I still have the oil pan and oil pickup tube (it was in a VW Rabbit GTi for a while). No Rear drive transmission for it, maybe a Suzuki Samurai RWD transmission? I know the Diesel is the same trans mount points, and there is conversion parts for that.

Alternatively maybe a 4cyl e36 would be a better starting point for ecomodding.

Wondering what the Cd of an e30 with no mirrors is, also if removing the greenhouse and using a teardrop cockpit would be worth the trouble. I would love a pilot only open cockpit with a roll bar.