MyE28.com DEV

i saw a diff posted a while back tht would allow the car to be at 2000 r's at 80 mph does anybody know what gear ratio tht is? and how much they go for? i do alot of highway driving and want some better mpg's

Damn, probably a 2.79 or something out of a 325e!

Lugging the engine at freeway speeds doesn't necessarily equal better fuel mileage...

a stock 3.25 is fine, you wont see any more, MAYBE a 3.07 at the extreme, but once you start undergearing it, the engine will need to work harder causing more lug/load = less fuel economy
going to a 2.93 or a 2.79 (i think those were the correct ratios) is just too much gear.

I wouldn't go much lower than a 3.25. Sometimes I wish there was another gear, but that's so infrequent.

Welllllll.....for what it's worth, I put a 2.79 in my black beastie for the trip to Chattanooga for the fest back in May. And yes, the car was a bit more sluggish. But not so bad that I had to change it out the minute we got home.

BUT! I could get to 70mph in 2nd gear, and that was nice with but one shift followed by a good long pull

AND! the trip to Chattanooga averaged a bit over 27.5 mpg with my best tankful = 29.5 mpg. The overall average included a lot of stop and go around town driving, while we did some touring and sight seeing on that big ol' mountain they have there.

SO! There is a better level of fuel economy available.

Just so's you' d know,

Andrew.

the cost and time of install isnt worth that extra 1 MPG that you will only see on the highway, not to mention there is no need to drag 2nd out to 70 MPH ever, thats why gear ratios were made, to keep the engine speed to vehicle speed in a symbiotic relationship similar to the tzetze fly and the south african hippopotamus.

Taller gears help, but not much. Most of the fuel consumption is how much work is being done, not how many rev's are being turned. Back in E12's, 5 speeds only added 1 or maybe 2 to the MPG numbers over 4 speeds. It will make the car quieter and perhaps nicer to drive on that level, but don't expect anything like a straight line relationship on gears and gas mileage.

A bit of an OT story, I at one time had a mid 80's GM pickup at work with a overdrive auto (wow!!!) Granted it had a carb and was obviously geared for EPA mileage, but it turned into such a dog on the freeway I'd shift it into 3rd instead of D. Literally, I almost couldn't accelerate in high, with the lousy carb, it would stumble and jerk until I put my foot in it and it downshifted.

I wouldn't expect a 535 to do this, but still, I wouldn't expect to ever pay for the replacement diff, even if you did a pick and pull buy on it.

A 2.93 from an eta will almost do that.....especially with an auto top gear of .78 or so...

Jay3

I've got a 2.93 if you want for $300. perfect condition.

What the hell? I put my 2.93 lsd on the board, nobody replied! Not a soul! Heck, I didn't even ask a price, probably would have taken best offer. Guess I'll hang on to it.

Bimmerguy2002 wrote:not to mention there is no need to drag 2nd out to 70 MPH ever, thats why gear ratios were made, to keep the engine speed to vehicle speed in a symbiotic relationship similar to the tzetze fly and the south african hippopotamus.

Tell that to the engineers who made the Z06 capable of 120 115 mph in 3rd gear.

Oh wait, you know more than they do. :-/

Also, lots of cars are built to top out 2nd gear above 60 mph so that the published 0-60 times will only include one shift--makes for better marketing.

If one were going to be doing several hundred miles of highway driving per week, picking up a 2.79 might be worthwhile.

-tammer

Tammer in Philly wrote:

Bimmerguy2002 wrote:not to mention there is no need to drag 2nd out to 70 MPH ever, thats why gear ratios were made, to keep the engine speed to vehicle speed in a symbiotic relationship similar to the tzetze fly and the south african hippopotamus.

Tell that to the engineers who made the Z06 capable of 120 115 mph in 3rd gear.

Oh wait, you know more than they do. :-/

Also, lots of cars are built to top out 2nd gear above 60 mph so that the published 0-60 times will only include one shift--makes for better marketing.

If one were going to be doing several hundred miles of highway driving per week, picking up a 2.79 might be worthwhile.

-tammer

i mean for a practical car (specifically an E28), a daily driver, there is no need to drag 2nd out that far, i dont care about super cars because thats a whole 'nother ball game son.
Unless you are on the track there is no need to drag 2nd all the way to the rev limiter unless you are screwing around with some ricer, someone else with a turbo car here had a tall gear in the back that hit 130 in 3rd, thats a completely different animal from your everyday M30 car
Dont bother replying, i already know your lame responses, so save your time.