318ti.org forum - commuter - RPM's too high. Gonna swap in 2.93's

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- - commuter - RPM's too high. Gonna swap in 2.93's (http://www.318ti.org/forum/showthread.php?t=40474)

commuter - RPM's too high. Gonna swap in 2.93's

Hi - I just bought the car but i do over 150 miles per day, all higway at approx 75 mph and 3500 RPM's is too high.
I'd like to do the 2.93 swap I read in the stickies.
That should drop RPM's to 3000 RPM.

Have any of you guys done this swap but retained the M44? Just curious how much it'll reduce normal accelleration on an already slow car :)

I don't think my car has LSD (as per window build sheet) but I haven't confirmed it hasn't been swapped out by a previous owner. I guess i'll have to jack up the rear and turn the wheels to confirm.

Am I on the right track by looking at these diffs? Should be a bolt in installation (re-use stock output flanges and half shafts) but will need to use E30 diff cover I think.

http://hudsonvalley.craigslist.org/pts/4529756513.html

http://www.ebay.com/itm/BMW-e28-diff...1fc741&vxp=mtr

http://www.ebay.com/itm/BMW-E30-E28-...195089&vxp=mtr

Make sure the size is correct, the 318ti has a small case.

http://i135.photobucket.com/albums/q...ss76/diffs.jpg

Also, I am not sure if you are doing the gearing right, you want a higher gear ratio not lower ratio. (--edit, I was wrong, you want lower) What do you have now: 3.45 or 4.44?

I did this swap and responded on a thread here:
http://www.318ti.org/forum/showthrea...925#post361925

I really liked the change, definitely made it a better highway cruiser.
Also, you are going the correct direction, a 2.93 will lower you RPM's for any given gear and speed. The ratio is input rotations to output rotations.

I swapped in a 2.93 LSD out of an 87 325es so I can't comment on using a e28 diff, but the e30 diff was just bolt in when using the half axles from the e30.

thank you! awesome thread there. that's my plan now :)

Quote:

Originally Posted by derekkg (Post 364359)

Also, you are going the correct direction, a 2.93 will lower you RPM's for any given gear and speed.

yeah I know :) long time drag racer:biggrin:

oh i have 5 speed manual tranny with 3.45 gears :) this guy says he'd sell me the e28 diff. what price should i offer him?

also reading the above picture indicates my current diff is small case and his is bigger case, so by searching here, I would also need:

E30 ABS axles and studs or (optional unless lowered)
E36/5 Output Flanges
E36/5 Output shafts
New locking circlip for the output flanges - no idea what that is

ninja edit - searching says "I can use 318ti flanges with 318ti halfshafts "

when he says "plate" below, does he mean the diff cover (#1 in image below)?

Quote:

For any medium case diff install on the E36/5, you will need a ///M Coupe, ///M Roadster, any Z-series 6cyl plate or E30 (6cyl.) medium case differential plate. Z3 1.9 and small case differential plates from the E30 318 and m3 do not work with this upgrade. (This is essential to mount the diff to the car since the E28 doesnt have the same mount point)

http://i123.photobucket.com/albums/o...20Swap/222.png

Yes, he means #1 in the pic. The pic is the small case unit. You need the plate from the medium case 188 unit.

If you get the 2.93 from an E28, you will need a rear cover plate from an E30 medium case 188 differential (non-325iX unless you want to change the mount bushing)...or the M or Z plates you mentioned in your post.