RE: E28 Diff swap...

[Thi VanAusdal <tvanausdal@xxxxxxxxxxxxx>]

> I would rather have a quick car than a fast car, [it does 125
> pretty easy] so what ratios should I look at? The ole' 
> 4:11's? AND, can 'I'
> do this? Or is it something that a 'trained professional' 
> needs to do...
> 
> Oh, I have an 1988 528e 5 speed, 143hp?
> 
> >I did the swap from 3.25 to 3.73 on my '87 535is and love it.

The big thing to remember is that your biggest compromise with
a shorter gear is not the tire-shredding first gear, not the
top speed change, but cruising speed noise - do you want to 
turn too many revs there? 

I had a 3.90-geared '78 323i w/2.7e motor.  With the four-speed,
it would go through 205/60/13s like nobody's business in the low
gears and was ridiculous on the highway.  I was turning ~3700 rpm
at 70 mph.  When I dropped in the 325e 5-speed, that dropped to
like 3000 rpm.  It was still quick because of all the massive
torque of the 'e' motor in top gear, but the revs were bearable.
And I could go almost 120 instead of 105 (5500 rpm on a stock 'e')
then.

My suggestion would be to do this change.  A 4.11 car would have
an unusable first gear (you'd drop the clutch and shift in, like,
2 seconds at, oh, 20 mph at redline!) and top gear would be a little
short for the six-cylinder.

Go with a 3.73 at the most.  LSDs are plentiful (yeah, I think I just
saw an E30 325is, why, in my driveway! and all over the road! :) )
and, well, I guess there's not much in between anyway except a 3.45:1
which may not even exist in the application you need.

The torque curve of the super eta motor will make highway driving a
breeze with the 3.73; just point and squirt, as they say.  No more
4th gear downshifts!

 - thi vanAusdal

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