S52 Swap Goal: 80mph = 3,000 RPM

[Lakis]

Right now, it's 4200rpm!

I live in Utah, long drives and this diff is killing me.

I believe it's a 3.73 or 3.91 LSD. I forget honestly what I bought from the shop.

Anyways- what RPM are you @ when you're doing 80??

thanks

[nrubenstein]

What transmission are you running? What you need is to spend some time playing with a gear speed calculator, like the one at my330i.com. You can figure out exactly what you can get with any combination quickly and easily.

[Dj Buttchug]

hmmmmm want to trade? im running 2.93 in cedar city

[Lakis]

I will be in cedar city next week, driving to Vegas. My tranny is the factory man/5spd that came with 99' M3.

buttchug: what are you @ around 80mph?

[e30e]

I believe on my stock e36 m3 with a 3.23 rear end, I'm at 3500-4000 rpms at 80 mph; that being a 2.93 will be close to 3k rpms. I'll post later tonight, when I go to the gym and hit 80 on the freeway.

[Tchao]

Yep use a 2.93.

I have a 3.15 on ZF and I'm at 3.5k @ 80.

[surebimmer]

If you want 3,000 rpm at 80 mph looks like you'll want a 2.73.

http://www.endtuning.com/gearratios.html

[Dj Buttchug]

I will be in cedar city next week, driving to Vegas. My tranny is the factory man/5spd that came with 99' M3.

buttchug: what are you @ around 80mph?

2500 r3v.

hows your diff? good shape?

[e30e]

As I posted early I was at 80 mph at 3600 rpm on a stock e36 m3 5 speed with 3.23...... sounds like 2.9x will get you close.

[JGood]

On a 24" diameter tire (stock e30 size, such as 205/50/16 or 205/55/15), with a M3 trans, and 2.79 diff, you'll be at ~3100 RPM's at 80mph.

2.93 would be 3300 @ 80

3.25 would be 3600 @ 80

3.73 would be 4200 @ 80

3.91 would be 4400 @ 80

4.10 would be 4600 @ 80. You'd also have a mechanically limited top speed of 122mph, and could probably get there in about 10 seconds :)

[dreamchasin]

I have a 2.79LSD chillen in my shed, but you're in CA, I don't even know where to begin to ship it there.

[nando]

I think you're going to want a 6 speed.

I just don't get wanting to go 50mph in 1st gear...

[Wanganstyle]

I think you're going to want a 6 speed.

I just don't get wanting to go 50mph in 1st gear...

OP needs a 2.79 final drive to do this super cruising thing with a overdrive-less gearbox (zf 5th gear 1:1 is = 4th gear of the e30 original g240/260)

OR he needs a G260 in his car to have an overdrive and then effectively have a 4 speed + overdrive instead of the 5 speed "close" ratio ZF box with no overdrive.

This is a common issue with turbo guys as they cant spool the suckers without load (time) in gear.

calculating with 205/55/15 tire (e30 stock as calculated above)

my own e30 setup:
G260+2.93, 5th gear (.81 overdrive)@ 79 mph = 2700rpm


ZF 5th gear 1:1 + 2.93 @ 3,000 rpm = 71mph
ZF 5th gear 1:1 +2.79 @ 3,000 rpm = 75mph

[Lakis]

I have 215/40/17s in the back.
I like the idea of a 6 spead; just was afraid to visit the cost of one. Although my transmission and current diff are in excellent shape (trans has 32k on it) So I would get decent $ for them/trade.
Switching to a 2.93 would be great on the highway but I would probably lose lots of low end.
If a 6spd is astronomically expensive then the 3.25 sounds like a fair compromise...

[nrubenstein]

A quieter exhaust might also be a solution.