bmwkraftur.is

6-speed and differential upgrade

Conversion done by Brett Anderson of KoalaMotosport
web: http://www.koalamotorsport.com e-mail: brett@koalamotorsport.com

All '89-'94 M5s were equipped with the Getrag 280 gearbox. This is a good, robust gearbox that follows it's lineage back through the E28 M5's virtually identical 280, and the 265 and 260 used in the 535i, 533i, and 6-series variants. Despite a propensity to get a bit "crunchy" in 2nd gear, it can take a lot more power transmitted through it that BMW ever supplied. The 280 in my 475hp E28 M5 Turbo felt as good at 35K miles as any brand-new unit.

The differentials in M5s varied by market. '89-'94 cars sold outside of the USA had the 3.91 limited slip differential. This diff, coupled with the 5-speed's gear ratios, provided a good spread in ratios and reasonable highway cruising.

In the USA, only the '91 cars had the 3.91. Apparently for fuel economy reasons, the 3.73 gearset was used in the '92-'93 cars. Why "fuel economy" was a factor in the country that has almost the lowest gas prices in the world is a bit of a mystery.

In 1995, the last year of E34 production, BMW fitted the Getrag 280/6 6-speed transmission to the M5. The gear ratios are completely different than the 5-speed 280, and the differential gearset was changed to the 3.23 to take advantage of the change. Instead of installing a close-ratio box, the net effect of the 6-speed/3.23 combo is simply an additional overdrive gear. 1st-5th are basically the same as the 5-speed/3.91 combo, and the 6th allows low-rpm cruising. A performance change? No. This was done strictly for fuel economy as well.

Nevertheless, this does not preclude the possibility of re-configuring a few parts to create the best of both performance and economy worlds; enter the 6-speed and either 3.45 or 3.64 combination. These are not common gearsets, the 3.45 comes from various older 7-series models and the 3.64 from the 8-series. Thes gearsets are completely compatible with the M5's differential housing.

I originally used the 3.45, but eventually change to the 3.64. First, compare the numbers for the factory combinations and my combinations:



5-speed
with 3.73 TRANS
& DIFF GEAR OVERALL
GEAR MPH @
3000 RPM MPH @
7250 RPM
1st 3.51 13.09 17 40
2nd 2.08 7.76 28 68
3rd 1.35 5.04 44 105
4th 1 3.73 59 142
5th 0.81 3.02 73 175 Þetta er BARA hratt en svona er blæjan,, þeas bíllinn á möguleika í 280+ raunhraða

(( GULI HVAÐ ))

5-speed
with 3.91 TRANS
& DIFF GEAR OVERALL
GEAR MPH @
3000 RPM MPH @
7250 RPM
1st 3.51 13.72 16 39
2nd 2.08 8.13 27 65
3rd 1.35 5.28 42 100
4th 1 3.91 56 135
5th 0.81 3.17 69 167

6-speed
with 3.23 TRANS
& DIFF GEAR OVERALL
GEAR MPH @
3000 RPM MPH @
7250 RPM
1st 4.23 13.66 16 39
2nd 2.53 8.17 27 65
3rd 1.67 5.39 41 99
4th 1.23 3.97 56 135
5th 1 3.23 69 166
6th 0.83 2.68 83 200

6-speed
with 3.45 TRANS
& DIFF GEAR OVERALL
GEAR MPH @
3000 RPM MPH @
7250 RPM
1st 4.23 14.59 15 37
2nd 2.53 8.73 25 61
3rd 1.67 5.76 38 93
4th 1.23 4.24 52 126
5th 1 3.45 64 155
6th 0.83 2.86 77 187

As shown, the original equipment setup for the 6-speed/3.23 is effectively the same as my car's original 5-speed/3.91 combination. By building a diff with the 3.45 gearset, the effective result is a 7% lower 1st-5th gears and 6th gear taller than the original 5th by about 10%.

The results are excellent for most needs. Acceleration is quicker without having to abuse the clutch, and cruising rpm is noticeably reduced. 80mph in 6th gear is 3,000rpm... very relaxed, yet the 3.8l motor has enough punch to accelerate comfortably without downshifting. Top speed is a theoretical 187mph, certainly more than prudently fast on a public road.


Annars er linkurinn hérna .. http://www.robertlevinson.com/M5_Tourin ... ission.htm

_________________
Sv.H

E30 CABRIO V12 M70B50 ///
ALPINA B10 BITURBO 346 @ 507
E34 550 V12 JML


(OO[][]OO)

http://alpina.123.is/pictures/