stevebez

So why is a shorter diff ratio not a cost effective option if you want better 100+ performance ?

Think the E's gearing runs out at 336km/h so the final drive could quite easily be shortened without compromising top speed and helping 100-200mph performance. Also the effect in the shorter gears is quite small so any traction issues would be only marginally worse - if any.

MKB do a 2.82:1 conversion from the stock 2.65:1

Theoretical in gear speeds are as follows with the 2 final drives...

........stock 2.65........MKB 2.82
............mph................mph
1st.......48.30...............45.43
2nd......79.25...............74.47
3rd......123.09.............115.67
4th......173.55.............163.09
5th......209.10.............196.49

So 0-100mph times should be better as well as accel above 100mph. 1/4 mile will suffer though if you expect a 118-120 trap speed.

Top end suffers too but its still 316kmh !!! (theoretical)

Rgds Steve

P.S. Sorry for the repost but I think this got lost in a prior thread where a war was on the go .... geez lighten up guys !

Bernanke

gearing is always a good option... thats not the problem. the problem is mercedes (unlike bmw) has the gearing programed into the tranny ECU instead of a sensor in the differerential so its not nearly as easy as it is in most cars unfortunately. Afterall, differentials are the "poor man's supercharger" as they say.

stevebez

Hey vrus ....

here is a good comparo from the past ....

Also the 2.82 is the same ratio being used in the E63 and the SL so should be dead easy to source ... and while you change it ... may as well add a Quaife too.

jangy

I explored this idea with my inside man (at MBUSA) when making my mind up about getting the LSD. He strongly recommended against it, unless i planned to take on a huge challenge of playing the ESP/Active safety system modification game. His basic response was that the entire system would be very close to its tolerances and would trigger a "pull back" from the system much more easily. Case in point, all the people who have gone to larger diameter wheels (tire / rim combo) will likely see traction control kicking in MUCH sooner than those that have remained with the stock diameter. As we all know, changing the diameter is an even poorer man's way to change gearing.

Bottom line...can it be done? Yes...is it as easy as changing a part and a sensor / setting? No.

ChicagoX

In my opinion, the approx 10% gain in torque multiplication in the lower gears will be largely offset by the additional shift in the quarter.

Traction willing, the next 'step up' gearwise seems like a better value - more multiplication to offset the time lost on the shift.

ChicagoX

Is this not due to a differential in rollout, interpreted by the TC system as "slip" ?

If rollout differential is kept to a minimum F-R, shouldn't the TC issue be moot?

There may be a potential issue with the Cruise Control or other speed-dependent systems as well.

stevebez

BTW those MPH's above are with 6100 rpms (max HP)... not red line ....

Using 6400 its 47.66 , 78.13 , 121.36 , 171.11 , 206.16

Using 6500 its 48.41 , 79.35 , 123.25 , 173.79 , 209.38

Either of these shift points look like a danm good fit for the quarter.

ChicagoX

stevebez : I was under the impression that the Mph above was at redline.
I stand corrected; those look to be great 1/4 mile numbers.

enzom

Steve - I am not so sure. You may find that you will need an extra shift from 3rd to 4th just before the timing beam. The time you lose for the shift (including boost drop) may wind up netting you little, if any, benefit from the new rear.

stevebez

I think you should make it. Trap speed of 122/124 area is pretty solid. DerekFSU's 10.95 hit a TS of 131.23 ( ) so it may not work for K2+ cars but should be perfect for stock I would think.

If you go 19" and 285's x 30 then it climbs to 125.35 at 6500....