Sorry about that, he wasn't wrong, I was for not including that in that thread it was assumed that the stock ECU was in place. I should have commented on that.

 

...............For Ben or anone from Evosport regarding the MKB sport differential. MKB apparently has signed an exclusive contract in the US for the next 2 years with Renntech. We all know what that means as far as prices go. Are you aware of this contract and does it have a bearing on your ability to continue to sell the MKB sport differential?

..............Secondly, since you sell the MKB differentials and the EGS controller, do you have any info regarding the issues being discussed on this forom? Specifically, any numeric info from KB in germany regarding improvements in 0-60 or quatermile times if any? Thanks.

Ted

 

245/45/17
221bhp@5700
232 lb-ft@3000
redline is 5800

 

wuz the EGS controller and kb?

 

wuz the EGS controller and kb?

.........KB=mistake. Should be MKB
........EGS controller as I understand it is the electronic unit that controls traction, wheelspin etc. It turns out that changing the diff on your Mb is the easy part. Reprogramming the EGS controller so that ESP and tractyion control can understand what happened to your car is the problem. Otherwise ESP goes nuts and thinks that your car is spinning out of control. Therefore rear differential adjustment in in earlier MB's without traction control is no problem. Since the advent of traction control, this has becopme more difficult. I spoke with the people at Bergwerks yesterday and it turns out they have abandoned their rear differential adjustment project on newer Mb's because they can't figure out how to reprogram the EGS controller. The only people I know in the USA that can ACTUALLY ACTUALLY change your diff and reprogram your EGS controller or sell you a new one are outfits affiliated with MKB.

Ted

 

Others here are making excellent points regarding tuning issues. From a straight mechanical perspective... here are the calculated numbers for your car.

Tetza supplied data:
245/45/17
221bhp@5700
232 lb-ft@3000
redline is 5800
gearing 3.95,2.42,1.49,1.00,0.83 diff 3.07
max test speed for each gear is: 38,62,100,131,131

Understand that I am using a mathematical model to calculate the following information. Also, I do not know what the factory tire size is. I don't know if the above is stock or aftermarket. Using the above supplied size I calculate 25.68" tire diameter. Now, size can vary from tire model to model and this is for a new tire, if they are worn by 1/8th inch the diameter is 1/4 less. Any slippage is also not calculated.

So, with the above lawyer like disclaimer (I am not a lawyer ) Here are the calculated speeds:

3.07 gear, 5800rpm
1 = 36.5mph
2 = 59.6
3 = 96.9
4 = 144.3 (unlimited)
5 = 173.9 (unlimited)

3.27 gear, 5800rpm
1 = 34.3
2 = 56.0
3 = 90.9
4 = 135.5 (unlimited)
5 = 163.3 (unlimited)

Rear Wheel Torque, in pounds feet, using 20% drivetrain loss. In each gear, first number is at torque peak of 232tq @ 3000rpm, second is torque, at power peak of 204tq @ 5700rpm.

3.07 gear
1 = 2251 1979
2 = 1379, 1212
3 = 849, 747
4 = 570, 501
5 = 473, 416

3.27 gear
1 = 2397, 2108
2 = 1469, 1291
3 = 904, 795
4 = 607, 534
5 = 504, 443

RWTQ increase going from 3.07 to 3.27 gears in this application:

1 = 146, 129
2 = 90, 79
3 = 55, 48
4 = 37, 33
5 = 31, 27

Honestly, for this relatively small gain, I would think a better choice for improving your 0-60mph times would be an increase in torque converter (TC) stall. A 500rpm increase is quite reasonable and would IMO give a better result. I can't say for certain how the ESP would react but it should be tolerated. On a car with a locking TC there is very little tradeoff. The Lexus croud is almost unanimously happy with a TC change. A TC change would cost about $500 for the stall change and the R&R labor (probably about 4 hours) total cost around $1000.

 

1st - does not impact our ability.

2nd - working on it (problem is the info we have gotten from 3rd parties is not real)

 

If this mod was installed on a 55 engine with the limiter still intact, would I actually see a drop in top speed or no, since the 55 can easily attain 155 anyways. Also, assuming there is no loss in top speed, would the car be slower in any points in the powerband, affecting(slowing) quarter mile or 0-100 times?

 

I cannot answer your top speed question but I can give you a partial answer to your acceleration question(s).

The rate that a vehicle accelerates is a function of the amount of force acting upon the resistance to that force. By changing gears you will have more force (torque) available in each gear BUT (assuming no change in redline) that gear will max out at a lower MPH.

Example. If you car previously hit 37mph in 1st gear and after the change will redline at 34mph in 1st gear... your car will be quicker from 0-34 but SLOWER from 34-37mph. Same applies from second, third, 4th and 5th gears. Using the previous data I listed it would be: 0-34 quicker, 34-37 slower, 37-56 quicker, 56-60 slower, 60-91 quicker, 91-97 slower, 97-131 quicker (speed limiter) Over all the car is quicker, no question, feels stronger, has more force for 94% of the range.

 

Thanks

 

.................For an upgrade that costs$5K, it is too bad there isn't adequate infor mation from the vendors. Nonvenbdors seem to have more info and even then the information so far can be summarized as..........."if you get the sport differential, your car MIGHT go faster." Obviously, this is not enough info with which tp dish out $5K. I am certain that the vendors will sell more of these sport differentials if they provide more like is traditionally done for other performance products.

Ted

 

Ignoring the discussion of shifting points, all this talk is about how lower (shorter) gearing will increase acceleration. It is certain, however, that there is a point where lower gearing will cause a car to be slower, not quicker (e.g., my truck is much quicker in its normal gear range than it is in "low" range; you can imagine that a powerful car with a 10:1 axle ratio would not be nearly as quick as it would be with a "normal" differential). I think there is a fine balance between power and gearing that needs to be struck in order to optimize acceleration. Intuitively, it seems that greater power requires lesser mechanical advantage. Can any of you comment on optimum gearing? It simple has to be a function of power and weight, but I do not have the engineering acumen to figure it.

 

I agree. I did what you did, but went a bit further with my method of calculations for whether I should go to 1:3.46 gears on my C43AMG (stock is 1:3.07).

- Taking published test values for acceleration (from Car & Driver), measured torque curve, and known stock gear ratios, I created a spreadsheet relating speed to time to RPM at 100 RPM increments; interpolating torque @ each increment.
- Then calculated an altered force @ the wheels with shorter gears [yes, taking into account also that the car hits redline sooner ].
- Then from that calculated the reduction in time it would take to get through each previous rpm/speed increment with the increase in force @ the wheel, using basic physics calculations [formula evolved from the "Physics of Racing", aka 'PhoRS', text floating around out on the net ... and don't forget mass is in slugs not pounds if you try this yourself! ].

The end result was a realization that I'd reduce 0-60 time by only about 0.2 seconds. I was entering into this hoping it would prove to be close to a second.

It didn't seem worth the $4K-$6K at the time. But I'm beginning to think about it again. It would help if it was a limited-slip rear. Maybe that, plus a K&N filter, plus maybe even a chip ... that should spruce things up.

 

The MKB diff IS limited slip

 

I think it is important to identify a goal for the upgrade. If you are looking to shave a second off of 0-60, maybe a pulley kit (underdrive?), intake, optimized cams, port matching, or chip is the way to go. If limited slip and better gearing for turns on road courses are the goal, this would be the right upgrade, 0-60 improvements realized or not.

I think you could shave a second off you 0-60 for less then $5k.

I want to change the rear diff because the gearing doesn't feel right through medium turns, I hit redline before the end of the turn in second, third is to high, I bog then have to rebuild momentum. Just not getting optimized power applied at the right points.

 

c43amg, nice effort and a good example of the potential complexities in such a comparison. Your calculations are good and support my suggestion of a modified torque converter is a better means of achieving quicker 0-60 times. A torque converter core plus apx $300 for re-working plus removal and re-installation (R&R) should drop 3-5 tenths off 0-60 times for around $1000. I would be happy to assist anyone here with the work... just PM me.

 

.................I have checked into the torque converter and was made to understand that these are not available for MB's. Is my info incorrect. I'm interested.

Ted