C63 GEARING FOR ACCELERATION
02-02-2013, 01:39 PM
#1
Super Member
Thread Starter
C63 GEARING FOR ACCELERATION
Ok so I think most people on here have a pretty good idea on the basics of gearing and torque multiplication. What I've been looking into and researching is the wheel torque getting to the ground in each gear and the RPM's we are hitting after each shift in relations to our wheel hp/torque power band. The way to find your torque multiplication is taking the ratio of the gear your in and multiplying it by your final drive ration which is a constant while the gear ratios obviously change from gear to gear. Then i believe you multiply that number by your torque to get the wheel torque your putting to the wheels after its been multiplied by your transmission and final drive ratio. I believe you also have to divide it by your wheel radius to gets real final number but i will keep this out of the equation as it won't change much and can vary by aftermarket wheels/tires
Obviously MB and AMG really couldn't wait to replace the old 5 speed with the new 7Gtronic and later the MCT 7 speed. They obviously wanted it for better gearing for acceleration so your not stuck in unnecessarily tall gears for a while as well as improving mpg with a really tall last gear to get revs down on the highway. The 7G and MCT has really nice spread ratios to keep the car moving and its power band. The one problem i have looking into this is why did MB/AMG use such a tall final drive ratio. Its about 2.82
When accelerating in your car pay attention to your rpms or if you want to be safer just watch a youtube video of the c63 accelerating after every shift at redline its drops its shift to about 5000 rpm. We are able to get away with it because of the WIDE power band of the m156 and ability to make power at any rpm but the reality is that not where peak power is and in the higher gears your spending precious time at these lower rpms. Looking at my dyne graph I'm putting about 470 to the wheels and at 5000rpm I'm putting down about 415. If i was able to shift and only drop to 5500-5600 id be putting down 450+ before hitting 470 and flat lining to redline. I understand the logic of not having the gears to short down low so you can better use the traction available with the crazy torque of the m156. MB/AMG seems to know this as well as the flagship model the SLS has taken a very different approach using a very similar engine. They used a taller first gear with very similar gearing after that but a much higher final drive ratio at the end of 3.67
Lets take a look at the torque multiplication of each in relevant gear (minus 6/7
C63 GR FDR TQ Mult SLS GR FDR TQ Mult
1 4.38 2.82 12.35 1 3.40 3.67 12.48
2 2.86 2.82 8.06 2 2.19 3.67 8.03
3 1.92 2.82 5.41 3 1.63 3.67 5.98
4 1.37 2.82 3.86 4 1.29 3.67 4.73
5 1.00 2.82 2.82 5 1.03 3.67 3.78
As you can see they solve the 1/2 gear traction problem by simply using a lower gear ratio with the shorter final drive ratio and then the tq multiplication gets better gear by gear with a significant difference between the 2 cars. After you watch the c63 video watch an sls video and see that the revs only drop to right under 6,000 instead of 5,000 and the sls is in its peak power band the whole time.
What do ya think of my rant? anyway we can change our ratios to see what the results are? i know the els wouldn't work since its a DCT not a MCT and all other m156 cars have the same ratio as the c63 ..... except the SL63 body with the m156 had a 3.06 hmmmmmmmmmmmm
Obviously MB and AMG really couldn't wait to replace the old 5 speed with the new 7Gtronic and later the MCT 7 speed. They obviously wanted it for better gearing for acceleration so your not stuck in unnecessarily tall gears for a while as well as improving mpg with a really tall last gear to get revs down on the highway. The 7G and MCT has really nice spread ratios to keep the car moving and its power band. The one problem i have looking into this is why did MB/AMG use such a tall final drive ratio. Its about 2.82
When accelerating in your car pay attention to your rpms or if you want to be safer just watch a youtube video of the c63 accelerating after every shift at redline its drops its shift to about 5000 rpm. We are able to get away with it because of the WIDE power band of the m156 and ability to make power at any rpm but the reality is that not where peak power is and in the higher gears your spending precious time at these lower rpms. Looking at my dyne graph I'm putting about 470 to the wheels and at 5000rpm I'm putting down about 415. If i was able to shift and only drop to 5500-5600 id be putting down 450+ before hitting 470 and flat lining to redline. I understand the logic of not having the gears to short down low so you can better use the traction available with the crazy torque of the m156. MB/AMG seems to know this as well as the flagship model the SLS has taken a very different approach using a very similar engine. They used a taller first gear with very similar gearing after that but a much higher final drive ratio at the end of 3.67
Lets take a look at the torque multiplication of each in relevant gear (minus 6/7
C63 GR FDR TQ Mult SLS GR FDR TQ Mult
1 4.38 2.82 12.35 1 3.40 3.67 12.48
2 2.86 2.82 8.06 2 2.19 3.67 8.03
3 1.92 2.82 5.41 3 1.63 3.67 5.98
4 1.37 2.82 3.86 4 1.29 3.67 4.73
5 1.00 2.82 2.82 5 1.03 3.67 3.78
As you can see they solve the 1/2 gear traction problem by simply using a lower gear ratio with the shorter final drive ratio and then the tq multiplication gets better gear by gear with a significant difference between the 2 cars. After you watch the c63 video watch an sls video and see that the revs only drop to right under 6,000 instead of 5,000 and the sls is in its peak power band the whole time.
What do ya think of my rant? anyway we can change our ratios to see what the results are? i know the els wouldn't work since its a DCT not a MCT and all other m156 cars have the same ratio as the c63 ..... except the SL63 body with the m156 had a 3.06 hmmmmmmmmmmmm
02-02-2013, 01:44 PM
#2
Super Member
Thread Starter
That came out horrible.
C63 GR FDR TQ Mult
1 4.38 2.82 12.35
2 2.86 2.82 8.06
3 1.92 2.82 5.41
4 1.37 2.82 3.86
5 1.00 2.82 2.82
SLS GR FDR TQ Mult
1 3.40 3.67 12.48
2 2.19 3.67 8.03
3 1.63 3.67 5.98
4 1.29 3.67 4.73
5 1.03 3.67 3.78
C63 GR FDR TQ Mult
1 4.38 2.82 12.35
2 2.86 2.82 8.06
3 1.92 2.82 5.41
4 1.37 2.82 3.86
5 1.00 2.82 2.82
SLS GR FDR TQ Mult
1 3.40 3.67 12.48
2 2.19 3.67 8.03
3 1.63 3.67 5.98
4 1.29 3.67 4.73
5 1.03 3.67 3.78
02-02-2013, 01:53 PM
#3
MBWorld Fanatic!
Do we share our rear end with any chrysler cars, I'm sure they have gearing options. Only issue is ECU/TCU programming, not sure if the current vendors can change it.
02-02-2013, 07:40 PM
#4
Member
they don't need traditional rear gears with a 7 speed trans. a 4.38 1st gear is steep and anything over 12 for a street car is a lot, why do you think C starts in second? because shifting down to first with a steep gear is abrupt and then it shifts to second to fast for comfort.
numerically lower gears are also inherently stronger pieces as well. it's a lot easier to break 4.10s than 2.73s. more teeth on the same ring size means smaller/thinner teeth.
besides, you answered your own question. each gear in the trans is lower than the sls which compensates for the higher rear gear all the way up to fifth.
so what's the issue anyways?
numerically lower gears are also inherently stronger pieces as well. it's a lot easier to break 4.10s than 2.73s. more teeth on the same ring size means smaller/thinner teeth.
besides, you answered your own question. each gear in the trans is lower than the sls which compensates for the higher rear gear all the way up to fifth.
so what's the issue anyways?
02-03-2013, 12:27 AM
#5
I find the gearing to be perfect. Even with just headers, the gearing is low, 1st gear is spinning and second will spin if you hit on it hard enough.
You have to remember the SLS was designed with the DCT tranny that shifts very fast...
When the C63 came out with the 7G, it doesn't shift anywhere close to the DCT.... IF you had the shift points of the SLS it wouldn't have time to shift if 1st went to 2nd at 6000rpm, you would be banging off the rev limiter.
Even with the shift points how they are now, anyone with lots of HP will tell you they have to manually shift the 7G when racing because its not fast enough and will get caught on the rev limiter.
You have to remember the SLS was designed with the DCT tranny that shifts very fast...
When the C63 came out with the 7G, it doesn't shift anywhere close to the DCT.... IF you had the shift points of the SLS it wouldn't have time to shift if 1st went to 2nd at 6000rpm, you would be banging off the rev limiter.
Even with the shift points how they are now, anyone with lots of HP will tell you they have to manually shift the 7G when racing because its not fast enough and will get caught on the rev limiter.
