CA400

Question for all of you. I'm going to get my car on the dyno, what gear do you guys test these cars on? I've heard 3rd or 4th gear? What are the pro's and con's from doing it from either gear? Any insight will be very appreciated.

Alex

AhEmGee

In this car you want to use 6th gear. Which has a 1:1 gear ratio .

CA400

Wow, now we are adding 6th gear to the mix.

any other thoughts?

Alex

AhEmGee

Remember when performing a dyno run on a typical dyno, you want to be on the closest ratio to 1:1, to remove the torque multiplying effect of the trans mission's lower gears. In a higher numerical ratio ie higher than 1:1, you will get less accurate dyno figures.
This is a 9 speed transmission , so you will to need to run a higher number gear than an old school 5-6 speed obviously.
These are the gear ratios for this car : ( note 6th is exactly 1:1. )

Gearbox:

Daimler-Benz 9G-TRONIC
Transmission type:automatic
with manual shift mode
Number of gears:

9
Gear ratios (overall):

I
5.354 (16.44)
II
3.243 (9.96)
III
2.252 (6.91)
IV
1.636 (5.02)
V
1.211 (3.72)
VI
1 (3.07)
VII
0.865 (2.66)
VIII
0.717 (2.2)
IX
0.601 (1.85)
R
4.798

GuardianVA

It will depend on a few different things. Using the gear with the closest to a 1:1 ratio will give you slightly higher peak power numbers. If the dyno run is to get a print for just peak numbers, go with 6th, as AhEmGee said. However, if it's for tuning purposes, you are going for the comparative delta over a series of runs, so a lower gear like 5th is fine (and arguably better), because the run will be shorter and the wheel speeds will be lower. This helps with IAT over the series of runs. Some shops will do pulls in both gears: lower gear to dial based on delta changes, and then the 1:1 to give the nice looking peak chart.

jonathan358

Also, just because trans is 1:1, aren't you forgetting the differential?

GuardianVA

Final drive ratio may affect the horsepower peak reading, but will not affect the delta. If you run 6th gear in this car (1:1) with the stock final drive of 3.07, and then shorten the final-drive to, say, 3.27 like the C300, the peak dyno numbers will likely go down very slightly, but not the comparative delta.

alexasa

iTrader: (1)

he's in the 7g however.

GuardianVA

Good point, I didn't catch that either. OP, in your case, I 'd say fourth or fifth gear.