Mercedes-Benz Forum banner

What rear axle ratio is best for 617a with 5 speed?

11K views 8 replies 6 participants last post by  Forcedinduction 
#1 ·
If I stick the turbo 617a into the 280CE and still use the 5 speed, what would be the best rear axle ratio? Right now the car has a 3.58/1 in it, but I have a 3.07/1 and a 2.88/1 rear axle in stock that I can swap in. My plans right now are to keep the car, so I don't care if I lose the 2.8L straight six for the diesel. And I think the car will be worth more as a diesel anyway.
 

Attachments

See less See more
1
#2 ·
A 2.88 is too tall for even a 4-speed. You would constantly be shifting between 3rd and 4th, and 5th gear would only be usable above 75mph where the engine is above its 2400rpm torque peak. Even with the 3.07 your 5th gear minimum would be 68mph.

In 5th, your effective ratio would be 2.90 with a 3.58, 2.49 with a 3.07, and 2.33 with a 2.88.
1st is already parking-lot low with a 3.07 and a 617a. Lower diff ratios effectively make 1st a granny gear to it.
 

Attachments

#3 ·
You might get away with the 3.07, but the 3.46 (or the 3.58, since that's what you have already) would work best with the 5-speed.

The 717400 has an OD ratio of 0.84. The engine's torque peak, which is where it runs at its most efficient, is at 2400RPM. That means that, with the 3.58 diff, the cruise speed in 5th is 61mph, while it would be 71mph with the 3.07 diff. However, the engine could also be required to run at full throttle with low RPM, which is really bad for any engine.

My car currently runs a 3.69 diff with a 0.78 OD ratio (bastard 717413) and she does 60mph at torque peak, and 75mph (the maximum speed limit in South Africa) at about 3000RPM. I consider this to be the optimal gearing.
 
#4 ·
There are loads of handy calculators on the interweb that will give you an idea.

Failing that you can always work it out by hand - I could make you a little spreadsheet if you wanted (!)
 
#5 ·
3.07 is the sweetspot with a fivespeed, 2.65 with an automatic fourspeed

i ran a om602 NA fivespeed w201 with a 3.07 without any problems whatsoever (and thats a dog compared to your engine)

and the claim that a fourspeed manual is to tall with a om617A is not what i feel is correct.

thats a torn om616 (72hp) pulling a 300TE on a trailer behind a w115 in fourth gear at 55mph something without much sweat.
why on earth a om617A wouldnt work with a fourspeed and that gearing is beyond me.

i have a turbo converted om617 and used that with a 2.65LSD paired to a fourspeed manual. it was surprisingly fast and easy to drive, and at speed, wouldnt hurt with a fifth gear either.

The sweetspot in my world would be a 3.07 differential. it al depends on how you drive ofcourse, but 3.07 and turbodiesel fivespeed has worked out great for me for city and mostly highway driving.
2.82, 2.65 and esp 2.47 was a bit heavy paired to a fivespeed.


Edit:
3.07 would put you somewhere slight above 2000rpm in 60mph in fifth
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top