Quote:
Originally Posted by Frank Reiner
The gear ratios of that box were intended for use with relatively small displacement gas engines, that have low torque at low RPM.
1st gear is very short - 4.46:1
2nd is rather tall - 2.61:1
6th is .84:1
You would use a 3.46:1 final, and in 6th would have an overall ratio of 2.9:1; not too bad, actually. However, starting in 1st would be an overall ratio of 15.43:1, which is very short for an OM603. If you started in 2nd the overall ratio would be 9.03:1, a bit tall for other than level ground.
A gearbox with an ~3.75:1 first, and an ~.81 top gear would work much better.
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I disagree - the 603 has a little flatter power curve than the 617A so revving a little lower at a given ground speed is realistic/comfortable. The 603, .84 overdrive, and stock 3.07 diff from a '82-84 turbo W123 will have very nice highway manners, without a drastic spike in RPM's when downshifting to 5th for more acceleration, climbing a hill when not going real fast in 6th, etc. It probably wouldn't be prohibitive with the late 2.88 ratio, either.
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'82 300CD
"Pearl", the very first turbo diesel 123 coupe
Totaled 11/23/18, rebuild in progress.
'85 300TD, "Artemis".
'78 300D euro, "Ol' Red", mostly retired.
'85 300D, "Gandalf".
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