Date registered: Apr 2011
Vehicle: 72 220D , Furd escape, BMW R100RT
Location: West Michigan
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Got a nice 72 220D, Whats a better differential ratio?
I just bought a nice unrusted 72 220D and of course is gutless and winds up at 70. Because I'm a flat lander and plan on driving it on the highway I want to change the rear differential. Mine appears to be a 3.92 ratio. I'm interested in putting a 3.07 ratio from a W116 300SD or a 3.46 ratio from a W123 300D in this car. Are they directly interchangeable? After doing some gear ratio\ratio , ratio x engine speed x car speed calculations The engine at 70\4th gear is going at 3650rpm , with a 3.46it would be about 3200. 3200 rpm is about the speed that the 3.92 turns at 60, which seems to be a nice steady cruising engine speed. I was leaning on putting the 3.46 in the car and if I felt I needed(or could) lower the engine speed abit more, I could put abit taller tires on it..also, I'd use the GPS to find the real speed for speedo differences. However from my calculations with the red line in 3rd gear would be 64, I haven't did the calculations, but with a 3.07 ratio, I could use 3rd gear more from 55-65 and use 4th as an overdrive. I realize, I stress the clutch much more with a 3.07. Anyway , can I interchange the W123 300D 3.46 ration rear end with the W115 220D , and in the extreme, could I interchange the W116 300 SD 3.07 ration with the 220D. I got my data from the ADSITCO site.