85 300SD rear end ratio

if you have access to both cars jack up the rear trans in nutral mark the tire and the wheel well tape works turn the tire one revolotion count how many times the driveshaft spins (2.x times you got a 2.06 ect.) for better fuel milage good tires,injector balance and upgrade, diesel purge,filter change and a K+N air filter you'll be good to go! any one of these will gain you something. swaping the rear ends for a higher gear (numarically lower) i would (and have) done the listed things and it's just better all around for the car. I wish i could get about a 3.something gear insead of the 2 gear it came with but mercedes knows more than i do about staying in the powerband of the diesel engine they ENGINEERED! I think going higher will take you out of the powerband and you will not see as much or any differance. Go with the things I listed all that good stuff is sold on this site.