manwithtool Posted July 31, 2018 Report Share Posted July 31, 2018 My son has a 325i E46 Saloon M sport and he cruises at 3000 rpm which equates to 70mph. Yet my 325i Touring and the wifes 325 Convertible (both Autos) do nearly 90 mph at 3000 rpm. Can anyone explain the big difference and should my son think about changing the rear diff to get a slightly higher gearing for Motorways. His engine does feel and little too revvy at 70. Seems to be a few diff's and rear ends on ebay so wouldn't be too expensive to do a swap as we would do the work ourselves. anyone else done this or know what diff I need to look for ? Link to comment Share on other sites More sharing options...
CoupEdin Posted August 6, 2018 Report Share Posted August 6, 2018 Check out http://www.bokchoys.com/differential/GearRatios.htm Thinking of doing similar to cruise at 80 and 2500 revs Link to comment Share on other sites More sharing options...
manwithtool Posted August 7, 2018 Author Report Share Posted August 7, 2018 Cheers CoupEdin, Perfect. I can't see a ratio that will take my sons e46 325 manual from 70 at 3000 rpm to 80 at 2500 ? lowest diff ratio seems to be 2.93 from a manual 330i or 328i . If my maths is correct that will take it from about 70 to 77mph at 3000 rpm. Still a usefull increase without making the lower gears to high. Anything with a 2.93 diff seems to have lower 1st and 2 nd gear ratios. Thanks again Link to comment Share on other sites More sharing options...
manwithtool Posted August 7, 2018 Author Report Share Posted August 7, 2018 Just been on ebay and the list you sent doesn;t include any Diesel options. They seem to have much lower diff ratios. Assuming they still fit one of those might get your revs right down ! Link to comment Share on other sites More sharing options...
manwithtool Posted August 7, 2018 Author Report Share Posted August 7, 2018 Anyone know if a Diesel Diff will fit on a Petrol car. I can't imagine they would have a different rear subframe ? Link to comment Share on other sites More sharing options...
CoupEdin Posted August 7, 2018 Report Share Posted August 7, 2018 Realoem.com is your friend for that type of question Link to comment Share on other sites More sharing options...
