M42club.com - Home of the BMW E30/E36 318i/iS
DISCUSSION => Engine + Driveline => Topic started by: megz2000 on August 06, 2020, 04:33:11 AM
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i have e30 m42 turbo with stock Getarg transmission and 3.91 differential unfortunately my top speed is 188 km i want change it to reach more speed but i dont know what differential code will be suitable for me .
does any one can help me or have the same issue ?
attached picture for 5th gear rpm
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Hello
I don't think you have stock 318is E30 transmission
https://e30goodies.com/gearing-calculator/
based on the data given by you i think you have a E36 Getrag 220 transmission coupled with a 3.91 will give a top speed that you mentioned
https://www.e30zone.net/e30wiki/index.php/Differential here you have all the diff ratios just play with the numbers personally i would go with 3.25 or even a lower ratio 2.93
Antother alternative is to get the stock E30 Getrag 260 / Getrag 240
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Yeah, it definitely sounds like ratios are not stock in there somewhere. I have done ~210km/h with the G240 transmission and a 4.10 rear diff.
I do not know much about the G220, but the G240 is actually pretty good in that it is relatively lightweight and can handle a surprising amount of torque. Some guys with built NA M30 engines run the G240 and it seems to hold up well, so a turbo M42 should be fine too as long as you are not dumping the clutch too mcuh!
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+1 on the Getrag 220. It was the stock 5-speed on later M42 & M44 motors, the ratios are significantly shorter. I believe that the 220 used a direct drive 5th gear. The 240 is an overdrive 'box with an 0.8:1 5th gear ratio. A Getrag 240 with the M42 pattern bellhousing should be cheap, and they can handle a fair amount of torque in the lightweight E30.
With the wider 240 gears, I'd probably go with a 3.15 or 3.23, whatever was cheapest. You could also run larger circumference wheels, they'll drop your final drive ratio.
I actually happen to have both a 240 and a 220 in my garage, PM me if you wanted any firsthand specs.