BMW E21 Swapped M42b18 Diff Prob.

[7oss El Leel]

Hello Everybody
i'm new here
i don't own an E21 but i'll isA
it cost a lot of money Here in Egypt (around 4000 usd to get 318i that Runs fairly good )

so
my mate just swapped a M10 with a M42b18 in his 318 E21
which comes from an Euro 318is E36
and a Getrag 220 Gearbox (Manual 5 speed)
so he runs on a 3.91 diff

and she's very fast (brutal acceleration) on 1st , 2nd & 3rd
then 4th and 5th the car is too heavy
140kmh comes after a struggle on 5th @ 5000RPM
which is toooooooo slow
the car can't even go faster than 140 kmh

is a 3.64 diff will fix this Prob. ???
Thanks In Advance

[nas80]

The car the engine and box came from had 3.45

Try using 17" wheels.. unless you have a 3.64?

[7oss El Leel]

he runs a 3.91 diff
and 16'' Wheels

[nas80]

3.91 good acceleration but no top speed. V.max is roughly 120mph at redline in 5th

Maybe 3.64 + 16" will be ok i think. But If you had 3.45 then top speed would be about 140mph

[Duracel79]

140kph and 5k revs. Sounds more like the E36 ecu looking for a speed signal, forcing the ecu to run limp mode with limited revs.

Don't know how to sort it but simplest would be a remap with speed signal requirement removed. Otherwise looking at abs signal etc which would be a nightmare.

Hope this helps

Ben

[Jeroen]

Agree, that or mixture messed up, especially because it performs well in lower gears I'm pretty sure the diff won't be the cause.

[nas80]

Ah. I thought that he wasnt hitting the limiter. But yep if its obd2 he cant go over 5k im sure these came in obd1 guise though? if not then maybe he could use the e30 318is loom and ecu?

if it is e36 obd2 then you will need a speed signal to the ecu.. i.e hall sensor and tooth wheel somewhere.