Not enough Top End & Too much RPM? How do I solve this?

Post Wed Sep 21, 2011 8:53 am

Well just picking up a E30 with a M52 2.8 conversion.

It a 318 that has had all the 325 Sport Running Gear, with the 2.8

Problem I have is that first gear is near useless! and it is revin the nutz off its self on the motorway at 80!

How can I solve this?

Do I need to get a different LSD Diff with a longer final drive?

If so can anyone point me in the direction of what to do.

Thanks in advance.

Regards

Mark

Post Wed Sep 21, 2011 9:32 am

What box/diff have you used?

Post Wed Sep 21, 2011 9:52 am

Sounds like the diff may be short, what sort of revs is it at 70mph? Is it fitted with a slipper for sure then? If it is it will most likely be a 3.91, you might want to think about getting a 3.64 or lower.
This is providing they've used a e30 diff and gearbox.

Post Wed Sep 21, 2011 9:59 am

thats rediculously short if your only getting 80 and its reving its nuts off,gear ratios need changing for sure.

Post Wed Sep 21, 2011 12:29 pm

My brother kevo has quite a few diff ratios in stock. Knows lots about the conversions and ratios etc

Post Wed Sep 21, 2011 1:20 pm

I'm guessing they have retained the E36 gearbox, so the E30 diff ratios are useless. The best diff to source here would be a 3.25:1 E30 M3 diff, otherwise you end up with the expense of rebuilding E36 diff internals into an E30 casing.

On the other hand, the car may have a 4 pot E30 diff still fitted, which will give crazy gearing, but will also break if you give it any hard launches

Post Wed Sep 21, 2011 1:38 pm

You need to find out what gearbox and ratio diff you have to start with.

Post Wed Sep 21, 2011 2:34 pm

e36 gearbox and e30 325 sport lsd

;)

is the E30 M3 Diff the only option?

Post Wed Sep 21, 2011 2:46 pm

whats the ratio of an e36 gearbox? i had an e30 325 3.91 lsd diff in mine and it was ideal for the traffic light grand prix. run out of steam at about 130mph iirc though. the 3.64 was a little more reserved.
has it definately not got the original diff? would that be a 4.1 in a 1.8?

Post Wed Sep 21, 2011 2:58 pm

I bought a 318 touring some years back from Spadge.
It was fitted with a 4.10 diff and a gearbox alledgedly from an E36, had exactly the symptoms you describe. Very buzzy.

Post Wed Sep 21, 2011 5:20 pm

Picking up the car new week, so will get under and have a proper check.

Post Wed Sep 21, 2011 6:18 pm

sound about right e36 box plus e30 diff isvery low gear its like driving round in a lower gear as e36 boxes have no overdrive gear like e30s

Post Thu Sep 22, 2011 8:49 am

An E36 box in fifth gear has exactly the same ratio as fourth gear on an E30.
The choices are to change the box for an E30 one, which IMO is a retrograde step, or to find a more suitable diff.
As well as the US E30 M3 diff, medium case E28 diffs (with a change of backplate) and Z3 diffs are a direct fit.

Post Thu Sep 22, 2011 9:37 pm

So if I'm looking for a Z3 diff..... Which one am I looking for?

Oh and want it to e a LSD

Post Thu Sep 22, 2011 11:20 pm

2.8 used a torsen type slipper. 3.15:1, I think.

Post Sun Sep 25, 2011 11:48 am

I have a 3.15 Z3 2.8 slipper in mine, works well. 80mph is about 3500 RPM with the standard 15" wheels & tyres and an e36 box. It's a while since I swapped it but I think it needed the e30 back plate and flanges swapping over.

Can't e36 compact diffs be used too or did I imagine that?