Revs and Road Speed E30 M3

[jb1]

Hi, couple of qns for any E30 experts

Am trying to work out if the Differential has been changed on my E30 M3.

4,000 revs = approx 80mph in 5th

I'm told it might have been changed but I'm not sure given the revs.

It's a track car. Has any one changed the diff for lower top speed, better acceleration? I would be interested in hearing any feedback.

Also don't suppose anyone has a power and torque graph v.s. revs for a E30 2.5 engine they could post?

Many thanks, Jason

[r988]

jb1 said:

Hi, couple of qns for any E30 experts Am trying to work out if the Differential has been changed on my E30 M3. 4,000 revs = approx 80mph in 5th I'm told it might have been changed but I'm not sure given the revs. It's a track car. Has any one changed the diff for lower top speed, better acceleration? I would be interested in hearing any feedback. Also don't suppose anyone has a power and torque graph v.s. revs for a E30 2.5 engine they could post? Many thanks, Jason

Just to clarify, you do mean the M3 Four cylinder 2.5L as opposed to the 2.5L Six cylinder in the 325i.

[agent006]

the diff should have its ratio stamped on it. an LSD will start with S and then have the ratio without the decimal point. So a 3.91 would be S391 and tehn a load of random numbers.

[M3 Mitch]

80 mph at 4000 RPM - this sounds like a non-standard diff to me. I think my car is at about 3700. The 4.45 diff is pretty popular amongst track junkies although for my own taste the 4.11 stock is quite enough.

Having done the maths I really do think you have a 4.45. If you don't like it, you can probably exchange it for a standard 4.11 and get some cash to go with it.

[ian332isport]

M3 Mitch said:

80 mph at 4000 RPM - this sounds like a non-standard diff to me. I think my car is at about 3700. The 4.45 diff is pretty popular amongst track junkies although for my own taste the 4.11 stock is quite enough. Having done the maths I really do think you have a 4.45. If you don't like it, you can probably exchange it for a standard 4.11 and get some cash to go with it.

I suspect you are US based if you are saying the 4.11 is standard. In the UK, the M3 had either a 3.23 or a 3.15 (on some of the Evolution models).

The difference is due to the different gearbox used in the US M3's. In the UK, the dogleg box has a direct top gear (1:1 in 5th).

Ian.

[jb1]

yes is 4 cylinder M3 (and a UK car)

Cool will have a look at the diff next time it is up on a ramp

I reckon it's probably standard though

Cheers

[stevesingo]

Here's my dyno plot from my 2.5 sport evo which is standard aside from Motec engine managment and a Milltek exhaust.



My car has a 3.15 diff and is geared at 22.5 mph/1000rpm i.e 4000rpm = 90ish

Steve

[jb1]

That's great thanks. Looks like mine might have been changed then. Will do some more tests.

How are you getting on with the Mo-Tec?

I had thought of getting one fitted but have heard mixed reports on the effect on engine reliability. How much more does it give you in terms of troque and power? Does it make much difference on the track?

Thanks, Jason

[stevesingo]

The Motec is great. Don't get me wrong though it is only as good as the effort that has gone in to tuning it. Powerstation mapped my car for all loads and engine speeds and that was the easy part. I have personally spent untold hours messing with idle settings, fuel overrun, part throttle response ect ect. Now the car runs great, better than standard in all areas.

As for gains, I didn't do a before and after but the biggest gains are in the mid range with much more go between 3-5k and seems tho go for the redline with more enthusiasm.

Not manages a trackday yet so wouldn't know and provided that it it properly tuned (not too lean) there is no reason why it woulsd affect reliability.

Steve

[stevesingo]

More Motec info here [url]http://autos.groups.yahoo.com/group/M3_EFI_Project/[/url] (you need to register).

If your on standard 205/50 15 tyres then the 3.25 diff will give 3800rpm at 80 and the 320iS 3.46 diff will give 4000rpm at 80
If you tyres are 225/45 16 then 3.25 diff will give 3650rpm at 80 and the 3.46 diff will give 3900rpm at 80

Steve

>> Edited by stevesingo on Tuesday 22 November 20:37

[jb1]

Sounds cool, do you have to be quite techy and know what your doing with a laptop?

And how much did it cost? (If you don't mind me asking)

Thanks, Jason

[stevesingo]

The software (available free from the Motec website if you want to have a look) is pretty simple to operate and as the kit as supplied by Powerstation came with a base map the potentially tricky initial set up is done for you.

Cost is £2000ish plus fitting and mapping. Fitting is simple enough as th Powerstation kit comes with all the harnesses the only difficul area is fitting a new crank trigger wheel to the front pully.

Steve