MadaboutKitcars

Hi guys, not sure if I am barking up the wrong tree here but I am hoping someone can shed some light. With regard to engine and gearbox etc is the 525 the same as 325?

Thanks Glen

http://www.unixnerd.demon.co.uk/bmw.html

Gen Model Body styles   Engine 

E30 325i  All           M20

E36 325i  All           M50

E34 525i  early Saloon  M20 

E34 525i  late Saloon   M50

E39 525i  All           M54 

I'm assuming that M20's will share a common gearbox, as will M50's. No idea on M54s.

Although the basic engine and gearbox will be the same there's no telling what differences there will be on the engine anciliaries and gearbox ratios. I would look carefully before plumping for an M20 engine and gearbox from a different series...

IMHO

Robin

Glen
I think there will be differences with the gearboxes for sure, as there are differences within the 3 series range itself - some have sport close ratio gear sets, and others do not. Also I think the sump positions could be in different places? I have an M50 and have seen photos of M50s with the oil dip stick in a different place and a very different sump - I put this down to probably being that they came from different series donor cars, but that is only a guess?
As Robin says, do your research before you commit.

I would agree about researching beforehand but the M20 engine and gearbox in my Cabrio were from an E34 525i and I didn't encounter any significant problems (bearing in mind that this powertrain option was never originally intended for the Cabrio !).

As people have already said, I think that the engine and gearbox are fundamentally the same between the BMW 3 and 5 series.

I'm not sure what the ratios are in the 3 series but the E34 525i ratios are as follows

1st = 3.83
2nd = 2.2
3rd = 1.4
4th = 1.0
5th = 0.81

Final drive = 3.73

I assume you'll be using the BMW final drive, but the above ratios worked very well with the Sierra 3.92 diff in my Cabrio as you don't need the long gearing of the BMW (100mph is scary enough let alone 135mph !).

The reason I went this route was that it was far easier and cheaper to find a 5 series donor than 3 series.

Hope this helps!

Simon

Glen

The 3 series E36 ratios are different, as is the final drive:
1 = 4.23
2 = 2.52
3 = 1.66
4 = 1.22
5 = 1.00
Final drive =3.15 using 185 x 65 x 15 tyres.

This is probably more to do with the difference between the M20 engine and the M50, (I think the M20 reaches peak power at higher revs than the M50),
I have calculated that with a 3.38 Sierra diff, and 205/65/16 tyres I can achieve almost identical gearing as on the donor 3 series BMW.
Chris Cunliffe initially used a 3.62 diff with his M50, but found 1st gear was useless (too short, and set off in second), so changed to a 3.38: he is using 205/55/16 tyres.
Simon chose 215/55/17 rim/tyre combination, which have an increased rolling radius and compliment his 3.92 diff.
By carefully matching the engine characteristics, gearbox, final diff ratio and the rim/tyre size you can achieve the type of car/performance you want .

Mike