Speed with std diff

[Mattp87]

I will be running e36 325 engine and g/box along with a std e30 diff and was wondering what it'll be like speed wise as the car will be a toy rather than a daily driver. lots of drift days and track days rather than long jorneys.

I gotta get an lsd which is why i'm working out what gearing i want now so i can get an appropriate lsd.

[leeparkes]

what ratio is the E30 diff?

[Mattp87]

atm its a standard 320i open diff but been offered a 325i sport lsd, not sure of the ratio tho.

[Jhonno]

Even a 3.25LSD could be classed as short.. The Sport will be a 3.64 or 3.91!

[wullie325i]

the e36 2.5 m50 would need a ratio between 2.93 and 3.25 if using the m50 box aswell.

my choice would me an e30 m3 3.15 lsd.

wullie

[wullie325i]

the 320i diff should make it pull hard from standstill but will rev high on the motorway cruise ect.

i doubt it would last too long either running a m50b25 through it.

[leeparkes]

just use the M20 box.

[stonesie]

Sits at a funny angle though, the M42 box fits and keeps the gearchange in the right place with a 325 gear linkage apparantly...

[Mattp87]

might aswell use the e36 box as it comes with everything and the m20 is destined for smaller lighter things ;) so if i get a 325 lsd what am i looking at max speed?

[stonesie]

It depends on ratio, you need to know what ratio you are getting!

The E36 box will have a 5th gear ratio of 1:1, the same as the 4th gear on E30 boxes because the E30 boxes are what’s known as overdrive gearboxes. This is because in 5th the prop shaft is doing higher RPM than the engine.

[stonesie]

Because im bored i did this for a 1:1 gear ratio

205/55/15 = 845 rev/mile

RPM @ 60mph....................RPM @ 70mph...........RPM @ 120mph
3.64 diff = 3075.8..............3588.43....................6151.6

3.91 diff = 3303.95.............3854.6.....................6607.9

3.25 diff = 2746.25.............3203.96...................5492.5

Started at 60mph out of pure lazyness

[Mattp87]

cheers thats really helpful.
think i'll stick with the e30 diff for the extra acceleration.
anyone got a 325i sport lsd for sale??

[leeparkes]

anyone got a 325i sport lsd for sale??

big bavarian beautys normally have a few

[baptie0]

if you use an e30 sport diff, acceleration is good but its a bit pointless as 1st gear is so low its a waste of time using it.

dont waste money having to buy a diff twice like i did.

3.15:1 is the best ratio to have, either e30 m3 or z3m.

[toby]

http://www.juric.org/mopar/tools/topspeed.php
This should help you calculate the ratio you'll need.

By the way BMW gearboxes are strong!

[Soundstorm]

I made this tool in Excel once. You can select gearbox and differential. It then calculates maximum speeds for each gear and shows a graph.

I'll see where I can upload it. Although it still has some bugs in it. And of course, that's theoretical speeds, not depending on engine power.

Here you go: Link

If you want it in miles, just go to page 'calculations' and put 1.6 as divider.

[Soundstorm]

Hi,

I hade some time and fixed all the bugs in my tool. Added some new features as well.
Download link: http://users.telenet.be/NDTConsultancy/ ... ations.xls

You can add your own gearboxes and differentials if you go to the right tab. 20 of each are possible.
Tell me what you think.

[e301988325i]

I read on here recently that an E36 325 tds has a 2.56:1 rear diff, and the internals can be swapped into an E30 case, involving a full rebuild of course but this might be the answer for some. . .

[e30m30power]

hey,

can u not just run the complete centre from the e36? i have an e30 m30 powered and i am running the larger diff out of a e36 325is, bolted straight in. If it can handle a thrashing from an m30 it can handle your little m50 lol

[baptie0]

bolted straight in? what do you mean?

[e301988325i]

The E36 diff can't be bolted 'straight' in. The E36 diff rear cover mounts to 2 points on the chassis, neither of which is the same position as the single mount of the E30. Z3 diffs are a straight fit. . .

Are the rear covers interchangeable??