e30 m52 2.8 diff ratio too low 3.25???

[LagunaE30]

i've got a m52 2.8 and i'm running the 328 zf 5 speed gearbox, m20 flywheel, m20 clutch and a s3.25 lsd.

just want to now what diff other guys are running with the m52, i personally feel the s3.25 is a little bit too sluggish off the lights but gives me a nice cruising speed on the motorway.

i'm considering changing the diff for something which will be a bit more leary and aggressive, any ideas what ratio to go for?

[Motorhole]

Stock E36 is 2.97 IIRC. I've gone 3.15. 3.25 should be good I reckon. What wheel/tyre size you running? Lemme know and I will run the numbers for you

[eko]

Ive got 2.8 box,lightened M20 flywheel and 3.25 lsd.
Mine gets off ok

[LagunaE30]

i'm running 16x9 wheels tyre size is 225/45/16

dont get me wrong it isn't slow off the lights, i'm running a lightened m20 flywheel so it revs up quite well but to be honest i'd prefer it to be a bit more rapid off the line, it does give a good smooth power throughout the rev range and then really starts pulling towards the higher rpm's.

i'm mainly around town so i hardly get into higher revs mostly low rpm's so i think a higher ratio diff would suit me better, is anyone here running a 3.64/3.73?? and can comment on what it's like to drive around town and on a longer journey , motorway perhaps?

[leeparkes]

Im running a 3.46, its great round town with frantic acceleration but very tiresome on motorway runs.

[Motorhole]

i'm running 16x9 wheels tyre size is 225/45/16

dont get me wrong it isn't slow off the lights, i'm running a lightened m20 flywheel so it revs up quite well but to be honest i'd prefer it to be a bit more rapid off the line, it does give a good smooth power throughout the rev range and then really starts pulling towards the higher rpm's.

i'm mainly around town so i hardly get into higher revs mostly low rpm's so i think a higher ratio diff would suit me better, is anyone here running a 3.64/3.73?? and can comment on what it's like to drive around town and on a longer journey , motorway perhaps?

Ah bollocks, left the spreadsheet on my work computer. Will run the numbers on Monday. But 225/45/16 is sensible enough.

There's a guy on youtube, StoneyX. He has/had a 3.64 diff in his track car with the 328i 'box and he said it topped out about 125mph. Good for track, not so good on the motorway! I'd imagine he'd be doing about 4000rpm at 70mph with that diff...

[Motorhole]

As promised, here are speed/rpm charts for the various diff ratios, with the E36 328i ZF 'box and your 225/45/16 tyres. These naturally assume that my data regarding gear ratios etc is good:

[Supafly]

I'm on a 3.46 with a 328 box too and it's great around town and acceleration is a spot on compromise I would say. However, motorway speeds have you constantly wishing for an extra gear. I've considered the six speed box but talk of it being weak have put me off.

[bss325i]

I'm on a 3.46 with a 328 box too and it's great around town and acceleration is a spot on compromise I would say. However, motorway speeds have you constantly wishing for an extra gear. I've considered the six speed box but talk of it being weak have put me off.

They are not weak, bit of a myth that one.

[e30s50b30]

I was on the 3.64 4000 rpm at 70 and got beat by a Volvo v70 t5 topped at about 130 in the last car which was not well made a huge pile of a Sh...t job . Acceleration was mental but once you overtake u go nowhere ! I'm currently looking at a diff too wanting that 3.25 !

[Green]

How accurate are these figures as I've had my clocks past 140 with a small case diff?
(Although thinking about it there must be some sort of inaccuracy between the wheels and the speedo that would cause it to read higher)

Haven't had to pleasure of maxing out the rev range with my 3.91 though.

[Motorhole]

Provided the data is correct regarding gear ratios (which I plucked off the net), the main error in the numbers will come from the assumption that the distance between the edge of the rim and the tread is exactly the tyre profile as a percentage of tyre width, and that the tyre width is accurate. As we all know, there are variations within tyre sizes depending on manufacturer, model etc.

The graph also refers to 225/45/16 tyres. But in all honesty, the difference in rolling diameter between, for instance, 195/55/15 and 225/45/16 results in only a small difference in the speed at a given rpm (~2%).

Also bear in mind that your speedometer will typically over-read by around 5-10%. If you use an E30 'box rather than an E36 'box (as these numbers assume), the graphs will change significantly for a given diff ratio too, given the overdrive 5th gear.

[e301988325i]

You also need to account for the 3% slip factor, the tyres are not keyed into the road surface like a rack and pinion.

On stock wheels and tyres my speedo is reading + 7mph at indicated speeds over 115mph, compared to satnav speedos.

[DanThe]

You really dont want to change to a shorter ratio diff than 3.25 for a road car, I use a 3.38 on my track car and it does my head in driving on A road/motorway, tyres are smaller though 205/50/15

[Supafly]

Thanks for the heads up regarding the six speeder BSS325i.
Is there much physical difference between the e36 5 speed and 6 speed box. As I think I would be very happy with an overdrive 6th gear for cruising.

[magpie]

what's needed to fit a 6-speed box ? and what car do you get the box from ?

[Supafly]

I'm not sure myself. I think the box may be longer so change of prop etc and also may be heavier???
As for cars, I'm aware of the e36 m3's not sure about any others though...