Changing M3 3.2L Rear Diff Ratios

[m3f_Type H]

Euro Evo 3.2 (ratio: 3.25) shares same sized ring & pinion gears as E34 M5 (ratio 3.73).


Anyone knows if US M3 3.2 shares the same larger diff as Euro Evo M3 3.2? Are there other ratios from US M5 to choose from?


I know there are zillion ratios for M3 3.0 but only one for M3 3.2 (is it true?) so here's another million $ question...


Many thanks & Merry Christmas! http://m3forum.com/ubb/smile.gif

[m3f_eduardo go_61bf44b0e1]

I know that AC SHNITZER had that mod for the 3.2 M3. Why do you need to change the ratios of your car? I have one problem wich i think it could be solved with a mod like this. My car reaches the rev limiter in fifht gear (five speed) on the highway. If i change the ratios could this be fixed?

Would i loose much power?

[m3f_Type H]

Yes, definitely! Simulations showed that with 3.73 diff, stock engine will reach 7,250RPM in 6th gear at max speed. This is lower than 3.23 reaching 7,600 RPM in 5th gear at max speed of 280km/h or so.


Stock Evo M3 with 3.23 diff takes about 130 seconds from zero to max, but with 3.73 it reaches the same speed of 280km/h in about 150 seconds.


With 3.73 diff max speed will increase by ~8km/h to 288km/h only if you have done some good mods (+30PS) to the car. Zero to 280km/h in ~60s & zero to 288km/h in ~130s (yes, over 1 minute for extra 8km/h) for 3.73 in 6th. But with 3.23 diff, max speed stays at 280km/h but again it takes only 60 seconds from zero (in 5th gear)!!


Because E36 body is not as sleek compared to Ferraris & Lambos; these beasts hit ~300km/h under 130 seconds from zero because of better aerodynamics.


Your car with +30PS mods & 3.73 diff should reach 288km/h in 6th at 7,400 RPM before hitting redline http://m3forum.com/ubb/smile.gif

[m3f_eduardo go_61bf44b0e1]

It`s all very clear to me. The problem is that my car is a five speed 3.0 and the rev limiter shows at about 7.300rpm max wich in fifht gear is equal to 270km/h.

That`s my worst nightmare. http://m3forum.com/ubb/smile.gif

Eduardo.

[m3f_Type H]

Oh, in that case you need to use 3.07, 2.93 or 2.79 diff to replace your 3.15 stock diff.


Note max speeds for stock car as follow: 267km/h for 3.15 & 3.07, 266km/h for 2.93 & 265km/h for 2.79 because stock engine is "underpowered".


You can justify use of lower diff ratios & actually get higher max speeds if you have added at least +20~30PS. No more bad dreams http://m3forum.com/ubb/tongue.gif

[m3f_eduardo go_61bf44b0e1]

I dont think that you understood my problem.

I think i have those ~20 or ~30hp gains "available" in my engine because i already have some mods like complete exhaust system, modified air induction and a chip. The problem now is that the car reaches the rev limiter (7300rpm) in fifht gear (270km/h on the speedometer). If i change to those ratios you told me the car would get worse, i mean, it would be easier to reach the rev limiter wich the car already does very easy.

I think what i need is the ratio from the 3.2 wich is higher, dont you think?

Thanks.

Eduardo.

[m3f_Type H]

Without special airbox or cams M3s cannot gain 30HP from induction, chips & exhaust alone (my car gained roughly 12~18HP with foam filter + chip + de-cat + muffler).


You see, rear diff ratios lower than stock 3.15 will give you lower engine speeds at any given wheel speed. This means lower engine revs for any given speed so engine will hit redline later for each gear change. Agree?


I quoted lower max speed figures for lower diff ratios not because your car runs out of engine RPM but because your engine is running out of power in lower regions of the same power band because of use of lower diff ratios; i.e. less torque & power at any speed.


When you have less mechanical advantage with low ratio diffs, e.g. cars like Lambos & McLaren F1, you can reach 330km/h! But it is possible only if your engine has enough torque & power... you can gear ordinary cars like that but they'll not even hit 250km/h... the wind sucks up all the power from the engine before redline coz before redline wind drag already equals to driving force generated by your engine so it cannot rev up.


You are very safe because you will never run out of revs in 5th gear with 2.79, 2.93 & 3.07 at max speeds because aerodynamic drag stops your car faster than your engine generates power to speed & rev up to redline.


Look, you need +350HP engine to run out of revs at max speeds with lower diff ratios.

[m3f_eduardo go_61bf44b0e1]

So...if you were in my position, what would you choose:

leave the ratios stock or change?

If you decided to change, what would be your choice?

Thanks.

[m3f_Type H]

If you really have ~30HP gain over stock, 2.93 gives you max top speed, best acceleration & torque over whole speed range.


Have you dyno tested your car? What numbers?


You need lower diff ratios only if you have radical changes like adding a kompressor.


Ciao & Merry X'mas! http://m3forum.com/ubb/biggrin.gif

[m3f_eduardo go_61bf44b0e1]

I am looking to find SantaClaus to see if he`s going to buy me that G-POWER kompressor kit for my car. But the bastard is being hard to find, hehehehe. http://m3forum.com/ubb/smile.gif http://m3forum.com/ubb/smile.gif

Merry X`stmas to all of you.

Eduardo.