Rev matching M52

[Rob175kks]

Hi guys,

I have an M52 engine conversion with an e30 325i diff, which seems fairly common here.

Does everyone with this setup have to heel & toe on the downshift from high revs? Or are my engine & diff miss-matched in some way i don't understand?
(if I don't heel & toe, I lock up the rear and slide)

Cheers, Rob

[jmc330i]

What gearbox has been used?

[Rob175kks]

It's a 328 box, the one that was originally with the engine. What other (better) options are there?

[ross_jsy]

The problem is you are using too low a ratio diff for that box, thus magnifying the effect of engine braking.

You need say a 3.15:1

[jmc330i]

^^^ This.

[Rob175kks]

Cheers guys.
I've just checked my paperwork and it's supposedly got an 3.64.1 ratio diff. Is that the standard 325i diff?
Whatever it's got, it makes the car very lively & quick off the mark. I do like it but I have to be really on the ball with heel toe to not lock up the rear, I've had a few hairy moments on track!!

What can I nick a 3.15:1 ratio diff from?

[ACJJ619]

Z3's have the same rear end as an E30 so any of those diffs fit. Most of the 6cyl Z3's have lower ratios so I got a nice 3.09 from a 2.8L Z3. As a bonus, a lot of the Z3 diffs are Torsen

[Brianmoooore]

Cheers guys.
I've just checked my paperwork and it's supposedly got an 3.64.1 ratio diff. Is that the standard 325i diff?

The E30 325i came with ratios of 3.64, 3.73 and 3.91 (and a 3.46 on some ancient stuff), depending on model, so you already have one near the right end of the range for your application.
It gives an overall gearing ratio in fifth which would be the same as a 4.49 fitted behind an E30 gearbox - not greatly different from the 4.45 fitted to auto versions of some 316i, 318i and 320i models.