[djgandy]

So a few questions on the N54/335 and some in general.

Transmission

6MT
What is the rough torque limit on the standard manual transmission clutch set up?
Is the 6MT set up used in the 335i the same as the one used in the 330d? The BMW part numbers are different but the manufacturer id is the same. This box is used in the 550i too and quite a few other higher rated cars.
Would it be fair to assume that the reason the 335d didn't come in MT is because the 6MT set up cannot handle that much torque and it wasn't feasible to use a larger box / clutch set up?
Or would it be because they would never sell any as the upgraded clutch/flywheel would make an awful daily drive (or expensive to manufacture)?

6AT
Any idea why the diesels got the higher torque boxes despite the 6AT seeming to hold up pretty well under tuning? The 325d has the same box and torque as the 335i. Is this just a bit of luck that the box holds up / very conservative engineering from ZHP?

7DCT
What's the torque limit for this? 400 lb·ft?
335is has overboost to 370 lb·ft so I assume this is not a problem.

Tuning

What is the best way to stop the torque drop off from 4.5kRPM+ on the N54?
Is there a way without going single turbo?
Why does the torque drop off so much?
Do you just have to resign to the fact that the N54 will never be a 'revvy' engine? (by no means do I mean that it has a low red line, just that it doesn't make its best power up the top)



References

http://en.wikipedia.org/wiki/BMW_3_S...Specifications

335d
6AT (GA6HP26Z) - http://www.realoem.com/bmw/showparts...16&hg=24&fg=05

335i
Clutch - http://www.realoem.com/bmw/showparts...27&hg=21&fg=05
6AT (GA6HP19Z) - http://www.realoem.com/bmw/partgrp.d...64&hg=24&fg=15
6MT (GS6-53BZ/DZ) - http://www.realoem.com/bmw/showparts...26&hg=23&fg=05

330d
Clutch - http://www.realoem.com/bmw/showparts...34&hg=21&fg=05
6MT (GS6-53BZ/DZ) - http://www.realoem.com/bmw/showparts...26&hg=23&fg=05
6AT (GA6HP26Z) - http://www.realoem.com/bmw/showparts...16&hg=24&fg=05

N57 model
6MT (GS6-53DZ) - http://www.realoem.com/bmw/showparts...66&hg=23&fg=05

550i
6MT (GS6-53BZ) - http://bmwfans.info/parts-catalog/E6...sion_gs6_53bz/

[phil200tdi]

The manual can handle big power/torque it's the clutch that becomes the weakness.

The 335i box is the same fitted to the E60 m5 manual available in the USA.

The power drops off as a result of turbo efficiency range. The only way to reduce this is to tune the car for a more progressive curve (at the expense of power) or fit a bigger turbo.

[djgandy]

Originally Posted by phil200tdi

The manual can handle big power/torque it's the clutch that becomes the weakness.

The 335i box is the same fitted to the E60 m5 manual available in the USA.

The power drops off as a result of turbo efficiency range. The only way to reduce this is to tune the car for a more progressive curve (at the expense of power) or fit a bigger turbo.

OK. So you'd just end up limiting your low end torque so your top end feels more powerful and you don't wreck your clutch.

The new M3/M4 seems to have solved the power drop off a bit, although power still drops off from 5500. Any idea how they have done this with a twin set up? Are the stock 335i turbos just tiny? I guess they'd have to be to give decent torque at such low rpms?

I'd like to get an E93 DCT and give it a bit more guts, but I'd prefer not to mess with the DCT box if possible and the clutch upgrade kit is very pricey too. Hence I'd like to see more power up the top end and not so much torque at the low end. If I could get 400lb/ft all the way to 6kRPM that would be ideal ~450hp. I'm guessing that is probably beyond the limits of the stock turbos though?