[redz06]

Just wondering what a reliable torque limit is for the N55 6MT and the rest of the drive line, including guibos, torque tube, differential, differential, and rear axles? I did a search and could not find any threads that answer this question.
What clutch should be used that will fit the bell-housing and transmit 480 lbft of torque?

Answers for above should consider that full power standing starts are not a consideration and be sure to state whether you are talking about flywheel torque or wheel torque.

[redz06]

I guess no one here knows this answer. I was assuming that owners running bigger and dual turbos know this answer for an N55 driveline. My bad.

[darkfires102]

Hi, these forums are dead for N55. It's pretty much the same as N54 on E90 chassis on how much power each component can handle. F30 forums are more alive for N55, however MT is very rare.

You can do a 550i clutch or 335is clutch for up to 450 lb-ft/stage 2 clutch, however, the weakest link on N55 is the gearbox itself. The synchros cannot handle the power transmitted through them. You'll probably lose 2nd or 4th gear even with stage 2+ tune.

The then weakest links are
Driveshaft to diff CV joint
Axles
Differential

Needs big single turbo, 700+ HP type. Not very common for N55 builds. The M/T is weaker and people typically swap to N54 M/T from the get-go on big power builds.

A FBO car easily puts down about 350 HP and 500 LB-FT torque.

[oVeRdOsE.]

N55 was not produced as much as n52/54 in the e90 chassis.

FXX chassis got way more N55, from 1 series to X.

[redz06]

Originally Posted by darkfires102

Hi, these forums are dead for N55. It's pretty much the same as N54 on E90 chassis on how much power each component can handle. F30 forums are more alive for N55, however MT is very rare.

You can do a 550i clutch or 335is clutch for up to 450 lb-ft/stage 2 clutch, however, the weakest link on N55 is the gearbox itself. The synchros cannot handle the power transmitted through them. You'll probably lose 2nd or 4th gear even with stage 2+ tune.

The then weakest links are
Driveshaft to diff CV joint
Axles
Differential

Needs big single turbo, 700+ HP type. Not very common for N55 builds. The M/T is weaker and people typically swap to N54 M/T from the get-go on big power builds.

A FBO car easily puts down about 350 HP and 500 LB-FT torque.

So if I understand, the torque capacity of the 550i or 335is clutch will be 450 ftlbs. Will this be flywheel torque or rear wheel torque?
The torque capacity of the 6MT gearbox synchros is less than that, so lets say 400 lbft at the flywheel for reliable service. If this assumption is wrong, please correct me.
So for the driveshaft/guibos, differential, and drive shafts the maximum torque capacity should be above 450 lbft at the flywheel. Is that correct?

The reason I am asking all of these questions is that I am getting pretty sick of the N55 engine fault codes and am considering swapping my 100k N55 engine for an LS3 crate engine, so I need to consider what other component swaps are necessary to allow the LS3 engine to work without breakage. It seems like the E90 N55 transmission and clutch must go, which is a shame as the great gearshift on my BMW N55 transmission and clutch must go.

I still need more data to decide on my guibos/driveshaft, differential, and axle shafts. Go or stay?