How much power can a 135i N55 transmission handle?l

[txgrown]

I have been searching for a while now and have come up empty. Does anyone know what the 135i N55 trans càn handle in terms of pôwer? Thañks.

[Ian///M]

501.2974 HP

[Rowdy]

Originally Posted by Ian///M

501.2974 HP

How did you come up with that one? Some mathematical formula? Or is that what yours was making before it came apart?

[cooler2442]

The DCT can only handle a max of about 410whp and 470wtq. Manual can handle more.

[txgrown]

Where are you guys finding these numbers?

[cooler2442]

Originally Posted by txgrown

Where are you guys finding these numbers?

Experience. DCT starts slipping at around 410whp and 470wtq.

[bogart]

I agree with those numbers.

[GeeRam]

Originally Posted by cooler2442

The DCT can only handle a max of about 410whp and 470wtq. Manual can handle more.

Really......

Info I've read says the DCT is rated at 600Nm whereas the 6MT is only rated at 430Nm.

I know of a 135i in the UK where the gearbox gave up after 50k miles behind a remapped N55.


It's the reason BMW don't offer the manual trans bolted to the back of the 335d.

[cooler2442]

Originally Posted by GeeRam

Really......

Info I've read says the DCT is rated at 600Nm whereas the 6MT is only rated at 430Nm.

I know of a 135i in the UK where the gearbox gave up after 50k miles behind a remapped N55.


It's the reason BMW don't offer the manual trans bolted to the back of the 335d.

Yes really. The people pushing those numbers have the DCT slipping while the manual has no problems. BMW's ratings have never really been truly accurate.

[Freon]

You don't hear many stories of people breaking either transmission, so it would seem the answer is, "more than anyone has bothered to put in their 135i."

A lot of this has to do with drivetrain slop (dual mass flywheel, driveshaft isolator, bushings, etc), tires, and abuse. I wouldn't worry too much until you are running on slicks with a solid flywheel, unsprung clutch, and beating the hell out of it.

[alexmtl_135i]

Originally Posted by GeeRam

Really......

Info I've read says the DCT is rated at 600Nm whereas the 6MT is only rated at 430Nm.

I know of a 135i in the UK where the gearbox gave up after 50k miles behind a remapped N55.


It's the reason BMW don't offer the manual trans bolted to the back of the 335d.

600Nm = 440lb/ft torque, which seem to be inline with what cooler said.

Not sure about the manual rating, 430Nm seems very close to the base engine spec of 400Nm torque.

[geared]

no way an auto coming out of factory BMW cars handle more power than a 6spd....not happening with today's tech/price ratio.

[hyper1]

maybe you should ask the question to a profession mechanical engineer at BMW.
if not possible.....a good shop that built performance transmission.
just my opinion

[Pete_vB]

Originally Posted by txgrown

I have been searching for a while now and have come up empty. Does anyone know what the 135i N55 trans càn handle in terms of pôwer? Thañks.

This is probably the wrong question. As others have noted, transmissions are rated in torque, not power, as torque is the limiting factor (assuming proper cooling). Regardless of the rating on the 6MT, we know the factory delivered it in cars with up to ~370 ft/lbs (500 Nm) wheel torque in the 1M. We also know based on experience that this is conservative, and the transmission will take significantly more than 450 wtq (with reduced durability).

Your question asked about power, however, and power at a given torque is a function of RPM, and hence how the motor is built/ tuned. If the motor is built and tuned for high rpm power but limited peak torque, then 450 ft/lbs at 7000 rpm would give you 600 whp and be perfectly safe for the transmission. Of course most N54/ N55 motors are tuned exactly opposite this, with more torque than HP, but this illustrates how high power can be made with limited peak torque.

The logical conclusion of this philosophy was shown in F1 V8s before the 18,000 rpm limit, where engines were making well north of 750 hp at almost 20k rpm, but peak torque was only a little more than 200 ft/lbs, allowing tiny and light weight 7 speed gearboxes that weigh well under 100 lbs.

[Guardian]

Originally Posted by Pete_vB

This is probably the wrong question. As others have noted, transmissions are rated in torque, not power, as torque is the limiting factor (assuming proper cooling). Regardless of the rating on the 6MT, we know the factory delivered it in cars with up to ~370 ft/lbs (500 Nm) wheel torque in the 1M. We also know based on experience that this is conservative, and the transmission will take significantly more than 450 wtq (with reduced durability).

Your question asked about power, however, and power at a given torque is a function of RPM, and hence how the motor is built/ tuned. If the motor is built and tuned for high rpm power but limited peak torque, then 450 ft/lbs at 7000 rpm would give you 600 whp and be perfectly safe for the transmission. Of course most N54/ N55 motors are tuned exactly opposite this, with more torque than HP, but this illustrates how high power can be made with limited peak torque.

The logical conclusion of this philosophy was shown in F1 V8s before the 18,000 rpm limit, where engines were making well north of 750 hp at almost 20k rpm, but peak torque was only a little more than 200 ft/lbs, allowing tiny and light weight 7 speed gearboxes that weigh well under 100 lbs.

Excellent explanation.

[ian.j]

i might be wrong but people talking about slippage, this would not be gearbox failure, more clutch. in my experience of gearbox failure it goes bang and you lose some teeth which rattle around and before you know what hit you the box is scrap.

i am well aware it is easy to up-rate a clutch in a manual and not so easy on the dct

[hyper1]

Originally Posted by Pete_vB

This is probably the wrong question. As others have noted, transmissions are rated in torque, not power, as torque is the limiting factor (assuming proper cooling). Regardless of the rating on the 6MT, we know the factory delivered it in cars with up to ~370 ft/lbs (500 Nm) wheel torque in the 1M. We also know based on experience that this is conservative, and the transmission will take significantly more than 450 wtq (with reduced durability).

Your question asked about power, however, and power at a given torque is a function of RPM, and hence how the motor is built/ tuned. If the motor is built and tuned for high rpm power but limited peak torque, then 450 ft/lbs at 7000 rpm would give you 600 whp and be perfectly safe for the transmission. Of course most N54/ N55 motors are tuned exactly opposite this, with more torque than HP, but this illustrates how high power can be made with limited peak torque.

The logical conclusion of this philosophy was shown in F1 V8s before the 18,000 rpm limit, where engines were making well north of 750 hp at almost 20k rpm, but peak torque was only a little more than 200 ft/lbs, allowing tiny and light weight 7 speed gearboxes that weigh well under 100 lbs.

well done
thanks

[GeeRam]

Originally Posted by ian.j

but people talking about slippage, this would not be gearbox failure, more clutch.