[MatthewLC]

I'm wondering if anyone has gone down or explored this path?

Some background, my car is need of a new clutch/flywheel (clutch is slipping due to tune and my flywheel recently started rattling).

Started doing some research and it seems as though the S55 6spd clutch and flywheel can easily handle 600wtq with no issues and still has oem driveability. Using this flywheel requires the use of the S55 6spd trans due to the output shaft length required for the clutch/flywheel combo. Started looking around and found a local dismantler parting an F80 m3 with 3000miles and offered me the trans at a ridiculous price, so this really got the wheels turning for me.

I've done some research on real OEM and google and it seems as though the clutch/flywheel/trans "should" bolt up to the n55. My concern is the overall length of the transmission? Anyone know if the dimensions are the same as F30 6spd trans? Or have a method to measure or share some overall dimensions for either trans? I'm concerned about the driveshaft length and it doesn't seem like the F80 driveshaft can work in the f30 without swapping the diff? Also are output flanges the same or can they be swapped?

I'm sure the the first comment is going to be "just go aftermarket clutch and SMF" but that is not an option for me. I have no interest in having any of the rattle associated with the SMF and would rather spend more on a solid OEM set up. My ultimate goal is 500wtq to redline with a larger turbo set up (top mount or bottom mount kit) which I believe this clutch/flywheel combination should easily handle.

Open to any input, I hope I don't end up being the guinea pig for this...lol

[upsidedownfunnel]

Another easier option would be to retrofit a 550i clutch and flywheel in which is a direct fit. It would obviously feel OEM.

[ceedawg]

Originally Posted by upsidedownfunnel

Another easier option would be to retrofit a 550i clutch and flywheel in which is a direct fit. It would obviously feel OEM.

This is the smartest thing to do 1000%

[terryd5150]

Originally Posted by MatthewLC

I'm wondering if anyone has gone down or explored this path?

Some background, my car is need of a new clutch/flywheel (clutch is slipping due to tune and my flywheel recently started rattling).

Started doing some research and it seems as though the S55 6spd clutch and flywheel can easily handle 600wtq with no issues and still has oem driveability. Using this flywheel requires the use of the S55 6spd trans due to the output shaft length required for the clutch/flywheel combo. Started looking around and found a local dismantler parting an F80 m3 with 3000miles and offered me the trans at a ridiculous price, so this really got the wheels turning for me.

I've done some research on real OEM and google and it seems as though the clutch/flywheel/trans "should" bolt up to the n55. My concern is the overall length of the transmission? Anyone know if the dimensions are the same as F30 6spd trans? Or have a method to measure or share some overall dimensions for either trans? I'm concerned about the driveshaft length and it doesn't seem like the F80 driveshaft can work in the f30 without swapping the diff? Also are output flanges the same or can they be swapped?

I'm sure the the first comment is going to be "just go aftermarket clutch and SMF" but that is not an option for me. I have no interest in having any of the rattle associated with the SMF and would rather spend more on a solid OEM set up. My ultimate goal is 500wtq to redline with a larger turbo set up (top mount or bottom mount kit) which I believe this clutch/flywheel combination should easily handle.

Open to any input, I hope I don't end up being the guinea pig for this...lol

Any updates?

I'm looking to swap an M4 6MT into an N55 435i so I can go with a big single turbo.

The stock 6MT the F32 came with probably wouldn't live well in that world.

[thejeremyman9]

Originally Posted by terryd5150

Any updates?

I'm looking to swap an M4 6MT into an N55 435i so I can go with a big single turbo.

The stock 6MT the F32 came with probably wouldn't live well in that world.

The 6MT can handle power the only "weak link" is the 1-2 syncro

[terryd5150]

Originally Posted by thejeremyman9

The 6MT can handle power the only "weak link" is the 1-2 syncro

I appreciate the perspective, but I'm not sure how that isn't a restatement of the concern.

Big power = no transmission.

Seems like the S55 M4s are getting into the +900whp range with upgraded clutches, so that transmission must have better power handling capabilities.

Plus, it must be dimensionally close to what the N55 6MT is as the F82 is essentially a nicer version of the F32 body.

[thejeremyman9]

Originally Posted by terryd5150

I appreciate the perspective, but I'm not sure how that isn't a restatement of the concern.

Big power = no transmission.

Seems like the S55 M4s are getting into the +900whp range with upgraded clutches, so that transmission must have better power handling capabilities.

Plus, it must be dimensionally close to what the N55 6MT is as the F82 is essentially a nicer version of the F32 body.

So is your concern handling power/torque, or with grinding gears, especially the 1-2 shift? Those are not the same thing... two totally different concerns based on different transmission components. The common syncro issue has nothing to do with the transmissions ability to handle power.

Also curious to know how the S55 transmission "must have" better power handling capabilities as compared to the N55 one, aside from anecdotal evidence based on S55 cars making more power? Is there documentation on the transmission internals?

[terryd5150]

Originally Posted by thejeremyman9

So is your concern handling power/torque, or with grinding gears, especially the 1-2 shift? Those are not the same thing... two totally different concerns based on different transmission components. The common syncro issue has nothing to do with the transmissions ability to handle power.

Also curious to know how the S55 transmission "must have" better power handling capabilities as compared to the N55 one, aside from anecdotal evidence based on S55 cars making more power? Is there documentation on the transmission internals?

I'm really not certain what the disconnect is here.

I get the synchro is the failure mode, trust me, but that's still an internal transmission component failing and rendering the transmission useless.

You seem to categorize this differently for some reason (?), as if a gear or shaft are the only items that can fail and "rightfully" qualify as a transmission failure?

I'm not certain what value splitting those particular hairs is creating?

As far as the power handling capabilities of the S55 6MT, that's simply empirical data. If you're looking for me to qualify that for you, I'd suggest this isn't the thread for that.

[thejeremyman9]

Originally Posted by terryd5150

I'm really not certain what the disconnect is here.

I get the synchro is the failure mode, trust me, but that's still an internal transmission component failing and rendering the transmission useless.

You seem to categorize this differently for some reason (?), as if a gear or shaft are the only items that can fail and "rightfully" qualify as a transmission failure?

I'm not certain what value splitting those particular hairs is creating?

As far as the power handling capabilities of the S55 6MT, that's simply empirical data. If you're looking for me to qualify that for you, I'd suggest this isn't the thread for that.

The distinguishing factor is i have never heard of a transmission "failing" due to a syncro issue. It just slows down the shift speed; the transmission is still completely usable. So, it's not really a "failure mode" as you put it as it would not render the transmission useless.

Also, you opened with:

"I'm looking to swap an M4 6MT into an N55 435i so I can go with a big single turbo.

The stock 6MT the F32 came with probably wouldn't live well in that world."

So once again, the syncro concerns have nothing to do with going big single turbo. You then reiterated the focus on "big power" in your subsequent posts. So my point is that I have never heard of a N55 transmission not holding power.

So yeah, there is a huge difference between a syncro becoming worn and slowing down your 1-2 shift than a transmission not being able to hold XXX hp where it would legitimately fail and be no longer useable. I would consider that far from splitting hairs lol.

I don't actively follow S55 so I can't even say with certainty if they don't have similar issues with syncros or what is fundamentally different about those transmissions. Happy to be informed though if anyone knows.

[terryd5150]

Originally Posted by thejeremyman9

The distinguishing factor is i have never heard of a transmission "failing" due to a syncro issue. It just slows down the shift speed; the transmission is still completely usable. So, it's not really a "failure mode" as you put it as it would not render the transmission useless.

Also, you opened with:

"I'm looking to swap an M4 6MT into an N55 435i so I can go with a big single turbo.

The stock 6MT the F32 came with probably wouldn't live well in that world."

So once again, the syncro concerns have nothing to do with going big single turbo. You then reiterated the focus on "big power" in your subsequent posts. So my point is that I have never heard of a N55 transmission not holding power.

So yeah, there is a huge difference between a syncro becoming worn and slowing down your 1-2 shift than a transmission not being able to hold XXX hp where it would legitimately fail and be no longer useable. I would consider that far from splitting hairs lol.

I don't actively follow S55 so I can't even say with certainty if they don't have similar issues with syncros or what is fundamentally different about those transmissions. Happy to be informed though if anyone knows.

A syncro failing is a transmission starting to tap out. Are you suggesting a transmission can live a healthy life grinding gears? Seriously?

Yes, you're definitely splitting hairs. A transmission not functioning is a transmission not functioning. Regardless of failure mode, I wouldn't want to pair that behind a big single - you can if you'd like.

Additionally, the N55 version of the 6MT is rated at 450nm of torque vs. 600nm for its N54 predecessor, so yes, the N55 is a weaker - I'd prefer something more robust in when going with a much higher rated turbo.

So, let me re-phrase my problem statement and see if we can get off this merry-go-round:

"I'd like to put a 68mm Garrett GTX series turbo on my car, but the stock manual transmission is a weak point for the N55.

I'd like a transmission that DOESN'T HAVE SYNCRO issues and can handle more power than the N55 version.

The feedback on M4 forums is that the MT in those cars doesn't suffer from either issue.

Further, it seems like an ideal swap candidate into an F-body as those platforms utilize the same frame.

This seems like a good thread to ask this question, as it's literally the title of this thread.

Does anyone have any feedback on that topic?"

thejeremyman9 if you'd like to start a thread debate on the merits of the N55 6MT, you're certainly more then welcomed to; however, this particular thread is about the S55 6MT as a swap candidate - again, see thread title.

[thejeremyman9]

Originally Posted by terryd5150

A syncro failing is a transmission starting to tap out. Are you suggesting a transmission can live a healthy life grinding gears? Seriously?

Yes, you're definitely splitting hairs. A transmission not functioning is a transmission not functioning. Regardless of failure mode, I wouldn't want to pair that behind a big single - you can if you'd like.

No, never said anything about running a transmission with syncro issue/grind or how long one could do so. I was just trying to understand why you introduced your question in terms of a big turbo upgrade / power holding capabilities and then somehow said that a syncro issue is exactly the same problem as not holding power when they are two fundamentally different issues... Completely understand the desire to want a "stronger" (in terms of holding power) transmission for an upgraded turbo application. In my original response i was just trying to understand your concerns with the N55 and what you understand to be different about the S55 transmission. Wasn't intended to start a debate.

Originally Posted by terryd5150

So, let me re-phrase my problem statement and see if we can get off this merry-go-round:

"I'd like to put a 68mm Garrett GTX series turbo on my car, but the stock manual transmission is a weak point for the N55.

I'd like a transmission that DOESN'T HAVE SYNCRO issues and can handle more power than the N55 version.

The feedback on M4 forums is that the MT in those cars doesn't suffer from either issue.

Further, it seems like an ideal swap candidate into an F-body as those platforms utilize the same frame.

This seems like a good thread to ask this question, as it's literally the title of this thread.

Does anyone have any feedback on that topic?"

thejeremyman9 if you'd like to start a thread debate on the merits of the N55 6MT, you're certainly more then welcomed to; however, this particular thread is about the S55 6MT as a swap candidate - again, see thread title.

Your revised statement makes sense because it correctly distinguishes the syncro issue from the power holding capabilities which are two entirely different things. So yeah, we can move on

Also if you have any threads or documentation on the N55 trans failing to hold power would be interested to read those. The 8AT is similarly rated for 450nm but is pushed far further without issue. I read basically every single post in the N55 technical forums and browse the others and haven't ever seen anyone post about an N55 trans breaking due to torque/power level. By no means saying it doesn't exist, legitimately asking for examples so i am informed on the topic.

[1KWIKBMR]

Did you do this swap, @terryd5150?

I have the same 1-2 synchro issues as everyone else and was also wondering about an m3/m4 6mt trans.

[sqwinny]

Subscribed as I'm looking to do the same to my n20 (nearing 400whp and want 550whp which brings torque with it).

[terryd5150]

Originally Posted by 1KWIKBMR

Did you do this swap, @terryd5150?

I have the same 1-2 synchro issues as everyone else and was also wondering about an m3/m4 6mt trans.

1KWIKBMR

I haven't yet, my synchros are holding up just fine at 89K miles on a Stage 1 tune - although, I don't dog the car either.

However, the moment my syncros fail, I'll be doing this exact swap.

When that happens, I'll pop back into this thread.

[terryd5150]

Originally Posted by sqwinny

Subscribed as I'm looking to do the same to my n20 (nearing 400whp and want 550whp which brings torque with it).

I'm faily confident the M3/M4 6MT is a straight bolt-in behind an N55; however, I've done zero research on the plausibility of this swap behind an N20.

[sqwinny]

Originally Posted by terryd5150

I'm faily confident the M3/M4 6MT is a straight bolt-in behind an N55; however, I've done zero research on the plausibility of this swap behind an N20.

I think it'll be slightly different, but if the n55 clutch disk fits the n20, at least the clutch disk + throw out bearing is the same. Need to find a n55 transmission to see if it'll mount up to my spare block. Otherwise all hail the getrag trans and hope it holds up …

[sonicnofadz]

FYI Im researching this trans (GS6-45BZ out of m2/m3/m4) as a candidate for my auto->manual conversion on my 6bolt e90 335i (n54). What I've found out is that it will definitely bolt up, however the bell housing for the M trans is slight bigger (compared to the gs6-45bz on the f30 n55 6mt cars) to accomodate the larger clutch/flywheel. I believe the overall transmission length is longer as well, so that might complicate driveshaft and shifter compatibility. Durability and strength on this transmission is better than the f30 trans, has better 1-2 synchro, however not sure what else is has been upgraded internally (possibly bigger shafts maybe). Because of the larger bellhousing, I am not 100% sure about fitment in e90/f30 chassis, I'd imagine there would be no issue, from what I examined via photos on ebay, the bellhousings are only slightly different dimensionally.

[xquatch]

What was the outcome? I ask because I apparently picked up the variant of the GS6 45BZ with the longer bellhousing by mistake for my 2011 e90 335i as a direct replacement. I started my own thread on this issue here.

[n55david]

Originally Posted by xquatch

What was the outcome? Does anyone know if/how to swap the bellhousing from one 45BZ to another? I have a 2011 335i rwd 6mt with bad synchros, so picked up a used (newer) unit from another N55, but now that I have both sitting out of the car side by side, the new one has a longer bellhousing (~3cm) . Wondering if anyone had swapped a bellhousing.

Wrong place to be asking tbh

[xquatch]

Originally Posted by n55david

Wrong place to be asking tbh

Noted and amended.