What’s the best aftermarket upgrade turbo for a 2013 R56 N18?

“Best”? Steer clear of anything from JMTC. Owens Development comes highly regarded. Also Borg Warner JCW spec or Airworks turbo would be a nice upgrade, assuming you have a Cooper S model.

Depends on your goals.

Want a little more power but keep powerband close to the same with minimal spool time, go JCW turbo.

If you want to spend more to get more, go with the 41mm Borg Warner upgrade. Expensive, but this would be my choice if budget allows.

If you want more, you're basically into the aftermarket zone with peaky output ranges and lots of prerequisites to deal with the power.

So if I were to go with something like the 41mm borg Warner I would need to upgrade other components according. Gotcha. JCW turbo sounds like a good start

The 41mm Borg Warner turbo flows just slightly more than the JCW turbo. It would also be a good drop-in replacement. You don’t “Have “ to add any other upgrades at the same time, but an ECU tune will get you the most out of the new turbo.

Who offers the 41mm? Just asking as I'm having a feeling that i will be replacing my turbo in the near future and I don't want a stock one.

This is the stock N18 JCW turbo:
https://www.ecstuning.com/b-borgwarn...1657649496~bw/

This is the upgraded Borg Warner version:
https://www.ecstuning.com/b-borgwarn...space-0146~bw/

I replaced my stock S turbo with this one:
5303 988 0298
is this just a stock JCW one or the upgraded one?

That is the Borg Warner part identifier for the stock N18 JCW turbo

When I get all the parts off my part car (2013 Roadster JCW) I was planning on using the turbo and exhaust from it on my S. Is anything else needed for the swap?

Not sure if anything else is needed, but a lot would be desired if you want more performance: Hi flow cat ( not sure if your exhaust will fit - so a 2.25 - 2.5 exhaust ); larger intercooler, upgraded MAP sensors if you go over the stock S boost range, a tune to take advantage of all this, perhaps a higher flow fuel pump ...

I have had the JMTC 42mm hybrid for about a month and love it. spools faster, gets into boost much quicker. it's a different car. throttle is more like an on or off switch. I have not put my nm tuner on yet. I did detune the peddle commander to get more pedal feel.

still happy with it?

May I politely request why you dislike/distrust JMTC? I suppose I have a dog in this fight because I have a JMTC turbo on an R60. At the same time I don't though, because the car is dead to me for other reasons. Not looking to start an argument is my point, I'd like to know what you think.

Their quality seems to be inconsistent.

Also, they sold solid single mass flywheels for a long time that had no timing hole on the back side. Most people that bought one didn't realize until they needed a timing job, and found that they had to remove the transmission to properly set the timing gears. I don't think they ever admitted it either. Then, they started selling solid clutch discs to be used with solid flywheels for street use. No a good combination for longevity.

In my opinion, they made some questionable design choices over the years that leads me to believe they don't have much of a clue about what they are doing.

Thank you, I appreciate it.

Are you familiar with inconsistent quality issues with their (JMTC) turbos? I'm still pretty new around here, and didn't find anything bad about them before I bought mine. My car is having problems, and actually over-boost would explain one of them (if an off the shelf assembled turbo is even capable of that). I know nothing about single mass flywheels but can understand a timing hole being important for camshaft alignment. Also know nothing about clutch/plate design, but from these two things I'd be likely to agree with you that they don't know what they are doing from an engineering standpoint. Certainly if by flywheel timing hole you mean the flywheel locking pin hole used in locking all the timing up (or equivalent in importance), big yikes to that oversight. I say thanks again for the sharing of experience.

Sadly, to the OP, I might've said my JMTC JM40 turbo is perfect. Indeed it may be good, but I only have a year on my otherwise-imperfect-engine and do have other problems. Thus I am not in a place to recommend anything.

I've heard stories of some who have used their turbos and had great success. I've also heard stories of some who have used their turbos and had nothing but issues. And its JMTC's policy to point the finger at the car not being properly maintained, or having some pre-existing issue, only to finally replace the turbo and find out it was the turbo all along.

I have had the turbo on since October 24 and it still is pulling strong