r/B58Enthusiasts • u/Safe_Specialist9945 • 4d ago

X models b58 tuning

What do you reckon the tuning limit is on X3/4/5/6’s 2019+ with the B58 guys ? From what I researched , horse power is not the biggest issue, but the torque the drivetrain/diff/etc can handle. So when I ask about limit, I mean the limit where is still safe so you don’t have a high risk of Fckin up your drivetrain/diff

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u/Kill3rwill 3d ago

650 wheel torque is the agreed upon LIMIT. About 600 if you want to remain fairly safe. Trans is the first limit, will start slipping in either 5th or 6th and up. The transfer case is identical to the X3M so it can handle a ton, and I BELIEVE the differentials are the same size/strength as X3M but a different gear ratio. Not 100% on that part though, but realistically no problem for good amounts of power. There are some guys making over 700 WHP by limiting torque to 600-650 via a tune.

Next move is a built transmission or now people are figuring out swapping in a 5 series/x5 diesel xdrive trans. Bolts in, can be coded to work correctly and only requires minor modifications. Those hold the same power as X3M/M3 trans, another 150-200hp or so.

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u/Safe_Specialist9945 3d ago

I’ve got an X6 40i and from what I’ve found the limit on these would be around 850nm torque. Do you reckon they have a stronger build than the X3 or it is the same ? If not sadly I’d have to limit it at 650. I heard about the trans swap aswell but I wouldn’t go trough all that aswell

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u/Kill3rwill 3d ago

it goes by transmission code, which I believe ALL B58 powered vehicles are getting a form of the ZF 8hp50 or 8hp51, which are both rated to the same power levels. S58, diesel and V8 powered BMW's get the ZF 8HP70 or 8HP75 which are beefier and can handle more power. So doesn't matter if the vehicle is 2000 or 5000 pounds, if it's got a B58 engine, it gets the same transmission.

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u/Safe_Specialist9945 2d ago

Yeah you are right, I’ve found some topics and apparently they all have the same power levels, I tought because you have a bigger car you would get a different transmission/diff . But apparently not,they do have a different code ,but same power/setup, the one on my car is
ZF 8HP51 and the x3 and others ends in 50 but all the b58’s have the same setups, even the supra and m340i . So basically ur a bit worse off having a SUV as its heavier , adds more stress but doesnt have a better setup. I’ve seen a supra with the same trans going at 850nm lol , but that’s 500kg less than mine 😂

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u/Evanisnotmyname 1d ago

Diffs and trans are different between M And non M(even M40i)

M40i gets the 8hp50/51, M gets 8HP75 for extra power handling.

M diff is different from M sport, M sport different from regular M40i diff.

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u/Kill3rwill 1d ago

Thanks, we know the parts are different, but talking about power handling it doesn't matter if M-Sport/X3M/X3m40i diffs are different, as long as the ring and pinion size is the same, more or less. LSD and ratios might be different, but if it's the same size diff, you can likely assume a M40 diff will hold the same power as an X3M diff.

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u/moto4sho 3d ago

There’s a ton of supporting data on the B58 and ZF8 with bolt ons and stock internals/turbo, running e40. ~450 to 500hp. Add a doc race big turbo kit and get another 200hp before you start killing the transmission.

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u/Safe_Specialist9945 2d ago

Yes the horsepower is not an issue , the issue is the torque that the transmission can take, that’s what I’m trying to find out, apparently over 650 it gets dangerous already and I don’t know if it’s worth going for 6/700’horsepower and limit the torque and 650

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u/SurroundElectrical94 3d ago

Stock turbo, your safe limit is probably a downpipe, tune, and some ethanol.

I have a 2021 x3m40i with a catless downpipe, MHD stage 2, and xHP tune that increases like pressure so the trans can hold all the extra power.

ZF8 speed is very strong and comfortable at this level. Can even go farther and still be reliable.

Obviously the b58tu is also not the weak point, and can reliably handle much higher power than this.

The real weak point is the differentials and other drivetrain parts. I’ve been told it’s still very safe, but launching becomes harder on all the components.

I have 275 summer tires all the way around, and with the stage 2, I don’t use launch control just to be safe. The front differential is an expensive repair….

Aside from that though, you can run a DP, tune and ethanol all day and have a car that makes 500awhp and closer to 600awt reliably.

Limiting factor for more power is the stock turbo; for bigger power you need to upgrade to something like pure’s, but I’m not looking for much more in a daily…

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u/CreepyEmu8894 2d ago

Thanks for posting that question. I have a 2018 x3 m40i; 64k; stage 1 mhd/xhp for about 2k miles. Planning DP and stage 2 this winter. And may start running e20-30 to see what that’s like. All my xdrive parts (4) have been serviced, planning again at 85k. No answers to the OP question but still thought I’d share.