[Dreculah]

Originally Posted by Solid67

The ZF8 has been in production since 2008. There are plenty of high power N55 cars out there that have been using this transmission with hardly if any transmission upgrades besides a tcu flash.

Also, car owners who are putting down big power aren't worried about their transmission going to 75-100k. What made me laugh about your initial comment was the fact that you think stg 2 93 is big power (it's not). Unless you are planning on running "high power", you should not be worrying about stg 2 93 grenanding your transmission or significantly reducing the life of the transmission.

Good info, thanks. "Big power" is relative...I remember when Shiv cracked 700WHP with the N54 and I got an amazing ride in his test vehicle (E92). Dyno queens have gotten a lot more since then, like over 1000WHP.

The B58 is closed deck with forged internals, so I'll bet we see some great numbers from it.

The point is, the ZF8 has sturdier versions than what got put in this car, and it still strikes as a weak point relative to what the B58 can produce.

[EstorilM240]

Originally Posted by MassNerd

That article has some gaps which I'm curious to know.
#1: Why would middle of the range (4th for the 6 speed, 3rd and 6th for the 8 speed) have lower torque limits and lower line pressure? That doesn't seem to make sense? Maybe a gradual decrease in limits as you go up the gears would make more sense? I would be surprised if BMW and ZF just randomly tuned the transmission that way.

I read this deep dive a while back on the theory of the ZF8 and found it interesting: https://www.thetruthaboutcars.com/20...eed-automatic/. I suspect the limits have something to do with the particular gear sets driven and the torque transfer.

5th in the 6 speed (not 4th) and 6th in the 8 speed both have the low torque limits, and both are the 1:1 drives... Perhaps transferring torque through fewer gear sets = lower mechanical limits? Any mechanical engineers care to chime in?

[MassNerd]

Originally Posted by EstorilM240

I read this deep dive a while back on the theory of the ZF8 and found it interesting: https://www.thetruthaboutcars.com/20...eed-automatic/. I suspect the limits have something to do with the particular gear sets driven and the torque transfer.

5th in the 6 speed (not 4th) and 6th in the 8 speed both have the low torque limits, and both are the 1:1 drives... Perhaps transferring torque through fewer gear sets = lower mechanical limits? Any mechanical engineers care to chime in?

Great link Estoril. Very interesting even though much of it was over my head.

As much as a tried to find some common mode of operation between gears 3 & 6, I could not. Perhaps they have torque limitations for different reasons.

I think it's safe to say, this automatic is much more complicated than I realized. So thank you again for the link!

[Dreculah]

I asked ZF why the ZF8 in our cars has a lower torque rating than models higher in their range, and this is what they said:

"The 8hp 45/50 is a smaller version of the 8hp70/75. The clutch drums, planet sets and TC are of a larger diameter. The components are able to handle more input torque as a result of the sturdiness of the components."

[Dreculah]

Originally Posted by marcthedark

The ZF is used worldwide and I'm sure some people running big TORQUE (aka diesel owners) in Europe did a lot of miles.

I'm not sure they are using the same version of the ZF8.

[DaleHeinz]

I don't know what the second page of responses has for you, but after reading the first page, no one had an educated or first hand knowledge based response. For good reason. I'm sure there is no true number that says you can push it to here, but beyond is dangerous. The manufacturer recommended what they did. Anything beyond that science is up to us to figure out. We haven't figured it out yet. That's a long term game, based on a lot of factors.

[POMFKIMOCHI]

What about the manuals in b58s? Has anyone seen that manual swapped supra? Not sure what trans he used (eag)

[moejoe10500]

hey yall i have a 340i RWD 2018 with bootmode3 stg 2 93 and had xhp on stg 2 my transmission was fucked after about 10,000 miles but it wasnt because of transmission failure it was actually tranny cooler failure so if you want to upgrade something upgrade your tranny cooler cause if that blows your done good news is car was covered under warranty

[SpencerC_6MT]

Originally Posted by POMFKIMOCHI

What about the manuals in b58s? Has anyone seen that manual swapped supra? Not sure what trans he used (eag)

IIRC they used then trans out of a European 520d, in hopes of it holding up better. F22Ruben on Instagram was pushing 672whp when he blew 5th gear, but the way he shifted that thing ("Human DCT") is probably more to do with the failure than the raw torque figures. He did an autopsy on the shredded tranny and it seems like 3rd was on the way out too.

https://www.instagram.com/f22ruben/

[freakystyly]

Kern417 is constantly putting together well made youtube videos of the B58.

https://f30.bimmerpost.com/forums/sh....php?t=1871349

This link has his "writeup" of the transmissions (I assume the 2er and 3er get the same one).

[jordan24c]

Originally Posted by freakystyly

Kern417 is constantly putting together well made youtube videos of the B58.

https://f30.bimmerpost.com/forums/sh....php?t=1871349

This link has his "writeup" of the transmissions (I assume the 2er and 3er get the same one).

He also just put out a video on transmission strength. Kern is the fuckin man.