I have saw only a few auto trans turbo build, I'm pretty sure every one resulted in a blown trans.

 

IIRC the mfgr date 2001/09 and later auto transmissions were very slightly beefed up from the pre 2001/09 transmissions, but that's mainly WRT the reverse drums.

I wouldn't have any faith in that transmission with much more than about 250hp, and that's only 25hp more than stock. Any more than that and I think you're begging to blow it apart.

I can't (easily) find the hp/torque limit specs on the 330 trannies but my best guess from other transmissions I've seen used (by BMW) where specs were published, they run them pretty close the hp/torque output of the car in stock form so not much margin for error.

 

Audi uses the same transmission in the A6 2.7T bi turbo, runs about 10 to 11 psi boost max.

 

are we sure Audi doesn't have specific trans tuning/higher line pressures to account for the extra torque that BMW doesn't have? sometimes they tune those things to pop the shifts off faster if more torque is applied.

or else you'll get slip. slip=wear

 

What you need to know is how much torque the engine will be putting out after the boost. According to this site (click me), the max torque for the 5l40e is 494 lb-fts. I would err on the side of caution and say 475 or even 460.

 

+1

Boost level alone doesn't mean anything---it's what it translates to in terms of torque that kills transmissions.

 

As it sits, we see auto trans failures at 150-200k. So if you have 150k or more, your borrowed time just got cut even shorter. If this is a toy car to take on the track occasionally, knock yourself out. But for a daily, I wouldn't without a dedicated trans build.

 

Your A5S325Z is rated at 325 Nm. The GM A5S390R is rate at 390 Nm.

More details here.
https://www.bimmerfest.com/forums/attachment.php?attachmentid=357533&d=1358132490

 

exactly. A guy at the bmw parts counter gave me a link to the site they use. I unfortunately have the 325 nm transmission. He said those were guidelines for continuous torque, not thresholds. even still.... not sure its worth doing. Unfortunate too, because I really like this convertible. in its stock form, it just doesnt have enough balls to be fun. My research has shown that there really arent any legit ways to squeeze power out na.

 

MY other option is to go manual. I was told though that doing the swap is a PIA since the trans controller communicates with the ecm. No controller would confuse the ecm. or so I was told.

 

The engine computer (DME in BMWeze) would have to be reflashed to accommodate the manual tranny.