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E90/E91/E92/E93 (2006 - 2013)
The E9X is the 4th evolution of the BMW 3 series including a highly tuned twin turbo 335i variant pushing out 300hp and 300 ft. lbs. of torque. BMW continues to show that it sets the bar for true driving performance! -- View the E9X Wiki

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Old 01-21-2012, 06:21 PM
brusk brusk is offline
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Has anybody clearly figured out the forged piston question

I've been searching and reading for an hour and have yet to find any conclusion on if there were a date or pattern to if the N54 had forged pistons or not. I've seen some posts indicating they think in late 08 or 09 they switched to cast pistons. How critical has this been? can the stock cast pistons handle another 100HP. I'm looking at an 09 model year and concerned that maybe I should find an 08.
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Old 01-21-2012, 06:44 PM
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Quote:
Originally Posted by brusk View Post
I've been searching and reading for an hour and have yet to find any conclusion on if there were a date or pattern to if the N54 had forged pistons or not. I've seen some posts indicating they think in late 08 or 09 they switched to cast pistons..
Yes, I can't recall the forum, but there was a person in E90Post or N54Tech that discovered his MY09 E92 had cast pistons during a rebuild of his N54. The conversation got a bit ridiculous with resultant panic, something on the equivalent of "ZOMG, I might as well be driving a Prius! My engine sucks!"

Kinda funny to read, actually.

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Originally Posted by brusk View Post
How critical has this been? can the stock cast pistons handle another 100HP.
There are people in E90Post and N54Tech who claim they've pushed their MY09/10 E90s and E92s up to 400 rwhp (meaning well over an additional 100 hp at the crank) without any issues.

Is that much power a recipe for longevity? Likely not, and personally I'd be more worried about the transmission at that point.
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Old 01-21-2012, 07:34 PM
brusk brusk is offline
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yeah that would be well over what I'm going to be looking for. I would say most of the time I'd be happy with an additional 60-80 with the basic filter, intercooler, down pipes, exhaust and a tuner. I've heard the the step trans should be fine with those levels with a better cooler, not track or strip racing it. I've found posts of people stating that they also found some cast pistons in earlier models as well. I was hoping though there was a simple answer by now I find it hard to imagine a mixed and matched setup unless it was by certain models or something. Either way if nobody has had noticeable issues with their 09 or 10 models running more power then I guess I shouldn't worry about it. I'm being overly cautious here as I'm used to working on turbo cars that I never had to worry about internals for that little bit of increase supra's, mr2's, neon SRT's, Eclipses and Evo's. Haven't heard of very many engines running turbo and cast pistons at least any that people were actually getting performance out of without grenading them all over the place.
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Old 01-23-2012, 06:46 AM
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Originally Posted by brusk View Post
I've heard the the step trans should be fine with those levels with a better cooler, not track or strip racing it.
Just as a FYI, the one thing I've seen verified is that the 335i's ZF 6HP21 (designated by BMW as 6HP19) 6AT has a design limit of 332 lb-ft. of input torque... http://www.e90post.com/forums/showthread.php?t=46224 (Better info plus a posted ZF AT brochure on the second page of the thread.)

I doubt it's a coincidence that BMW's OEM Power Performance Kit brings the crank torque up to 332 lb-ft. with the 6AT. However, I wouldn't be concerned with the AT's design limit if I was someone who wasn't concerned with long-term drive train reliability.

Cheers.
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Old 01-23-2012, 08:20 AM
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I'm not familiar with the various model #'s on the ZF 6AT step, but my understanding is that the reason the 6AT step is used in the 335d is that it's the only transmission that can handle the 425lb-ft of torque of the diesel. Seems like there would be a whole lot of tranny failures from the multitude of people using JB3's, JB4's, vishnu's, etc. if the design limit was 332 lb-ft.
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Old 01-23-2012, 08:39 AM
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Originally Posted by 335i Driver View Post
I'm not familiar with the various model #'s on the ZF 6AT step, but my understanding is that the reason the 6AT step is used in the 335d is that it's the only transmission that can handle the 425lb-ft of torque of the diesel. Seems like there would be a whole lot of tranny failures from the multitude of people using JB3's, JB4's, vishnu's, etc. if the design limit was 332 lb-ft.
Different models of ZF AT in the two cars...

The E9x 335i has the 6HP21 (designated by BMW as the 6HP19) that is rated at 332 lb-ft of input torque... http://realoem.com/bmw/showparts.do?...24&hg=24&fg=05 and http://realoem.com/bmw/showparts.do?...24&hg=24&fg=05

The E90 335d has the 6HP28 (designated by BMW as the 6HP26) that is rated at 443 lb-ft of input torque... http://realoem.com/bmw/showparts.do?...16&hg=24&fg=05

You can see the difference in the attached ZF brochure -- e.g., in the left column on page 5:

"Input torque
6HP21 max. 450 Nm
6HP28 max. 700 Nm"

And it's not a brightline issue... Exceeding the design limit of a component by 20% (as an example) generally doesn't result in immediate failure, but it typically does shorten the component's life. IMO, the E9x hasn't been out long enough for tune-induced transmission failures to happen on a noticeable scale even with the early MYs.
Attached Files
File Type: pdf ZF 6HP 2nd Gen Brochure.pdf (941.2 KB, 326 views)

Last edited by Verts4Ever; 01-23-2012 at 09:41 AM.
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Old 01-23-2012, 08:46 AM
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So I'm driving a Prius? Great. Where's my MPG!?!?

I tried following the various forged/cast piston debates and decided it wasn't worth the trouble. People seemed convinced that the 335is N54 would have forged internals, but if it were true, BMW marketing would have made some mention of it somewhere.
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Old 01-23-2012, 11:23 AM
brusk brusk is offline
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Well I was hoping by now as many people that race them, mod them either everything is known to be strong and hold together if not enough of them that have been had melt downs to see a pattern. As for the Steptronic concern I would hope the same thing seeing how many 2nd gear launch videos on the web. I know launches and heat are always a major concern on any transmission but feel it would be alot more stress on the transmission trying to push around one of the bigger BMW family haulers trying to pass traffic and haul gear that the extra stress of pushing a 1er at highway speeds. But again I'm just guessing that's why I'm on here hoping by now there's been enough people that has found out for sure.
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Old 01-23-2012, 12:19 PM
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Originally Posted by brusk View Post
But again I'm just guessing that's why I'm on here hoping by now there's been enough people that has found out for sure.
The problem is that you're looking for anecdotal evidence of a trend (or lack thereof), when most people who have significantly modded their cars and then had failures are going to hide that fact in hopes of getting the necessary repair work done under warranty.

Even in the anonymous world of the forums, I can point you to a number of posts about E9x engine and transmission failures from people who claim their car had no power-related mods, a claim that's highly suspect given some of the poster call-signs -- e.g., "IModdedTheLivingCrapOutOfMyE92FTMFW ." It's human nature for someone not to want to admit that he or she was the cause of the failure and that the repair work consequently should be done out of warranty.

Only vendors and teenage fanboys will tell you "don't worry, be happy" when it comes to engine performance mods, and the former will be conspicuously unavailable for contact in the event of a failure. But after 25 years of modding cars, I've learned through the occasionally painful moment to my wallet that there's a very simple thumbrule to it all: increasing engine output means possibly decreasing reliability over the long-term.

Power mods probably won't cause you to blow your engine or transmission, but they could increase the possibility of it happening. In the end, it's your decision and your risk to take. Personally speaking, I've always thought it was worth the risk to squeeze a bit more fun out of the car, but that's just my opinion and I've paid for it when I was wrong.

Last edited by Verts4Ever; 01-23-2012 at 02:20 PM.
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Old 01-23-2012, 02:02 PM
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I am pretty sure that I heard Steve Dinan say that the modern engines, including BMW (i.e. N54) engines have cast pistons...i.e. sintered metal
Quote:
"the metallic equivalent of chip board".
These are the weak point in the engine when they test their tunes

[M3's have forged pistons.]
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Old 01-23-2012, 02:17 PM
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I am surprised with all the potential for catastrophic failure at the 20lbs+ some guys are running that no one has had the opportunity to open one up after it grenaded to see what is inside.
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Old 01-23-2012, 02:17 PM
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Originally Posted by ///M-ratedE90 View Post
[M3's have forged pistons.]
Ha, yet another item to add to my list of justifications for buying a F33 M3.

I'm working on the talking points now: "Sure, Honey, it's effectively useless as a M3. But the tri-turbos will go a long way toward pushing the extra cabrio weight, and it has forged pistons for added reliability!"
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