Weren't N55s supposed to have weak crank shafts?

Originally Posted by AWSAWS

Weren't N55s supposed to have weak crank shafts?

People are dumb.

Originally Posted by bnks334

People are dumb.

Yeah. That's why cast n55 cranks end up breaking
Attachment 59789

Originally Posted by AWSAWS

Yeah. That's why cast n55 cranks end up breaking
Attachment 59789

Yeah, lets find a second instance of that...

not bad at all nice to see more N55s putting in work. 600whp at redline is decent. They need a larger turbo!

Originally Posted by AWSAWS

Yeah. That's why cast n55 cranks end up breaking

Ghassan probably put that crank in a vice to straighten it and broke it lol People aren't breaking N55 crank shafts. That's literally the only example that exists. At least not at <700whp they aren't. You know what else has cast cranks? All those junkyard 1000whp LS engines people love so much... pretty much the same size 2" rod journals as well on those cast cranks.

It's almost 2020 and people still believe every word they read on the internet... and from people trying to up-sell them on junk N54 parts none the less lol

https://www.facebook.com/GhassanAuto...359169692/?t=0

Well if you're worried about the cast crank the m235i, m235ir, and m2 have a forged crank which solves all this weakness issue.

But like bnks334 said, the only instance of the crank snapping is from Ghassan so not really the most evident proof that the n55 has a weak crank imo.... Especially when there are guys making double the factory whp on these "stage 3" turbos and no one has had any reports of the crank breaking.

Originally Posted by F87Source

Well if you're worried about the cast crank the m235i, m235ir, and m2 have a forged crank which solves all this weakness issue.

I wonder why BMW offered a cast crank on certain N55's then changed their mind? Probably supply issue I would assume or a purchase contract.

Originally Posted by Sticky

I wonder why BMW offered a cast crank on certain N55's then changed their mind? Probably supply issue I would assume or a purchase contract.

N55's came out in 2011 so no m235i, m235ir, or m2's yet. So to make mass production engine for multiple platforms including SUV's factoring how many people will race or mod and the 300hp from the factory a cast crank is cheap and easy to mass produce. I guess when they moved to the F series and started to think about a racing chassis for the new generation, one of them being the 2 series, they wanted to give it a stronger set of internals. So that's why (imo) only the m235i and m2 (and x4 m40i) got the forged crank because they're derived from the m235ir and what bmw considers a car that alot of people will trash on and they want it to last. They probably thought the F30 335i (2012) demographic would mainly be daily users and thus gave it a slighly revised 2011 n55 motor until in 2014 the m235i was made when they started to give it a forged crank.

But yes it could be contracted for the n55 life cycle so some n55's had to take a hit, then they made the go ahead on the m235i so they could reflect their m235ir racing line up and have a car compete against the audi s3 range of cars. Either way m235i cranks are pretty cheap on Ebay and they should be a drop in fit with new rods + pistons of course since its balanced differently.

But all in all a cast crank really isn't that weak, if it is tuned properly and isn't knocking all day long then it should last, keep that torque curve a little higher in the RPM range and you should be golden. For eg look at speedtech's F30, over 600whp (and probably more now) and it is fine.

They didn't change their minds about anything. N55's got a lighter cast crank. High output variants got a forged crank (M135i, M235i, M2, 735i...). Regular N55 got a cast crank all the way to the end of production. There are several different engines just like there are several different B58's. High output B58 in the Z4M gets a regular 6 port exhaust manifold. Supra got the medium output engine with the headifold.