The car is an 07’ 335i with around 100K on it. A couple of years ago a put a set of RB Two turbos on it, and have been running it on a custom E40 tune that peaks at around 25psi with no issues. Even after several high 10-second ¼ mile passes last year…it runs great. This thing is well maintained, and doesn’t get beat on.
Recently I was driving around town, and I noticed that the idle felt a little funny. Nothing bad enough to see it on the tach, but I could feel it through the seat of my past…just a little stumble. No smoke, no misfires, no codes…it actually still ran really well, just has that bobble in the idle.
I finally got around to diving into it last week. Went ahead and checked the compressor on each cylinder….all were 160-165psi except #4, it was only 50psi. Dumped a little oil into the cylinder and the psi shot up to 120. Definitely a cracked ring and/or broken ringland.
So here is my question…..any idea as to what could have caused this? Is this a common failure for these motors? Based off of my ET and MPH’s….the car is making close to 580-600hp (10.90 @ 129mph). I know the N54’s use cast pistons…..is that pretty much the limit of what they can hold before something like this happens, or did something else cause it? Too tight of a ring gap? I always read that these N54’s are pretty stout…and 600hp is nothing for them (is that no true?). Could a faulty injector have caused this?
I’m going to pull the motor this fall when I have some extra time…..just trying to figure out if I need to go with a new set of forged pistons (and rods?) to keep this from happening again, or (depending on the condition of the cylinder bore) just throw another OEM piston in there with new rings and call it a day?
I’m not looking to add any more power…I just don’t want to have to pull the motor again in a year or two if the same thing happens again.
Thoughts?
Recently I was driving around town, and I noticed that the idle felt a little funny. Nothing bad enough to see it on the tach, but I could feel it through the seat of my past…just a little stumble. No smoke, no misfires, no codes…it actually still ran really well, just has that bobble in the idle.
I finally got around to diving into it last week. Went ahead and checked the compressor on each cylinder….all were 160-165psi except #4, it was only 50psi. Dumped a little oil into the cylinder and the psi shot up to 120. Definitely a cracked ring and/or broken ringland.
So here is my question…..any idea as to what could have caused this? Is this a common failure for these motors? Based off of my ET and MPH’s….the car is making close to 580-600hp (10.90 @ 129mph). I know the N54’s use cast pistons…..is that pretty much the limit of what they can hold before something like this happens, or did something else cause it? Too tight of a ring gap? I always read that these N54’s are pretty stout…and 600hp is nothing for them (is that no true?). Could a faulty injector have caused this?
I’m going to pull the motor this fall when I have some extra time…..just trying to figure out if I need to go with a new set of forged pistons (and rods?) to keep this from happening again, or (depending on the condition of the cylinder bore) just throw another OEM piston in there with new rings and call it a day?
I’m not looking to add any more power…I just don’t want to have to pull the motor again in a year or two if the same thing happens again.
Thoughts?