[ArcticWhite]

N54's seem to be decently reliable at 450 to 500whp. Does anyone have experience with the N55 at this level?

I'm FBO right now, but would like more. I'd do a pure stage 2 but am worried about the reliability.

It is my understanding the N54 has a forged crank. It seems to me starting to push 450 to 500whp out of a 6 cylinder is starting to stress the rotating assembly pretty good. Even if the ultimate strength of the crank and rods can handle it, I would think that they would fatigue quicker at that HP level and not really have the longer term reliability.

If I knew it would be similar in reliability to the N54, I'd do it in a heartbeat. Not sure if the experience is really out there yet?

Anyone else concerned about pushing the N55 in the 500whp range?

[dannyle27]

No problems so far. I rarely go pedal to the floor on the street though due to traction problems even with LSD lol. Only time I ever do is if I see like a GTR or something worth playing around with.

[CantCatchMe]

You'll be fine. Just keep up on other maintenance because obviously the engine will be working harder due to more power being put down. If you're really that nervous upgrade the rods, it's about $1k. There's plenty of guys running the PS2 turbo with 500whp+ daily, they can chime in to tell you the same thing.

[weehe126]

500whp is easy for a N55 with a stage 2. Extremely reliable for the power.

[deemarr 335i]

No issues here, almost 2 yrs now 😆

[JETmn]

Originally Posted by ArcticWhite

It is my understanding the N54 has a forged crank. It seems to me starting to push 450 to 500whp out of a 6 cylinder is starting to stress the rotating assembly pretty good. Even if the ultimate strength of the crank and rods can handle it, I would think that they would fatigue quicker at that HP level and not really have the longer term reliability.

I don't understand why people get so focused on forged cranks. The stock LS3 crank has taken over 1,600whp and it is not forged. There are a lot of processes and material changes that have taken place where forging isn't as needed any more. Nodular iron has become pretty standard and I would bet that is what is in the N55. While it isn't forged, it is strong and cheaper to make.

Another huge improvement in engines is the mounting system for the cranks. They are much better than they used to be and that means the crank doesn't have to be as strong. FEA analysis in design has really helped with rods also, but I would say they are usually the weak point in most engines. The only N55 rod failure I have seen so far has been one that was low on oil and a bearing likely seized.

I wouldn't even think twice about 450whp on an N55, go for it.

[kamfa39]

I agree as a N55 owner pushing 450+ with AT.
It is my DD running pure stage 2

[ArcticWhite]

I have seen a lot of non-forged cranks hold LOTS of power. It isn't ultimate strength that I am concerned about. Typically, forged cranks do not fatigue as readily and therefore can hold the power longer before failure. This is of importance in a higher mile daily driver vs. a low mile weekend car. I like as few problems as possible. All of the higher hp cars I have and have had, have been built right and trouble free for the whole time I have owned them.

I've tried not to get into this game with my DD's, but I like the BMW so much, I think it would be perfect in the 450 to 500whp range, and not as pricey as some of my other cars to get it there.

In my mind, there is no question that the change in cranks from N54 to N55 is a downgrade. However, it appears at the HP levels I am interested in, it has not been of concern, from the current experience.

Still deciding whether to role the dice on this one. This is the last car I really want to get into an engine rebuild on (as it is not one of my toys). We shall see!

I very much appreciate the experienced comments.

[weehe126]

Originally Posted by ArcticWhite

I have seen a lot of non-forged cranks hold LOTS of power. It isn't ultimate strength that I am concerned about. Typically, forged cranks do not fatigue as readily and therefore can hold the power longer before failure. This is of importance in a higher mile daily driver vs. a low mile weekend car. I like as few problems as possible. All of the higher hp cars I have and have had, have been built right and trouble free for the whole time I have owned them.

I've tried not to get into this game with my DD's, but I like the BMW so much, I think it would be perfect in the 450 to 500whp range, and not as pricey as some of my other cars to get it there.

In my mind, there is no question that the change in cranks from N54 to N55 is a downgrade. However, it appears at the HP levels I am interested in, it has not been of concern, from the current experience.

Still deciding whether to role the dice on this one. This is the last car I really want to get into an engine rebuild on (as it is not one of my toys). We shall see!

I very much appreciate the experienced comments.

No one has reported any crank problems that I am aware of on a N54 or N55. There have been maybe 3 reported N55 failures I've seen on the forums, 2 were flukes at stock power and a third from running lean for months at 600whp. TBH getting a stage 2 and only running 18psi would actually be better for your engine than running 18psi on the stock turbo.