Technical #4 Cylinder is dead…any ideas as to what caused the failure?

IQraceworks

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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?
 

kulixo

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May 26, 2020
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My stock engine blew a ring land and bent two rods at 650hp/900nm.
I would think this is pretty common, especially on hybrid twins
 

carabuser

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I think bent rods are probably the biggest risk. Sending it at low RPM with hybrid turbos.

Or a bad injector causing cylinder wash.
 
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martymil

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Stock motors can handle 600 max but its a ticking timebomb, if anything goes wrong like a problem coil, sparkplug or injector its
bye bye charlie.

Seen it happen so many times.
 

IQraceworks

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I'm assuming the only way to make the motor "reliable" with the power it's currently making is to go with forged pistons and rods?
 

IQraceworks

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I think bent rods are probably the biggest risk. Sending it at low RPM with hybrid turbos.

Or a bad injector causing cylinder wash.

My tune was pretty conservative.....low boost in the low/mid rpms, and it ramped up in the higher rpms for the soul purpose of taking it easy on the rods. The low/mix torque/power was about on par with a standard MHD Stage 2+ tune....but in the upper RPMS when the boost ramped up, it really pulled like a train. I've been running that same tune for a few years, and never had an issue.

I'm guessing it could have been an injector issue...or possibley just bad luck. I wasn't even running it hard when I first felt the problem with the idle....just cruising around town. I don't know how well the stock cast pistons like 25psi boost and 600hp?
 

carabuser

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My tune was pretty conservative.....low boost in the low/mid rpms, and it ramped up in the higher rpms for the soul purpose of taking it easy on the rods. The low/mix torque/power was about on par with a standard MHD Stage 2+ tune....but in the upper RPMS when the boost ramped up, it really pulled like a train. I've been running that same tune for a few years, and never had an issue.

I'm guessing it could have been an injector issue...or possibley just bad luck. I wasn't even running it hard when I first felt the problem with the idle....just cruising around town. I don't know how well the stock cast pistons like 25psi boost and 600hp?
It does sound like a fairly aggressive tune with those figures. Do you have any logs?

I'd also question if the stock knock tables were in place. Tuners don't often tell people, they just bake it into the map to reduce complains about corrections.
 

IQraceworks

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It does sound like a fairly aggressive tune with those figures. Do you have any logs?

I'd also question if the stock knock tables were in place. Tuners don't often tell people, they just bake it into the map to reduce complains about corrections.

Here is one of my 3rd gear pulls from back in early 2021. As far as I can tell, everything looks nice and safe. The HPFP pressure is starting to get a little low on the top end, but nothing that should cause any issues (I think). I really didn't want to mess with port injection.

I don't know how many full 1/4 drag strip passes I made last year on that tune....none with a single issue. I would have thought that if it the tune would have had a problem...it would have shown itself during those 1/4 mile passes.

Thoughts?
 

Attachments

  • 2021-08-11 06_19_11 I8A0S IQRace_N20_RB2_E40_v04.mhd.csv
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carabuser

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Here is one of my 3rd gear pulls from back in early 2021. As far as I can tell, everything looks nice and safe. The HPFP pressure is starting to get a little low on the top end, but nothing that should cause any issues (I think). I really didn't want to mess with port injection.

I don't know how many full 1/4 drag strip passes I made last year on that tune....none with a single issue. I would have thought that if it the tune would have had a problem...it would have shown itself during those 1/4 mile passes.

Thoughts?
I wouldn't be happy with that tune. 14afr, 10* and 19psi at 3400rpm, also just seems to target quite lean all through the midrange. And that will be flowing more air than stockers at 19psi. Timing seems aggressive for e40, but then you don't have many corrections in that log so either the knock control is turned down or the fuel quality is great.

Aside from that the load target is really low, looks like a the tuner hasn't scaled the boost well (just using the full 36psi range when you only need 25). That means the calculated airflows will be way out and the knock control uses that value all over.
 
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IQraceworks

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I do run 93 mixed with my E85 (actually E70 at the pump) to get my E40. I did have several timing corrections in the previous versions of that E40 tune that needed to be adjusted out, so I'm pretty sure the knock control wasn't dialed back (or turned off). As far as the scaling goes....that's out of my wheelhouse, I'm not failure when it comes to tuning these motors.

I guess it goes back my original question...if it was a bad tune that caused my broken ring/ringland, wouldn't it have caused problems a long time ago during my multiple 10-second 1/4 runs I've made over the last couple of years? Not wanting to drop any names, but the guy who made the tune is very well regarded on this site so I'm assuming he knew what he was doing. Now if it would have popped on the first pass after the new tune....sure, I would say it was a tune issue.......but I've been running that tune for a few years, and mutliple 1/4 passes without a single issue.

Wouldn't it make more sense to say it was just bad luck, or a weak piston, or an injector that could have went a little lean? Seems like most people say at around 600hp...the N54 is on borrowed time, and that's pretty much what that motor was making.

Thanks for the info! I'm always up for learning more about these cars.....
 

Torgus

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Wouldn't it make more sense to say it was just bad luck, or a weak piston, or an injector that could have went a little lean? Seems like most people say at around 600hp...the N54 is on borrowed time, and that's pretty much what that motor was making.

That is what I would bet on. Especially as you ran the tune for so long and had no issues. There was a specific event in that cylinder that caused the low compression/ring issue. Just shitty luck or good luck given how long you ran the car at this level, just depends on how you look at it.

The good news is you can upgrade the pistons/rods or just throw in another motor from a yard. Given the hassle of an engine swap, I would build, but up to you. Then again if you get another 3 years out of a junk yard motor #sendit.
 

carabuser

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It's not as binary as that. I've seen people post logs of cars with all kinds of issue that they've been running with for long periods of time and their engines are still intact. The thread on here recently with the guy running hybrid turbos on a stage 2 OTS map is a perfect example. These engines can put up with a lot of abuse.

I don't think it's a fair statement to say the stock engine can't take power. There's a lot more nuance than that. For example your tune is pretty aggressive down low with the afr and timing where rod bending is a risk, but up top you're also pushing a lot of air where turbo exhaust housing may be causing a lot of back pressure.

I'm not saying the tune is the sole reason, but it does seem to be a contributing factor. Certainly not what I would call conservative, but then the tune file was labelled as RACE.
 
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IQraceworks

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It's not as binary as that. I've seen people post logs of cars with all kinds of issue that they've been running with for long periods of time and their engines are still intact. The thread on here recently with the guy running hybrid turbos on a stage 2 OTS map is a perfect example. These engines can put up with a lot of abuse.

I don't think it's a fair statement to say the stock engine can't take power. There's a lot more nuance than that. For example your tune is pretty aggressive down low with the afr and timing where rod bending is a risk, but up top you're also pushing a lot of air where turbo exhaust housing may be causing a lot of back pressure.

I'm not saying the tune is the sole reason, but it does seem to be a contributing factor. Certainly not what I would call conservative, but then the tune file was labelled as RACE.

It was labeled "RACE" because my email address is IQRaceworks ....so the tune is called IQ RACE :)
 

IQraceworks

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That is what I would bet on. Especially as you ran the tune for so long and had no issues. There was a specific event in that cylinder that caused the low compression/ring issue. Just shitty luck or good luck given how long you ran the car at this level, just depends on how you look at it.

The good news is you can upgrade the pistons/rods or just throw in another motor from a yard. Given the hassle of an engine swap, I would build, but up to you. Then again if you get another 3 years out of a junk yard motor #sendit.
From what I’ve found, a used motor is going to cost me anywhere from $2K-$3K, and that’s really not going to guarantee that the same thing won’t happen. Although I’ve never built an N54, I’ve built several SBC, BBC, and LS motors over the years…so I have experience building motors, and I have good connections with local machine shops.

I’m assuming that as long as I go with a quality set of forged pistons and rods, I shouldn’t have to deal with broken ring lands anymore (assuming I don’t add any more power or change the tune). Right?

As far as pistons and rods go, what are most people going with? It looks like Mahle has a set of forged pistons for around $1K, and Manley and others make some nice looking rods for around $900. There seems to be all kinds of options out there.

I think I know the answer….but what about those KingTec forged piston and rod kits I’ve seen online for the N54’s? Looks like around $1k for both. Are they good quality, or total China junk? I think MaxSpeed is another company that makes some cheap forged pistons and rods. Are these worth looking at? Or run way?
 

SlowE93

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I agree with @carabuser on his assesment regarding tune.
While many newbies got familiar with Ken because of MHD, prior to that MANY complaimed about his tunes.
As time passes, people gain experience, but quite a few people were unhappy with tunes back then.
So "highly regarded" to one, may be quite the opposite for another.