Greetings, working on my 2.9 stroker M50 swap.

[triggrhaapi]

Uhh

1. No they are not, you can tell just by looking at them, plus I weighed them side by side, and you're wrong.
2. They are 140mm, not 135mm, I need 135mm

[triggrhaapi]

Let me show you what I mean...



The NV rod is on one side, the M52b25 (identical to Tu, but cracked cap, not seperate cast so actually lighter than Tu) on the other.

[SiGmA_X]

Could you take a picture of both of them on a digi scale and and post it for us? Yeah, the rod length is different, I didn't realize that you need the shorter 135mm's.

[triggrhaapi]

I'll have to find my Digi scale, but sure.

They are lighter mostly due to being 5mm shorter... but they are lighter never the less.

[triggrhaapi]

I'm sure the first picture settles the argument about which is stronger. I've seen S50 rods (same 135mm length as NV) curl up on themselves like a curly q when the crank on my buddy Allan's first S50 came loose from the first bearing due to the shop that rebuilt it not torquing it down properly. I really can't see that happening with the NV rod, what with it being so much wider and more reinforced. For the record the middle section of the NV rod is less than half the thickness of the M52 rod, you know, where it's at it's thinnest. More of the structure comes from the A beam shape, as opposed to the stock I beam shape.

[SiGmA_X]

I'm no engineer but Mike (Techno550) mentioned that just because the NV rods are "beefer" does not mean they are stronger.. And they may be in fact weaker. But its chill, they can take multiple hundreds of hp (over a set, not per each) and so you will be fine. I am looking forward to seeing you run and post a dyno too :)

[matt]

BMW is pretty smart about not replacing a part with one that isn't better.

IE SOHC belt drive> DOHC chain drive> DOHC Vanos > Double Vanos > Valvetronic

Plus longer rod = better rod ratio = more power, less chance of breaking a piston or rod, and less wear on the cylinder bores.

Also, techno550 is pretty smart.

[triggrhaapi]

BMW is pretty smart about not replacing a part with one that isn't better.

IE SOHC belt drive> DOHC chain drive> DOHC Vanos > Double Vanos > Valvetronic

Plus longer rod = better rod ratio = more power, less chance of breaking a piston or rod, and less wear on the cylinder bores.

Also, techno550 is pretty smart.

Except for a few things:

1. the block on the M50NV has thicker walls
2. the M50NV has dual valvesprings that handle higher revs better
3. the M50NV needed those and the stronger rods because it didn't have knock sensors. The double valvesprings are to compensate for the hotter cam profile used to make up the difference in power from not getting the extra cylinder fill at lower RPM that VANOS provides. (EDIT: Alternatively, they may have been used as a carry over from the M20 which has double valvesprings as stock then removed from the Technology upgrade to save cost)

I'm not saying that technoS50 is stupid or anything, he just doesn't happen to be right in this instance. The NV rods are not beefier because they weigh more, they are beefier because they have a stronger structure, A beam versus I beam. The triangular shape of the rod provides extra rigidity for it's given weight by translating compression force outward laterally, where the metal's strength is taken advantage of not only in compression but also in tension. If you notice also, where the rod meets the wristpin is wider considerably, which provides more resistance to torsion that would cause the metal to fold one way or the other.

As for the rod ratio, it's identical as the rod ratio of the S50 because I am using the same crank and same length conrod. Also, as a counterpoint to your faith in BMW's increasing use of "superior" parts as engines evolve, let me point out that the seperate casting/forging method of producing conrods as used on the M50 and M50TU is structurally superior to the cracked cap method of production as used on the M52 and M54, which is considerably cheaper as only one pattern is needed as opposed to two patters which are needed if you cast and forge seperately. Also pay attention to the fact that without any ability to detect predetonation, BMW had to overbuild the M50NV so that it could withstand detonation if necessary, hence the shorter conrod length (which as you say is less conducive to happy revving) and thicker piston (by the extra 5mm of piston height that using a 5mm shorter conrod would require) These are all to increase structural rigidity re: a detonation event that would put sudden and intense strain on the bottom end assembly in a downward thrust manner.

Still with me so far? Ok good.

Now, with the technological advent of knock sensor microphones, BMW could significantly reduce the possibility of detonation, so they could reduce rotational weight by making pistons thinner (the 5mm of piston material is much heavier than 5mm of conrod material), improve the connecting rod ratio and save on cost by building a conrod that used less complex methods of manufacture. Ironically, the Tu was still heavier by 4kg than the NV at 198kg. I'm guessing this is due to the weight of the VANOS unit and accompanying hardware.

[triggrhaapi]

I am looking forward to seeing you run and post a dyno too :)

Me too. Engine break in is two stages, 600 miles then 1000 with an oil change after each. It should be over about a month before Bimmerfest, so if I get an opportunity to hit the dyno before then I most certainly will. I also want to get baselines for A/F and all that so I can get as much information as possible about what to change on the TMS M3 tuning to match my motor more advantageously and produce more power. I will be tuning to run 96 octane (half 100 octane race gas, half 91 octane pump gas per tank) because I need it for the high comp anyway, so my ignition timing might as well take advantage of that. For now the extra fuel that the M3 dumps will keep predetonation at bay to help keep the ignition as advanced as possible, but I'll be trimming fuel to optomize A/F as well.

[triggrhaapi]

Ahh, now that I see the M50 rod I see what he's talking about. The M50 rod is radically different than the M52b25 rod. RADICALLY different. I hadn't seen one of them that looked like that before. The ones I have seen look like the M52 rods, but cast as two pieces. The rods he's talking about are stronger diagonally, which they would need to be to handle a detonation event with more timing advance. Man they really skimped out by 1995, because S50 rods look identical to the rod I showed but shorter.

[techno550]

Except for a few things:

1. the block on the M50NV has thicker walls

Does it? and if it does, this is an advantage how?

2. the M50NV has dual valvesprings that handle higher revs better

which is very useful especially when mated to a bottom end that can't handle it... like it can even breathe past 7k anyway.

3. the M50NV needed those and the stronger rods because it didn't have knock sensors.

we know they are stronger how?

The double valvesprings are to compensate for the hotter cam profile used to make up the difference in power from not getting the extra cylinder fill at lower RPM that VANOS provides. (EDIT: Alternatively, they may have been used as a carry over from the M20 which has double valvesprings as stock then removed from the Technology upgrade to save cost)

*MAY* have been a carry over? kinda like the thick valve stems too? perhaps?

I'm not saying that technoS50 is stupid or anything, he just doesn't happen to be right in this instance. The NV rods are not beefier because they weigh more, they are beefier because they have a stronger structure, A beam versus I beam. The triangular shape of the rod provides extra rigidity for it's given weight by translating compression force outward laterally, where the metal's strength is taken advantage of not only in compression but also in tension. If you notice also, where the rod meets the wristpin is wider considerably, which provides more resistance to torsion that would cause the metal to fold one way or the other.

Compressive force is "translated" outward how? Compressive force is compressive force. The M50TU rod actually has more substantial gussets between the pin location and the main section of the rod than the NV rod. This is clearly seen in the picture as well.

what does the width of a beam give us when the beam is in compression?

As for the rod ratio, it's identical as the rod ratio of the S50 because I am using the same crank and same length conrod.

If you are using the same length rod and same crank... why not use the same rods? The S50 rods. Its definately a better rod.

Also, as a counterpoint to your faith in BMW's increasing use of "superior" parts as engines evolve, let me point out that the seperate casting/forging method of producing conrods as used on the M50 and M50TU is structurally superior to the cracked cap method of production as used on the M52 and M54, which is considerably cheaper as only one pattern is needed as opposed to two patters which are needed if you cast and forge seperately.

fractured caps are much better than seperately machined ones. the fractured surface can withstand more loading. This is why many who make high performance engines/connecting rods has gone to this method.

Also pay attention to the fact that without any ability to detect predetonation, BMW had to overbuild the M50NV so that it could withstand detonation if necessary, hence the shorter conrod length (which as you say is less conducive to happy revving) and thicker piston (by the extra 5mm of piston height that using a 5mm shorter conrod would require) These are all to increase structural rigidity re: a detonation event that would put sudden and intense strain on the bottom end assembly in a downward thrust manner.

Knock on a NA motor like the M50 won't be enough to bend a rod. It'll break ring lands way before the rod has an issue. the NV rod is essentially a carryover from the M20. They tried slimming the top as being wider than the pin by a good bit is unnecessary.

The piston crown thickness likely isn't terribly different M50 to M50TU, they primarily moved the wrist pin location up so that they could use a longer rod.

Still with me so far? Ok good.

i follow, but I don't agree.

Now, with the technological advent of knock sensor microphones, BMW could significantly reduce the possibility of detonation, so they could reduce rotational weight by making pistons thinner (the 5mm of piston material is much heavier than 5mm of conrod material), improve the connecting rod ratio and save on cost by building a conrod that used less complex methods of manufacture.

the pistons aren't 5mm thinner. the crown is the same thickness, and the distance to the first ring is the same. The skirt is shorter though. The wrist pin height is different too, and thats your 5mm.
Fractured conrods are a much more advanced method of manufacture. A better one at that.

Ironically, the Tu was still heavier by 4kg than the NV at 198kg. I'm guessing this is due to the weight of the VANOS unit and accompanying hardware.

the ETK lists both the M50 and M50TU remanufactured engines at 132kg.
The vanos bits do add weight, but more than make up for it in both torque and drivability.

[matt]

we know they are stronger how?

Just look at them, duh. It's beefier.

[techno550]

Ahh, now that I see the M50 rod I see what he's talking about. The M50 rod is radically different than the M52b25 rod. RADICALLY different. I hadn't seen one of them that looked like that before. The ones I have seen look like the M52 rods, but cast as two pieces. The rods he's talking about are stronger diagonally, which they would need to be to handle a detonation event with more timing advance. Man they really skimped out by 1995, because S50 rods look identical to the rod I showed but shorter.

I hope we aren't trying to apply intuition to something in which we don't have a very solid background.

Engineering isn't intuition, it is learned. If it were intuitive, we wouldn't go to school for it. If we don't have a solid background in it, and we try to apply intuition, we end up wrong.

Observations without knowledge behind them are very easily misunderstood. Applications of observations should NOT be confused with applications of knowledge.

[triggrhaapi]

Does it? and if it does, this is an advantage how?

It does. I would say that I would be less concerned with heavy structural integrity and be looking for ways to save weight if I had knock sensors that would severely reduce the possibility of a detonation event.

which is very useful especially when mated to a bottom end that can't handle it... like it can even breathe past 7k anyway.

It starts to puff out on it's cams around that, yeah. I'll concede that the double valvesprings are an M20 carryover and we'll call that part of the argument over.

we know they are stronger how?

Compressive force is "translated" outward how? Compressive force is compressive force. The M50TU rod actually has more substantial gussets between the pin location and the main section of the rod than the NV rod. This is clearly seen in the picture as well.

Since I think we are talking about different rods let me tell you that the M50Tu rod you have in your picture I would agree is stronger than the M50NV rod, however the rods which replaced it on later models AND I would say the S50 rods as well are weaker. I am willing to bet the S50 rods are a hair lighter since they're 5mm shorter than the M52b25 rods and the M52b25 rods were only a minute amount heavier despite being longer, since they are practically the same, cracked cap method aside.

what does the width of a beam give us when the beam is in compression?

Resistance to bending. If you saw what happened to Allan's S50 rods you'd know what I'm talking about. The thing buckled and bent 180 degrees, then broke at the end, grenaded the piston skirt and threw that as well as the wristpin out the side of the block, while the piston crown went shooting up to the top of the cylinder.

If you are using the same length rod and same crank... why not use the same rods? The S50 rods. Its definately a better rod.

Um well to be perfectly honest, if you had read this thread all the way through, you would know that I bought those rods because they were 135mm, not because they were some sort of godly amazing invincible superrod. They were cheaper than S50 rods and it just so happens that they ended up being stronger.

fractured caps are much better than seperately machined ones. the fractured surface can withstand more loading. This is why many who make high performance engines/connecting rods has gone to this method.

Ok I'll buy that, they're also cheaper to mass produce, you have to admit that, when you consider that the extra tooling to crack the cap is cheaper in the long run than having to produce seperate pieces.

Knock on a NA motor like the M50 won't be enough to bend a rod. It'll break ring lands way before the rod has an issue. the NV rod is essentially a carryover from the M20. They tried slimming the top as being wider than the pin by a good bit is unnecessary.

Ok. I'll concede that too, again, we're talking about two different rods here. The later M50Tu rods that I have seen look exactly like what I have in my picture, minus the cracked cap stuff. That is the rod I was comparing it to. I hadn't before seen the other M50Tu rod of which you speak, because my M50tu bottom end is still all intact because I'm lazy and I don't have the conrod bearings from my parts guy yet so I can't even do a mock build up to test my math and measurement yet.

The piston crown thickness likely isn't terribly different M50 to M50TU, they primarily moved the wrist pin location up so that they could use a longer rod.

Actually you misunderstood, I never said the crown was thicker, I don't even think I said I used the word "crown." I said the piston was 5mm thicker (which I meant to say taller, but whatever) It looks like I was right. Yup.

i follow, but I don't agree.

Wrong on both accounts, you don't follow, and I don't disagree with you at all.

the pistons aren't 5mm thinner. the crown is the same thickness, and the distance to the first ring is the same. The skirt is shorter though. The wrist pin height is different too, and thats your 5mm.
Fractured conrods are a much more advanced method of manufacture. A better one at that.

First you say likely isn't much different and now they are absolutely not different. And again, I don't necessarily disagree with you, you just misunderstand me.

the ETK lists both the M50 and M50TU remanufactured engines at 132kg.
The vanos bits do add weight, but more than make up for it in both torque and drivability.

My source lists the BMW engineers as it's immediate sources, so whatever, I don't want to get into an embittered argument over 4kg.

[triggrhaapi]

I hope we aren't trying to apply intuition to something in which we don't have a very solid background.

Engineering isn't intuition, it is learned. If it were intuitive, we wouldn't go to school for it. If we don't have a solid background in it, and we try to apply intuition, we end up wrong.

Observations without knowledge behind them are very easily misunderstood. Applications of observations should NOT be confused with applications of knowledge.

Look asshole, I got my ASE when I was 16 fucking years old, my family have been mechanical engineers, electrical engineers and doctors, and I also built my first motor (Supra TT) to 427whp on stock turbines and moderate boost gains when I was 17. Don't go calling my intelligence into question, as I have thus far been respectful to yours. Don't make me call you an arrogant ass.

My grandfather on my dad's side built the house he lived in for 40 years practically by himself (workers aside) and he built his first car out of two different cars when he was 16. My grandfather on my mother's side was one of the engineers who designed the Sparrow air to air missile. My father graduated from Exeter, Harvard and Rutgers Medical school. My mother has two masters degrees in both software engineering and art history.

I have studied fluid dynamics, mechanical engineering, archetecture and I've been building cars for almost ten years now. Read what I've written again, and you'll see that we don't really disagree. I doubt you would say that the M52 rods shown in the picture I posted are stronger than the M50NV rods. I believe that was the point of the argument in the first place.