Greetings, working on my 2.9 stroker M50 swap.

[triggrhaapi]

Re-read what I wrote...
Do you have a solid background in connecting rod design for spark ignition engines? An engineering or physics degree? Can you do the math on beam stress for either of those shapes without looking it up?

No, but to be perfectly honest, I would contest your assumption that having a degree equals having experience. I have several generations of engineering to fall back on and I've read every engineering book that my family has because that shit fucking fascinates me. Some of those are even from harvard, like the fluid dynamics book my dad gave me.

I'm very clear and very matter-of-fact in my tone. The point is precision, and my words are usually selected carefully. If someone makes a statement that shows their hand, I don't see an issue with calling their bluff. Your statements were fairly obviously a shot in the dark, and based on observations that aren't necessairily directly tied to what the laws of physics say.

Your words were selected to establish that you are "obviously" superior to me in some way and you wanted to establish dominance in as short order as possible, which is what I meant by condescension. You assume that you are more intelligent or have more experience or know more or whatever, but so far you haven't proved any of your points any better than I have, you've just turned to attacking my qualifications to justify your arguments. Stick to the facts and prove me wrong with that. I'll have more respect for you that way, and your chances of convincing me will increase.

Everything is a compromise. It is very important to understand that.

I don't think I ever said anything that contradicted that statement. All things being equal, you want the most rigid rod possible. Rigidity is characterized by lack of movement, so as a term it can be used to define either tensile or compression strength. Remember when you said you choose words carefully? So do I.

Ignition should never be violent. The point of peak pressure in a boosted motor and in a NA motor should be largely the same. the peak pressure will vary though.
A wider rod isn't necessairily more rigid either.

I meant violent in the sense that if you have more fuel/air and you are aiming for the same ignition advance point, etc etc, more fuel and air means more energy is released in any given moment. Perhaps violent wasn't the right word. Let's call it more intense, would that be more accurate?

the plane of the beam makes a difference. in-plane stiffness is changed with the shape change.
Aftermarket rods often have different shapes for different purposes. That can be weight, compressive strength, etc... Some of that is design, some is metallurgy, some is machining, etc...

That is the truth I won't doubt you there. Perhaps my point wasn't clear in that I find that the A beam shape is more rigid at angular compression (I, for example would like to see as much as 20 degrees of ignition timing advance if I can when I tune my motor for boost, which would place the point of ignition at a point where the conrod is not perfectly up and down) and will handle what I want better. I have never disagreed that the rigidity in that sense is negligable for N/A even at high compression.

Something with a little flex in the appropriate plane can be more forgiving.

I don't think I agree that the conrod should be the forgiving part in this equasion. Maybe this is due to my belief that when a conrod tweaks everything goes to hell in a handbasket and repair becomes more difficult. I personally disagree with the way that you appear to dismiss failure mode engineering. I think that I would rather see a piston shatter than a conrod deform. At least when that happens the block has a better chance of surviving and staying useable.

NA motors will need strong connecting rods. they won't see tons of loading in compression like a turbo motor though. They need light rods for high revs, but the rod also needs to be increasingly strong in tension. Turbo motors usually have compressive rod failures. NA motors have tensile failures of the rods. it all comes down to how you make your power.

What do you mean by increasingly? I personally have never seen a BMW rod fail in tension. I agree that the narrower shape that has a thicker core would be stronger tensively than the A beam shape, but I hardly think that the A beam rod would fail in tension. As I've said, I think the real benefit is in the weight reduction. Not to offend you or the engineers who made the rods, but calling the benefit tensile strength is jerking off. And this tensile strength argument also contradicts your previous arguments about the newer rods having more compression strength.

A machine shop has machinists... not engineers. Also, see above. Lighter is better, unless it is at the expense of strength.

I disagree with your assumption that machinists are better than engineers. I know alot of machinists who design their own parts, including connecting rods and pistons from scratch, and I would say that a machinist with 40 years of experience is superior to an engineer with a degree and 5 years of experience. Also, I believe that I have repeatedly said that the tradeoff is weight, which I do agree, lighter is better. As for machining the M50NV rods, there is alot of metal that can be shaved without touching the rod structure at all. For example, if you look at the NV rods around the wristpin bearing, there are two protrusions that serve no real purpose. I bet you that's easily 2 grams worth of useless metal right there.

There's a fine line between stiffness and strength.

Ok. Define it. Also notice that I don't use the word "stiffness" ever, I say rigidity, as in to say resistance to movement. In a device where tolerances are as close as they are in an engine, I would say that you don't want things to change their shape very much. Also, if flexibility is a desirable trait, why would forging a rod be desireable? Forging makes metal less pliable and more brittle, which would be bad if you want flexibility. I really need to see how you define this fine line to see if I agree with you here.

turbo motor has a lot more fuel in that fire. bigger boom means more damage. Piston damage can be detonation. it can also be too lean but without knock. certain combinations of mixture and timing run fine, but put a lot of heat into the combustion chamber. you can overheat components and break them that way too.

Yes that's true, metallurgy and design being equal, more material will handle more heat better, as the effective caloric concentration per gram of metal is reduced simply by having more mass to absorb the heat. That is a tradeoff against weight, as more metal is more weight. A classic example of the negative effects of too little weight is the early mazda rotaries, which were known to melt. Without knowing the specifics of the metallurgy of the two rods I decline to make any conclusions either way on this subject as applied to our discussion.

usually if the rod is intact, but the little end is free, the block doesn't survive. a rod slinging around freely in the block usually takes out both sides, the oil pan, the cylinder walls, etc... Never a pretty sight.

I see that you and I have different ideas of what block survival is. I define it as being able to be reused after being reconditioned. I would agree that having the rod slinging around with a broken piece of piston scoring the bore is not my idea of a good time, but despite this, if the bore isn't cracked or scored past a certain point, you can machine it out, put in oversize pistons and call it a day. If the bore is scored past that point, but the block is intact, you can press in new cylinder liners and recondition it that way. Both of those I would say are preferable to the block being destroyed entirely.

see above.

as a side note, people break blocks in the US with race motors, the first thing they do is figure out how to stiffen/reinforce the block. those who choose that path may eventually find a way to stiffen everything enough to not break blocks, and then move on to breaking cranks. (add 4 bolt mains, pan girdles that bolt to the mains, etc...) This is especially true of american engine builders who work on european designed engines.
The europeans go the other way. the block will move with the crank... and thus NOT break. stiffer isn't always better.

Actually I don't think I ever said anything about strengthening blocks or cranks. I think I was talking about rods. So far I think we have established a few things:

1. I agree with you that under boost the rod design should be stronger in compression, and in N/A design a rod should be stronger in tension.

2. The NV rods are stronger in compression and particularly compression at slight angles (resistance to bending) than the S50 rods.

3. I will be ultimately building this motor for boost under twin Mitsu 16Gs, and as an N/A application I originally bought the NV rods because I needed them to be 135mm not because of any of their design characteristics which I really didn't know about until I had them in my hands.

Well I've been on break for almost two hours now so it's back to work for me.

[techno550]

As for turbo550 and wanting to see numbers, I would simply reply by saying, you haven't posted any definitive evidence and neither have I so we might as well be arguing the existence of god.

you made a fairly definite post stating that the NV rod was stronger.... with nothing to back it up and your only "proof" being your observations... and thus you applying your intuition to the matter.

My understanding of the physics behind the shape suggests otherwise. Especially on a NV vs vanos rod comparison.

[techno550]

Actually I didn't flip out about the applying intuition part, it was the part where you assumed I had no idea what I was talking about, when in fact I do.

Re-read what I wrote...
Do you have a solid background in connecting rod design for spark ignition engines? An engineering or physics degree? Can you do the math on beam stress for either of those shapes without looking it up?

I really don't like condescension. You have to admit you drip it everywhere you go. Don't get any on your shoes now. See? I was being condescending there.

I'm very clear and very matter-of-fact in my tone. The point is precision, and my words are usually selected carefully. If someone makes a statement that shows their hand, I don't see an issue with calling their bluff. Your statements were fairly obviously a shot in the dark, and based on observations that aren't necessairily directly tied to what the laws of physics say.

Is stiffer preferred? I would say yes.

Everything is a compromise. It is very important to understand that.

Connecting rods don't serve any dampening function at all,

Very true, but I don't know why anyone would ever think a connecting rod would ever get things wet.

and under forced induction, which eventually these rods will be getting, the point of ignition will be violent and will see the rod recieving the point of ignition at an angle, where a wider rod will be more rigid.

Ignition should never be violent. The point of peak pressure in a boosted motor and in a NA motor should be largely the same. the peak pressure will vary though.
A wider rod isn't necessairily more rigid either.

I would say that if rigidity weren't an issue, why would built aftermarket motors use titanium H beam rods? Or forged A beam rods? If rod rigidity is a negligable factor, why does Carrillo even exist?

the plane of the beam makes a difference. in-plane stiffness is changed with the shape change.
Aftermarket rods often have different shapes for different purposes. That can be weight, compressive strength, etc... Some of that is design, some is metallurgy, some is machining, etc...

Rigidity is a tradeoff against weight. I think that's the point you're trying to make, right? Or is it that you actually believe that the later designs with the narrower beam are that way because it's more rigid? I think they're that way because as you so eloquently put it,

Something with a little flex in the appropriate plane can be more forgiving.

it's not like an N/A motor is going to need a stronger connecting rod, and trimming weight on rotational masses is good for revvability.

NA motors will need strong connecting rods. they won't see tons of loading in compression like a turbo motor though. They need light rods for high revs, but the rod also needs to be increasingly strong in tension. Turbo motors usually have compressive rod failures. NA motors have tensile failures of the rods. it all comes down to how you make your power.

On that note I would like to point out that if I really wanted, a machine shop could trim the few grams difference off of the rod no problem, so close are the two weights.

A machine shop has machinists... not engineers. Also, see above. Lighter is better, unless it is at the expense of strength.

And you still haven't addressed my point about resistance to bending.

There's a fine line between stiffness and strength.

While I've never seen detonation on an N/A motor blow it up in one shot, I have seen turbo motors pop because of it. The block is never really the issue. It's the rods that are always the weak part. Pistons turn into shrapnel when shit goes bad, but a good rod can survive that.

turbo motor has a lot more fuel in that fire. bigger boom means more damage. Piston damage can be detonation. it can also be too lean but without knock. certain combinations of mixture and timing run fine, but put a lot of heat into the combustion chamber. you can overheat components and break them that way too.

Generally if the rod survives, or at least doesn't break or bend too much, the block will survive. I've seen alot of motors explode in my day.

usually if the rod is intact, but the little end is free, the block doesn't survive. a rod slinging around freely in the block usually takes out both sides, the oil pan, the cylinder walls, etc... Never a pretty sight.

Thank god none of them have been because of me and knock on wood they never will, but strictly from a point of observation, I can call the broken rod to broken block correlation a general rule of thumb.

see above.

as a side note, people break blocks in the US with race motors, the first thing they do is figure out how to stiffen/reinforce the block. those who choose that path may eventually find a way to stiffen everything enough to not break blocks, and then move on to breaking cranks. (add 4 bolt mains, pan girdles that bolt to the mains, etc...) This is especially true of american engine builders who work on european designed engines.
The europeans go the other way. the block will move with the crank... and thus NOT break. stiffer isn't always better.

[triggrhaapi]

Rods generally fail after cyclic fatigue has caused the micro cracks in the metal grow to critical levels, and fail from rupture in tension. The I beam you show has smoother transitions through it's geometry, reducing stress concentrations. However, since I don't have the rods with me, I don't know the overall thickness variation between the rods.

I would say that BMW has never made a bad conrod. BMW motors go for fucking ever under normal conditions, so whatever knits we may pick about this and that, nothing is going to fail just driving around or even running the engine to hell and back. I still say that under forced induction, I would rather have the M50 NV rod, despite the extra weight versus an S50 rod. Ultimately though, I would rather have an H beam rod made of titanium (and might if I can find one that doesn't have a logo embossed on the damn thing, which severely reduces the strength of the rod)

As for turbo550 and wanting to see numbers, I would simply reply by saying, you haven't posted any definitive evidence and neither have I so we might as well be arguing the existence of god. I have my opinion you have yours and I don't think either of us will be swayed to the other's side. If you want to ruin a couple rods and really quantify which is better, be my guest.

[triggrhaapi]

I agree the NV rod would provide greater bending resistance, however I don't feel bending is really the predominant mechanism of failure in the normal operation of an engine. Once things get out of wack, such as your S50 'rod taffy' you mentioned :D, sure, then the bending resistance of a NV rod caused by the wider cross section of the A beam (and overall larger moment of inertia) would be superior to the I beam rod, but those circumstances are rarely considered, since the whole system has already failed.

Rods generally fail after cyclic fatigue has caused the micro cracks in the metal grow to critical levels, and fail from rupture in tension. The I beam you show has smoother transitions through it's geometry, reducing stress concentrations. However, since I don't have the rods with me, I don't know the overall thickness variation between the rods.

Shot-peening reduces the chance of failure from crack propagation by putting residual compression forces on the surface of the metal, allowing more tension to be transmitted at the surface (by first having to negate the residual compression)

Shot-peening also cleans up the surface of the metal, and removes any irregularities that would produce stress concentrations (sites of crack growth)

Lets keep this a good civil discussion guys :up: In no way is a debate on an internet forum considered a valid test of intelligence

I don't disagree with you. I never said that them being stronger gave me any sort of advantage in normal N/A operation. I would agree that it in fact doesn't. I will also reiterate that under boost and in the event that things go south for whatever reason, a stronger rod will increase the chances of my block surviving, a point which I freely admit is based on strict observation and nothing else. I saw a guy blow up a motor once under something around 25psi and the rod survived entirely, the piston disintegrated and then the leftovers scored the hell out of the block, but it lived and after some machine work and second oversize pistons, it was back in business.

EDIT: iirc, the NV rods are thinner in the middle, but thicker along the edges where the majority of the structure of the rod is.

[triggrhaapi]

Show me the numbers. Stronger in tension? compression? resistance to twist? by how much? Or are you just GUESSING? Applying intuition based on rod shape alone?

Is this stronger? or stiffer? is stiffer preferred? is there such a thing as too stiff? too little flexability?

I make a general post about "be careful applying intuition" and you flip out.

There's a difference between making a guess and making an educated guess. There's also a big problem with people making a guess and passing that off as fact.

Actually I didn't flip out about the applying intuition part, it was the part where you assumed I had no idea what I was talking about, when in fact I do. I really don't like condescension. You have to admit you drip it everywhere you go. Don't get any on your shoes now. See? I was being condescending there.

Is stiffer preferred? I would say yes. Connecting rods don't serve any dampening function at all, and under forced induction, which eventually these rods will be getting, the point of ignition will be violent and will see the rod recieving the point of ignition at an angle, where a wider rod will be more rigid. I would say that if rigidity weren't an issue, why would built aftermarket motors use titanium H beam rods? Or forged A beam rods? If rod rigidity is a negligable factor, why does Carrillo even exist?

Rigidity is a tradeoff against weight. I think that's the point you're trying to make, right? Or is it that you actually believe that the later designs with the narrower beam are that way because it's more rigid? I think they're that way because as you so eloquently put it, it's not like an N/A motor is going to need a stronger connecting rod, and trimming weight on rotational masses is good for revvability. On that note I would like to point out that if I really wanted, a machine shop could trim the few grams difference off of the rod no problem, so close are the two weights. And you still haven't addressed my point about resistance to bending. While I've never seen detonation on an N/A motor blow it up in one shot, I have seen turbo motors pop because of it. The block is never really the issue. It's the rods that are always the weak part. Pistons turn into shrapnel when shit goes bad, but a good rod can survive that. Generally if the rod survives, or at least doesn't break or bend too much, the block will survive. I've seen alot of motors explode in my day. Thank god none of them have been because of me and knock on wood they never will, but strictly from a point of observation, I can call the broken rod to broken block correlation a general rule of thumb.

[BimmerToad]

I agree the NV rod would provide greater bending resistance, however I don't feel bending is really the predominant mechanism of failure in the normal operation of an engine. Once things get out of wack, such as your S50 'rod taffy' you mentioned :D, sure, then the bending resistance of a NV rod caused by the wider cross section of the A beam (and overall larger moment of inertia) would be superior to the I beam rod, but those circumstances are rarely considered, since the whole system has already failed.

Rods generally fail after cyclic fatigue has caused the micro cracks in the metal grow to critical levels, and fail from rupture in tension. The I beam you show has smoother transitions through it's geometry, reducing stress concentrations. However, since I don't have the rods with me, I don't know the overall thickness variation between the rods.

Shot-peening reduces the chance of failure from crack propagation by putting residual compression forces on the surface of the metal, allowing more tension to be transmitted at the surface (by first having to negate the residual compression)

Shot-peening also cleans up the surface of the metal, and removes any irregularities that would produce stress concentrations (sites of crack growth)

Lets keep this a good civil discussion guys :up: In no way is a debate on an internet forum considered a valid test of intelligence

[triggrhaapi]

That's an inside joke having nothing to do with you or this thread.

It's alright, I forgive you.

[techno550]

They were cheaper than S50 rods and it just so happens that they ended up being stronger.

Show me the numbers. Stronger in tension? compression? resistance to twist? by how much? Or are you just GUESSING? Applying intuition based on rod shape alone?

Is this stronger? or stiffer? is stiffer preferred? is there such a thing as too stiff? too little flexability?

I make a general post about "be careful applying intuition" and you flip out.

There's a difference between making a guess and making an educated guess. There's also a big problem with people making a guess and passing that off as fact.

[BimmerToad]

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.

The tooling required to crack a rod probably is negligible compared to the stamping and die equipment needed for a separate forging.

A cracked cap rod is also superior since the crack keeps the rod and cap in line of the grain of the metal, producing a more seamless fit.

[triggrhaapi]

Which one is which? NV on the left?

NV on the right.

[BimmerToad]

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.

Which one is which? NV on the left?

[matt]

You are such a schmuck. Way to call in the guy who's actually smart enough to argue on my intellectual level and then ride on his coattails to deliver a cheap shot.

That's an inside joke having nothing to do with you or this thread.

[triggrhaapi]

yeah i slowly building my nv 2.9 but i was going to use a .98" vac mls hg to get compression to 11.4-1. im using all nv m50 stuff execpt for the later 2.5 piston and s50 crank. i have not test fitted the block and head with the stock hg yet should do that this weekend.also are you reliving the valves your self or having the machine shop do it?

The machine shop. I'm smart enough to know that I don't have the equipment to measure the valve pockets or the necessary skill with any of the machining tools one could use to take out .45mm only and not a hundredth more. Or, for that matter, the tools.

[triggrhaapi]

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

You are such a schmuck. Way to call in the guy who's actually smart enough to argue on my intellectual level and then ride on his coattails to deliver a cheap shot.