Greetings, working on my 2.9 stroker M50 swap.

[triggrhaapi]

Now lets look at a connecting rod. We have a BEAM with bearings on both ends. if we apply an in-plane load to it, nothing moves. if we put a lateral load on it, there is no load change on the beam, and it just moves sidways pivoting on the bearings. I'd hate to be forced to draw you a picture. (I got good at those while getting my physics degree.)

Hahahahahaha I get to reply to this with a quote from my last post!

You're assuming too much. You're assuming that the conrod bearing and crankshaft bearing are properly aligned and lubricated. First you ignore failure mode engineering and now you suck at talking about it. Ok, when something fails, what happens? It doesn't work right. Let's go under the assumption that... um... ok how about a big rock hits the oil pan and the oil goes out and now your bearing is starved for oil and seizes. No lubrication in the bearing at all. Now your translative force is applied to the rod at the same time as the engine pings and BOOM. The rod compresses hard under high boost knock and fails, now the translative force is applied and it bends. Now what happens?

- failure modes. I covered this already, but bending is WAY better than breaking. A bent rod is still attached to the piston and crank, and might not even touch the cylinder walls. A broken rod does bad things.

Yay! I get to save time and do it again!

If it had more resistance to bending, which I believe would mean that it bends less (not doesn't bend at all which is what you seem to think I'm saying) it wouldn't break it would bend less

- Notice that I give an engineering reason behind something, like the difference between H beam and I beam rods, and you come back with some OBSERVATION like someone has used them in an engine that did X. Thats not a good argument. I can move the level of discussion between rod designs up to the math behind it, can you? would your "my buddies EVO used those rods and didn't break" hold up well in those cases? If its an engineering discussion, keep it that way.

Fair enough, let's look at the structure then. An H is an I turned sideways, and in this case turned in such a way that, as you said before, the bulk of the beam is two flat plates joined in the middle. The whole reason that those rods exist in the first place at all is to resist bending. The structure isn't terribly resilient bending it the direction perpendicular to the to the direction of rotation, so clearly this design points out that stresses in that direction are non existant, which makes alot of sense. However, the H beam design is very very strong in the plane of the direction of rotation, more so than an I beam design. The fact that people make these should really prove something to you. There is a lateral translative force applied here,and it only rears it's ugly head when the system starts to fail. You're still ignoring that if the crankshaft suddenly doesn't want to rotate properly, the rod stops undergoing compression only along the length of the beam. You're still assuming that when something fails, the system still works and that makes about as much sense as a fat girl buying a size 1 bikini, while being admittedly much less repulsive.

-

I'm amused that you think you're a surgeon and that engineers are gods. but if thats the case, why are you arguing with me? You very ovbiously don't understand this stuff. reply with a diagram of the forces on a connecting rod and maybe I'll explain it to you some more.

[/QUOTE]

Notice that I said relative terms? God I have to explain everything to you. Ok, what does god do? He makes stuff. What do engineers do? They make stuff.. Still with me? Ok. What do surgeons do? They fix people when they break (that is probably using the least elegant terms possible to describe the job, but whatever). What do mechanics do? They fix cars when they break.

So therefore surgeons pointing out god's mistakes are akin to in this case a mechanic pointing out an engineer's mistakes, using something I learned in college, the literary device known as metaphor.And yes, I was saying that you only seem to think that you're an engineer. Prove it and design a better rod with a superior failure mode.

[techno550]

Well this proves that trying to be curteous during an argument on the internet is pointless.

Here's another translation from an engineer buddy of mine:

"wtf? Hell, just the fact that H-beams exist should be proof that there are lateral forces: those lateral forces are more evenly distributed in an H-beam rod, which is why they can be stronger in compressive stress situations."

Thats a translation? what language does he speak?

Lets look at H beam versus I beam here for a sec...

H beam: easy to machine from billet. made popular ~4 decades ago by carillo. Still popular mostly because its an obvious change from stock. Usually long thin ribs that are much longer in the plane of the rod. The ribs being deeper increase the stiffness in plane, but they are also generally so thin that they want to flex at the outside edges allowing the beam to bend.

I-beam: easier to forge. Typical OE construction for rods. It allows for more in-plane flex and is generally more forgiving because of that.

Both are approximately equal in tensile strength.

H beam rods are more popular in applications where no detonation will occur. I beam is more popular in applications where detonation may occur as they are more forgiving. At least thats how it works in engeering race cars world. The street car side of things loosely follows this as its "engineering" is largely based on occasional observation of what race cars do... and not always looking at a comparable race car setup.

We can go as deep into this topic as you'd like.

[techno550]

Replying to your post line by line is too time consuming and you're too stupid to see what I'm saying anyway. You twist my words and misunderstand my points and arguments. It is PAINFULLY obvious you don't understand the argument. that was my basic math example above...
so down to bullet points.

- you continue to say "angular compression". In physics i know of no such thing as it applies to a connecting rod. I can apply it to light, and I can apply it to data in a CS sense (I have 2 CS degrees, btw.)

Now lets look at a connecting rod. We have a BEAM with bearings on both ends. if we apply an in-plane load to it, nothing moves. if we put a lateral load on it, there is no load change on the beam, and it just moves sidways pivoting on the bearings. I'd hate to be forced to draw you a picture. (I got good at those while getting my physics degree.)

- failure modes. I covered this already, but bending is WAY better than breaking. A bent rod is still attached to the piston and crank, and might not even touch the cylinder walls. A broken rod does bad things.

the picture I wanted to link before is this:


- Notice that I give an engineering reason behind something, like the difference between H beam and I beam rods, and you come back with some OBSERVATION like someone has used them in an engine that did X. Thats not a good argument. I can move the level of discussion between rod designs up to the math behind it, can you? would your "my buddies EVO used those rods and didn't break" hold up well in those cases? If its an engineering discussion, keep it that way.

- I'm amused that you think you're a surgeon and that engineers are gods. but if thats the case, why are you arguing with me? You very ovbiously don't understand this stuff. reply with a diagram of the forces on a connecting rod and maybe I'll explain it to you some more.

[02stu]

Engineers suck

[FredK]

Hmm, I believe this is the thread with the highest average word count per post in r3vlimited history. This is a momentous day in history!

[triggrhaapi]

Well this proves that trying to be curteous during an argument on the internet is pointless.

Here's another translation from an engineer buddy of mine:

"wtf? Hell, just the fact that H-beams exist should be proof that there are lateral forces: those lateral forces are more evenly distributed in an H-beam rod, which is why they can be stronger in compressive stress situations."

[bmdubya84]

Actually, to be perfectly honest, this is more along the lines of a surgeon pointing out god's mistakes. Except you only think you're god, I know I'm a surgeon. In relative terms.

LOL! OMG TECHNO YOU GOT SERVED SON! god, please stop arguing....just pull out the ruler and end this madness

[triggrhaapi]

There's a lot of "tone" here, especially given that i'm trying to be nice and helpful in my corrections. You know when you try to help a 3rd grader with their math homework and they try 3 x 7 and come up with something other than 21... and argue with you over the answer?

Yes, I'm sorry billy, I'll give you a calculator so you can finish your arithmetic.

your selection of words shows me that you haven't covered a lot of engineering books. Your description of how things work also shows that. I'm not being an ass, I'm stating a fact.

Ok so because I don't use the same terms as you I can't possibly know what I'm talking about. Of course, how could I be so stupid. I use different terms, yes that's a great argument.

A degree means that you read the books, took the test, and PASSED. There are plenty of people who read the books and don't understand it as well as they should... and thus they don't pass and don't get a degree. Sorry, thats not just how I feel, its how it works. Guess which group you have something in common with...

The group that never took the test I guess. That's really conclusive. Wonderful thinking dumbass. Now what about the standards of the test? Hmm I know alot of morons who graduated college with engineering degrees. Memorizing things for the span of a final is the ultimate way to demonstrate intelligence. Don't make me get into that. You didn't graduate from any terribly impressive school or you would have mentioned that by now. I know because you're arrogant and you would have worked that in. Without any reasonably groundbreaking standard, I'm still not impressed. I have passed many of my college classes (in computer science, in the engineering department of my unimpressive college) while not trying in the slightest. Sorry, not convinced there. Just because I had a different major, don't mistake me for a fool.

By that definition, when is the rod not at an angle? TDC and BDC? We were discussing your "angular compression". which is just compression ... where the rod happens to be at an angle to some other frame of reference? the rod is still just in compression. The force is still compressive. in the middle of the rod, what does the force look like? Is it at some funky angle, or is it just in the plane of the rod?

Actually I'm talking about angular compression in a failure mode, where resistance to bending is important. You never addressed that ever. I've seen the rod you're talking about fail. With eyes that are in my head and attatched to my brain. I.E. real world application not just some stupid test you took about how shit SHOULD work. This is how it does. The rod bent really well, yes sirreeee... 180 degrees then it snapped. Remember how you said that was bad? Well it was. Really bad. If it had more resistance to bending, which I believe would mean that it bends less (not doesn't bend at all which is what you seem to think I'm saying) it wouldn't break it would bend less and the piston grenading would have taken up the slack and it would have done just what i said, which is score the balls out of the block but live to die another day. Failure mode engineering, a term you keep ignoring.

the lateral translative force does not go through the rod. the rod has all in plane loading. the forces on the "other" axis go through the block.
The observation you made is possibly correct, but your conclusion is wrong. the bending always happens in the direction of rotation of the crank because the crank is emparting a force on the rod. the most common reason for bending like this is the piston can load the rod in such a way as to twist it. the piston can spin freely in the bore without issue, and translate that twist to the rod. the rod however cannot twist freely and without consequence, and binds on the big end grabbing the crank. Even if that isn't the main cause of the bend, it is part of it, and the reason for the direction of the bend.

You're assuming too much. You're assuming that the conrod bearing and crankshaft bearing are properly aligned and lubricated. First you ignore failure mode engineering and now you suck at talking about it. Ok, when something fails, what happens? It doesn't work right. Let's go under the assumption that... um... ok how about a big rock hits the oil pan and the oil goes out and now your bearing is starved for oil and seizes. No lubrication in the bearing at all. Now your translative force is applied to the rod at the same time as the engine pings and BOOM. The rod compresses hard under high boost knock and fails, now the translative force is applied and it bends. Now what happens?

Ok I suck at talking in your language apparently so I have officially called in a translator....

" The real instance of lateral force comes from the rotational component of motion inherant to the rod. It points always outward away from the crankshaft's center, but that's sometimes parallel, and sometimes, perpendicular, to the conrod's length."

And when that fails?

AHA!! A valid argument pertinent to our discussion! Eureka!

When an H beam rod fails, if and when that happens, I'm certain that it would buckle and bend inward, folding the structure on itself like when you watch an I beam bend on a bridge when it collapses. It would probably do so in a fairly linear manner and absorb a FUCKTON of energy in the process, thus averting disaster and saving our fair city. Err, engine.

I beam rods are more forgiving. they allow more flex in plane and thus are less likely to be damaged by detonation. H beam rods are stiffer in that plane, which isn't always a good thing. The H also usually has longer THINNER ribs that can flex and allow the rod to bend in a bad direction.

Which is why nobody in their right mind would buy a titanium H beam rod ever and put it into an EVO making almost 1000whp. Nope. You're right. I'm an idiot.

Crank twist is large. Hollow camshafts are unhappy in BENDING. They don't do that in a running engine. Much of the hardness required there is for wear properties. They don't have the harmonic issues of the crank either from both stiffness and reduced rotational speed.

Yes they are unhappy in bending but they like twisting. I'm actually not being sarcastic, I agree. I'm just using that to show that if I put words in your mouth and argue against them, I can be a jackass on the internet too. Now you know how I feel.

I notice that you are upset being wrong. Every time you reply you reveal more of what you think you know but don't. Perhaps you are in a family of engineers, but unfortunately knowledge like that isn't passed through the placenta. You've probably read or heard enough to know some of the lingo, but not enough to understand the principles.

Uh huh. You're so right. Yes. You are so superior to me. I'm sorry I ever doubted you. You are the master of the universe. All hail king you, master of the terminology.

My dad is a doctor, my mom is a nurse, I've read enough and been around enough to have a decent understanding of the basics, but I don't argue medicine with surgeons.

Actually, to be perfectly honest, this is more along the lines of a surgeon pointing out god's mistakes. Except you only think you're god, I know I'm a surgeon. In relative terms.

[techno550]

There's a lot of "tone" here, especially given that i'm trying to be nice and helpful in my corrections. You know when you try to help a 3rd grader with their math homework and they try 3 x 7 and come up with something other than 21... and argue with you over the answer?

your selection of words shows me that you haven't covered a lot of engineering books. Your description of how things work also shows that. I'm not being an ass, I'm stating a fact.

A degree means that you read the same books I have and took tests that I didn't. I'm sorry but unless you graduated from MIT or Cal Tech, I really don't think you have a better base than I do. Sorry if that concept is offensive to you but it's how I feel.

A degree means that you read the books, took the test, and PASSED. There are plenty of people who read the books and don't understand it as well as they should... and thus they don't pass and don't get a degree. Sorry, thats not just how I feel, its how it works. Guess which group you have something in common with...

Where the connecting rod is at an angle. See? Amazing.

By that definition, when is the rod not at an angle? TDC and BDC? We were discussing your "angular compression". which is just compression ... where the rod happens to be at an angle to some other frame of reference? the rod is still just in compression. The force is still compressive. in the middle of the rod, what does the force look like? Is it at some funky angle, or is it just in the plane of the rod?

Actually that's only partially true. The majority of the loading on the rod is in plane with the rod itself, however, some of the force is also laterally translated. If it were directly in line with the rod, then why would a weak rod always bend in the direction of the higher side of the rod (when cocked at an angle) I could build something of a mock up to prove this to you if you really want. I've experimented with that before, granted it's a bit different with metal than with a straw or something of the like, but it's the same essential idea.

the lateral translative force does not go through the rod. the rod has all in plane loading. the forces on the "other" axis go through the block.
The observation you made is possibly correct, but your conclusion is wrong. the bending always happens in the direction of rotation of the crank because the crank is emparting a force on the rod. the most common reason for bending like this is the piston can load the rod in such a way as to twist it. the piston can spin freely in the bore without issue, and translate that twist to the rod. the rod however cannot twist freely and without consequence, and binds on the big end grabbing the crank. Even if that isn't the main cause of the bend, it is part of it, and the reason for the direction of the bend.

Actually, somebody like me would look at something like what happened to the S50 rod and go ahead and say fuck that, and go with an H beam rod instead.

And when that fails?

I beam rods are more forgiving. they allow more flex in plane and thus are less likely to be damaged by detonation. H beam rods are stiffer in that plane, which isn't always a good thing. The H also usually has longer THINNER ribs that can flex and allow the rod to bend in a bad direction.

Ok, so parts deform, yes. Tiny amounts. The crank twisting under load is a relatively minute movement. By the way, if you want a prime example of what I'm talking about, the hollow camshafts that the M/S50 series engines employ are extremely brittle. Seemingly in contradiction to your design criteria. So brittle in fact that special methods of installation are required to avoid breaking them. Everything moves, sure but in such small amounts that the knits you're picking about my argument are invalid. Stop trying to make this about how smart you are and how dumb I am. It makes you look like a jerk. And in this case, a wrong jerk.

Crank twist is large. Hollow camshafts are unhappy in BENDING. They don't do that in a running engine. Much of the hardness required there is for wear properties. They don't have the harmonic issues of the crank either from both stiffness and reduced rotational speed.

What I take from it is that you get off on trying to correct people. And you're a jerk.

I notice that you are upset being wrong. Every time you reply you reveal more of what you think you know but don't. Perhaps you are in a family of engineers, but unfortunately knowledge like that isn't passed through the placenta. You've probably read or heard enough to know some of the lingo, but not enough to understand the principles.

My dad is a doctor, my mom is a nurse, I've read enough and been around enough to have a decent understanding of the basics, but I don't argue medicine with surgeons.

[triggrhaapi]

I think that was more of a comment on your ideas of how engines work...



as a side note, more material doesn't change any of that unless its adding surface area on the dissapative side. This is why oil sprayers are used. Something to carry the heat away. More material isn't a fix.

I never said it was a fix, did I, again you made an assumption.

Block survival is not breaking in the first place. A bent rod means the engine is rebuildable. a broken rod means the engine isn't, as it has a "ventilated" crank case and such.

you get 3 guesses at what did this:

I'm going to go ahead and point something out. When somebody says "survives in one piece, maybe bent a little, but one piece" that means that it did not break, whereas when they say "when it breaks" that means that it broke. I just have to be a little bit of a jerk, and I'm sorry.

Oh and 3 guesses as to what did what?

Now where did this come from? and what the hell is compression at an angle? compression perhaps? the force on the rod is still in one plane.

Actually that still isn't true. Since the application of force on the connection point isn't straight on, you get a slight lateral application of force (slight means a small fraction of the application in the plane of the rod), nothing remotely enough to bend it under normal load, but when the rod fails compressively (which I admit happens first) the extra force will always dictate what direction it bends when it fails.

definately read up on more motor stuff, engineering stuff, and especially IC engine theory stuff. A physics book or two probably wouldn't hurt either.

Why? Because I bought 135mm connecting rods? I'm just building a stroker kit out of stock parts man, jesus. $20 says that when I assemble it, install it in my car and turn the key, it will start, run and produce exactly the amount of power that I expect it to.

I'm going to offer you some advice in return.

1. Seriously, remove the stick from your ass. It's not supposed to be there I'm sure of it.

2. When you're having a discussion with somebody, stop waiting for them to make a mistake that you can jump on, because you'll lose focus on the discussion and, just as you have repeatedly done, end up looking like an asshole when you correct them without understanding what you're correcting.

3. What happens when you assume? Come on I know you've heard this one before...

[triggrhaapi]

Degree does not mean experience. but no degree often means poor or flawed understanding, and experience with flawed understanding isn't a good thing. It works well for some, as with many things its more important to know what happens and how to avoid it than WHY it happens. But when discussing the how's and the why's, understanding is key.

Drop a bowling ball and a feather at the same time and which one hits the ground first? why? what does the uneducated man take away from this? Does that apply in a vacuum?

A degree means that you read the same books I have and took tests that I didn't. I'm sorry but unless you graduated from MIT or Cal Tech, I really don't think you have a better base than I do. Sorry if that concept is offensive to you but it's how I feel.

As for the bowling ball/feather thing, in atmosphere the feather will flutter around as the air passes around it, slowing it's rate of descent. The same clearly does not apply if there is no air. I actually did that experiment in high school, if they taught you that in college then I'm sorry.

My tone is a corrective one as I am correcting things. More of this below...

You are so arrogant. Holy hell are you arrogant.

You don't want the most rigid anything possible. its a compromise. rigid usually ends up being brittle too. soft and springy can apply, but in a very relative sense.

You also don't read very well, I actually brought this up.

its not an explosion that happens at the instant the plug fires. The plug firing lights the charge. Its then a smooth controlled burn. Its like lighting a log. The initial bit is energy input to start the reaction, then the energy release is growing, but still in a stable fashion. More wood will mean a bigger fire, but at no point should violent be a term used to describe the burn.

Did I say explosion? No, stop putting words in my mouth. I'm actually starting to hate you because you keep doing that. You still suck at reading.

Honestly, I stopped reading after this bit the first go-round. There was definately a "not worth my time" moment had, but for your sake, and the sake of others in this thread, I will reply to all of it.

I still hate you here.

There is no angular compression. its just compression. Moreover, I suggest looking into an IC engine theory book.

You're about to prove yourself wrong. Keep talking.

when you tune ignition timing, you play with the time of peak cylinder pressure. the usual "best" is whatever gives you peak pressure 10-15 degrees after TDC where it can give lots of work from the pressure.

Where the connecting rod is at an angle. See? Amazing.

At all points though, the loading on the rod is in the plane of the rod. Crank angle does not change the load characteristics of the rod. Crank speed can to an extent, but thats through drag on the rod via its connection points.

Actually that's only partially true. The majority of the loading on the rod is in plane with the rod itself, however, some of the force is also laterally translated. If it were directly in line with the rod, then why would a weak rod always bend in the direction of the higher side of the rod (when cocked at an angle) I could build something of a mock up to prove this to you if you really want. I've experimented with that before, granted it's a bit different with metal than with a straw or something of the like, but it's the same essential idea.

For starters, a rod is only as strong as its weakest point. This is why most are I or H beam rods. In tension, both are equal. In compression, they are different, and each has its advantages.

Rod stretch is a very real problem though. that is virtually ALL of the rod failures in a naturally aspirated engine. Inertia is a bitch like that.

So how do I disagree with you here again?

I didn't say that they were. Engineers and machinists generally take very different approaches to solving problems. A machinist will look at a rod that failed and make the part that failed thicker. An engineer will look at that same rod and same point... then leave that point alone and make everthing else smaller and lighter.

Actually, somebody like me would look at something like what happened to the S50 rod and go ahead and say fuck that, and go with an H beam rod instead.

BTW, the other thing that bothers me is when non-engineers such as yourself look at something like the protrusions on a connecting rod and assume that they serve no real purpose. You think those are there because someone said "hey Klaus, lets put some random fucking bumps on the little end of this rod... maybe it'll stir some shit up on an internet forum in 15 years." Kinda like the random triangular protursion from the airbox or the unnecessairily heavy pulley with some weird rubber layer in the middle on the front of the motor.

Well ok then if it serves such a noble purpose then why did BMW eliminate those protrusions from the later rod designs?

resistance to movement is probably not the best description. What we are shooting for here is something that relates to deformation. Axial stiffness or bending stiffness.

Ok, so parts deform, yes. Tiny amounts. The crank twisting under load is a relatively minute movement. By the way, if you want a prime example of what I'm talking about, the hollow camshafts that the M/S50 series engines employ are extremely brittle. Seemingly in contradiction to your design criteria. So brittle in fact that special methods of installation are required to avoid breaking them. Everything moves, sure but in such small amounts that the knits you're picking about my argument are invalid. Stop trying to make this about how smart you are and how dumb I am. It makes you look like a jerk. And in this case, a wrong jerk.

I continue to correct you with the word stiffness because of my background. You continue to say rigidity because of yours. take from that what you will...

What I take from it is that you get off on trying to correct people. And you're a jerk.

On the things in the engine not changing shape... good luck with that. The crank will bend and twist and flex, as do the rods, as do the pistons, as do the cams. They vibrate, they shake, they resonate, they MOVE. They do this for hundreds of thousands of miles of abuse. You make them stiff, or too stiff, and they snap... quickly.

Things that can move a little can still be strong. often stronger and more resilient than things that would be stiffer and snap.

Yeah uh huh, I refer you back to the M50 camshafts.

[techno550]

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.

I think that was more of a comment on your ideas of how engines work...



as a side note, more material doesn't change any of that unless its adding surface area on the dissapative side. This is why oil sprayers are used. Something to carry the heat away. More material isn't a fix.

I see that you and I have different ideas of what block survival is.

Block survival is not breaking in the first place. A bent rod means the engine is rebuildable. a broken rod means the engine isn't, as it has a "ventilated" crank case and such.

you get 3 guesses at what did this:

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:

those were examples.

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.

I was just highlighting the differences.

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

now where did this come from? and what the hell is compression at an angle? compression perhaps? the force on the rod is still in one plane.

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.

definately read up on more motor stuff, engineering stuff, and especially IC engine theory stuff. A physics book or two probably wouldn't hurt either.

[techno550]

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.

Degree does not mean experience. but no degree often means poor or flawed understanding, and experience with flawed understanding isn't a good thing. It works well for some, as with many things its more important to know what happens and how to avoid it than WHY it happens. But when discussing the how's and the why's, understanding is key.

Drop a bowling ball and a feather at the same time and which one hits the ground first? why? what does the uneducated man take away from this? Does that apply in a vacuum?

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.

My tone is a corrective one as I am correcting things. More of this below...

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.

You don't want the most rigid anything possible. its a compromise. rigid usually ends up being brittle too. soft and springy can apply, but in a very relative sense.

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?

its not an explosion that happens at the instant the plug fires. The plug firing lights the charge. Its then a smooth controlled burn. Its like lighting a log. The initial bit is energy input to start the reaction, then the energy release is growing, but still in a stable fashion. More wood will mean a bigger fire, but at no point should violent be a term used to describe the burn.

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.

Honestly, I stopped reading after this bit the first go-round. There was definately a "not worth my time" moment had, but for your sake, and the sake of others in this thread, I will reply to all of it.


There is no angular compression. its just compression. Moreover, I suggest looking into an IC engine theory book.

At 20 degrees of advance, you are shooting for lighting the charge then. The crank is not at TDC yet, and the rod is likewise not in plane with the crank/piston either. There is basically no pressure increase from the burn at this point though. Even through TDC, the pressure increase is building slowly. The point of peak pressure is usually targeted around 10 degrees ATDC. Ideally, one could target 90 degrees, as this is maximum torque from maximum leverage on the crank, but its just not fesable.
You also would never want to have peak cylinder pressure terribly early. before TDC and it resists the crank turning. at TDC, it does NO work and only loads the main bearings. The whole point of lighting the charge in the first place is to get work out of it.

when you tune ignition timing, you play with the time of peak cylinder pressure. the usual "best" is whatever gives you peak pressure 10-15 degrees after TDC where it can give lots of work from the pressure. the pressure falls off quickly after that as the volume grows quickly then too. Before that point, and you have no leverage on the crank.

At all points though, the loading on the rod is in the plane of the rod. Crank angle does not change the load characteristics of the rod. Crank speed can to an extent, but thats through drag on the rod via its connection points.

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.

I don't think you realize how much the insides of a motor bend, twist, and flex. The crank will twist some number of degrees on firing events. Rods wiggle and flex too. If they don't they snap. The size of the plane of the rod dictates how much it can move without stress issues.

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.

For starters, a rod is only as strong as its weakest point. This is why most are I or H beam rods. In tension, both are equal. In compression, they are different, and each has its advantages.

Rod stretch is a very real problem though. that is virtually ALL of the rod failures in a naturally aspirated engine. Inertia is a bitch like that.

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.

I didn't say that they were. Engineers and machinists generally take very different approaches to solving problems. A machinist will look at a rod that failed and make the part that failed thicker. An engineer will look at that same rod and same point... then leave that point alone and make everthing else smaller and lighter.

BTW, the other thing that bothers me is when non-engineers such as yourself look at something like the protrusions on a connecting rod and assume that they serve no real purpose. You think those are there because someone said "hey Klaus, lets put some random fucking bumps on the little end of this rod... maybe it'll stir some shit up on an internet forum in 15 years." Kinda like the random triangular protursion from the airbox or the unnecessairily heavy pulley with some weird rubber layer in the middle on the front of the motor.

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.

resistance to movement is probably not the best description. What we are shooting for here is something that relates to deformation. Axial stiffness or bending stiffness.

I continue to correct you with the word stiffness because of my background. You continue to say rigidity because of yours. take from that what you will...


On the things in the engine not changing shape... good luck with that. The crank will bend and twist and flex, as do the rods, as do the pistons, as do the cams. They vibrate, they shake, they resonate, they MOVE. They do this for hundreds of thousands of miles of abuse. You make them stiff, or too stiff, and they snap... quickly.

Things that can move a little can still be strong. often stronger and more resilient than things that would be stiffer and snap.

[triggrhaapi]

And just to reiterate for the third or fourth time, I am talking about the S50 and later M52 rod, an example of which i have posted on page 2, which is different than the M50Tu rod that I think you are talking about.

[triggrhaapi]

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.

Umm you really haven't done anything differently. I don't see any definitive evidence, I just see opinion and conjecture based on your experience and training. I'm not impressed by this argument.