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  1. #1
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    Titanium connecting rods with holes in the shaft to remove material for less weight?

    Titanium is already lightweight and in a connecting rod it is used obviously for strength. Well, have you seen this approach before? Taking a titanium rod and removing material.

    Seems like self-defeating but I guess since the material is titanium it is still stronger than some OEM cast rod while being much lighter. Material is obviously removed to keep it as light as possible so in a high revving application that is paramount.

    These are going in a 12000 rpm all motor Honda B-Series stroker:

    Click here to enlarge

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    Those look $#@!ing sexy. Click here to enlarge

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    Click here to enlarge Originally Posted by DFM Click here to enlarge
    Those look $#@!ing sexy. Click here to enlarge
    Yes but I wonder how strong they still are.

    Still, very cool.

    Everything that tuner does is insane.
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    We have sold titanium S62 rods in the past. Made by Arrow Precision (same company who makes our S54 stroker crank and the finest BMW rods available)

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    Click here to enlarge Originally Posted by Mike@VAC Click here to enlarge
    We have sold titanium S62 rods in the past. Made by Arrow Precision (same company who makes our S54 stroker crank and the finest BMW rods available)
    Yes of course but have you done any rods like this?

    I'm wondering how much weaker this is than a standard rod.
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    4 out of 4 members liked this post. Reputation: Yes | No
    Im willing to bet the strength reduction is negligible. It depends on if they did their HW on where to cut metal out of them. On compression (which is the biggest force on a con rod) the material will attempt to spread in a lateral direction (perpendicular to the direction of the force vector). its all a matter of having enough material (in the right places) to counter this lateral spread.

    Now I'm deviating from what I know to be true and just speculating. The very high RPM will probably put a lot more stress on a regular con rod than it will this one, due to the reduced weight. Having less stress due to high RPM's means that what strength there is in these "holey" con rods will be better optimized to deal with the compressing force applied on it from the piston. like I said, just speculation. could be just talking out of my $#@!...im no expert on this stuff.

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    Click here to enlarge Originally Posted by DFM Click here to enlarge
    Im willing to bet the strength reduction is negligible. It depends on if they did their HW on where to cut metal out of them. On compression (which is the biggest force on a con rod) the material will attempt to spread in a lateral direction (perpendicular to the direction of the force vector). its all a matter of having enough material (in the right places) to counter this lateral spread.

    Now I'm deviating from what I know to be true and just speculating. The very high RPM will probably put a lot more stress on a regular con rod than it will this one, due to the reduced weight. Having less stress due to high RPM's means that what strength there is in these "holey" con rods will be better optimized to deal with the compressing force applied on it from the piston. like I said, just speculation. could be just talking out of my $#@!...im no expert on this stuff.
    I wasn't expecting this good of a post out of you.
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    Click here to enlarge Originally Posted by Sticky Click here to enlarge
    I wasn't expecting this good of a post out of you.
    ...thanks? I have a very intelligent mind when it comes to all things mechanical, just no will power to apply it (yet).

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    Probably good for high revving etc but maybe not for boosting applications. Honda motors always high hp no torque.
    Burger Motorsports
    Home of the Worlds fastest N20s, N54s, N55s, S55s, N63s, and S63s!

    It is the sole responsibility of the purchaser and installer of any BMS part to employ the correct installation techniques required to ensure the proper operation of BMS parts, and BMS disclaims any and all liability for any part failure due to improper installation or use. It is the sole responsibility of the customer to verify that the use of their vehicle and items purchased comply with federal, state and local regulations. BMS claims no legal federal, state or local certification concerning pollution controlled motor vehicles or mandated emissions requirements. BMS products labeled for use only in competition racing vehicles may only be used on competition racing vehicles operated exclusively on a closed course in conjunction with a sanctioned racing event, in accordance with all federal and state laws, and may never be operated on public roads/highways. Please click here for more information on legal requirements related to use of BMS parts.

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    Click here to enlarge Originally Posted by fastgti69 Click here to enlarge
    Probably good for high revving etc but maybe not for boosting applications. Honda motors always high hp no torque.
    My question is could you still rev as high with a rod that didn't have the material removed?
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    Click here to enlarge Originally Posted by Sticky Click here to enlarge
    My question is could you still rev as high with a rod that didn't have the material removed?
    Haha, good question. That might make the difference between 10k and 12k.. who knows.
    Burger Motorsports
    Home of the Worlds fastest N20s, N54s, N55s, S55s, N63s, and S63s!

    It is the sole responsibility of the purchaser and installer of any BMS part to employ the correct installation techniques required to ensure the proper operation of BMS parts, and BMS disclaims any and all liability for any part failure due to improper installation or use. It is the sole responsibility of the customer to verify that the use of their vehicle and items purchased comply with federal, state and local regulations. BMS claims no legal federal, state or local certification concerning pollution controlled motor vehicles or mandated emissions requirements. BMS products labeled for use only in competition racing vehicles may only be used on competition racing vehicles operated exclusively on a closed course in conjunction with a sanctioned racing event, in accordance with all federal and state laws, and may never be operated on public roads/highways. Please click here for more information on legal requirements related to use of BMS parts.

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    Click here to enlarge Originally Posted by DFM Click here to enlarge
    Im willing to bet the strength reduction is negligible. It depends on if they did their HW on where to cut metal out of them. On compression (which is the biggest force on a con rod) the material will attempt to spread in a lateral direction (perpendicular to the direction of the force vector). its all a matter of having enough material (in the right places) to counter this lateral spread.

    Now I'm deviating from what I know to be true and just speculating. The very high RPM will probably put a lot more stress on a regular con rod than it will this one, due to the reduced weight. Having less stress due to high RPM's means that what strength there is in these "holey" con rods will be better optimized to deal with the compressing force applied on it from the piston. like I said, just speculation. could be just talking out of my $#@!...im no expert on this stuff.
    Someone with some expertise want to correct me? if im wrong about any of this id like to know.

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    Looks pretty cool

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    Click here to enlarge Originally Posted by DFM Click here to enlarge
    Someone with some expertise want to correct me? if im wrong about any of this id like to know.
    Here's a good read if you want to learn more about it --> http://www.engdyn.com/images/uploads...aper_(kea).pdf

    It's a bit of a boring read, but is detailed - and explains the tension and compressive pressures acting on the rod. I didn't really understand the lateral expansion - not sure if that's true - definitely some stretching and compression occurs. I guess it could expand outwards - but I think the main stress is acted longitudinally. Could be wrong - been a long time since the ridiculous amount of physics classes I had to take.

    I am guessing that the amount of weight that is cut offsets the reduction in strength. I am guessing rods like that are magnafluxed, shotpeened, etc. - but who knows. They definitely look up to the task for those high RPMs though. Bad ass stuff.

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    Click here to enlarge Originally Posted by inlineS54B32 Click here to enlarge
    Here's a good read if you want to learn more about it --> http://www.engdyn.com/images/uploads...aper_(kea).pdf

    It's a bit of a boring read, but is detailed - and explains the tension and compressive pressures acting on the rod. I didn't really understand the lateral expansion - not sure if that's true - definitely some stretching and compression occurs. I guess it could expand outwards - but I think the main stress is acted longitudinally. Could be wrong - been a long time since the ridiculous amount of physics classes I had to take.

    I am guessing that the amount of weight that is cut offsets the reduction in strength. I am guessing rods like that are magnafluxed, shotpeened, etc. - but who knows. They definitely look up to the task for those high RPMs though. Bad ass stuff.
    The lateral expansion is a result of pushing the material to its breaking point with compression force. as the con rod approaches its breaking point with compression force, the material tries to push out laterally, because its the only direction the force can go. If you take something long and skinny, compress it really hard from both ends, it will turn into a flat pancake (lateral expansion). Make more sense? not sure if I explained it any better or not, lol.

    EDIT: TY for the tech article. reading now

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    Right - I see what you mean... I thought you were saying that the lateral expansion was the sole/only resultant of the force vector - which isn't true... I gothca now.
    Last edited by inlineS54B32; 05-17-2013 at 06:14 PM. Reason: clear intent

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    2 out of 2 members liked this post. Reputation: Yes | No
    Titanium is still a material that wear quite a lot, and that concerns me when it comes to the hobby performance market.

    I made a comparison of H-profile forged steel rods for mye M20 turbo a few years back and compared them to stock cast rods in a metalurgy x-ray machine. The operator told me that the allignment in the metal structure/molecule almost was as important as the material chosen. He also spoke about the rod angle being a factor you had to calculate when making an extreme reving engine. Square engines are a given for longevity. He had done many x-ray jobs for different drag race top fuel teams and usually got a set of 40 rods from a manufactorer (where half usually was returned), and the team told him to pick out the 16 most suited for their application on the base of the metal structure alignment and the data they supported him on angles, pressures and such. He told me high end manufacturers usually had good quality control and did perform sample x-rays from time to time, but it was no where near good enough for "extreme" engines such as top fuel and Formula 3. If the metal molecules was densed up in the in the top end of a H-beam rod the chanse for it to break was bigger than if the molecules was evenly distributed.

    He also had tested many low end "china" rods, and many of the cheaper onces where nowhere near as strong as the material they claim they had used should support. I witnessed myself when he performed a strech test on a cast and forged h-rods. The cast just went into pieces, where the forged just snapped of into two parts leaving a "strech mark" on either side.

    Anyway, maybe i went a bit of topic. And sorry for the bad grammer Click here to enlarge The theory behind " a perfect engine" interest me. The Veyron I belive has Titanium rods, but as every production car they have big displacment and low boost. I'm curious to find out how long they would have lasted if it was the other way around, as it is for us tuner guys.

  18. #18
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    Click here to enlarge Originally Posted by oddis Click here to enlarge
    He also spoke about the rod angle being a factor you had to calculate when making an extreme reving engine.
    This is a very important part in high revving engines absolutely.
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    Thanks for that info, @oddis
    rep'd

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    if you look at pinnacles of competitive Motorsport with engines turning even much higher than this you dont see things like this. it looks like this rod was designed by someone who considered loads applied statically. id be concerned about the stiffness of the rod. by looks of it machining a I-beam or H-beam rod would be lighter

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    Click here to enlarge Originally Posted by digger Click here to enlarge
    if you look at pinnacles of competitive Motorsport with engines turning even much higher than this you dont see things like this. it looks like this rod was designed by someone who considered loads applied statically. id be concerned about the stiffness of the rod. by looks of it machining a I-beam or H-beam rod would be lighter
    Interesting input and you are right I don't think I have ever seen anything like this is any motorsport.
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    Click here to enlarge Originally Posted by Sticky Click here to enlarge
    Interesting input and you are right I don't think I have ever seen anything like this is any motorsport.
    if they machined those teardrops and slots from bothsides and not all the way through leaving 2mm in the centre the stiffness (so it is has shear strength for carrying bending loads) would be alot better for not much weight. Modern concerns with rods is stiffness because of the effect on ring seal and bearing life. materials and processes these days are exceptional in high performance aftermarket rods failure is mostly from bad tunes creating detonation, oiling issues, rod bolt problem or over revving. a failure in the main beam is less common than before and largely why I-beam and H-beam and X-beam all coexist, each can be made to work

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    Click here to enlarge Originally Posted by digger Click here to enlarge
    if they machined those teardrops and slots from bothsides and not all the way through leaving 2mm in the centre the stiffness (so it is has shear strength for carrying bending loads) would be alot better for not much weight. Modern concerns with rods is stiffness because of the effect on ring seal and bearing life. materials and processes these days are exceptional in high performance aftermarket rods failure is mostly from bad tunes creating detonation, oiling issues, rod bolt problem or over revving. a failure in the main beam is less common than before and largely why I-beam and H-beam and X-beam all coexist, each can be made to work
    Good post. Leaving the 2mm of Ti in the middle is a really good idea. You/someone capable should test this out.

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    4 out of 4 members liked this post. Reputation: Yes | No
    Click here to enlarge Originally Posted by DFM Click here to enlarge
    Im willing to bet the strength reduction is negligible. It depends on if they did their HW on where to cut metal out of them. On compression (which is the biggest force on a con rod) the material will attempt to spread in a lateral direction (perpendicular to the direction of the force vector). its all a matter of having enough material (in the right places) to counter this lateral spread.
    This is partially correct.

    The material does expand in the lateral direction under compression, just as it shrinks in the lateral direction under tension, but this isn't very important. The relationship you're referring to is Poisson's ratio (http://en.wikipedia.org/wiki/Poisson's_ratio).

    For pretty much all compression members except for those that are very short and stubby, buckling is the failure mode (.http://en.wikipedia.org/wiki/Buckling) Buckling is governed by the elastic modulus of the material, the bending moment of inertia (this is a property of the geometric cross-section, and by far the most important property to look at after selecting the rod material), and the radius of gyration (which is the square root of the inertia divided by the gross area of the cross section). Use inertia if you want a buckling force, radius of gyration if you want a buckling stress. Length and end conditions are also a factor, but usually the length is the length and you're not going to make any changes there. End conditions can also be considered a constant.

    I said bending moment of inertia is the most important factor, now here is some of the math behind it. To simplify things let's assume a solid square rod with a perfectly square cross-section. The bending inertia is (1/12)*width*height^3. This property is calculated along two axes. Think of a credit card. You can hold it flat on each end and bend it easily and it's very flappy. Hold it right side up and try to bend it and your fingers will probably start slipping because it's now too stiff to bend. That is the bending moment of inertia at work. You haven't changed anything about the material but now you're trying to bend it on its strong axis and it has much more strength/resistance.

    What you're seeing is the effect of the height being cubed in the inertia equation, this is incredibly important to recognize. For every linear increment the height is increased, the maximum stress is reduced exponentially. There is also an area*distance^2 component (think about the top and bottom flanges of an I-beam when it is bending. We'll keep it simple and forget about that for now though).

    I'll leave it to the reader to do the math. But basically when you have a solid cross-section, the moment of inertia is not drastically affected when material is removed near the center. It's all about keeping a lot of material on the edges.

    That's the how and the why those cut outs. The locations and shapes are in the details, but it's all based around maintaining a minimum moment of inertia (on both the strong and weak axis).

    I suspect tension is mainly looked at for the rod bolt/wrist pin design, and has little effect on the design of the main part of the rod. I may be wrong though, I design bridges for a living, not engines.

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    Click here to enlarge Originally Posted by anotherm3 Click here to enlarge
    This is partially correct.

    The material does expand in the lateral direction under compression, just as it shrinks in the lateral direction under tension, but this isn't very important. The relationship you're referring to is Poisson's ratio (http://en.wikipedia.org/wiki/Poisson's_ratio).

    For pretty much all compression members except for those that are very short and stubby, buckling is the failure mode (.http://en.wikipedia.org/wiki/Buckling) Buckling is governed by the elastic modulus of the material, the bending moment of inertia (this is a property of the geometric cross-section, and by far the most important property to look at after selecting the rod material), and the radius of gyration (which is the square root of the inertia divided by the gross area of the cross section). Use inertia if you want a buckling force, radius of gyration if you want a buckling stress. Length and end conditions are also a factor, but usually the length is the length and you're not going to make any changes there. End conditions can also be considered a constant.

    I said bending moment of inertia is the most important factor, now here is some of the math behind it. To simplify things let's assume a solid square rod with a perfectly square cross-section. The bending inertia is (1/12)*width*height^3. This property is calculated along two axes. Think of a credit card. You can hold it flat on each end and bend it easily and it's very flappy. Hold it right side up and try to bend it and your fingers will probably start slipping because it's now too stiff to bend. That is the bending moment of inertia at work. You haven't changed anything about the material but now you're trying to bend it on its strong axis and it has much more strength/resistance.

    What you're seeing is the effect of the height being cubed in the inertia equation, this is incredibly important to recognize. For every linear increment the height is increased, the maximum stress is reduced exponentially. There is also an area*distance^2 component (think about the top and bottom flanges of an I-beam when it is bending. We'll keep it simple and forget about that for now though).

    I'll leave it to the reader to do the math. But basically when you have a solid cross-section, the moment of inertia is not drastically affected when material is removed near the center. It's all about keeping a lot of material on the edges.

    That's the how and the why those cut outs. The locations and shapes are in the details, but it's all based around maintaining a minimum moment of inertia (on both the strong and weak axis).

    I suspect tension is mainly looked at for the rod bolt/wrist pin design, and has little effect on the design of the main part of the rod. I may be wrong though, I design bridges for a living, not engines.
    Great post @anotherm3 and welcome to the forum. Thank you for clarifying that for me. I really enjoy learning about the physics involved with cars and the math behind it.

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