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Billet aluminum connecting rods

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  • Billet aluminum connecting rods

    We are all familiar with the commonly available forged steel connecting rods on the market, but what are your thoughts on billet aluminum rods? LOTS of drag race and V8 street/strip builds use aluminum rods. They have apparently been shown to withstand power loads similar or greater to comparable steel parts, and reduce the weight of your rotating assembly so much (especially with lightweight pistons) that the inertial load decrease would permit easily another 1000-2000rpm with the same margin of safety.

    Now, maybe I'm just reading into this too much... but I can get custom billet rod sets made for under $900 easily. Why don't I ever see Z31 people do this?

    Billet AL connecting rods are CNC machined from special extruded aluminum alloy plates that provide a combination of high strength, high fracture toughness and very good resistance to fatigue crack propagation at high stress levels. Another small benefit is they can come highly polished, so it moves through oil windage easier because less oil clings to the rod during operation.

  • #2
    In a somewhat related topic... boy I'm quite a dork tonight... I just read this guy's entire paper and actually really liked it:

    http://em-ntserver.unl.edu/Mechanics-Pa ... s%20VI.htm

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    • #3
      They might withstand a lot of power yes, but for how long is my question...I am speaking about long term only of course and for a street driven car. It seems to me that with the malleability of aluminum, you'd always risk the possibility of "egging" your rods over time no matter how tight your tolerances (like aluminum driveshafts). I am however speaking purely from a speculative standpoint, as I do not have any experience with this, and I'd always be open to listening to other ideas or stories.

      1987 Nissan 300ZX Turbo (Budget Supercar)
      1987 Nissan 200SX SE (Old School FR)
      1994 Nissan Sentra SE-R (Balls To The Wall Track Car)
      2000 Nissan Maxima SE (Daily Driver)
      2006 Scion tC (Wife Whip)

      In an ideal world I would have all ten fingers on my left hand, so my right hand could just be a fist for punching.

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      • #4
        Jason84NA2T wrote: In a somewhat related topic... boy I'm quite a dork tonight... I just read this guy's entire paper and actually really liked it:

        http://em-ntserver.unl.edu/Mechanics-Pa ... s%20VI.htm
        Why did he caluclate the compressive force of the combustion, then use a tensile strength plot to decide what range to stay out of? The rod bolts are the most likely to fail before the rod itself from tensile stresses, the rods are beefy to withstand the compression forces, so you'd need to calculate when the rod is likely to buckle. That diagram is like this:


        http://www.efunda.com/formulae/solid_me ... _steel.cfm

        btw- I'm placing an 'I just woke up' qualifier on all the thinking I've just done in case I missed something obvious 8)
        *****************************
        1988 300ZX Turbo SS
        2000 BMW 323Ci
        2003 BMW 325XiT

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        • #5
          Wow this place makes me feel so dumb sometimes! That graph reminds me of math class, god I hate math lol
          http://youtube.com/c/zcartube

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          • #6
            yes, I for one wouldn't trust aluminum on anything but a low powered small cylinder application, if the compression/heat is too high it will deform that is a given

            how much? how soon? dunno....

            then think about the possibility of stripping out the threads in the rod studs -- you will need thru-bolts for all of them

            then how about collapsing/squishing/distorting the aluminum ends where those bolts are creating excessive slop leading to failure

            even if good aluminum has similar strengths to steel in a particular case... good steel will still be approximately 4x stronger for the same quantity material

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            • #7
              G-E wrote: yes, I for one wouldn't trust aluminum on anything but a low powered small cylinder application, if the compression/heat is too high it will deform that is a given

              how much? how soon? dunno....

              then think about the possibility of stripping out the threads in the rod studs -- you will need thru-bolts for all of them

              then how about collapsing/squishing/distorting the aluminum ends where those bolts are creating excessive slop leading to failure

              even if good aluminum has similar strengths to steel in a particular case... good steel will still be approximately 4x stronger for the same quantity material
              Well, I initially had the same doubts as you guys, but found not only are they use in a few OEM applications, but also many people use them on everything from SBC's to 1400hp supercharged V8 buicks spinning at 8000RPM. Do some searching and reading, apparently egging due to the maliable nature of the material is a non-issue. They're talking well over 100K lifespan on lower powered engines.

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              • #8
                why not just go out and order a custom set of Oliver titanium rods? :twisted:

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                • #9
                  I've got a local company that can make alluminum and titanium connecting rods (GRP) http://www.grpconrods.com/

                  I have no experiance with the aluminum rods however time and time again I have heard that they are NOT good for daily driven cars, only race cars. Ironically these are all people that have never tried the rods and they have just heard what I have heard. :roll:

                  what is the weight of an aluminum rod for one vehicle compared to a steel rod for the same vehicle? typically you have to use allmost twice as much aluminum to be equal to the strenght of steel :shock:
                  85 Z31 6.0 LSX turbo 766whp/792wtq
                  04 GTO, LS6, big cam, porting, N20... underway for summertime daily driver.

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                  • #10
                    After reading a couple articles like this one, I'll stick with steel.

                    http://www.rrconnectingrods.com/choosing.htm

                    1987 Nissan 300ZX Turbo (Budget Supercar)
                    1987 Nissan 200SX SE (Old School FR)
                    1994 Nissan Sentra SE-R (Balls To The Wall Track Car)
                    2000 Nissan Maxima SE (Daily Driver)
                    2006 Scion tC (Wife Whip)

                    In an ideal world I would have all ten fingers on my left hand, so my right hand could just be a fist for punching.

                    Comment


                    • #11
                      Taris Blue wrote: After reading a couple articles like this one, I'll stick with steel.

                      http://www.rrconnectingrods.com/choosing.htm
                      That was a good explination as to why an aluminum rod CAN break sooner than a steel rod.
                      85 Z31 6.0 LSX turbo 766whp/792wtq
                      04 GTO, LS6, big cam, porting, N20... underway for summertime daily driver.

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                      • #12
                        The most stress on the rods is on intake stroke.
                        BLOZ UP.com
                        It is not recommended to confirm proper installation by driving into walls or other barriers as this could cause personal injury or damage to the vehicle.

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                        • #13
                          In those SBC's running 1400 hp with aluminum rods most of the engines are torn down and inspected every few runs. I understand that our rides will not be inspected like these and we will not be running those insane numbers but I could see the rods lasting quite a long time... I am thinking like 20-30k before rod failure at the longest.

                          Another issue could be clearance, the rods will be larger. Will the block have to be modified? What will need to be changed to make a set work?

                          I would like to have actual data taken from this build, if someone does decide to go this route. I can set up data recorders and instrumentation for this data.
                          Shiro Special # 981 Being assembled in my spare time Chromoly acquired!
                          Originally posted by BoostedMamma
                          Heads up makes teh panties drop. BUT I don't have a penis OR a fast car, so I guess my opinion doesn't count.

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                          • #14
                            Racinjitter wrote: In those SBC's running 1400 hp with aluminum rods most of the engines are torn down and inspected every few runs. I understand that our rides will not be inspected like these and we will not be running those insane numbers but I could see the rods lasting quite a long time... I am thinking like 20-30k before rod failure at the longest.

                            Another issue could be clearance, the rods will be larger. Will the block have to be modified? What will need to be changed to make a set work?

                            I would like to have actual data taken from this build, if someone does decide to go this route. I can set up data recorders and instrumentation for this data.
                            I'm hearing they don't really have issues with fatigue, and more modern alloys have replaced those known to have had problems in the past. Who knows if it's true. Bob at Finnishline was telling me he had over 1000 passes on a set that was used in one of his 750hp NA engines, then he sold them used to a guy who has since put another 200 passes on them in a new boosted engine. He also claims they have been shown to be reliable in street-strip setups for many years.

                            They can apparently be machined to whatever size can be accommodated by the engine in question, and typically drop over 40% of the rod's reciprocating mass. Mind you, that's reciprocating, NOT rotational mass! That translates to huge gains in the engine's engine acceleration AND the inertial loads placed on the rod itself.

                            I still remain skeptical of everything until I try it, so I'm reading information on both sides and wondering what the real truth is. Who knows, it may be something to try in the future when I have lots of spare money to throw around (yeah, right).

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                            • #15
                              well i did some looking into aluminum and titanium rods when i started my det build.first ti rods are way too damn expensive over 500 a rod,all of the aluminum rods i have found had the note "all rods are .010" shorter than advertised" why is that? could it be that they will stretch?almost all people that are looking for serious hp have the block deck cut to have a zero deck height.now if you had alum rods and had block cut down for zero deck height when the rod streched it wuold smack the head.i just dont like the fact that the rods are going to stretch period.
                              live fast,drive hard,and enjoy the ride!

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