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    • You will want to build your BMW F80 M3 / F82 M4 S55 motor past 700 lb-ft of wheel torque - Bent rod

      What you see here is a bent S55 rod. What caused it to bend? Abuse at around 763 rear wheel horsepower and 748 lb-ft of rear wheel torque. BimmerBoost will not tell you the tuner or turbo kit as that is not the point here. The point is the S55 will not last long past 700 lb-ft at the wheels.


      How it is driven and tuned of course play a factor and this S55 the owner knew he was going to pop it. He kept pushing the turbos and beating on the car knowing full well an engine rebuild would come sooner or later. That was part of the testing procedure.

      If you want peace of mind, upgrade the rods and you might as well do the pistons when getting into the 7XX+ range too. Otherwise, it's just a matter of time.

      This article was originally published in forum thread: You will want to build your BMW F80 M3 / F82 M4 S55 motor past 700 lb-ft of wheel torque - Bent rod started by Sticky View original post
      Comments 30 Comments
      1. 135idct's Avatar
        135idct -
        same as n55 rods
      1. Sticky's Avatar
        Sticky -
        Click here to enlarge Originally Posted by 135idct Click here to enlarge
        same as n55 rods
        I assume the rods are different?
      1. martymil's Avatar
        martymil -
        anything past 600 hp is a ticking time bomb, all it takes is a bad batch of fuel or not so ideal conditions.

        I bad missfire or a set of repeated super kocks on the same cylinder for what ever reason eg bad spark plug, coil or injector and your kissing 15k goodbye.

        You can almost halve your rebuild cost if you rebuild prior to the engine letting go.

        As stated it's not if but when.
      1. YouAreMyWorld's Avatar
        YouAreMyWorld -
        Click here to enlarge Originally Posted by Sticky Click here to enlarge
        I assume the rods are different?
        Actually, if I recall correctly, the N55 & S55 share the same exact rods.
      1. Sales@KRATOS's Avatar
        Sales@KRATOS -
        Click here to enlarge Originally Posted by martymil Click here to enlarge
        anything past 600 hp is a ticking time bomb, all it takes is a bad batch of fuel or not so ideal conditions.

        I bad missfire or a set of repeated super kocks on the same cylinder for what ever reason eg bad spark plug, coil or injector and your kissing 15k goodbye.

        You can almost halve your rebuild cost if you rebuild prior to the engine letting go.

        As stated it's not if but when.
        We would have to respectfully disagree. Repeated misfires and knocking in the same cylinder from bad spark plugs, coils, or injectors is not common at all on the S55 platform. If we were discussing the N54 platform, then it would be understandable. Typically, these scenarios would only occur as a result of extremely poor or inexperienced tuning which would result in engine failures even well below 600whp with stock turbos.

        We've have several beta test S55's both on the street as well as full endurance race cars with stock engines that we have limited the power from 650-700whp/wtq via BM3 with our turbos system due to stock internals. These cars have been at this power level for over a year and a half now without issue or fail. Keep in mind that our beta test cars do include a 25 Hour Endurance Race Car that is constantly pushed well beyond the limit of what any daily driver would ever see. It's been our experience that anything over 700whp/wtq run consistently or on a daily basis is just not reliable with stock connecting rods. Therefore, we tend to be on the conservative side and recommend that 650-675whp/wtq is safe and reliable on stock internals. However, we do recommend with any turbo upgrade an upgraded crank hub should be installed as well.
      1. Sales@KRATOS's Avatar
        Sales@KRATOS -
        Click here to enlarge Originally Posted by YouAreMyWorld Click here to enlarge
        Actually, if I recall correctly, the N55 & S55 share the same exact rods.
        Many people across this platform as well as some top level rod manufactures share this same opinion. To the point that some rod manufacturers have even printed it in their catalogues that way. Unfortunately, it is not correct though. The stock N55 connecting rod is in fact longer than the S55 and is a completely different part number. However, that doesn't mean it won't fit or work. The stock N55 rod will fit in the S55, but will bump compression up from 10.2:1 to 11.8:1 compression with the stock head gasket based on the calculation used to deduce Vsw (Swept Volume) and Vcl (Clearance Volume). We caught this issue when building our own S55 blocks. Any experienced engine builder should have caught this a long time ago, so we were extremely surprised when one particular and very popular manufacturer told us that they'd been selling this package to quite a few shops and customers for well over a year now. What makes this information so important is that when comparing dyno information of a stock engine with turbo upgrades vs. a built engine with turbo upgrades, it's not a fair analysis without knowing which connecting rod length or compression ratio was used for the built engine. In the end, more than a whole point higher in compression will result in much higher hp/tq at the same boost level as well as less lag.
      1. Sales@KRATOS's Avatar
        Sales@KRATOS -
        Click here to enlarge Originally Posted by Sales@KRATOS Click here to enlarge
        Many people across this platform as well as some top level rod manufactures share this same opinion. To the point that some rod manufacturers have even printed it in their catalogues that way. Unfortunately, it is not correct though. The stock N55 connecting rod is in fact longer than the S55 and is a completely different part number. However, that doesn't mean it won't fit or work. The stock N55 rod will fit in the S55, but will bump compression up from 10.2:1 to 11.8:1 compression with the stock head gasket based on the calculation used to deduce Vsw (Swept Volume) and Vcl (Clearance Volume). We caught this issue when building our own S55 blocks. Any experienced engine builder should have caught this a long time ago, so we were extremely surprised when one particular and very popular manufacturer told us that they'd been selling this package to quite a few shops and customers for well over a year now. What makes this information so important is that when comparing dyno information of a stock engine with turbo upgrades vs. a built engine with turbo upgrades, it's not a fair analysis without knowing which connecting rod length or compression ratio was used for the built engine. In the end, more than a whole point higher in compression will result in much higher hp/tq at the same boost level as well as less lag.
        A correction needed to be made on this post, but unfortunately we didn't catch it in time to edit the original post. The compression ratio information we posted previously was accidentally posted incorrectly. The stock compression on the S55 is 10.2:1. However, if the N55 connecting rod is used with the stock head gasket the compression ratio will increase to 11.6:1 not 11.8:1.
      1. sahyoun's Avatar
        sahyoun -
        Click here to enlarge Originally Posted by Sales@KRATOS Click here to enlarge
        A correction needed to be made on this post, but unfortunately we didn't catch it in time to edit the original post. The compression ratio information we posted previously was accidentally posted incorrectly. The stock compression on the S55 is 10.2:1. However, if the N55 connecting rod is used with the stock head gasket the compression ratio will increase to 11.6:1 not 11.8:1.
        That is incorrect. The part number is 11247624615, the same as all n55 engines. You can run the part number if you dont believe me. The rods are the same, they have to be since the cranks are dimensionally the same and the s55/n55/n54 all share the same stroke and comp ratios. The rods between the n54 and n55/s55 are identical except there is an extra machining operation on the wrist pin whole to create a more distributed load when the wrist pin slightly bends in the elastic region. This is all from the bmw technical documents. All the turbo 4 and 6 rods are forged steel fracture split rods.
      1. Sales@KRATOS's Avatar
        Sales@KRATOS -
        Attachment 57585Attachment 57586
        The part number 11247624615 you listed is correct for a N55. However, the correct part number for the S55 connecting rod is 11247624408. Please see the pictures attached of the stock S55 connecting rod out of one our own M3's. There are 2 pictures attached so you can see the part number as well as the complete piston and rod assembly. You can clearly see where the numbers 7624408 are stamped on the connecting rod. Listed below are the centerlines of the wrist pin bore as well as the centerlines of the crankshaft bore for the connecting rods for the N54, N55, and S55. These values were taken from the CMM which is the industry standard and not from a set of calipers.

        N54: 5.709"CC
        N55: 5.683"CC
        S55: 5.642"CC

        The differences may seem minute, but when calculating compression there is a vast difference. Although, they all share the same compression that doesn't necessarily mean they have the same rod length CC. Here's the formula below to deduce compression ratio for the S55 engine with stock head gasket and stock compression piston with the N55 connecting rod part number you listed. All you have to do is increase the stroke value to reflect the difference in rod length CC between the N55 and the S55 connecting rods.

        CR= (Vsw + Vcl)/Vcl
        Vsw (Swept Volume) = (Cyl Dia/2)² x π x Stroke
        Vcl (Clearance Volume) = Vcombustion (Cylinder Head CC) + Vpiston (Piston CC) + Vgasket (Compressed Thickness x .7854 x Bore²) + Vdeck clearance (Bore Dia/2)² x π x Deck Clearance)
      1. Eleventeen's Avatar
        Eleventeen -
        Click here to enlarge Originally Posted by sahyoun Click here to enlarge
        The rods are the same, they have to be since the cranks are dimensionally the same and the s55/n55/n54 all share the same stroke and comp ratios.
        This is not necessarily the case. You can have a longer rod with the same stroke, volume, and CR by moving the wrist pin higher up the piston. This helps to reduce side loading of the piston, a common practice on performance engine builds.

        http://www.enginebuildermag.com/2016...ng-rod-ratios/
      1. martymil's Avatar
        martymil -
        What are you disagreeing wiith ?

        All I said it doesnt take much for things to go pear shaped past 600hp for things to turn ugly fast and gave a few examples not thats the what will cause them to fail and that it will be cheaper to rebuild the engine before it does so it doesnt happen and it doesnt cost as much

        Our fuel is $#@! and inconsistant here in oz and ive seen a couple of engines engines go bad here from spinning crank hubs and bent rods.

        Its easy to say we have plenty of engines running around with those power levels with no issues and when one lets go what do you say, oh sorry its the first one, bad luck ?

        Prevention is cheaper than cure.
      1. sahyoun's Avatar
        sahyoun -
        I understand but in light of bmw cost cutting it would make no sense to change rod dimensions. The part number you gave me doesn't really pull up anything but did find a few sets of used n55 rods for sale with the same number. The s55 single rod part number is 11247846593 but they may have revised it. The n55 does not have the part number since it is only sold as a set of 6 and not individually. I called my local dealer to confirm what realoem shows, they are the same rods. Realoem may be wrong but the part numbers I pull up for the rods matches with the dealer. This wouldnt be the first time there are incorrect part numbers but the dealer did confirm it which is strange.
      1. Sales@KRATOS's Avatar
        Sales@KRATOS -
        Click here to enlarge Originally Posted by martymil Click here to enlarge
        What are you disagreeing wiith ?

        All I said it doesnt take much for things to go pear shaped past 600hp for things to turn ugly fast and gave a few examples not thats the what will cause them to fail and that it will be cheaper to rebuild the engine before it does so it doesnt happen and it doesnt cost as much

        Our fuel is $#@! and inconsistant here in oz and ive seen a couple of engines engines go bad here from spinning crank hubs and bent rods.

        Its easy to say we have plenty of engines running around with those power levels with no issues and when one lets go what do you say, oh sorry its the first one, bad luck ?

        Prevention is cheaper than cure.
        The disagreement was based on the theoretical figure of 600hp you stated as a ticking time bomb, which is simply not true on this platform as long as the crank hub is upgraded.

        Inconsistent fuel can have the same effect on a 550whp stock turbo car as well as 600whp turbo upgraded car and could cause the same damage. What we're discussing here the is the safe limit of the stock engine with all other factors being equal.

        What you're not taking into account is the increased cylinder pressures and heat when running stock turbos or hybrid turbos at levels of boost not designed for stock manifolds with small AR ratios. This is where running larger manifolds with increased AR ratio reduces cylinder pressure and heat at a given boost level. This exponentially reduces the risk of engine failure when comparing a hybrid turbo stock manifold car vs. a car with fully upgraded turbo with larger runners and increased AR ratio manifold both running at 650whp.

        The argument of what if one fails is also theoretical since we're discussing factual data and not the assumption that something might fail or go wrong. The discussion and our position is based on our experience with real world data under the harshest of environments which is endurance track racing.

        We are both in agreement that it is best to prevent engine failures by building the engine preemptively when planning on doing any sort of major hp adders, as waiting for the engine to fail first could be catastrophic and cost much more in the long run. However, our disagreement is at what level of power is this a necessity or requirement. Based on the beta testing and data we've collected since the S55 platform was released, we know the limits we recommended can be had safely with our hardware as high cylinder pressures and heat play a major role at a given hp level when running stock manifolds. As we respect your opinion, we would have to agree to disagree.
      1. Sales@KRATOS's Avatar
        Sales@KRATOS -
        Click here to enlarge Originally Posted by sahyoun Click here to enlarge
        I understand but in light of bmw cost cutting it would make no sense to change rod dimensions. The part number you gave me doesn't really pull up anything but did find a few sets of used n55 rods for sale with the same number. The s55 single rod part number is 11247846593 but they may have revised it. The n55 does not have the part number since it is only sold as a set of 6 and not individually. I called my local dealer to confirm what realoem shows, they are the same rods. Realoem may be wrong but the part numbers I pull up for the rods matches with the dealer. This wouldnt be the first time there are incorrect part numbers but the dealer did confirm it which is strange.
        It may not make sense, but the part number is stamped on the rod as shown in the picture which is different. Also, the stock N54, N55, and S55 connecting rod CC length as measured by the CMM are also not the same. Unfortunately, this is not the first time we've seen this type of mistake with BMW and their part numbers online or in their system.
      1. martymil's Avatar
        martymil -
        Well I'm talking about a stock engine with stock turbos no upgrades besides the basic bolt ons like down pipes, filters and so on with a tune.

        600hp is the limit from what I seen, crank hub will take you a little further. as you stated 650 to 675hp

        Even at 600hp the stock crank hub is not safe but borderline.
      1. sahyoun's Avatar
        sahyoun -
        Click here to enlarge Originally Posted by Sales@KRATOS Click here to enlarge
        It may not make sense, but the part number is stamped on the rod as shown in the picture which is different. Also, the stock N54, N55, and S55 connecting rod CC length as measured by the CMM are also not the same. Unfortunately, this is not the first time we've seen this type of mistake with BMW and their part numbers online or in their system.
        Sounds like used deformed rods were measured. Most of the bmw rods i've seen dont even have a part number stamped on them (including my n54) and have a weight class and/or batch number. Ive called several dealers now to confirm that the s55 and n55 share the same rods. CP-Carillo even lists the s55 and n55 as the same rod here: https://cp-carrillo-catalog.cld.bz/C...January-18/112
      1. Sales@KRATOS's Avatar
        Sales@KRATOS -
        Click here to enlarge Originally Posted by sahyoun Click here to enlarge
        Sounds like used deformed rods were measured. Most of the bmw rods i've seen dont even have a part number stamped on them (including my n54) and have a weight class and/or batch number. Ive called several dealers now to confirm that the s55 and n55 share the same rods. CP-Carillo even lists the s55 and n55 as the same rod here: https://cp-carrillo-catalog.cld.bz/C...January-18/112
        Please read our second post in this thread regarding some well known connecting rod manufacturers that have misinformation printed in their catalogues. Unfortunately, CP/Carrillo is one of them. Our in house engine builder has a very good relationship with CP/Carrillo for many years and considers them as pretty much one of the best in the business. He caught this issue in their catalogue and sent the stock S55 rod to CP/Carrillo to be measured on their CMM to confirm. They confirmed they had indeed published wrong information and are rectifying it now with a new part number and the same connecting rod CC length we stated in our previous post. You're more than welcome to contact their tech department to confirm and discuss with them why you feel they measured a deformed connecting rod. Btw, the mistake they made was with the N55 and S55 part numbers only. The N54 part number is listed correctly and uses a different part number as it should since it is the same connecting rod CC length as we listed in our previous post as well.

        Unfortunately, the people you spoke to at the dealer are not engine builders and are simply going by whatever they read off of the screen. At the end of the day everyone is human and people make mistakes, even top level piston and rod manufacturers like CP/Carrillo. What sets people like them apart from most others is when they can humbly admit they're wrong and be so gratious as to thank us for helping them catch the mistake so they can have an opportunity to rectify it.
      1. sahyoun's Avatar
        sahyoun -
        Click here to enlarge Originally Posted by Sales@KRATOS Click here to enlarge
        Please read our second post in this thread regarding some well known connecting rod manufacturers that have misinformation printed in their catalogues. Unfortunately, CP/Carrillo is one of them. Our in house engine builder has a very good relationship with CP/Carrillo for many years and considers them as pretty much one of the best in the business. He caught this issue in their catalogue and sent the stock S55 rod to CP/Carrillo to be measured on their CMM to confirm. They confirmed they had indeed published wrong information and are rectifying it now with a new part number and the same connecting rod CC length we stated in our previous post. You're more than welcome to contact their tech department to confirm and discuss with them why you feel they measured a deformed connecting rod. Btw, the mistake they made was with the N55 and S55 part numbers only. The N54 part number is listed correctly and uses a different part number as it should since it is the same connecting rod CC length as we listed in our previous post as well.

        Unfortunately, the people you spoke to at the dealer are not engine builders and are simply going by whatever they read off of the screen. At the end of the day everyone is human and people make mistakes, even top level piston and rod manufacturers like CP/Carrillo. What sets people like them apart from most others is when they can humbly admit they're wrong and be so gratious as to thank us for helping them catch the mistake so they can have an opportunity to rectify it.
        So you're telling me not only is there a CP-Carillo error in their catalog, but the BMW dealer etk and realoem also have an error on the exact same part? I'll contact carillo myself but it's more likely that the error is on your end but i'll wait for more evidence.
      1. Sales@KRATOS's Avatar
        Sales@KRATOS -
        Click here to enlarge Originally Posted by sahyoun Click here to enlarge
        So you're telling me not only is there a CP-Carillo error in their catalog, but the BMW dealer etk and realoem also have an error on the exact same part? I'll contact carillo myself but it's more likely that the error is on your end but i'll wait for more evidence.
        Your claim was that the N45, N55, and S55 all share the same exact dimensions based on what you read rather than your experience with actually building these engines. We are telling you that they're not the same exact part as we've proven with real hard facts and data. We posted a picture of a stock S55 connecting rod with the part number stamped on it that is different than what you claimed. Even the CP/Carrillo catalogue as well as Pauter's catalogue shows that the N54 connecting rod CC length is also not the same as the N55 or S55. When we spoke with CP/Carrillo they said they made the assumption that the S55 and N55 were the same based on the same misinformation you received from BMW. Unfortunately, they did not have the physical rod for the S55 in hand to measure until they received ours.

        So, it seems the error is not more likely on our end. Remember,
        one of our jobs as a vendor is to discuss our knowledge and experiences on the platform to help others in the community. Our intent is to do just that with these discussions and not to disrespect or offend any forums members in the process just to get our point across. That being said, we hope you will keep us all posted once you speak to CP/Carrillo.
      1. Weehe's Avatar
        Weehe -
        The part I don't understand here is that if I were to go to BWM with a S55 vin and ask for rods they would give the the N55 rods. Unless you have a S55 engine with 0 miles on it, how did you send new rods out for measurements?