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    • How shitty tuning can melt a piston

      There is cracking a ringland or scuffing a piston but few people ever melt one. Well, it happens and frankly with people experimenting with tuning on their own probably more often than you think. This VW piston looks like it went through hell.


      In order to get what you see in the picture you literally have to temps so high as to melt metal.

      How does that happen? Any number of ways. A bad injector that is cracked or just flooding fuel in the cylinder. It can be done with too much timing or super high EGT (exhaust gas temperature).

      Seeing something like this rare. Usually what you have to watch out for is detonation. What is detonation? When cylinder pressure exceeds a fuel's octane rating and things literally start detonating before they are supposed to. You can get multiple flame fronts at the same time from preignition and the spark plug lighting the mixture. Even a strong forged piston will get beaten to death.


      Several things can contribute to this like carbon buildup, wrong heat-range plugs (usually way too hot for application), or a really lean and aggressive tune.


      If boosted a lot of air pressure without enough fuel will cause problems in a hurry.

      You can scuff a piston as well with cylinder wall contact. This sometimes happens with low oil pressure or a loss of lubrication. You can also have this happen from bore distortion over time or if a cylinder loses its shape.


      Any of things aren't nearly as bad as to cause whatever happened to that melted VW piston above. We would love to know what the hell the tuner did to annihilate that piston.

      This article was originally published in forum thread: How shitty tuning can melt a piston started by Sticky View original post
      Comments 12 Comments
      1. AWSAWS's Avatar
        AWSAWS -
        Surely flooding a cylinder with fuel will cool the cylinder. You need to be super lean to melt a piston.
      1. alex@ABRhouston's Avatar
        alex@ABRhouston -
        *pop*
      1. Zel335's Avatar
        Zel335 -
        Any idea where this picture came out of, US or international?
      1. Mykk's Avatar
        Mykk -
        As a DIY tuning enthusiast I think this article shouldn't strike fear in anyone interested in tuning. The key is educating yourself before beginning. Utilizing the correct tools (wideband 02, knock sensors, plug reading...etc) and familiarizing yourself with your specific flavor of operating system you should be able to completely avoid this scenario. Most engine failures this catastrophic are assembly errors... ::cough:: ring gap ::cough::
      1. LessIsMore's Avatar
        LessIsMore -
        that pic of the swirl baked into the piston is super-cool, never seen that before.
        Taking logs and checking them regularly, or when you change something, will keep this from happening (barring any catastrophic hardware failure).
        Personally I think running meth makes melting stuff much more likely - most blown engines I have noticed were using meth.
      1. maxnix's Avatar
        maxnix -
        Yeah, too much alcohol surely does not help lubrication of the cylinders.
      1. Sticky's Avatar
        Sticky -
        Click here to enlarge Originally Posted by AWSAWS Click here to enlarge
        Surely flooding a cylinder with fuel will cool the cylinder. You need to be super lean to melt a piston.
        It was one of the things listed as a possible culprit. If you ignite what is in the cylinder somehow you can melt it.

        I don't know but apparently leaky injectors have been responsible in the past.
      1. Sticky's Avatar
        Sticky -
        Click here to enlarge Originally Posted by Mykk Click here to enlarge
        As a DIY tuning enthusiast I think this article shouldn't strike fear in anyone interested in tuning. The key is educating yourself before beginning.
        Wasn't my goal. Really, I was just blown away by that piston looking like that.

        You're right, education is key.
      1. Sticky's Avatar
        Sticky -
        Click here to enlarge Originally Posted by Zel335 Click here to enlarge
        Any idea where this picture came out of, US or international?
        US. A tuner for Volkswagens in the US. Car had an upgraded turbo and the damage came at 19 psi so something was really, really wrong.

        That's all I know.
      1. AWSAWS's Avatar
        AWSAWS -
        Click here to enlarge Originally Posted by Sticky Click here to enlarge
        It was one of the things listed as a possible culprit. If you ignite what is in the cylinder somehow you can melt it.

        I don't know but apparently leaky injectors have been responsible in the past.
        A leaky injector yes but it's not because of flooding. It's because it introduces a small amount of fuel into a hot oxygen rich environment. It detonates or burns super lean (and hot).

        What would be great on our cars would be actual exhaust gas temperature sensors.

        Meth by itstelf might be risky. Mainly as it's a fuel people are used to, running on a secondary system which may well be more prone to failure. However add in a good mix of water and you have a great deal of protection. Anti knock and cooling.
      1. Sticky's Avatar
        Sticky -
        Click here to enlarge
      1. kingtal0n's Avatar
        kingtal0n -
        I can tell you though from experience, you can get an engine EGT very high, using 93 octane, hot enough to cause the piston rings to lose tension. Perhaps this occurs around 2500*F or so. high quality forged piston rings lost tension at some insane high EGT around 22psi of boost. The A/F ratio was approx 15:1 or leaner.

        And the engine produced 400RWHP (Instead of 480rwhp if it had the fuel) this way,

        And it did not detonate. This was a 2.0L SR20det engine. I ran it back to back to back and it never detonated. Everything came out looking brand new. Just the piston rings had lost their tension. I changed the rings put it back together and its been fine since (that was 7 years ago).

        It is a very forgiving engine, but I learned something, I don't believe that temperature alone is enough to cause detonation when an engine is properly prepped for high temperature 93 octane in and of itself. The EGT should be limited somewhere around 1300*F between turbo and manifold in many applications because purely by specification most turbine manufacturers recommend a peak turbine inlet temp around 1380*F. Using water injection is best way to accomplish this. Alot of people love methanol because they see the a/f drop it provides and equate this with safety, however it is overlooking a major concern of EGT gas temperature rising at high Wattage (horsepower) output, especially of a small displacement engine. I'd rather have a 3.0L at 22psi with 100% distilled water and 12:1 a/f ratio than the same engine with 10.8:1 using 100% methanol to get the drop in a/f. The EGT on the leaner engine would be lower at the same output because water does a better job of cooling things down, which helps the piston from expanding so far the rings tear it apart.