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    I heard some people complaining that JE pistons make some noises in the block especially when engine is still cold ! Is this trough ? Have any one experienced this ?
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    Quote Originally Posted by emvin View Post
    I heard some people complaining that JE pistons make some noises in the block especially when engine is still cold ! Is this trough ? Have any one experienced this ?

    forged pistons are quite to common to rattle when cold as they have different expansion rates to cast pistons
     
     

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    Forged and cast pistons can both slap from cold, and if badly specified or worn they can also slap when hot. Nothing to do with them being forged or cast, its down to the composition of the alloy. The recipe if you will.

    Cast pistons are normally made to tighter tolerances than forged as its an easier process to control, typically they will have large amounts of silica in the alloy. This adds thermal stability to the cast and makes them quiet whether hot or cold. A typical piston in a new engine now a days may have 22% silica, this could require 0.75 thou to bore when cold, and close to 0.5 thou at full running temps. That will be as quiet as a mouse.
    Forged pistons are typically low in silica and there fore thermally unstable. Cold clearance on a force induced engine (Supercharger or turbo, it makes no difference) can be up to 5 thou, especially if used in conjunction with N02. My Toyota has 3.75 thou to bore cold and that is 0.5 thou at full temp at 2.2 bar boost.

    So why not add more silica to forged pistons?
    Forged pistons are normally used in force induced engines because they resist det far better than cast ones, the forging process makes them tough as hell. Problem with silica is it makes the cast very brittle. That’s not good in a force induced engine, a bit of det or ring flutter can, and often does, shatter high silica forged pistons. Semi forged pistons are high silica and great from cold, but they are the devils own design. Brittle hell.

    So bottom line, forged or not the noise is down to thermal stability and silica levels.


    JE pistons are in the region of 7% silica and a VERY good quality piston. Good det resistance. Light weight, fair thermal stability and medium priced. I always use them in my rebuilds.
    CP pistons have a bit more silica and are a quiet piston, still a good piston but not my choice.
    Ross again are a fair piston, and then others like woosner etc, all very good.

    BUT, the next rebuild I do will have Mahle. I have been to have a look at an engine today that was rebuilt with them. It’s as quiet as any engine I have seen. But then so are JE for the first 500 miles, then they get slowly more slap, but then I use mine on track only and rev to 8500rpm at times sitting on the limiter for some distance.

    The most important thing in any rebuilt, the thing that makes 100 times more difference than anything else, reliability, power, slap, everything. BUILD QUALITY. Its no good banging it together in a shed with an adjustable spanner. Clean, clean and clean. Measure twice, be anal with it! You wont regret it.

    Sorry for the long post, it just went on as I typed lol.
     
     

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    Oh, and a longer stroke to bore puts the center of the big end out side the foot print of the piston at 90 and 270 degrees, that will reduce life span of the engine and add wall stress to the block.
    You should always reduce comp ratio via shorter rods, not thicker head gasket, raising the head with a thicker gasket will elongate the path for the back of the timing belt of chain and throw the cam timing out wildly, you can adjust that if you have adjustable cam pullies or multi positional cam pully fitment angles. But the correct way is rods or pistons changed. Its fine adjusting the pullies untill the next guy who doesnt know they are meant to be like that puts them back to zero. It works tho.
    If you use a laminated steel gasket as I always recomend, then blowing them is highly unlikely. If you cant get one thick enough buy 2 and remove the rivets to delaminate them both, then use the required number of leaves to get the thickness you need. The rivets are simply for alignment and have no mechanical valve. Head and block must be super clean and flat tho!
     
     

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