Mi16 high comp pistons
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  1. #1
    1000+ Posts cav91's Avatar
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    Default Mi16 high comp pistons

    Hey all again,

    My series one is appearing that its going to need a engine rebuild in the future.
    So my thoughts are, since i bought it to be a track car should i build it up to a little bit higher standard?

    I know Graham got some high comp pistons out of europe for one, Just the standard euro spec ones. Would it be worth my time trying to get some of these? And while im at it should i get some peterT cam regrinds? If I do all this would I need to Remap the ECU?

    Thanks Chris

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  2. #2
    1000+ Posts PeterT's Avatar
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    I will tell you everything I know (which isn't much really). The XU9J4 conrod is located by the piston. Whereas the XU9J2 and XU10J4 pistons locate the rod by the crankshaft. None of the XU9J4 forged pistons I have bought have had the rod located and have thus needed modifying. The alternative is to fit XU9J2 rods. This means having to bush the small end to make it "full floating".

    To modify a forged XU9J4 piston you need to machine inside the piston, creating flat surfaces and turn up suitable size thrust washers. This is where the term "blueprinting" really starts to mean something, as the fit of the thrust washers on the pin needs to be precise else the washer will flog about. The OEM thrust allowance also needs to be maintained. If you don't do this, the con-rod will flog about from side to side and eat up hp in friction losses.

    It's a great time to buy pistons as the dollar has never been better. I recently priced a set of XU10J4 forged pistons from JE at AUS$800 delivered. I'm happy to share my XU9J4 piston designs if you want to get a set made by JE. I like to minimise the valve pocket depths and machine as required, in order to maximise CR. Off the shelf pistons from IAPEL or WOSSNER have very deep pockets, which is great for huge race only camshafts, but then they need a huge dome to restore CR. Having a huge dome is detrimental to flame travel.

    Attached are pics of the IAPEL piston showing the required mods. With a standard head gasket, CR is 11.25:1.

    I don't suggest fitting "other" pistons to your existing liners as they will be worn out. Unless your engine is low km, you will need to bore to 83.50mm.
    Attached Thumbnails Attached Thumbnails Mi16 high comp pistons-iapel-thrust-washers.jpg   Mi16 high comp pistons-p1010017.jpg  
    Last edited by PeterT; 27th May 2011 at 10:50 PM.

    '92 205 Mi16
    '90 Mi16x4

  3. #3
    Fellow Frogger! chez00's Avatar
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    Quote Originally Posted by PeterT View Post
    The XU9J4 conrod is located by the piston. Whereas the XU9J2 and XU10J4 pistons locate the rod by the crankshaft. None of the XU9J4 forged pistons I have bought have had the rod located and have thus needed modifying. The alternative is to fit XU9J2 rods. This means having to bush the small end to make it "full floating".
    Does this mean the big end crank pin is much wider than the width of the conrod journal in the XU9J4 engine? Is that the case with the 8v?

  4. #4
    1000+ Posts PeterT's Avatar
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    The journal widths are the same between XU9J2 and XU9J4. The XU9J2 big end is wider but they still take the same bearing.

    '92 205 Mi16
    '90 Mi16x4

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