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  1. #16
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    I was trying to think of what the car guys called it.

    Quote Originally Posted by ksfastman View Post
    It's called gas porting, ok on a race engine, but on a 2 cycle it tends to carbon up fast...whether it's top, side or ring ported. I imagine it was an economical alternative to more precise piston to wall clearance.
    I'd rather be competitive w/junk I built in my garage than win w/stuff I bought.


    I refuse to allow common sense to interfere w/my boat buying decisions.


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  2. #17
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    High rings are one thing, the drilling of holes to access the back side of the ring is another. The drilling I believe was outlawed by some racing rules. Chrysler did high rings too , ring was the top in the real stackers. They also did consumer high ring in the big motors and triples and 65 twin. All were 165psi, stackers 195psi.

  3. #18
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    yes but in a crossflow 2 stroke you have a huge amount of heat buildup and need extra clearance for oil to get into as much as possible.

  4. #19
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    The OMC crossflow was not the only engine OMC used this style of ring. Example would be the 3.5 bore 86/7 90 degree looper, they used the same ring as the 3.5 bore crossflow and same design as the 3.625 bore version. The engines with a lower top ring had very little trouble with these and most of the high ring version piston it was more of a locating pin issue that allowed the ring to spin hook a port and then rip the top ring groove off. On any of my race engines using these rings we actually ran less clearance to keep the piston as straight as possible in the bore to minimize side load on the ring.

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  6. #20
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    Racer is Right as always.. 3.5 86/87 piston
    Attached Thumbnails Attached Thumbnails 20230202_142043.jpg   20230202_142114.jpg  
    Last edited by H2OPERF; 02-02-2023 at 08:51 PM.

  7. #21
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    late 235 piston

    Picture shows the ring and pin detail from a big bore 235 and how little material is there. I suppose most would call the top ring a keystone ring although the angle is more severe than most.

    Click image for larger version. 

Name:	TRW 326704 rings.jpg 
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Size:	212.2 KB 
ID:	515137

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  9. #22
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    That ring was called a L ring bad part of the design wasn’t ment for high rpm the ring would get too hot from combustion temp directly on the ring causing it to expand an warp into port causing failure mainly used in 74-77 cross flow engines 78 they used keystone tapers upper rings were lowered on the piston 200ths and in 80 they used for both upper an lower an continued for this till the end of production
    Last edited by MrG; 03-04-2023 at 06:21 AM.

  10. #23
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    Always heard the opposite true, low RPM lugging, not hot cleaning burn results in failure by build up.
    Since most didn't use the potential it was problematic and dropped along with psi.

  11. #24
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    Quote Originally Posted by FMP View Post
    Always heard the opposite true, low RPM lugging, not hot cleaning burn results in failure by build up.
    Since most didn't use the potential it was problematic and dropped along with psi.
    Yes, part of the draw of the dykes ring is the large face to transfer heat out of the ring and into the cylinder wall... which let them put the ring higher on the piston.

    We gas ported some 4S kart pistons and it work great for power but the ring life was terrible in cast iron cylinders. Then we nic'd some aluminium bore motors and the rings lasted longer even with the gas porting.

    Let's just go ahead and make America great again!

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