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Captain Rehab
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Which are considered better for high RPM Small block marine engines? Hypereutectic or Forged pistons?

Thanks
 

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Sit N' Spin
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Forged all the way in a performance engine! NO EXCEPTIONS!!!

A hypereutectic is basically a cast piston with a higher content of silicon. And just like a cast piston, they can still come apart.

IMO, cast ANYTHING (except cam, oil pump and piston rings) has no place in a jet boat engine rotating assembly.
 

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I agree that forged is a better part and my first choice. That said, years ago I needed an unusual combination for a 550 HP SBC drag engine. Nobody but KB hypereutectic had something off the shelf so I went with them. Had to machine the dome for the proper CR and was really surprised in the material qualities. Not like a typical cast piston at all.
Long story short, we put about 400 passes on that engine shifting at 6800 and through the lights at 7200 RPM. Pulled it apart when the engine developed a water leak. Pistons looked fine and I would have run them another season or 2 if we didn't have to sleeve 1 cylinder and bore the block.
My preferance will always be a forged piston but I wouldn't be afraid of running a hypereutectic piston in a mild, lower RPM application.
 

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I've got KB pistons in my engine right now with no problems so far. I've also done a few searches on hyper pistons and there are a lot of people using them in performance engines, and just as many saying to stay away from them. If I had to do mine again, I might go forged just for peace of mind...

BTW, my engine is basically the 574 HP build from this book...

 

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Sit N' Spin
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A buddy mine with a 460 Ford had TRW hypers in his motor. Boat came outta tha water, overrevved, blah blah blah. Ripped the rod right off the piston and tried to shove the rod into the adjacent cylinder!!!

A hypereutectic piston may not fail by itself, but if something else fails, it can cause a lot more damage to the piston and if it comes apart or a rod seperates from it, you can pretty much kiss the block goodbye. Unlike a forged, they can still come apart whereas unless you're running top fuel or well over 1,000 horsepower, the most you'll probably do to a forged piston is put a hole in it.
 
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