hypereutectic pistons
 

whats the diffrence between forged and hyperetectic pistons?are they the same as a cast piston?i was told to stay away from them in a marine applaction.

Hypers are cast pistons with a hardened coating for a slight increase in strength over cast. I believe they can be brittle and crack under heavy stress. They are lighter than forged but now nearly as strong.

They are no substitute for forged pistons in a motor over 450hp

I do not think its a coating exactly, but rather the piston alloy is different in that it has much more silicon than traditional pistons. It does make them much stronger, but at the expense of brittleness. In terms of cost, you go from standard cast as the cheapest, to hyper at the middle, to forged at most expensive. Most GM based marine engines in the last 10 years had hypers except for those that specifically had forged pistons, such as high performance 454 and 502. My Searay with a L29 based 454 (2000) has hypers, as does my L29 454 '97 Suburban.

http://en.wikipedia.org/wiki/Hypereutectic_piston

Ken

Yes, more silicone in the alloy. Makes them swell less under heat. I ran them for many years in perf marine engines, the last few in blower motors. They performed extremely well. The trick is to not get into detonation with them as they are more brittle than forged. They will break apart destroying an engine where a forged piston under detonation will blow a hole in the piston with often little damage to the rest of the engine. That is why they are often not recommended in perf marine engines. You really need to know what you are doing to make them work well in hipo marine applications.

I have a 454 Mag efi motor that was rated at 385hp. I had my engine rebuilt 2 yrs ago and know the engine builder used the hypereutectic pistons in the rebuild (we called 5+ places and NO ONE had the forged pistons in stock). I have no interest in ever putting a blower on my motor and was told that these would work perfectly and be much better than cast. I hope what I was told is true. I really wanted to stay with forged but didnt want to wait a month to get the motor put back together.
So far Ive put about 80 hours on and she runs strong...

i have just over 600 hrs on a 496 HO with hypereutectic pistons no problems at all.

People like to blame hypereutectic pistons for failures on 496ho engines that were supercharged. The source problem is rarely with the piston and usually with the lack of ability to properly tune the fuel curve with the fuel injection.

This guy pretty much much nailed it. They are cast with higher silicon content which does several things. First they do not absorb heat as much as cast or forged pistons and are therefore more effecient (the less heat absorbed by the piston the more that energy is used to propel the piston). In addition the piston does not swell or expand as much as older cast or forged pistons and therefore you can also run tighter bore clearance which results in less piston rock a better and more consistent ring seal which results in less blowby which results in more power, better fuel effeciency, and lower emissions (why most of the OEMS use this type of piston). Lastly they are cheaper than a forged alternative. The huge downside is they are brittle/fragile (silicon/glass see the correlation). Another thing to consider is there are forged alternatives these days that also use higher silicon alloys that can run almost as tight on the bore clearance as the hypers, though these are typically only offered in the most common applications. Personally I am not a huge fan of the hypers... I used to work in the automotive engine building profession and saw where these failed over and over (of course this was back in the mid 90's when this technology was fairly new, perhaps they are better now). If it were up to me I would choose a forged replacement piston (preferably one using the higher silicon content so I could run tighter bore clearance) and then get it coated both on the skirt with an anti-friction coating which makes it safer to run those tighter clearances and then also get the tops ceramic coated which would give the forged pistons all of the advantages of the Hyper's without the huge disadvantage of possibly blowing up your motor (though at a much greater cost).