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Discussion Starter · #1 ·
Well I have a little while before I go turbo but out of curiosity are hypereutectic pistons direct drop when rebuilding? Or it doesn't matter if you go forged or hypereutectic you still need to machine the cylinder head for clearance? I ask because I have some experience with rebuilds so I was wondering if I got hypereutectic pistons with forged rods and a forged crank if it will be as simple as rebuilding the engine with them or I have to still make sure the clearance is right. Now before any one flames me and says forged is the way to go I was thinking of some of the draw backs of forged and it possibly might be easier to go with stronger cast pistons. Plus I'm not looking for more than 250 whp maybe eventually 300. I know stock internals could handle that Just wanna make sure my car will still be reliable as it is my dd.
 

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Aurelius Pardus
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machine the head how?

Pistons are pretty much the same process with the exception of knowing which materials expand more and adjusting for that. so clearance will have to be checked of course.

If you're going boosted one thing I can say about hypereutectic pistons is that make sure your tune is good good good..... detonation destroys the hell out of engines with them, being that the pistons are very brittle.
 

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Discussion Starter · #3 ·
Well I really have no idea how the clearance thing works to be honest. I was just wondering if it will be a direct bolt on deal if I went with a cast piston vs forged just so I know if I could save some money by building my own engine. So would you recommend forged? Im just worried about the whole cold startup thing getting annoying I'm not totally against using them in my build
 

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Hypereutetic alloy cast pistons have been the standard OE piston material since the mid 80's. So your engine already has them.

Also, modern forged pistons use alloys that do not expand with temperature the way they used to so piston slap at cold start up really isn't an issue any more.

One of the advantages of the hypereutetic piston is that they are very hard and don't wear giving you a long life. This becomes a disadvantage when you start dramatically increasing the power. Where a standard cast or a forged piston can give a little the hypereutetic will fracture. That is why
they are not the best choice for forced induction or with nitrous.

Not sure what you mean by machining the cylinder head for clearance. Unless you are going with a domed piston that extends above the deck of the block there should be no machining of the head to fit pistons.

Now the bore in the block needs to be the correct size for the diameter of the piston. Typically when you rebuild an engine the block is bored out to except an oversize piston. The bore is machined to the nominal oversize and the clearance is built into the piston. For example a 4" piston will actually be around 3.998" and the cylinder is bored/honed to 4.000". The size of the piston will take into account the expansion that is a forge will be smaller than a hypereutectic.
 

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Difference between the two is forged will take more of a beating, and are nowhere near invincible, Of course every one knows this. With a safe tuneyou will buy some time before the pistons melt or the powdered rods break.
 

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Very few stock production engines come stock with hypereutectic pistons almost all cars come with cast pistons , piston strength goes like this

Cast weakest

Hypereutectic middle but in my opinion junk and would rather have cast

Forged this is as good as it gets , takes more heat , abuse , ware then any of the rest and for boost in my opinion a must have

Tom
 

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You want forged pistons for a turbocharged/supercharged/nitrous build, the others will not hold up for long. I would also try to get the compression in the 9:1 area, this will allow you to run more boost and spark before knock occurs on 91-93 octane premium pump gas.
 

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Aurelius Pardus
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mine has hypereutectic from the factory with a cr of 7.8:1 and max 12psi but I could go more if it was chipped. I'm scared of hitting fuel cut for this reason. I don't need to bust it.
 

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Very few stock production engines come stock with hypereutectic pistons almost all cars come with cast pistons , piston strength goes like this
Tom
With the exception of a few performance applications every Chrysler product since the mid 80's has had cast pistons made with a hypereutetic alloy from the factory.

I know the Ford 5.0 switched from forged to hypereutetic alloy pistons around 92. I think that you will find that virtually all Ford pistons these days are cast from hypereutetic alloy if they are not forged. They may be referred to as cast since they are but the alloy used is hypereutetic.

The reason the manufactures started switching to hypereutetic alloy for their cast pistons in the 80's is that the high silicon content that makes the alloy hypereutetic results in a piston that is much more thermally stable allowing the piston to cylinder wall clearance to be much tighter improving emissions. The side benefit to the consumer is the silicon also makes the surface much harder which reduces wear. It's the hypereutetic alloy in the piston and the moly coated rings that has had a huge impact on the ability of engines to last well past 200,000 miles without needing a rebuild.

Even though hyperutectic cast pistons are stronger than non hyper casting alloys that was not the primary reason the manufactures made the switch.
 

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FWIW, I did a little digging and the aluminum alloy that Duretec engines are cast from is Mahler 124. This alloy has 13% silicon content which classifies it as hypereutetic.

I am not trying to be a nut buster here, I just don't want to see someone spend money thinking they are getting something they already have.
 

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Discussion Starter · #11 ·
Thanks for all the answers guys :) I'll just go forged then planning on boosting my car next year can't wait lol.
 

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LOL, ok to clear things up for the OP, there are 3 types of aluminum alloys that are used to produce pistons. The amount of silicon content in the aluminum is what determines whether it is hypoeutectic, eutectic, or hypereutectic, NOT whether it is casted or forged as these simply refer to the way the pistons are manufactured and not the alloys themselves.

The more silicone content you have in a piston, the less it will expand and thus the tighter piston to bore clearances you can run, which will result in little to no piston slap on cold starts and the better your emissions will be for the EPA. However adding too much silicone makes the piston brittle and not good for F/I apps were detonation may occur.

Hypoeutectic - less than 12% silicon (more durable / loose clearance)
Eutectic - 12% silicon
Hypereutectic - greater than 12% (more brittle/ tighter clearance)

Difference between cast and forged

When a piston is cast, the alloy is heated until liquid, then poured into a mold to create the basic shape. After the alloy cools and solidifies it is removed from the mould and the rough casting is machined to its final shape. For applications which require stronger pistons, a forging process is used.
In the forging process, the rough casting is placed in a die set while it is still hot and semi-solid. A hydraulic press is used to place the rough slug under tremendous pressure. This removes any possible porosity, and also pushes the alloy grains together tighter than can be achieved by simple casting alone. The end result is a much stronger material

You will find that aftermarket forged pistons typically are made from 2618 alloy which would be classified as hypoeutectic, the only manufacture I know that uses 4032, which is eutectic, for foci is Supertech.
 

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Cosworth uses 4032 alloy as well. The compression ratio's they offer are not looking turbo friendly though:)

For me its a no brainer, if rebuilding an engine for a FI application, spend a few extra bucks on forged bits.
 

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I dont feel a high silicone content makes a true hypereutetic piston yes I know its the silicone content that makes cast pistons hypereutetic but i think the stock production ones are pure crap and nothing more then cast pistons

Pistons like the Keith Back are a more "true" hypereutetic but I also wouldnt run those either

Tom
 

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Hypereutetic is a metallurgical term and in the case of aluminum alloyed with silicon the percentage content above 12% silicon is what makes it a hypereutetic piston, there is no other consideration as to whether it is hypereutectic.

Keith Black Sivolite pistons are one of the very best hypereutetic pistons available. They have gotten a bad rap by folks that fail to follow their ring end gap requirements. KB pistons place the top ring closer to the top of the piston where it runs hotter and requires a large ring end gap, don't do it and the butt ends and break the top of the piston off.

I know folks that have 1000's of 1/4 mile runs on small blocks with a 200hp shot of nitrous with no issues on KB Sivolites.
 

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Discussion Starter · #17 ·
So what do you guys think of the fs werks forged 9:1 pistons? I mean they seem to know what they are doing plus there turbo kits are pretty popular, so there pistons should be good right? I'm not buying the oversize ones by the way and I am gonna buy there turbo kit wen I can because there local to me :).
 

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I would look around for Forged pistons , try C-F-M they have some good deals on there , there isnt a bad Forged piston out there and I have used them all maybe McNews as well

Tom
 
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