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cast vs hypereutectic pistons


lzarnch

lzarnch

15+ Year Member

Joined
Dec 17, 2007
Messages
58
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3,101
City
California
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1987 & 1986
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Manual
what is the differences between the two types of pistons? what is better?:dntknw:would a bigger compresion distance give a lower compresion ratio ?:dntknw:
 
hyper has a silicon content that makes them slightly stronger than cast pistons and nowhere near as strong as forged pistons.


a bigger compression height should mean more compression all other things being equal.
 
Actually hyper eutectics are made of an alloy that has a smaller coefficient of expansion.

The point being that the pistons expand less so that they may be fitted
more closely to the bores. This closer fitting means the engine can be
"tighter" when cold so theoretically the engine will run cleaner when cold.

Unfortunatly hypereutectic pistons are more brittle than conventionally
cast pistons.

Forged pistons are the strongest, but to allow for their greater expansion from cold to hot they must be set more "loosely".

Some performance engines "back in the day" were famous for sounding like a garbage pail full of bricks rolling down a staircase after a cold start and until they warm up.
One of the noisiest was the 289Hi-Po engine.

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AllanD said:
Some performance engines "back in the day" were famous for sounding like a garbage pail full of bricks rolling down a staircase after a cold start and until they warm up.
One of the noisiest was the 289Hi-Po engine.

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Click to expand...

Not trying to argue with you, but I don't remember the K code having forged pistons.....it DID have solid lifters, which would be noisy.
 
hypers are not as bad as people give them credit. i bet most people who down them have never used them. ive been running them for over 10 years on a couple motors and spraying them with up to a 250 shot and 0 failures. just gotta know how to tune
 
so would hyper pistons hold up to a 50-100 shot with the right rings or would cast be better?
 
yes they will hold up as long as you dont lean it out or detonate
 
what about cast pistons with a gapless second ring allowing for mild nitrous or boost
 
i would not run anything gapless or cast
 
if i wasnt to use nitrous would cast pistons be ok with chrome iron rings
 
lzarnch said:
if i wasnt to use nitrous would cast pistons be ok with chrome iron rings
Click to expand...
Chrome rings are very hard, and this make them very hard to seat. If they don't seat properly, they will use oil. Usually, chrome rings are for vehicles used in harsh conditions such as dust, severe duty, etc.

Moly or cast iron rings work fine for normal useage. Plasma moly are good for durability without the seating/hardness problems associated with chrome. They are, however, a bit pricey.
lzarnch said:
would a bigger compresion distance give a lower compresion ratio ?:dntknw:
Click to expand...
Define compression distance. Anything that gives more volume to the combustion chamber lowers the compression ratio. shady






shady
 
Last edited:
on the pistons specs it says compresion distance. for the pistons i plan on using its 1.511" for the stock pistons its 1.461", thats what i found on a website (motorsports svo catalog) was the sorce they used. i believe compresion distance is the distance from the piston pin to the top of the piston, thats what i heard
 
that would usually mean your pistons are higher in the deck...probably higher than the deck which would be bad. at any rate, even if it fit, your compression would be higher
 
Factory Ford Rings are chrome.

OK those that had the coin to buy a ford with a hi-po 289 would also rebuild them with forged pistons

I can't actually claim to have seen an unmodified 289.
mostly because back then nobody left things alone.

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