Piston Material
Thread Starter
Melting Slicks
Joined: Aug 2004
Posts: 3,078
Likes: 101
From: Riverhead New York
Piston Material
several internet sites of perfomance/rebuilders warned of the use of
hypereutechic pistons. Very brittle, will not tolerate detonation,etc. and they are warning to be very careful in their use v.s. forged. Any comments?
hypereutechic pistons. Very brittle, will not tolerate detonation,etc. and they are warning to be very careful in their use v.s. forged. Any comments?
Melting Slicks
Joined: Aug 2004
Posts: 2,056
Likes: 553
From: Sun Prairie WI
OK, here comes a metallurgical engineers' reply. Agree with Muncieman's symbols -- don't be dazzled by website bs. A EUTECTIC alum-silicon alloy (such as 4032; commonly used for pistons) contains ~12% Si & has decent wear resistance & fairly low thermal expansion characteristics. All of the silicon is 'disolved' in solid solution -- there is no 'free' silicon present in the structure. A HYPOEUTECTIC alum - silicon alloy contains >12% Si. Since anything over 12% cannot be absorbed, it is present in the structure as fine silicon particulate. Special processing is done to keep these particles very small & spherical in shape -- were they large &/or angular, they would indeed embrittle the alloy. Result -- better abrasion resistance & elevated temp properties. Not sure about your " ... vs. forged ..." phrase. Recall that some pistons are made by forging & others are made by casting. Doesn't have anything to do with hypo/hyper eutectic stuff.
Melting Slicks
Joined: Dec 2000
Posts: 2,130
Likes: 1
From: mesa,az
well the engine i just built with KB cast hypowhatever pistons will tell the tale for me. I certinly hope it's all internet BS cause a few people havegiven me the glum nod when i told them wich pistons i am using.
Last edited by panchop; Sep 13, 2004 at 07:02 PM.
Burning Brakes
Joined: Mar 2004
Posts: 1,108
Likes: 4
From: Plano Texas
67vetteal,
I put hypereutectic pistons in my 82 Mustang 302 that I built in 1992. After 62,000 miles, and wanting to sell, I tore the engine down to the shortblock and rebuilt it. I hammered the car pretty hard when I drove it during those twelve years . When I pulled the heads, the pistons looked perfect and the cross hatching was still visible in the bores. I ran Mobil 1 10w-30 and changed every 3,000 miles with filter. The engine burned no oil. I would use hypereutectic pistons any day. However, no more Fords for me, thank you!!! Good luck!!
I put hypereutectic pistons in my 82 Mustang 302 that I built in 1992. After 62,000 miles, and wanting to sell, I tore the engine down to the shortblock and rebuilt it. I hammered the car pretty hard when I drove it during those twelve years . When I pulled the heads, the pistons looked perfect and the cross hatching was still visible in the bores. I ran Mobil 1 10w-30 and changed every 3,000 miles with filter. The engine burned no oil. I would use hypereutectic pistons any day. However, no more Fords for me, thank you!!! Good luck!!
Team Owner
Joined: Sep 2003
Posts: 88,393
Likes: 2
From: eville in
Originally Posted by vark_wso
OK, here comes a metallurgical engineers' reply. Agree with Muncieman's symbols -- don't be dazzled by website bs. A EUTECTIC alum-silicon alloy (such as 4032; commonly used for pistons) contains ~12% Si & has decent wear resistance & fairly low thermal expansion characteristics. All of the silicon is 'disolved' in solid solution -- there is no 'free' silicon present in the structure. A HYPOEUTECTIC alum - silicon alloy contains >12% Si. Since anything over 12% cannot be absorbed, it is present in the structure as fine silicon particulate. Special processing is done to keep these particles very small & spherical in shape -- were they large &/or angular, they would indeed embrittle the alloy. Result -- better abrasion resistance & elevated temp properties. Not sure about your " ... vs. forged ..." phrase. Recall that some pistons are made by forging & others are made by casting. Doesn't have anything to do with hypo/hyper eutectic stuff.
yea' what he said 
go forged if you are going to hit it with giggle gas or high boost, I'm using them in a 383 i'm ptting togetherand may hit it with 75HP shoot(not offten) but i will retard timing
Burning Brakes
Joined: Jul 2004
Posts: 825
Likes: 17
From: Rowlett, TX
Originally Posted by 67vetteal
several internet sites of perfomance/rebuilders warned of the use of
hypereutechic pistons. Very brittle, will not tolerate detonation,etc. and they are warning to be very careful in their use v.s. forged. Any comments?
hypereutechic pistons. Very brittle, will not tolerate detonation,etc. and they are warning to be very careful in their use v.s. forged. Any comments?
Team Owner
Joined: Oct 2000
Posts: 38,897
Likes: 1,926
From: Washington Michigan
Originally Posted by Vipermike
Compared to a forged piston, hypereutectic pistons are relatively weak. Compared to a factory cast piston, hypereutectic pistons are significantly stronger. If you are going to do some serious drag racing or plan on running your engine above 6500-7000 RPM on a regular basis, then I would recommend forged pistons. Otherwise, hypereutectic pistons should provide all the strength you will ever need at about 1/2 the price of forged pistons.
I've used KB hypereutectic pistons in the last six or seven engines I've built, with no complaints; if you're going to thrash the hell out of it all day or spray it, go with forged. Hypers are significantly stronger than run-of-the-mill cast pistons, but are only slightly more expensive; pay attention to the piston manufacturer's recommendations for top ring gap.
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For restoration of SHP engines with forged pistons I always recommend the OE replacements from Federal Mogul fit to OE clearance specs since they are part of the visceral quality of SHP engines, particularly the noise they generate.
The two principal forging alloys are 4032 high silicon as discussed previously and 2618 low silicon. The 4032 have less expansion and can be fit a little tighter, but are not quite as strong as 2618, which must be fit looser because they have greater expansion; 2618s are the best choice for serious racing, especially if the engine is boosted. The Federal Mogul OE replacement pistons for SHP engines are 4032.
Forged pistons are no longer used by the OEs and the current Corvette including Z06 use a hypereutectic, fit tight to reduce noise and with a polymer skirt coating as an aid to prevent cold scuffing due to the tight noise abatement clearance, and hypereutectics are suitable for any street engine buildup where you are not concerned about duplicating the original configuration.
Duke
The two principal forging alloys are 4032 high silicon as discussed previously and 2618 low silicon. The 4032 have less expansion and can be fit a little tighter, but are not quite as strong as 2618, which must be fit looser because they have greater expansion; 2618s are the best choice for serious racing, especially if the engine is boosted. The Federal Mogul OE replacement pistons for SHP engines are 4032.
Forged pistons are no longer used by the OEs and the current Corvette including Z06 use a hypereutectic, fit tight to reduce noise and with a polymer skirt coating as an aid to prevent cold scuffing due to the tight noise abatement clearance, and hypereutectics are suitable for any street engine buildup where you are not concerned about duplicating the original configuration.
Duke
