unknown_host

iTrader: (1)

I was reading a book i have about building small block chevys on a budget. I am sure everyone has read about how hypereutectic pistons are bad for nitrous and how they are prone to cracking. Here is a blurb from the article, let me know what you guys think:

"It has been found that using 18% silicone to make a hypereutectic alloy has improved the material for high performance pistons while keeping costs nearer that of regular cast pistons.

The only drawback to producing hypereutectic pistons is that the free silicon in the aluminum wears out regular carbide machine tools much faster than non-hypereutectic alloys and mandates the use of diamond tools. As far as use in a performance engine is concerned these alloys are really what the high performance street engine builder was looking for. Because casting allows metal to be put exactly where it is believed to be required, hypereutectic-cast pistons need not give away any real strength advantage to a forged piston. With forged pistons the forging die must be removed from the forging so undercuts in pin bosses cannot be directly formed. To make a forged piston significantly lighter than a cast piston requires much more machining. Because of the process and material involved, hypereutectic pistons are just about as strong as forged pistons but can be run with mcuh tighter initial clearances and wear much slower. Just before Sealed power introduced its first Chevy hypereutectic piston I was sent a set to use in one of my street nitrous motors. About 50 pulls on nitrous at levels wtween 530 and 560 hp had no visible effect on them. Since then, several other companies have produced such pistons. The most notable is Silvolite with the Keith Black signature series. Although a little heavier than some of the lighter forgings, these pistons are proving to be race tough. I have used them up to almost 600 hp and there are racers with blown motors making several hundred more than this who are making it through several seasons on the same pistns. However, for this kind of reliability with cast pistons, I recommend modifying the block so the pistons are oil cooled... Without the aid of oil cooling, I limit the amount of nitrouspower augmentation to 150 horsepower when using hypereutectic pistons."

I would never put a hypereutectic piston in a motor i was building, but this makes me feel a lot better about the hypereutectic pistons that are in my 350HO crate engine when it comes time for spray .

614Streets

Hyperutectic pistons are physically strong , they could handle an amazing amount of load weight , but they shatter like glass when detionation is present. Forgings offer the extra protection. You will be fine with light loads of nitrous and running it with the correct tune.

stevedave454

hypertectics are what come in about every stock motor, and i know many people running 100-150 shot, as well as ATI/vortech chargers, i know one person running a D2 charger on 10 lbs boost on a 95 z28, the blower and headers is the ONLY mods this car has, and its been running fine being driven hard for almost 2 years now, and a friend of a friend is turned his NOS upto 250 a couple of times on his 99 vette... but he learned his lesson when it backfired and blew his plastic intake to pieces as well as seperating the fiberglass of his hood from the support frame, but internals are still OK!, so basically if your running less than 150 shot just have fun and make sure that IF the mix is wrong its at least rich not lean, and you should have no worries

fb305svs

i can sum up everthing everyone just said here really short-

just run a safe tune and you'll be fine.

83 Crossfire TA

iTrader: (2)

In a perfect world hypereutectic would be fine… they're actually stronger/harder then forged pistons, with a lot of better qualities. The problem with them is that it's not a perfect world and tuning gets messed up and engines detonate, and because of their harness hypereutectic pistons shatter, where a forged piston deforms somewhat and absorbs the damaging shock wave.

Past that you have to decide what you're willing to live with and how likely you are to mess up. I know of a few cars running in the 9's with hypereutectic pistons and I can even think of 2 running cast pistons in that rage, so it can work, but if I was building an engine/buying new parts that I intended to run a power adder on I would just use forged…

unknown_host

iTrader: (1)

Do you guys know for sure if the 350HO comes with hyp. or cast pistons? I am starting to think they are cast, it says cast aluminum in the description, but i could have swore i read they were hyp. somewhere...

83 Crossfire TA

iTrader: (2)

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Schultzy89GTA

Cast aluminum according to Sallee Chevrolet...

http://www.sallee-chevrolet.com/Chev...ckV8s/330.html


and it looks like that description came from gm...

http://www.gmpartsdirect.com (click on performance, click on crate engines, scroll down to 350 HO)

-Schultzy

86WS6_T/A

a hyper. piston is still a cast piston. Just the metal properties are diff (read: silicon)

Guest

Yes, but most pistons that are hypereutectic say so. If it just says cast, chances are thats just what it is, not forged and not hyper, but just a standard cast aluminum piston.

Thirdgens had cast aluminum pistons, thats what most older cars had. Some of the newer ones use forged or hyper, but theres still lots of cast aluminum out there too.

They are more brittle, but probably in most cases stronger than forged. When you screw up though, that doesnt mean much... the hyper is gonna break. And if you use them, make sure you obey any ring gap instructions the manufacturer gives you.

Fevre

Had a hyp piston shatter and it did a number on my alu heads, it was my first lesson on why not to mod a motor you know nothing about.

Damon

I've beat the snout outta hypereutectic pistons- massive nitrous hits, vicious over-revving, and now 2 supercharged engines.

99% of the complaints about hypereutectic pistons "shattering", in my opinion, come from improper setup/machining. Hypereutectis want tolerances that are very different from either a forged or a standard cast piston. Recommended ring gaps are usually much wider on a hypereutectic because the material and the design of the piston throws a LOT of heat at the rings. If you don't follow recommendations you'll butt the ring ends together (especially if you encounter detonation), instantly "shattering" the piston. Usually involving ripping the ringland above the top ring off the piston, and instantly destroying the engine.

Also, Hypereutectis want a bore-to-piston clearance much tighter than a typical forged piston- much more like a regular cast piston. In the range of .0015-.0020 for a N/A application, .0020-.0025 for a nitroused or blower application. Anything wider and you're just beating up the piston by letting it rock in it's bore too much.

I am currently using KB Hypereutectic pistons in my 383 blower motor. Top ring gap is a MASSIVE .032". Almost TWICE what a typical cast or forged piston would require. And exactly what KB recommends for my application. Works fantastic. I have personally, in the past, made the mistake of gapping too tight thinking I knew better than the manufacutrer (did them at .025). I was wrong. First time I hit detonation I butted the ring ends and ripped the top ringlands off the pistons, destroying the engine. I'd rather not discuss that unfortunate situation- too painful. Now that I've got the gaps set right I have encountered similar situations with detonation but the pistons held up just fine this time. Do it EXACTLY like they tell you to and you can push Hypereutectics a LONG LONG way. They aren't made of glass. They're tough little suckers.

I am NOT recommending that you throw hypereutectic pistons into your next boosted/nitroused motor. Forged pistons will still take more punishment, in my opinion. But ANY piston will eventually fail if you run it in detonation. Some just take longer to fail than others.

83 Crossfire TA

iTrader: (2)

Damon, I agree with everything that you said, but remember that you're running KB hyper... pistons, which are much better then most.

B4Ctom1

the guy I talked to in carson city (KB factory's home) told me they "ran 300 shot on kb pistons alot". After some ribbing he then conceded that they used advanced knock sensing, egt, and A/F ration safeties (laboratory conditions) and that it was on a big block (less pressure placed on each square inch of the piston surface and a beefier piston to begin with). The one thing he had to tell me I already knew well; "keep those ring gaps open!" The thermal conductivity of the pistons from the compound really carries the heat to the rings.

the other day I was looking at the summit catalog and saw they sell a whole 350 engine kit with forged pistons, rings, gaskets and bearings etc for some rediculously low (upper $300 range?) price!

the phoenix

iTrader: (1)

I'm looking at taking a 350 block and building a 383 stroker. I am NOT going to be adding nitrous or boost since my car needs a LOT of love once I get the stroker project done.

Am I understanding that the problems on these hyper pistons come from using power adders causing detonation? Does this mean that so long as the 383 is built correctly and I don't play with it after the fact, there should be a low % chance of having problems?

B4Ctom1

Yes, do that and just keep compression and timing reasonable you will be fine. wow way to dig up a 3 year old thread!

the phoenix

iTrader: (1)

'Search' is my friend