Hot Rod Forum banner

1 - 20 of 38 Posts

·
Registered
Joined
·
26 Posts
Discussion Starter #1
OK< guys! Most of us will NEVER take these cars of ours to any track at any time....so, why would we wanato spend the money (two, three or four times the cost of cast pistons) to buy forged? Or to buy hypereutectic? I was talkin' to an engine tech, and he told me that he was concerned about people using hypereutectic pistons in street cars instead of racers, said the expansion rate of the material was not as good as what was used for cast, that the cast ones expanded properly, and that many people didnt know that drag cars used special equipment to warm up their engines first, which we do not have, if we use hypereutectic ones. So...does anyone know the true deal here? Or are we just suckers for piston marketing departments? I'd like to hear what you know!
 

·
Registered
Joined
·
132 Posts
i personally dont like the hypertectic pistons at all they are soft and brittle compared to forged mayeb in a race car they last but not in street cars i have many friends that used them in their hot rods and street cars and over 50 % of the time they cracked cuz they couldnt take the heat we are all young so once we get a car running we give it everything we got and forged stands up to anything we can give it, and yea thre are selling gimmics out there that try to suck u in but thats what hotrodders.com is there for to tell u the real truths behind it all from professionals and builders and anyone else that knows about anything
 

·
Super Moderator
Joined
·
6,623 Posts
Guy, hypereutectic pistons were designed to expand at much the same rate as the surrounding cast iron cylinder which allows a tighter fit and hence less piston rock and less blowby. Cast pistons in comparison need steel inserts to perform similarily and are weaker than eutectics. Hyper eutectic pistons are not cast in the same manner as regular pistons also, they are high pressure injection molded under high vacuum and are more dense than a comparable cast piston. Most pistons today are eutectic from the factory because of these superior properties.

Forged pistons are about twice as strong as either cast or eutectic and can incorporate design features that require this added strength such as higher ring lands, relocated piston pins, thin skirts etc. Most people do not need forged pistons unless the engine will see high rpm repeatedly or the engine will be run on the ragged edge of detonation with lean mixtures etc., in these conditions forged pistons excell and are the natural choice for extreme duty engine use.

Since hypereutectic pistons are stronger than the old fashioned cast in steel supported skirt cast pistons the rules have changed and unless you need the extra strength of forged it is unlikely you need anything more. The other consideration is forged pistons need at least twice the clearance of a eutectic piston and hence will wear the rings faster due to piston rock.

What does this mean? If you take your 350 Chevy to the track occasionally and have invested in aftermarket rods and a forged crank and twist that motor past 7000 rpm during these occasions, forged pistons might be a good investment and could save your engine if it happens to run a little lean and it detonates at 7000 rpm. I run forged in every race engine I build but if it is driven on the street it gets the hypereutectics because it is rare for a street engine to run hard enough to require the extra margin of strength. Blown and turbo charged engines should have forged due to the extra heat and pressure they will see, I would consider this mandatory and a wise investment. It all depends on how well the engine is tuned and driven, if it is abused forged are good to have they will take a licking and keep on ticking.

[ May 07, 2002: Message edited by: 4 Jaw Chuck ]</p>
 

·
Registered
Joined
·
188 Posts
Ever seen what happens to ur nice fancy block, etc when a piston breaks? THAT is what people dont use cast pistons. My 460 runs hyper-whatever pistonns, and lots of nitrous... they have made 100-150 passes on the 1320 and see regular street use... it isnt a prob with an EFI motor... with a carb you can have some cylenders running at 13:1 A/F and others running at 15:1, annd THAT is where you blow pistons, etc... I cant afford EFI, so I am running the Nitrous system with a gas jet 1 size bigger than the norm... Keeps the A/F at 12:1 with the nitrous on, 13:1 on the motor... Keep the pistons cool enough, and you wont have a prob with the Hypereutics, cast is just a no-no with anything over stock hp...
 

·
Registered
Joined
·
123 Posts
chuck, what is the? eutectic that is so hyper?a surface coating?if a coating is it on the sides /top?what is it? jimm
 

·
Super Moderator
Joined
·
6,623 Posts
Jimm,
Eutectic refers to a special alloy mix that contains silicon in a proportion that when the aluminum solidifies the aluminum and silicon solidify at the same time. This allows the designer to produce a mold that is very intricate and ensures his aluminum/silicon mix will solidify at the same temperature. You could say that silicon is to aluminum as carbon is to steel, it is a hardening agent but has the undesirable property of uncontrolled grain growth which leads to large silicon crystals that will settle out of a molten mixture which makes it hard to produce a homogeneous alloy with identical properties throughout. Eutectic alloys (steel, aluminum, titanium etc.) melt at one temperature without the alloys melting/solidifying at different temps. The phase change diagram shows a single phase change line at which the material is either solid or liquid.

WHAT THE HELL DOES THAT MEAN?!!! it means a harder, stronger, more heat/wear resistant alloy that can be cast in intricate shapes and have the alloying ingrediants solidify at the same time as the rest of the mixture ensuring proper distribution and crystal size. It also happens to expand at a lower rate than plain cast aluminum or forged.

The "hyper" part is just a marketing ploy.

Here's a few links that describe the process and properties somewhat.

<a href="http://math.nist.gov/~GMcFadden/eutectic.html" target="_blank">http://math.nist.gov/~GMcFadden/eutectic.html</a>

<a href="http://www.kb-silvolite.com/page03.htm" target="_blank">http://www.kb-silvolite.com/page03.htm</a>

<a href="http://www.kb-silvolite.com/page11.htm" target="_blank">http://www.kb-silvolite.com/page11.htm</a>

Did that make sense?
 

·
Registered
Joined
·
26 Posts
Discussion Starter #7
OK, 'nother question:

What about what "shagginwagonvic" said above, in his post, about the hypereutectic pistons getting so easily damaged? Why? Are the guys doing something wrong with them, do these pistons need some sort of babying, or what? How do you avoid damaging them like he said, if this happens?
 

·
Registered
Joined
·
26 Posts
Discussion Starter #8
Hmmm...on their web site, Silvo-lite claims that, unless heat-treated, the hypereutectic aluminum 390 alloy is WEAKER than the good ol' $80 a set cast pistons!!! Hey, then how many sets by other manufacturers are indeed, heat treated? Sounds like we may have been buying a bill of goods and paying twice the price for weaker pistons! Hmmmm...maybe this explains those busted hypereutectics mentioned earlier!
 

·
Super Moderator
Joined
·
6,623 Posts
Heat treat on aluminum is very important and can lead to the types of problems that are seen with any aluminum product, technically it is a solution heat treatment that will change molecular bonds, distribute alloying ingrediants and realign crystal matrices. This is a very complicated subject that has many interrelated factors that can be specific for each alloy type.

<a href="http://www.burnsstainless.com/TechArticles/Aluminum_article/aluminum_article.html" target="_blank">http://www.burnsstainless.com/TechArticles/Aluminum_article/aluminum_article.html</a>

I will agree that Eutectic pistons are more brittle especially if overheated (you will destroy the heat treat) because you don't get something for nothing, they are stronger and lighter compared to regular cast pistons but are more suseptible to brittle fracture if abused where a regular cast piston would just melt the ring land or collapse it. I don't consider them a racing or heavy duty alternative to forged pistons but basically a better cast piston.

If you are destroying Eutectic pistons then you need forged for your application, regular cast pistons would have given up the ghost under the same conditions but may fail in a less catastrophic manner, eg. melted ring lands, hole in the piston top, collapsed ring lands etc.

So to summarize what we have been talking about these are some observations,

-If you are rebuilding a grocery getter that will never see the track and never be turned high enough rpm to stress the rods, regular cast or eutectic pistons will do just fine.

-If the engine you are building will be a 1Hp/CI engine but will never be raced just cruised, cast or eutectic will do just fine also.

-If the engine you are building is going to have it's neck ringed every weekend and bang shifted at every opportunity and you are going to enjoy every minute of it, forged pistons are for you.

From every standpoint of durability and strength forged wins hands down and is the logical choice for any heavy duty application, as hotrodders the extra money spent on forged will never be a bad investment, just remember they are heavier and if your rods are marginal at the rpm you want to turn upgrading the rods would be wise. In my opinion most rodders would be better off with forged pistons in their engines if for nothing more than piece of mind.
 

·
Registered
Joined
·
10 Posts
SO IF IM RUNNING A EVERYDAY USE ENGINE AND JUST LIKE TO FLOOR IT EVERYNOW AND THEN. I WOULD BE WASTING MY MONEY ON FORGED PISTONS?
 

·
Super Moderator
Joined
·
6,623 Posts
Gonzalez, I don't think buying forged is ever a waste of money but I doubt you would ever need their superior properties in the manner you describe.
 

·
Registered
Joined
·
123 Posts
chuck,hey guy! thanks for the info and links.lot of cool stuff there,a guy could spend a long time just giving it the once over.by the way, since the dollar has reared its ugly head in this topic,what is the difference between some good forged pistons and good eutectics?[i like forged ,dont know what eutectics cost]if a hundred dollar bill is all that stands between a guy[difference that is]and some good forged pistons....?see ya!jimm
 

·
Super Moderator
Joined
·
6,623 Posts
This is not a good area to be saving a few bicks in my opinion, part of the problem is the piston manufacturers advertise the eutectic pistons as a low cost alternative to forged which they really are not. Yes they are stonger and a better piston compared to a cast piston but how much? Not nearly enough for me to compare them to a forged piston. I have eutectic pistons in my 400M engine that puts out around 375 HP, would I take it to the dragstrip? Not on your life because I didn't build the engine with that goal in mind, beside the 400M rods are the weak link and I don't turn it over 5000 RPM. If I had put heavy forged pistons in maybe my RPM limit with the stock rods would only be 4500 RPM? That would be a kind of a backasswards engine build in my opinion. Now if I took that same engine and put in an forged aftermarket crank with some aftermarket rods and some heads that could flow and was intending on spinning it to 7000 RPM I think forged pistons would be the wisest investment you could make, although the eutectics could probably handle the extra load for a while it would be a game of what is the weak link. If I ever ran that engine into detonation at 7000 RPM (you would never hear it) say bye bye to those eutectic pistons, where the forged would handle it and maybe just have a light 4 corner seizure from the extra heat from the detonation. At least my other engine components would not end up on the pavement like the rods I posted here.

<a href="http://www.hotrodders.com/cgibin/ubb/15/000462/1" target="_blank">http://www.hotrodders.com/cgibin/ubb/15/000462/1</a>
 

·
Registered
Joined
·
14 Posts
dude just get the forgged they will turn out to be a better investment in the future if you end up wanting to super charge turbo or maybe some good old hp in a bottle ya know what i mean
 

·
Registered
Joined
·
188 Posts
cast pistons are fine for you 350 chevvy and 5.0 guys... most piston failuress damage the block... for a 350, you can just go pull another one... Id rather not lunch my 460 block.. you wouldnt believe how hard to find those things are around here...
 

·
Registered
Joined
·
26 Posts
Discussion Starter #16
Kinda weird...two days ago, my job took me to a Job Shop trade show, where I got a chance to talk to some people running a foundry business, which makes among other things, connecting rods. I asked about Silvo Lite's "390 Aluminum" they say they use in their hypereutectic pistons. These casting people I spoke with had never heard of anything called 390 aluminum. They were familiar with T6 heat treatiung however, and felt that the secret was probably in that rather than the unknown 390 alloy. I submit that the frugal hotrodder could heat treat his own cheap cast pistons and have some good ones, as the Cast piston people admit that a big reason forged pistons are stronger than cast is simply (a great deal) because the metal is thicker, in turn just because casting can just make the pistons thinner by the casting process itself. doing it yourself you could heat 'em up, then let cool slowly over a long period of time, possible quenching them. Personally, I think the jury is still out on using the forging process with aluminum to actually "strengthen" aluminum, aluminum tends to stress and shatter rather than bend like steel does. Steel can be "hammer welded", ever heard of anyone doing that with aluminum? Two different metals, two totally different reactions to the stress of forging.
 

·
Registered
Joined
·
188 Posts
The Hypereutics get their strength from the high silicon content in their alloy... every piston company has its own alloy of AL... Forged AL is MUCH stronger, almost as strong as some steel...
 

·
Registered
Joined
·
291 Posts
Originally posted by 4 Jaw Chuck:
<strong>The "hyper" part is just a marketing ploy.
</strong><hr></blockquote>

Hmm, I understood that "eutectic" meant an alloy with 12% silicon (I think it's 12) and "hyper" is any alloy with more than that...
 

·
Super Moderator
Joined
·
6,623 Posts
Red, there is no mention in the Machinist Handbook or Marks Standard Engineering Handbook on the term "Hyper" in reference to any alloy. By definition Eutectic refers to an alloy with one common solidification temp amongst the alloys. I will do more digging to see if there is reason for the term "Hyper". I could be wrong?!
 

·
Registered
Joined
·
291 Posts
It's what I have always read in the mags, but that could just be another myth. Hot Rod or Chevy High Performance, one, did the last article I read that said that.

I do realize that just because it is in a magazine doesn't mean it's true...

Hmm...now my interest is piqued. We'll get to the bottom of this by golly!
 
1 - 20 of 38 Posts
Top