whats the most power you can run on cast pistons?


a friend of mine just picked up a reman shortblock, and he has some pretty strong top end pieces he intends to put on them...

he asked me what i thought the cast pistons could take, and ot be honest, i donno when the limit really is... ive always used better stuff when i made a bottom end....


whats the most boosted hp you can run with cast pistons?

and how much do you think he can spray with it?



hes talking to me about not intercooling it, but just spraying a 50 shot at the track to cool it..... i think hes nuts and will probly throw a rod before the piston burns thru but thats not the question.

 

Just tell him hyperuetectics(sp) are $150, its worth piece of mind. Even if its only slightly stronger.

I wouldnt ever do much boost or nitrous on anything but forged, there is too much to mess up.

The motor might be free/cheap, but he has to think of the cost to build a new one when he breaks his free/cheap one.....

 

ok, heres another add on to it.


i think i have him talked into swapping pistons, but he wants to keep the rods..... however he wants to add ARP rodbolts instead of keeping whats on there...


now, if he swapps em, wouldnt he have to get the rod checked? i mean, the TQ specs on a ARP rod are diffrent... i would expect it to SLIGHTLY change how round it is, right?





he just needs to get a new shortblock for his good stuff...

anyhoo... just replacing the rod bolts with arp bolts, will that cause a problem?

 

Yes, he may need to have them resized.

 

well i use 345np pistons cast 10.2:1 with 64cc, cast crank, and stock rods . have put 150 n2o to them. last dyno was 359 rwhp and 539 rwtq. still driving it.

 

not much reson not to upgrade pistons if you're upgrading HP. i'd guess something in the 350-400HP range would be the limit on cast parts ,but it depends too on how long and how often the engine really runs or produces the max HP. as for resizing the rods after changing bolts. you'd need to have a shop press the bolts in, unless you have a press at home. it can be done but it's hard to press rod bolts with the pistons on the rods. if you swap pistons any shop will check the rod and i'd guess if you swap rod bolts they'd check the rods, if it needs resized either they'll do it reguardless or tell you about it to limit their liability.

 

Fellow racer/performance engine shop owner/operator has a '37 Chevy pickup with huffed 383. The thing weighs 3700 lbs going down the track, runs mid-12's at sea level. Drove it from Denver to race at Topeka in '01.

He only uses cast pistons. Says as long as you don't let it go lean, they'll last as long as forged.

Hypereutectic aren't as good for power adders as cast are.

 

hes has a set of ported Dart Iron Eagles (same heads as me) but hes running a 177 (i think) blower... its one of the smaller roots blowers... well "smaller" its alot bigger then my M112, but its not huge... carb on top.

you think he'll be ok with the reman shortblock? i looked at it today and its a 400 block taken 40 over... i donno how close he is to the waterjacket either...



he seems dead set on running it unless i can show him its going to blow his block apart..

apparently, after i dragged it out of him, he ordered a reman 400 block for a truck because he couldnt find anyone that had a 400 shortblock he could afford... and he really wants a 400..

so is that bottom end doomed, or is there a chance it'll hold together if he runs it a lil rich?

 

Prove it

 

What would you accept as "proof"?

 

Just seems like a pretty bold statement that goes against the statements of world renowned engine builders.

But hey, what do they know.

 

everything i've heard from those engine builders say don't use hypereutectics with power adders, as they will shatter and break, as opposed to cast and forged designs that will begin to melt before breaking, potentially allowing you to catch a potentially more expensive problem.

 

go to www.ls1motorsports.com check out the turbo formula... its hypertecs, not cast, but still 630 HP and 680 TQ... thats nuts, and its been holding up for awhile... also i've known several people to run 6-71's on cast pistons with 9.0:1 compression and kept the boost low, and ran rich and didn't have problems for a long time... but they had the mind set that if it blew up ohwell... so if he is concerned bout not blowing it up then definately get something better

 

That is exactly what Ive read also, and five7kid doesnt just blert out answers that arent true.

If I have a question on the boards, hes the one I want to see responding because I know Im getting a non BS answer. Whereas some will tell you what they heard from a friend, who learned from a friend, who read an article a few years ago...

 

hypers have a higher tensile strength than any other piston, they also are the most brittle and also reflect the most heat back to the chanber and conversely hold the most heat on the top of the piston. the reason you wouldn't want to run hypers in a power adder applkication is becasue of the brittleness factor and the increased likelyhood of detination which would increase the chances of the piston to fail.

 

lol, to be honest i donno..

looks like all this is a moot point anyway... hes basicly scared of taking it apart, and he wont let me take it apart... like theres some voodoo magic that i'll upset or somthing...

so in it goes as-is.... im sure if it blows up and throws a rod thru the block or somthing, i'll post pics

 

OK. You want to know what I want as proof?

Pictures.

True stories of people running boost or nitrous on cast pistons, then built a similar engine using hypers and them shattering.

AAMOF, the last engine I disassembled had cast pistons with holes that were literally BUSTED out. Not melted, but busted.

I also know five7kid isn't a BS'er. Neither am I. I never implied he is. But until there's proof that what he said is true, it isn't.

As far as I'm concerned, it's another wive's tale. Right up there with Coca Cola eating a galvanized nail in 2 days.

Obviously they're not as strong, or resistant to detonation as forged pistons, but I'm will never believe they're weaker than cast pistons without proof. Never.

 

"As far as I'm concerned, it's another wive's tale. Right up there with Coca Cola eating a galvanized nail in 2 days."

You don't work for Coke, do you?

I think it depends on the application, but to answer the original question, it depends on RPM, size of the engine and other factors. I am running cast pistons in my 406 and hope to have 425-440 HP and 475 lb/ft of torque...

 

heh, this subject got me curious enough to look elsewhere... from what im seeing from the past, as long as theres no mechanical failure, or going lean, there have been people running blowers on cast pistons for decades....

im still taking a wait and see approch with this though... i donno about reman stuff... i mean, i doubt this shortblock was built with power in mind, but eh... i'll see what happens... *hopes for best*

 

5 kid may be right, no I don't have "proof" but I do remember an old time engine builder saying that cast pistons will make more power than forged, as I recall, and this was about 30 years ago, it had to do with the cast pistons retaining heat better than forged. Let's qualify that, if you keep putting power to something, like say a blower, eventually the cast pistons will give up with less boost than the forged. So, in that case you could say the forged pistons made more power.However, in stock form, and this guy was a stock-class racer, he always ran cast pistons whenever he could, and he held a national record back then with a 2-4bbl 283 1959 corvette.

 

And I should be more careful with blanket statements.

There are variations in quality/engineering between cast pistons, as well as hyper. Some hypers may last longer than some cast in some power adder conditions.

Conventional wisdom says if you go power adder, use forged. But, there are those who buck convention and get away with it.

FWIW, this good-ol'-boy hurt his 383 a couple of years ago when he went from Bandimere to Topeka - had to slow it down to stay within the Sportsman class at the lower elevation, so he went from two 4bbls to one - and didn't get the jetting right for his first few time trials. He didn't know he'd done any damage, made his runs, drove it home, put the 2-4bbls back on, and sprayed piston & ring parts all over the upper end two weekends later. Had he been using forged pistons, he maintains, he wouldn't have been able to drive it home.

But, what does a guy who's been building engines & racing for 40 years really know, right?

 

Either you flunked English Lit. or I did.

I have NO IDEA what you're trying to say, except... if the guy (you maybe?) used forged pistons over hypers, that he would have messed them up?

I dunno. Looks like the message board slang and vague slurs are rubbing off on you.

 

not that your going to run a blower but do not use cast pistons with any type of boost the wrist pins will start to pull out of the bottom of the piston breaking off the skirts had this happen to me long time ago, got about 50,000 supercharged miles on the same motor since with forged pistons

 

another thing to consider is chromemoly rings again from personal experience if you have any type of detonation they will shatter and then you collapse ring lands ductile rings are much more forgiving. I have never used hyper. pistons but I would think that the more brittle the material is the less forgiving it is

 

heh, well he should have it running this weekend... we'll see how long it holds together.

 

All 5-7 is saying is that its generally unwise to use hypers with a power adder. They are sorta like a table saw blade tooth: hard as f*ck, but one little hit the wrong way will shatter it.

Cast and forged pistons are much more forgiving in that way than hypers are because they can handle detonation much better than a hyper can.

 

I'm with Camaro Driver. I won't ever believe that without seeing it.

Because they're harder, they're stronger than cast pistons which makes them MORE resistant to melt-down than cast pistons.

What happens is because they're harder, they don't melt as easy. Cast pistons just melt, but because hypers are stronger, they break. But keep in mind; It takes A LOT more abuse to break a hypereutectic piston than it does to melt a cast piston.

Granted, they're not as resistant to detonation or heat as forged pistons are, but that doesn't make them bad. They're an alternative that's stronger than cast, yet cheaper, albeit weaker than forged.

What this reminds me of is when aluminum wheels became popular in the late 80's. EVERYONE was so against them because "Steel wheels are better because they bend. Aluminum wheels break." That's true, however, I can bend a steel wheel with a 2 lb. sledge hammer easier than I can break an aluminum wheel.

The common problem that's been seen with hyper pistons is broken rings. Because they're heat resistant, the heat stays in the combustion chamber, which improves efficiency. This obviously causes the ring to expand more from the increased heat, so normally wider gaps are needed.

Keith Black addresses this with their pistons. Speed Pro on the other hand says normal ring gaps can be used. To be on the safe side, I'd still recommend gapping on the high side (.005" per 1" bore) even with Speed Pros.

I'm not trying to step on any toes, I just want to make sure that people understand that hypers are a lot better than the doubtful think.

 

umm, the hardness of a metal doesnt have anything to do with its melting point...

to use your steel wheel vs alum analogy:
if you hold a torch to the steel wheel, it glows.. you hold it to the alum wheel, it melts... you add oxygen and the steel wheel melts too, but it takes more heat to melt then the alum.

melting point and hardness are two diffrent propertys... perhaps im reading it wrong, but it sounds like you're saying they are one in the same....

 

I suppose so. Trying to keep the number of words down in a long dialogue. Sorry.

No, I'm not talking about myself. And, he was using cast pistons, not hypereutectic or forged. He'll readily admit that forged are stronger than cast, he just says the cast are more forgiving, and forged will melt with a lean mixture just like cast will (at least at his power levels). Keep the mixture from going lean, the pistons will last (again, at his power levels). The one time when he did let the mixture go lean for a few runs, he's saying the forged pistons wouldn't have gotten him home under those conditions, but the cast did. Hope that helps clarify things (probably not, though).

Strength & melting point are related in this case because each type of piston uses a different aluminum alloy. And, each alloy has a different melting point. And, obvioiusly, the final products have different strengths and ductility.

(FWIW: Back to the orginal "how much power can cast pistons take" question: This 383 blower guy says a stock LG4 doesn't have enough power to run his blower. Think about it: The pistons have to withstand the power being produced in the cylinders required to both run the blower and what actually gets to the flywheel. And he uses cast pistons.)

 

Hypers can handle boost up to ~16-18psi. After that, they are more likely to shatter under wot conditions. Hypers are only 70% as strong as forged pistons, but forged are more likely to melt under lean conditions. When it comes to boost, hypers are more likely to fail/shatter when detonation is involved.

Basically, if you are going to be running boost over 20, forged. If you are below that, then run whatever you feel like. But always keep the detonation down and keep away from lean. Forged would also be better if you don’t live in Texas(hell), either that
or make sure your car can keep cool. ;-)

 

Don't get me wrong here... I am not bashing any of the 3 kinds of pistons.. all 3 have their pluses and minuses. Hypers are good because, as mentioned before, they help make an engine make power more efficiently by keeping the heat in the cylinder better than cast or forged can because they are significantly harder. The problem they have though, is that they are too brittle (with hardness come brittleness) to handle much detonation, and that is probably the best reason NOT to use them with a supercharger or something, because they will shatter, which will cause alot more engine damage than a melting cast or forged piston will.

Cast pistons work fine in general for most purposes, and they are good because they only cost around $10 a piston.

Forged is the best because it can handle alot more power and stress than a cast piston can, and is a MUCH better choice for a non-NA engine because it can put up with detonation better than a hyper can because it will not shatter. On a NA engine though, they will make an engine a little less efficient because it cannot trap as much of the heat in the cylinder as a hyper can.

Just my $0.02

 

hey, im going to be living in DFW soon too.... you might see my car...
are you in NTTGA (north texas thirdgen assoc.)??
our message board is here if you're intrested: http://www.gmperformance.org/NTTGA/

 

When I was talking about the wheels, I was referring to people that are so BONE HEADED to accept the fact that hyper pistons are WAY BETTER than cast pistons. It was an anology on PEOPLE not METAL.

And yes, the hardness of hyper pistons has everything to do with the melting point IF YOU'D READ

Where cast pistons would melt, hypers won't because they RESIST heat better. But when they do reach the point of getting beat to death (by detonation), they're more likely to break before they melt, where cast piston would have broke a long time before that.

Maybe I'm wording wrong. I flunked English Lit. to.

And to Air_Adam,

If you're paying $10 for a cast piston, you're getting hosed. Hypers are usually in that price range.

 

Even I can understand it when you put it that way...

In case anyone is interested, the "eutectic" point of an aluminum allow refers to the amount of silicon it contains so that it melts in a single "phase" - i.e., goes directly from solid to liquid. If the silicone content of an alloy is on either side of that point, when it starts to melt it will be a mixture of solid & liquid, until it gets to a higher temperature at which point it will all be liquid. However, the temperature at which liquid starts to form is the same, regardless of the amount of silicon (within certain bounds).

For the purpose of casting, it's easiest if the whole thing is liquid or solid (same thing for lead-tin solder, by the way). So, the typical cast piston is made from eutectic aluminum alloy.

However, the higher the silicon content, the harder and stronger the alloy will be. So, a hypereutectic piston ("hyper" meaning "above") has more silicon in it to give it better strength properties, and therefore the casting process has to be more tightly temperature controlled to ensure that the material flows and cools properly.

The downside to higher strength is that ductility goes down. Therefore, detonation (a shock event) will tend to damage a hypereutectic piston before it will damage a cast piston.

There are other alloying element differences between cast & and hypereutectic pistons than just silicon, however. I don't have the phase diagrams for each in front of me, so I won't comment further about the liquidus line of each (I suspect they're the same, though). The other elements also effect the eutectic point.

 

HEY!!!

I think I figured out what we can compare them to that will at least help me understand what you're thinking.

We have two panes of glass;

1 everyday, normal glass that you buy for windows in your garage.

Then we have 1 pane tempered glass.

The cast piston is the normal glass, where the hyper piston is the tempered glass???

I assume that’s what you mean by losing the ductility? Ignore the fact that the way tempered glass is made. That’s not the part I was trying to understand.

Why is it that by using the higher level of silicon makes the metal lighter? Because Speed Pro brags that since the metal is lighter, they can use more of it, making the pistons thicker. But in reality, is this what they have to do to help keep them from breaking?

I’ve always understood what makes a hypereutectic piston a “hyper”eutectic piston, but is the only real benefit of doing this to allow for tighter clearances since hyper pistons don’t expand and contract as much?

I actually think you’re creating more questions in my head than you’re answering. No that it’s your fault though.

 

Ductile & brittle are opposites. When a material is more ductile, it will deform before it breaks. When a material is brittle, it fractures with little or no deformation. A ductile material can withstand shock better than a brittle material can.

Say you have a 2 foot bar of cast iron and a 2 foot bar of carbon steel, for instance, that are the same size and same strength. Secure them so one end is fixed and hanging over an anvil at the middle - wack the other end with a sledge hammer: the cast iron is more likely to break, whereas the steel will bend. Cast iron is brittle, alloy steel is ductile.

There are all sorts of alloying and heat-treating things that can be done to increase strength while maintaining some of the ductility of the softer material. Same situation as above, except one bar is plain carbon steel and the other is a high-strength super-alloy like Inconel. Neither will break, but the carbon steel will bend more.

I'm not sure about the relative densities of cast and hypereutectic piston alloys. It doesn't sound like the statement can be taken at face value, but what the hyper material probably allows you to do is move the material thicknesses to where you can better use them for better strength for the same final mass. I'm not sure of the details there.

I have heard, though, that the forged piston alloy is more dense (heavier for the same volume of material) than cast alloy.