Wich pistons!

[letsgetthisdone]

HOLY SHIT^^^

 

 

 

here's mine, although it doesn't really compare......

 

 

tha hole actually goes through, its about 1/2 an inch long and around 2mm wide...

Edited May 26, 2007 by letsgetthisdone

[RNBRAD]

Wow, amazing picture and a testament to the maleability of forged pistons A cast will fracture every time. The reason is a cast's inherent % of silicon is what makes it brittle. A forged unit would fracture during it's production if it was as brittle. This is why a forged piston has less silicon than a cast piston. Also the % of silicon is what makes the cast piston more dimensionally stable though at the same time making it more brittle.

 

 

Anyway FH, I think you are starting to get it. Now just understanding why a cast is more dimensionally stable.

What makes it that way and not a forged? Why can't forged pistons use as high of a silicon % as cast? As we all know that silicon provides excellent lubricating properties. Ever heard a forged piston will wear out a bore faster than a cast? Anyone ever wonder why? Ask a builder, they will tell you,

 

Anyway this is a great thread and a good learning opportunity for all of us. Makes people think a little more when selecting a cast or a forged piston. Both have their pros and cons. I will agree in the race engine market that forged is the way to go. A forging is a stronger piston and under the stresses of turbo's, exotic fuels, and the list goes on... you can't lose with a forged unit. BUT.... if your engine does not need nor require a forged piston, your motor will be better off with a cast. It's just one of my peeves when someone says that a forged piston is always better, that's just not true.

[FireHead]

Here is why I like forged pistons over cast. See how the forged Wiseco didn't shatter like a cast piston would have under extreme over-rev? It stayed together and folded into itself instead of grenadeing...

This piston is exactly as I found it. I pulled the exhaust...the piston pin fell out of the chamber onto the garage floor. I pulled the head, reached into the cylinder and pulled this out of my RD350. The rod was broken in half and wedged into the cylinder wall. :: Ouch!! ::

That is near the top of my list of best piston failures from an ATV.

[FireHead]

Wow, amazing picture and a testament to the maleability of forged pistons A cast will fracture every time. The reason is a cast's inherent % of silicon is what makes it brittle. A forged unit would fracture during it's production if it was as brittle. This is why a forged piston has less silicon than a cast piston. Also the % of silicon is what makes the cast piston more dimensionally stable though at the same time making it more brittle.

Anyway FH, I think you are starting to get it. Now just understanding why a cast is more dimensionally stable.

What makes it that way and not a forged? Why can't forged pistons use as high of a silicon % as cast? As we all know that silicon provides excellent lubricating properties. Ever heard a forged piston will wear out a bore faster than a cast? Anyone ever wonder why? Ask a builder, they will tell you,

 

Anyway this is a great thread and a good learning opportunity for all of us. Makes people think a little more when selecting a cast or a forged piston. Both have their pros and cons. I will agree in the race engine market that forged is the way to go. A forging is a stronger piston and under the stresses of turbo's, exotic fuels, and the list goes on... you can't lose with a forged unit. BUT.... if your engine does not need nor require a forged piston, your motor will be better off with a cast. It's just one of my peeves when someone says that a forged piston is always better, that's just not true.

 

First off, the silicon content of a cast piston vs. a forged piston can be the same or different. There is no rule of thumb there. Just because a piston is cast does not automatically mean it has more silicon in it, that is just BS.

 

A cast piston is not more dimensionally stable! Forged pistons have a higher overall max and min value for growth on the o.d. of the piston during a heat cycle. A cast piston will actually change shape during a heat cycle, not just expand and contract.

 

I am afraid that you keep referencing generalities that are well over thirty years old and are out dated.

 

A word of caution when speaking to a builder about pistons. Please make sure you have read atleast enough on the subject you are asking the builder about to spot some verbal poo. I have heard some pretty strange things (second or third hand of course) on here that people said a builder told them. At the end of the day a builder is going to tell you what he has had the most success with. Right or wrong, that's what works for him. :thumbsup:

[RNBRAD]

A forged piston may expand and contract more than a cast piston

 

That is dimensional stability no matter how you slice it. That's why a forged piston of the same size requires a larger bore. Fact, period, bar none, end of story, that is dimensional stability!

 

Yes forged and cast pistons have varying %'s of silicon. Silicon adds dimensional stability to cast and forged pistons, fact, period, bar none, end of story. Now tell me which piston has more silicon. It's the piston that has the least expansion and contraction. Or in other words the piston that is more dimensionally stable meaning the dimensions adhere closer and tighter to there original manufactured specification when heated.

 

Does this mean that every cast piston has more silicon than a forged, no but I would bet it's 98 to 2.

[Bansh-eman]

Brad, maybe im reading his posts differantly then you are. cause from what im getting , he is saying that a forged piston expeands more yes. it also contracts more yes.

 

but the CAST will deform? it will take on a differant shape? and wont return to it same demintions once it contracts?

 

is this what your saying mark?

[FireHead]

Brad, maybe im reading his posts differantly then you are. cause from what im getting , he is saying that a forged piston expeands more yes. it also contracts more yes.

 

but the CAST will deform? it will take on a differant shape? and wont return to it same demintions once it contracts?

 

is this what your saying mark?

You are correct. This is the message I have been trying to get across. I was beginning to think I was retarded or something. :biggrin:

[RNBRAD]

Brad, maybe im reading his posts differantly then you are. cause from what im getting , he is saying that a forged piston expeands more yes. it also contracts more yes.

 

but the CAST will deform? it will take on a differant shape? and wont return to it same demintions once it contracts?

 

is this what your saying mark?

 

Not sure myself, never heard of it. It's not dimensional stability which is what I am reffering to. No reason to over sophisticate this. Dimensional stability is one thing that I stated above and nothing else. We also need to remember that this is a discussion of pistons, not casting and forgings in general. :thumbsup:

[FireHead]

That is dimensional stability no matter how you slice it. That's why a forged piston of the same size requires a larger bore. Fact, period, bar none, end of story, that is dimensional stability!

 

Yes forged and cast pistons have varying %'s of silicon. Silicon adds dimensional stability to cast and forged pistons, fact, period, bar none, end of story. Now tell me which piston has more silicon. It's the piston that has the least expansion and contraction. Or in other words the piston that is more dimensionally stable meaning the dimensions adhere closer and tighter to there original manufactured specification when heated.

 

Does this mean that every cast piston has more silicon than a forged, no but I would bet it's 98 to 2.

 

Silicon content can be the exact same between a forged and cast piston. Due to alloying processes and forging techniques the generality of a cast piston having a higher silicon content than a forged piston is no longer true. If I were to pull a decade out of my butt, I would say it hasn't been true since the 1950's.

[FireHead]

Not sure myself, never heard of it. It's not dimensional stability which is what I am reffering to. No reason to over sophisticate this. Dimensional stability is one thing that I stated above and nothing else. We also need to remember that this is a discussion of pistons, not casting and forgings in general. :thumbsup:

I was talking about pistons..............nothing else.

 

What would you rather have, a piston that expanded and contracted less, but changed shape and did it differently every time, or a piston that expanded and contracted more, but did it the same every time? This is why a forged pisston is better and why you don't see too many folks running cast pistons in a mission critical application. :ohmy:

[RNBRAD]

Silicon content can be the exact same between a forged and cast piston. Due to alloying processes and forging techniques the generality of a cast piston having a higher silicon content than a forged piston is no longer true. If I were to pull a decade out of my butt, I would say it hasn't been true since the 1950's.

 

Then tell me why the forged contracts more than cast in general. Now granted a wiseco probably has one of the tightest cylinder to bore clearnaces. Reason is that it has a higher % of silicon than other forged pistons. But it still does not have as high a % as an oem or a pro-x cast unit.

 

Not sure I'm catching your information about a cast piston changing shape non-uniformly. Where is the disadvantage manifested on this statement? Horsepower? Wear on a certain side of the cylinder wall? Where's the evidence of this phenomenon in regarsds to piston performance?

[FireHead]

Then tell me why the forged contracts more than cast in general. Now granted a wiseco probably has one of the tightest cylinder to bore clearnaces. Reason is that it has a higher % of silicon than other forged pistons. But it still does not have as high a % as an oem or a pro-x cast unit.

 

Not sure I'm catching your information about a cast piston changing shape non-uniformly. Where is the disadvantage manifested on this statement? Horsepower? Wear on a certain side of the cylinder wall? Where's the evidence of this phenomenon in regarsds to piston performance?

 

Disadvantages are: decreased reliablility, poor ring engagement, increased skirt wear, increased wrist pin misalignment. IF a piston is wearing out a cylinder wall something is wrong. This piston is always the sacrificial entity in the rotating assembly.

 

I don't know where you got your silicon information from. I am not sure I can even speak to it. If want to talk about alloys that pistons are made of that's fine, but there is absolutely no way you can truthfully say a cast piston always has more silicon in it. For piston to function, you really only need a trace amount of silicon in the alloy, but you'll need to treplace it with something such as titanium, etc. :geek:

[RNBRAD]

Disadvantages are: decreased reliablility, poor ring engagement, increased skirt wear, increased wrist pin misalignment. IF a piston is wearing out a cylinder wall something is wrong. This piston is always the sacrificial entity in the rotating assembly.

 

I don't know where you got your silicon information from. I am not sure I can even speak to it. If want to talk about alloys that pistons are made of that's fine, but there is absolutely no way you can truthfully say a cast piston always has more silicon in it. For piston to function, you really only need a trace amount of silicon in the alloy, but you'll need to treplace it with something such as titanium, etc. :geek:

 

Honestly, I could never specifically say the % of silicon is in each brand of piston cast or forged, I'm sure that info is probably confidential for most manufacturers, I dunno. I can only go by what properties the type of piston has. Silicon has certain properties it adds to a piston. It controls thermal expansion and strength to wear ratio among other things. I'm not saying in every circumstance that a cast has more silicon. I'm one of those guys that hates to use the term "always" liberally. The medical profession taught me that. But to say using a forged piston is "always " better to use than a cast piston is untrue.

 

Don't get me wrong here, forged units are great pistons, I currently use them, yes they have come a long way in technology and design. They are stronger and exhibit many better properties than cast and vice a versa. This doesn't mean in my next engine, depending on what it is, that I will use a forged piston.

[FireHead]

Honestly, I could never specifically say the % of silicon is in each brand of piston cast or forged, I'm sure that info is probably confidential for most manufacturers, I dunno. I can only go by what properties the type of piston has. Silicon has certain properties it adds to a piston. It controls thermal expansion and strength to wear ratio among other things. I'm not saying in every circumstance that a cast has more silicon. I'm one of those guys that hates to use the term "always" liberally. The medical profession taught me that. But to say using a forged piston is "always " better to use than a cast piston is untrue.

 

Don't get me wrong here, forged units are great pistons, I currently use them, yes they have come a long way in technology and design. They are stronger and exhibit many better properties than cast and vice a versa. This doesn't mean in my next engine, depending on what it is, that I will use a forged piston.

 

I agree as I generally do not use the term "always" if at all possible. If I remember, I will see if I can put something together with regard to silicon content of several pistons for a given engine. I will need to row my way through a bunch of the boxes that came out of my office when I moved, but I am pretty sure I have quite a few metrogical reports on various pistons.

 

Hopefully, I got the point across that I was speaking to a performance oriented mission critical application. If I had a relatively stock engine, and wanted Jim-Bob at my local machine shop to do the machining work, then you had better believe I am putting a set of Pro-X pistons in the holes.

 

The other thing I would like to float across here is that if you have a choice between a forged piston and a piston made from a billet, I would always choose the billet piston. Much of the higher end racing engines in a wide range of series use such a thing. NASCAR is particularly retarded as JE is a corporate sponsor of the series's and makes it real tough to use anything else. Of course we did, CP and Mahle were always somewhere in the top 20 numbers dialed on my Blackberry when I was at TRD. To compound things, I did not have a very good relationship with a couple people on the engineering side (or atleast that's what they call themselves) at JE. They got all butt hurt when I suggested that Probe Pistons, a small company down the street in Huntington Beach, had more going for it then they did (not necessarily true as JE is owned by PMI, but I was trying to get the point across that "accidentally" not inspecting a batch or two of pistons, which was clearly defined in our PO was not acceptable).

[YamahaBanshee69]

I'm pretty sure the Pro-X pisonts are casted. Not unless they just started making forged pistons. I've had good luck with the casted Pro-X pistons on my dune motor. I've tried a few different pistons and the only one I've had bad luck with is the wiseco's.

what hapen with the wiseco piston?????