Pistons: Cast VS Forged?

[SIKDMAX]

What are everyone's thoughts on Cast VS Forged pistons? For people that have built motors, what are you using and why?

And yes, I know that all these questions could be answered by giving Guy a call, and believe me I will be doing that when Im set to order all my parts and have him assemble my motor, but Im doing this not only for my own benefit but for the benefit of others on the site as well who may be interested or like to participate in discussion :hug:

 

[Stingpuller]

Pistons

I run forged because i'm not taking a chance. Anything can be hurt, but I bet it will not crack. Also there lighter. I think anytime you can get weight of the pistons and rods/crank its a good thing. jeff

 

[Darius6t9]

If I remember correctly, forged have less of an expansion rate so you can run tighter tolerances. Casts biggest advantage is they are cheaper.

 

[paint94979]

Why not run forged? if im spending 20k on a build whats another 1200$ to insure my pistons arent going to crack at 750hp... just doesnt make sense

 

[SIKDMAX]

Thats the thought process I had Paint. Looks like its only about a $600 difference between the two...... definitely not worth the chance.

 

[Turbo Buick 6]

If I remember correctly, forged have less of an expansion rate so you can run tighter tolerances. Casts biggest advantage is they are cheaper.

Exact oposite

 

[mytmousemalibu]

Yupper, Forged slugs need more clearance. hats why forged piston motors can be kinda clattery till there all warm which brings up another point, they need to warm-up 1st before you beat on them IMHO. Cast slugs are actually very thermally stable to a certain point till execdinglly high tempature can go runaway and cause failure. Newer forgings are getting better through the years and now coated forged slugs are letting us run tighter clearances.

 

[slowlmm]

Why not run forged? if im spending 20k on a build whats another 1200$ to insure my pistons arent going to crack at 750hp... just doesnt make sense

Daily diven aplications forged have not been proven yet. and as mentioned the rate of grow is greater. and fyi there right about the same price forged vs cast. seeing as the amount of cut mahle cast pistons cracking or coming apart is extreamley low and are very good for daily driver. jmo now if you plan on runnig stupid ammounts of nos or meth then i would just go straight to forged.

 

[Darius6t9]

I knew it was something like that.

 

[codyn]

Yupper, Forged slugs need more clearance. hats why forged piston motors can be kinda clattery till there all warm which brings up another point, they need to warm-up 1st before you beat on them IMHO. Cast slugs are actually very thermally stable to a certain point till execdinglly high tempature can go runaway and cause failure. Newer forgings are getting better through the years and now coated forged slugs are letting us run tighter clearances.

i ran forged pistions for 23000 miles and they never had a clattery sound when they were cold. truck sounded the same as it was stock

 

[Redbone]

Couple other questions, if someone could clarify:

1) IIRC, forged pistons have no way to allow for pin oiling. True? Pics if available please.

2) Isn't there a steel backup surface in the cast pistons to protect against deformation in the top ring land? What's being done with forged pieces to protect against this.

3) Which of these pistons use a keystone top ring?

4) Has anyone tried gapless rings, or total seals, in our application?

 

[eds04max]

Daily diven aplications forged have not been proven yet. and as mentioned the rate of grow is greater. and fyi there right about the same price forged vs cast. seeing as the amount of cut mahle cast pistons cracking or coming apart is extreamley low and are very good for daily driver. jmo now if you plan on runnig stupid ammounts of nos or meth then i would just go straight to forged.

Yea.......what he said. I wanted a 'long-life' motor for everyday driving(hopefully 200K ) so I chose the cast (cut & coated) pistons. I do not spray anything so I felt like I would be O.K. as long as I don't let her get too hot!
If I were building a race-only motor..........they certainly would be forged.
JMO.

 

[codyn]

Couple other questions, if someone could clarify:

1) IIRC, forged pistons have no way to allow for pin oiling. True? Pics if available please.

2) Isn't there a steel backup surface in the cast pistons to protect against deformation in the top ring land? What's being done with forged pieces to protect against this.

3) Which of these pistons use a keystone top ring?

4) Has anyone tried gapless rings, or total seals, in our application?

gapless rings or total seal rings are for comp use only. some forged pistions have wrist pin oiling holes on the bottom two per side. they use hell fire rings which when they were taken out there was nothing wrong with them and we did a compression check first to check them before we took the heads off. ring lands looked fine when we tore the motor down for inspection. these with the testing was done with another company forged pistions

 

[Leadfoot]

Couple other questions, if someone could clarify:

1) IIRC, forged pistons have no way to allow for pin oiling. True? Pics if available please.
Forged pistons do not have a cavity in them that allows for piston cooling as cast pistons do. Howards rods have the ability to get pressurized oil to the pin if that is an issue.

2) Isn't there a steel backup surface in the cast pistons to protect against deformation in the top ring land? What's being done with forged pieces to protect against this.
As of right now, nothing that I know of for everyday high production pistons. There may be a few that have encorporated a steel backing but nothing commercially available yet

3) Which of these pistons use a keystone top ring?
Cast pistons use a keystone ring. The forged ones use a traditional or flat ring (from what I can gather), and it was thought to be an issue, but we are starting to hear differently (maybe due to increases in material and machining quality)

4) Has anyone tried gapless rings, or total seals, in our application?Not sure

Someone please correct me if this is wrong

 

[McRat]

So far, I've only played with OEM pistons. Have not lost a piston from cracking yet, but it's important to "de-lip" them. My current problem is melting/igniting the top of the pistons, which is something forged pistons probably cannot halt.

I believe the answer to avoiding melting pistons is better piston cooling.

 

[mytmousemalibu]

i ran forged pistions for 23000 miles and they never had a clattery sound when they were cold. truck sounded the same as it was stock

Sorry i shoulda clarified! I have seen this in gasser/alky drag motors, just somthin that came to mind when referencing for increased piston clearance. I wasn't sure if this would be an issue on a forged diesel piston, glad to hear its not! We had a SBC with forged slugs in it and you could hear a touch of noise from them before it was warmed well. But now thinkin bout it these also had pretty short skirts too and that will exacerbate this but beeings all the pics of any diesel piston ive seen has a good skirt lenth, especially in undersquare engines. So my mistake!:hug:

 

[duratothemax]

I just pulled the heads off my motor. 15,000 miles of abuse, EGT;s, etc..

pistons look 110% as perfect as when I put them in. Can hardly even see the "star" pattern on them from the injectors. These were your basic delipped LB7/LLY pistons, no coating.

 

[ripmf666]

Can you save any of them Ben

 

[duratothemax]

Can you save any of them Ben

All but two. Im going to have Johnboy cut the pistons in the shortblock hes selling me, so I will probably just sell the remaining 6 good pistons, like I said they look perfectl, although one has BARELY visible evidence (you cant even feel it with your fingernail) of piston to valve contact, because when all hell broke loose in the engine, most of the pushrods bent.

 

[Leadfoot]

Sorry i shoulda clarified! I have seen this in gasser/alky drag motors, just somthin that came to mind when referencing for increased piston clearance. I wasn't sure if this would be an issue on a forged diesel piston, glad to hear its not! We had a SBC with forged slugs in it and you could hear a touch of noise from them before it was warmed well. But now thinkin bout it these also had pretty short skirts too and that will exacerbate this but beeings all the pics of any diesel piston ive seen has a good skirt lenth, especially in undersquare engines. So my mistake!:hug:

I did hear one of the first forged pistoned Duramax's and there was definitely a clatter until warm. I believe this was mainly due to clearances that it ran (as they err'ed on the side of caution). As materials and machining get better, tolerances can be tightened up and the associated noise lessened. I'm hoping over the next 24-30 months that forged pistons are going to advance light years in DD diesels as people are going to be subjecting them to varying conditions and gather data......Time will tell.