OK all this talk about pistons got me thinking about something I've been wondering about for awhile....

First of all... we all know forged pistons are better than stock cast pistons...... but I'm having a hard time fiquring out the difference...

In a forge... you melt down metal..... and if the metal is melted you have to use a cast.... so doesnt that make it a cast piston?

Or am I thinking the wrong way and they heat up the metal to where its soft and stamp / compress it to shape? And if thats true.... why does that make it stronger?....

Also... do they make machined pistons? and how well do those work if they do?

And are pistons still made of steel or are they aluminum now too?



Another thing..... why is the piston the weak point of the combustion chamber? This part doesnt make sense to me at all...

I'f your running NO2 or high boost people but forged pistons (and internals) in the block.... the piston being forged so you dont burn a hole through it...

The piston isnt the only thing in the combustion chamber.... you still have the cylinder walls and head....

If your making enough heat that a stock cast piston cant take it....how come the stock head, valves, and cylinder walls can? The piston is the only thing moving away from the explosion and the head and walls are aluminum (on newer engines at least).

I know some people will say that the force of the explosion is directed toward the piston but it isnt..... an explosion expands equally in all directions until restricted then it finds the path of least resistance (or weak point) and forces itself in that direction... being right through the wound paper of a stick of dynamite or by means of the only part of the combustion chamber that moves out of the way aka the piston.

Is it because the head of the piston is the closest thing to the spark plug and its significantly hotter where the initial spark occurs? but even if that's true the head and valves are right there also...

I've just never understood how this physically makes sense...

Forged pistons are not "better". The forged piston is usually heavier. It just can take more abuse.

A forged piston is machined from a block of aluminium. It's not melted and molded.

All the pistons I've seen we're made of aluminium.

There's a few reason for pistons to break.

The head or cylinder wall don't melt because they are cooled by the coolant running through the block.

The forged piston is made of stronger material. A cast piston is not as strong as a forged piston. You can still burn a hole through a forged piston.

When detonation occur, the piston is not tightly inserted in the cylinder. It as a gap and that it enough to put pressure on the edge of the piston head.



Gilles
2.3 Ho

pistons cast vs forged look here http://www.motorcycleproject.com/motorcycle/text/cows-pistons.html

basically, its a totally different process,

forged means it gets the living crap beat out of it, aligning the molecules, making it VERY strong and heat resistant.

cast = melted and put into a mold, its also waayyy heavier.

you need to look more into alloys that just steel vs steel.




why do pistons melt and heads dont? simple, piston is what 1/4 thick? head is what, 3 inches? plus, if youve ever been into the head of a 2.4 or eco, you would notice, its aluminum, not steel. aluminum transfers heat, away from the combustion chamber, and disperses it amongst the head, including the water jackets, which cool it. pistons have no water jackets, they just melt. pistons also haul ass up and down the cylinder, making them F;n hot FAST, which melts them too. ever hear of a piston seized to the cylinder?

Why doesn't the block melt? once again, water jackets and its very thick, it takes a ton more to heat it to the point of melting.

heres an experiment for you. go get a thin peace of steel, like a key or something, then go get a bigazz peace of steel, like an engine block, heat both with torch, observe.

about the valves...they DO melt...dont fool yourself there, ive seen valved F'd up beyond imagination, ive seen a lot of people running performance V8's melt the @!#$ out of valves. valves are very small and heat goes to all sides of them, making them vulnerable.


if your running NO2, the added heat will fry a piston fast if your not careful or if you go too extreme or if you run a DRY SHOT.


i think i answered your question...if not, just ask



nwuonline.com
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JBO member since 2004

just noticed i made a mistake, your are right, forged piston is heavier than cast.



nwuonline.com
Proud member on JBNW.org
JBO member since 2004

Mfk-223 wrote: A forged piston is machined from a block of aluminium. It's not melted and molded.

Your confusing Forged with Billet

The forged pistons are still machined. I wasn't sure if they were completly machined or not. You know, the skirts are machined, the valves pockets are, the domes on my wiseco pistons were, ...


Gilles
2.3 Ho

Darkstar - Thanks for the correction btw. I tought they were from a block of aluminium.

The head is not 3" thick. The thickness between the combustion chamber and the coolant passage on a 2.3 head is under a quarter of an inch. Between the cc and the ports, there's a bit more than .25 inches.


Gilles
2.3 Ho

How it's made forged piston



Location: Montreal, Quebec

Jebadiah04 wrote:if your running NO2, the added heat will fry a piston fast if your not careful or if you go too extreme or if you run a DRY SHOT.

Gee, that's funny... because the 85-hp dry shot I used to run never fried anything..

i didn't watch the video about how to make forged pistons in the thread, but, something you guys need to know, billet is made of a solid piece of metal, and then cut down to the right specs. cast is melted and poured into a molding. forged is also melted(how do you think they mix silicon with it???) but once it's in shape, it is pressed together, or squeezed, down to the right size. then machined in all of the precision areas that were already mentioned above. since it's denser, it can take more stress. and, the other parts mentioned do take a lot of heat, and will burn, or melt if they are left stock in an engine designed for high power.

if the aluminum head bothers you that much, go ahead and get a custom one made somewhere out of superior metals that are lighter...we'll all just sit here and enjoy our money instead...wait...i don't have money.... lol.

hope this helps!

Not to bump this back up... but

I knew damn near all that all ready... some people over explained things by a lot LOL

I was foggy on how exactly Forges work and that vid answered my question.

as for the head and walls... I didnt think about the coolant in the engine for some reason. That makes sense...

As for the valve... im assuming someone makes them out of a more heat resistant metal for some of these high horsepower engines.

Thanks all..

Dave... I dont have any problems with my engine LOL.... I was just asking for no other reason than I like to know things.

The valves are exposed to extreme heat, especially the exhaust valve(s). The valves are made out of a more heat resistant material, but the most important thing to keeping the valves cool is proper valve seat material. The valve transfers the heat to the seat, which transfers that heat to the liquid cooled head. The majority of the heat is absorbed buy the valve is at the head, which is disapated throught the seat. The valve stem which doesn't get as hot, will transfer some heat through the valve guide, but nowhere near the amount of heat as through the head and seat.

I won't go into hypereutectic pistons, coatings, ring and ring land designs, dish/dome design, etc....

well, if you went into coatings, i wouldn't mind...maybe different thread?