Steel pistons?

So according to what I can find, aluminum gets substantially weaker at operating temps, at a peak operating temp of 350 Celsius 6061 drops to 21MPa in strength, while stainless steel 304 drops to 60% of its strength.. while cast steel is still 100%

So cast steel will still be 248 MPa
And stainless 304 will be 621 * 0.6 = 373 MPA.

Cast steel should be 3.9x stronger than 6061 aluminum at 350 Celsius. While stainless 304 will be 5.8x stronger.
Now if we made pistons the same weight as the aluminum pistons, they’ll be thinner, so if we account for the approx 3x higher density.

If our goals outgrow stock pistons, why are we paying for forged aluminum pistons again? I know stuff like nickel coating pistons are supposed to lower temperatures of the piston etc, since it has lower thermal conductivity than aluminum and more heat would be pushed out exhaust, but I’ve never found by how much. But steel has half the thermal conductivity of nickel and that would be the whole piston so would lead to lower temperatures for piston and cylinder head if nickel coating aluminum pistons works.
>noooo that’s ultimate tensile strength
So is for the 6061, even if we compare the ultimate tensile strength to the lowest figure for yield strength for 304 /and/ adjust for density and assume they’ll reach same op temp, then that yield strength is still double the ultimate tensile strength of 6061
>muh thermal expansion
6061 has a linear expansion per degree 35.2% higher than stainless 304. Stainless could run tighter tolerances.

  1. 1 week ago
    Anonymous

    The only thing I can think of is because you may want the point of failure to be the pistons so you don’t fuck the rods and/crankshaft and entire block if something goes wrong

    • 1 week ago
      Anonymous

      So we build the lock out of 316 stainless too, and it won't rust.

  2. 1 week ago
    Anonymous

    >why are we paying for forged aluminum pistons again?
    They're extremely light compared to cast steel and can withstand similar amounts of pressure. Its why so many parts of the engine are aluminum. The weight savings for fuel economy is huge. You may have an engine design that doesn't generate anywhere near 21MPa therefore aluminum is a completely acceptable material for pistons.

    Also Aluminum conducts heat better. That means aluminum heats up and cools down faster which is great for efficiency.

    • 1 week ago
      Anonymous

      Efficiency is gay tho take the bus if you’re worried about that

      • 1 week ago
        Anonymous

        tard moment

      • 1 week ago
        Anonymous

        Efficiency means you can up the RPM if your aluminum engine dissipates heat faster, retard

    • 1 week ago
      Anonymous

      I think you missed the part about matching weight, steel would be thinner walled, there wouldn’t be a need to make them heavier than aluminum pistons. They can’t withstand as much pressure at operating temperatures at the same weight. The advantage is at room temperature. And the lower thermal conductivity is desirable. It’s why there are piston coatings, to get them into a lower operating range and reduce cylinder head temps by transferring less heat into the block from piston. A set of forged pistons is around about $1000 here, not sure how much it is in the US.

      You’d have to have the right design for the steep pistons though, smaller clearance, include the slight taper, and smaller clearance on the wrist pin so it doesn’t come loose etc.

      • 1 week ago
        Anonymous

        What kind of temperatures do you think engines in reach in daily drivers? There aren't any tangible benefits of using steel pistons purely because aluminum meets standard uses without issue.
        >And the lower thermal conductivity is desirable
        For what purpose? For every day engines you want the engine to cool off faster. The thermal capacity of steel is undesirable, you DON'T want to retain heat.
        >piston coatings
        are for reducing friction
        >get them into a lower operating temperature
        there are other ancillary devices you can use like banjo bolts which reduce piston temperatures, again you don't want the pistons to retain heat.
        >by transferring less heat into the block from piston.
        Whats your block made of? If its an aluminum block with an iron sleeve you're not going to derive this awful amount of heat because it'll be cooling well enough though the normal cooling system.

        • 1 week ago
          Anonymous

          Piston coatings on the crown dumbass.
          >much every day engine
          Go back to OP
          >If our goals outgrow stock pistons

          >Slowing the transfer of heat into internal components could actually increase efficiency a bit.
          Not really, typical economy cars won't gain efficiency through those means. Higher piston temps and higher pressures just mean more knock. Its absolutely possible to have an engine be too hot and start knocking like crazy. Complete combustion through accurate fuel and air measurement is more desirable from an efficiency standpoint. These engines aren't going to run at higher temperatures, they're going to run the oil and coolant around 100C. Any hotter and you start stressing the other parts, inducing knock, and causing increased air temperatures.
          Generally speaking, a cooler engine is a more efficient engine.

          Dead wrong. You ignite the fuel. Temp and pressure rapidly rise, if you have lower thermal conductivity of internals exposed to the combustion chamber, then less heat will be absorbed by internals, those internals will stay a bit cooler. In that instance it may be a small amount. But pressures inside the combustion chamber will stay higher post ignition meaning a little more torque a little more efficiency due to a little less heat loss to internals.

          This will also mean /cooler/ temps pre-ignition, as the higher chamber temps are pumped out the exhaust and less heat absorbed by the internals and less residual heating of new fresh air and fuel mix. Less stress, less chance of knock, lower air temps pre-ignition, a little more heat turned into work.

          • 1 week ago
            Anonymous

            >>much every day engine
            >Go back to OP
            OP didn't fucking mention what he even wanted to do with a particular engine. So why even talk about steel pistons if MOST engines are never going to touch pressures that aluminum can't work at?
            >Dead wrong. You ignite the fuel. Temp and pressure rapidly rise, if you have lower thermal conductivity of internals exposed to the combustion chamber, then less heat will be absorbed by internals, those internals will stay a bit cooler. In that instance it may be a small amount. But pressures inside the combustion chamber will stay higher post ignition meaning a little more torque a little more efficiency due to a little less heat loss to internals.
            You're just inducing hotter piston temps. We're already at the limits for pump gas. Its why cars try to regulate IAT's, charge temps, and turbo boost pressure so much. They try to use the atomization of the fuel in Direct Inject engines to cool the cylinder cavity. They DON'T want that fuel going off early. If your piston can't shed that heat, you seriously run the risk of preignition before the piston gets to TDC and thats REALLY BAD. You want the internals to shed that heat quickly, its why engine oils and coolants are so important at staying around 100C. Steel will stay hotter longer.

            You're making all these material science presumptions in an automotive engine but never asked "why aren't any car makers using steel pistons?"

            • 1 week ago
              Anonymous

              Piston coatings on the crown dumbass.
              >much every day engine
              Go back to OP
              >If our goals outgrow stock pistons
              [...]
              Dead wrong. You ignite the fuel. Temp and pressure rapidly rise, if you have lower thermal conductivity of internals exposed to the combustion chamber, then less heat will be absorbed by internals, those internals will stay a bit cooler. In that instance it may be a small amount. But pressures inside the combustion chamber will stay higher post ignition meaning a little more torque a little more efficiency due to a little less heat loss to internals.

              This will also mean /cooler/ temps pre-ignition, as the higher chamber temps are pumped out the exhaust and less heat absorbed by the internals and less residual heating of new fresh air and fuel mix. Less stress, less chance of knock, lower air temps pre-ignition, a little more heat turned into work.

              Also if what you said was true about steel then we'd make intercoolers out of steel, but we don't because steel is half as conductive as aluminum. We WANT to shed that heat and aluminum is really good for that.

              • 1 week ago
                Anonymous

                You want to shed waste heat. Combustion chamber heat is not waste heat. It’s not waste heat until it enters other materials then it won’t be used for work.

                Lower thermal conductivity means they won’t absorb as much heat from the combustion, meaning the combustion chamber internals will be cooler. The aluminum block will still transfer heat into coolant just as well.

                With a lower thermal conductivity not only will internals be cooler, they will transfer heat slower into incoming air. So less pre-heating prior to ignition. We came fill with a little more air in that case.

                I can’t believe you are this dumb. It’s literally the opposite for intercoolers, you want to suck the heat out of the air with an intercooler.

                If you suck heat out of the combustion gasses post ignition prior to expansion you will reduce the pressure that drives the cylinder down and thus less heat will turn into work.

              • 1 week ago
                Anonymous

                >You want to shed waste heat
                Yes, and aluminum is better than steel at that. Heat Capacity works both ways. Aluminum heats up and cools down faster. It physically contains less energy per unit mass.
                >It’s not waste heat until it enters other materials then it won’t be used for work.
                Physics 2; heat is heat, it doesn't impart anything in terms of work on any of the parts. The only part that is doing work is the pressure generated from combustion.
                >Lower thermal conductivity means they won’t absorb as much heat from the combustion,
                Correct, however we don't want to retain that heat at all because its lingering and not shedding. Its far better to quickly heat up then cool than to resist heating up only to have a hard time cooling it. In theory your engine works better initially but will heat soak badly because its not shedding as much energy to the coolant and oil which is entirely why we love aluminum engine blocks.
                >The aluminum block will still transfer heat into coolant just as well.
                Like twice as well compared to steel.
                >With a lower thermal conductivity not only will internals be cooler
                They will be cooler initially, but will heat soak purely because you aren't shedding it.
                >you want to suck the heat out of the air with an intercooler.
                No you retard, you want the hot charged air to pass its heat to something with really low heat capacity which is aluminum, you then want that aluminum to shed its heat to the atmospheric air quickly. We don't use steel because it is worse at conducting and shedding that heat.
                >If you suck heat out of the combustion gasses post ignition prior to expansion you will reduce the pressure that drives the cylinder down and thus less heat will turn into work.
                Not substantially, you're talking about a dozen psi maybe in an engine environment that might produce like 1000psi at WOT. Either way you don't address the fact that we're very much at the zenith for pump fuel. 87 octane will auto ignite in your scenario.

              • 1 week ago
                Anonymous

                No, it won’t. The air fuel mixture will be cooler prior to combustion with lower thermal conductivity internals because those internals can’t impart as much heat into the mixture. And also can’t take as much heat in from exhaust gasses. That benefit is in both directions - less heat into the internals and less heat back into the air fuel mixture. The engine will still warm up, the peak operating temperature will end up lower, and again the air fuel mixture won’t absorb as much heat from the intervals coming into the chamber.

                Aluminum is great at heating up the incoming air, nickel coatings, hard anodized aluminum, steel, etc is less effective at pre-heating the incoming air.

                Aluminum will auto-ignite a mixture before lower thermal conductivity internals will.

                The higher pressure and temperatures happen /after/ ignition. The excess heat not being absorbed or cooled from expansion and load on the crank will be pumped out the exhaust - the exhaust will be hotter, not the engine.

              • 1 week ago
                Anonymous

                >he air fuel mixture will be cooler prior to combustion
                From where? Why would it be cooler? You're atomizing fuel into a cylinder cavity that is hotter because your piston never shed its heat effectively from its previous cycle. You talk a lot about "lower thermal conductivity resisting heat" but you realize that if you heat up slowly you cool down slowly. Thats the whole issue. The steel piston is physically hotter because it absorbed more energy over more cycles and shed less of it. A piston made of steel at 100C contains more energy per mass as an aluminum piston at 100C. You don't want to hold onto this heat, it doesn't matter how well it resists. You want to get rid of that heat fast. There is absolutely no reason to hold onto that heat. It won't measurably improve efficiency, it won't measurably improve performance and it won't measurably do anything but induce heat soak sooner. It's why Cletus Mcfarland's vortec corvette ran into so many cooling issues because he couldn't get the fucking iron block to cool after he cranked boost to 30psi or some shit.

                Why would they retool entire factories for cars they are fine on stock cast pistons that will also require a lot of additional testing when anything new is introduced and smaller clearances? Similar reason they don’t come with forged pistons stock. Go back to OP dumbass.
                >If our goals outgrow stock pistons, why are we paying for forged aluminum
                Etc

                >Why would they retool entire factories
                bruh factories have been retooled for new engines by all makers for decades. We've been using aluminum built engines for DECADES. Throughout all that retooling they've never adopted steel pistons for consumer gasoline engines. Its not a better material.

                >>If our goals outgrow stock pistons, why are we paying for forged aluminum
                Because your goals aren't outgrowing stock pistons, because forged aluminum is better and worth the cost for what makers get out of it which is better thermal efficiency and lighter engines.

                You aren't finding any manufacturers with steel pistons at all. You just juxtaposed some bullshit about "I'm outgrowing aluminum" no you aren't. You're talking about building engines. No one uses steel pistons commercially.

              • 1 week ago
                Anonymous

                >From where? Why would it be cooler? You're atomizing fuel into a cylinder cavity that is hotter because your piston never shed its heat effectively from its previous cycle. You talk a lot about "lower thermal conductivity resisting heat" but you realize that if you heat up slowly you cool down slowly. Thats the whole issue. The steel piston is physically hotter because it absorbed more energy over more cycles and shed less of it.
                Also just to elaborate on this, we aren't talking specifically about two pistons at 100C. We're talking about how your combustion cycle over many cycles has made your steel piston so much hotter than an aluminum piston that you're causing pre-ignition. Hot engines are BAD in every case.

              • 1 week ago
                Anonymous

                Are you retarded? The piston won’t absorb as much heat per cycle, meaning more heat will be pushed out the exhaust. Second the piston sits inside an IRON ring. What you said would also apply to the cylinder lining. Except it doesn’t work that way. The piston is not touching anything other aluminium to transfer heat away, any heat from an aluminium piston would have to transfer into the iron cylinder lining, or back into the air above and below it.

                There would be less total energy moving into a steel piston than an aluminium one. Regardless of how long you run it. That means more heat out yhe exhaust and less into the piston.

                It’s the same benefit as piston coatings
                https://auto.jepistons.com/blog/what-is-electroless-nickel-coating-for-pistons
                >“EN reflects heat away from the crown,”
                >Electroless nickel plating (EN) has many benefits including heat control, and detonation resistance.
                Why? Because it had a lower thermal conductivity than aluminium, thus the piston absorbs less heat, which in turn will put less heat back into the combustion chamber during the intake stroke, and then piston will be a little stronger running a little cooler.

              • 1 week ago
                Anonymous

                If you think you got it all figured out why does absolutely no car maker today make steel piston engines for consumer cars? The only reason people have ever used steel pistons is purely because they have an engine that needs to withstand obscene pressure far beyond aluminum. You aren't gonna find steel pistons in anything other than certain high performance race engines and diesel engines.

              • 1 week ago
                Anonymous

                Why would they retool entire factories for cars they are fine on stock cast pistons that will also require a lot of additional testing when anything new is introduced and smaller clearances? Similar reason they don’t come with forged pistons stock. Go back to OP dumbass.
                >If our goals outgrow stock pistons, why are we paying for forged aluminum
                Etc

    • 1 week ago
      Anonymous

      >efficiency
      Slowing the transfer of heat into internal components could actually increase efficiency a bit. Since higher temp = higher pressure, which means more pressure forcing expansions, means more torque on the piston and crank for the same amount of fuel, which would mean more efficiency.

      • 1 week ago
        Anonymous

        >Slowing the transfer of heat into internal components could actually increase efficiency a bit.
        Not really, typical economy cars won't gain efficiency through those means. Higher piston temps and higher pressures just mean more knock. Its absolutely possible to have an engine be too hot and start knocking like crazy. Complete combustion through accurate fuel and air measurement is more desirable from an efficiency standpoint. These engines aren't going to run at higher temperatures, they're going to run the oil and coolant around 100C. Any hotter and you start stressing the other parts, inducing knock, and causing increased air temperatures.
        Generally speaking, a cooler engine is a more efficient engine.

        • 1 week ago
          Anonymous

          Like the whole point of using Iron blocks and steel pistons is purely for really high pressure systems like diesel engines. Diesel engines are gonna make so much pressure due to the incredibly high compression, they rely heavily on making sure they can generate the temperature and pressure necessary to ignite that fuel.

          The retards over at cletus mcfarland got a corvette with a Vortec inside it and they cranked the boost up so fucking far it was insane. That was the whole advantage of having it. For any other instance though? Aluminum was always desirable due to weight and thermal efficiency.

  3. 1 week ago
    Anonymous

    These benefits are seen even in hard anodised pistons with substantially lower thermal conductivity
    https://blog.diamondracing.net/what-is-piston-hard-anodizing#:~:text=In%20certain%20conditions%2C%20anodizing%20can,the%20piston%20and%20cylinder%20wall.&text=Hard%20anodizing%20also%20affects%20heat,also%20transfers%20through%20the%20skirts.

    >While it is broadly understood that heat transfers to the cylinder walls and thus the cooling system via the ring interface, heat also transfers through the skirts. There are differing schools of thought primarily addressing final application. On one hand, it is desirable to retain heat in the combustion chamber to support greater power and efficiency.

    >In supercharged and turbocharged applications, more heat transfer from the piston is necessary. Some builders favor the tighter clearances and reduced piston rock of non-anodized pistons.
    This is still limited by air, and the thermal conductivity of the iron cylinder liner, where in those case specific scenarios hard anodized aluminium might be a bottleneck, but steel won’t be, steel wouldn’t have even tighter clearances than regular pistons.

  4. 1 week ago
    Anonymous

    https://www.yenmak.com.tr/en/products/steel-pistons-450
    >higher pressure
    >better thermal stability
    >tighter clearances
    >lack of deformation
    >can reduce engine height
    >can be used for more efficient cooling
    Simply put, yes they can be better in all scenarios when taking into account design considerations for their advantages

  5. 1 week ago
    Anonymous

    Operating temperature for a piston crown in a gasoline engine is typically around 270-310 C. Forged pistons are most often made of 2618 alloy, but sometimes 4032 alloy. Diesel pistons often see significantly higher operating temperatures and are commonly made of 8620 steel.

  6. 1 week ago
    Anonymous

    They're not using 6061. In sure they're using some alloy that significantly improved temperature tolerance

    • 1 week ago
      Anonymous

      It’s aluminium. They all drop like that.

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