Which Aluminium Alloy Are Our Pistons Made From?

[Blind Driver2]

I've been curious for awhile. We have much talk here about keeping EGTs under 1100* due to aluminum's melting point which is 1221*. Depending which aluminum alloy our pistons are made, I'm wondering what is the melting point.

Any idea?

 

[rhkcommander]

1100 is used because the gauge reads lower than what the internal temps are. Most have their sensor mounted on the exhaust mani.

As for the specific type, im not sure.

 

[G. Mann]

The real question is what is the metal yield temperature. That would be a combination of both temperature and pressure. Under hard load you have increase of both.

Also, as mentioned above you have a gage lagg both up and down. If the gage is reading 1200 degrees at the thermocouple, which is way downstream from the combustion chamber, the temp at the piston will be many degrees higher and the gage reading will be way behind what is actually happening there.

Bottom line is, set a threshold lower, with a good safety margin, and don't go over that. Unless of course you enjoy building new engines and spending money, have a good sponsor with loads of money... and winning is the only reason you are there.... then.. pump it till it breaks.

 

[Jake_IN]

Well this is kind of an apples to oranges comparison but the die casting facility i worked for made pistons for two stroke engines and they were made with 390 alloy.

 

[Jake_IN]

In fact pretty much all of the automotive parts we cast were 390 alloy.

 

[Knuckledragger]

I doubt the pistons we use are forged or die cast, they are probably permanent mold low pressure (atmospheric) castings. The most popular alloy is 356 which has a reported melting point of 1280 F. If you have 1100 f at the exhaust manifold where the thermocouple is located , you are flirting with danger, since that does not factor in the yield, which in our engines is considerable , considering the operating cylinder pressures. Especially under turbo load. Yikes.

I have seen enough people report 1100 degrees (but never higher for any amount of time) to believe that that temp is the highest tolerable operating temp you should try to experience. Like the man said, if you have sponsors with money that don't complain, go ahead and run hotter.

For purely educational reasons, it would be interesting to see the results of ultra high EGTs. But not from your truck.

 

[icanfixall]

All these idi engines came with a fordge piston from Mahle. Even the 6.9, 7.3 & 7.3 turbo piston crowns are the same thickness at around 560 to 580 thousands thick in the center. Thats the thinnest area of the crowns. Towards the edges its much thicker. Now this next item is really hard for me to explain in a simple way. Pistons have a barrier air boundry around the tops where the fire front travels across them. In simple terms the fire never actually touches them. They do get hot from two differant areas... From the sliding up and down in the cylinders and from the heat in the combustion area. Its really tuff for me to explain more about why the tops never actually see the heat because of the air barrier. I think its a psyhics question you need an answer to figure this out. Surely someone smarter than me. I know each piston manufacture has a secret material and amount in the aluminum. Some use silcon so the piston slips better in the cylinder ... Its not just one material making up the pistons.