Forged or Not, how to tell? 4a-gze Vs 1g-gze

[stradlater]

I wish I knew as much as you blokes. :-)

[Mr Revhead]

The word that Stuart is looking for is hyperuetere ...... something, I can never spell the damn thing!
The photo of the piston above show a cast piston, that's for sure because you can see the casting flashes where the mold sections join.
A forged piston has no suchs marks, as they have are forged under the hammering of a powerful hammer that forces the metal into the piston blank mold.
The hyperwhatsit pistons are made in a process pretty similar to forging, but are squeezed under pressure rather than hammered. Thus the metal grain structure is similar to that of forging.
And .... I have some news from a reliable friend in Malaysia that got some 4AGZE pistons tested by a metalurgist, they may well be the hyperwhatsit type, not forged as we've thought for years.

um.... my understanding is hypertutciticwtfever is the materiel, not the forming process.
as in they can be cast or forged?

[ViPeR_NiPPleX]

isn't hyperblah just a similar casting process to standard, but with more silicon added and particular heat treatment?.. I'm sure there was a thread on the topic not long ago.

[Mr Revhead]

Hypereutectic pistons can be forged, but typically are only cast

from the above wiki link.
and its also covered in the link i posted a page or two back

[river]

Hi,

I beleive so. Also, check the link in Bill's post (above) to Wiki, regarding hyperwhatever pistons.

However, for the lazy sods, here is a small extract.....

__________________________________________________ _________

Hypereutectic piston
From Wikipedia, the free encyclopedia

“Hypereutectic” means “Over” eutectic. The word eutectic refers to a condition in chemistry when two elements can be alloyed together on a molecular level, but only up to a specific percentage, at which point any additional secondary element will retain a distinct separate form.

Although internal combustion engine pistons commonly contain trace amounts (less than 2% each) of Copper, Manganese, and Nickel, the major element in automotive pistons is Aluminum due to its light weight, low cost, and acceptable strength. The alloying element of concern in automotive pistons is Silicon. Gold and Silver have no eutectic point, which means they can be alloyed together in any ratio. However, when Silicon is added to Aluminum they will only blend together evenly on a molecular level up to approximately a 12% Silicon content. For the purposes of this discussion, Silicon in this context can be thought of as “powdered sand”, and any Silicon that is added to aluminum at above a 12% content will retain a distinct granular form instead of melting. At a blend of 25% Silicon, there is a significant reduction of strength in the piston alloy, so stock hypereutectic pistons commonly use a level of Silicon between 16% and 19%. Special molds, casting, and cooling techniques are required to obtain uniformly dispersed silicon particles throughout the piston material.


The reason for their development
Most automotive engines use aluminum pistons that cycle in a steel cylinder. The average temperature of a piston crown in a gasoline engine during normal operation is typically about 600 degrees Fahrenheit, and the coolant that runs through the engine block is usually regulated at approximately 190 degrees F. Aluminum expands more than steel at this temperature range, so for the piston to fit the cylinder properly when at a normal operating temperature, the piston must have a loose fit when cold.

In the 1970’s, increasing concern over exhaust pollution caused the U.S. government to form the Environmental Protection Agency (EPA) which began passing legislation that forced auto manufacturers to make changes that allowed their engines to run cleaner. By the late 1980’s, auto exhaust pollution had been noticeably improved, but increasingly stringent regulations forced car manufacturers to adopt the use of electronically controlled fuel injection and hypereutectic pistons. It was discovered that when an engine is cold, a small amount of excess fuel during start-up became trapped between the piston rings. This admittedly small quantity of excess fuel affected the amount of hydrocarbons in the exhaust when the piston expanded as it warmed, and then expelled the excess fuel.

By adding Silicon to the pistons alloy, the amount the piston expanded could be dramatically reduced, which allowed engineers to specify a much tighter cold-fit. Silicon itself expands less than Aluminum, and it also acts as an insulator to prevent the Aluminum from absorbing as much of the operational heat as it otherwise would. Another beneficial effect of adding Silicon is that the piston becomes harder, and is less susceptible to scuffing, which can occur when a soft aluminum piston is cold-revved in a relatively dry cylinder on start-up.

The biggest drawback of piston Silicon is that the piston becomes more brittle as more Silicon is added, which allows the piston to develop cracks easier if the engine experiences pre-ignition or detonation.

__________________________________________________ ______

If you want any more info then search the net, or link to the Wiki-link that Bill posted above.

But you got to admit that "hypereutectic" is a cool word. It will be a challenge to drop that word into a normal conversation.

seeyuzz
river

[takai]

But you got to admit that "hypereutectic" is a cool word. It will be a challenge to drop that word into a normal conversation.

Nothing more to add other than i managed that tonight, which would be impressive, other than the fact that i was talking with other racing or motorsports guys.... (and a biochemist)

[oldcorollas]

silicon is added for a few reasons...

initially, it was added to aluminium to improve the fluidity of the molten metal when casting.
casting iron is easy cos it has a large heat capacity and high melting temp 8relative to mould temp).
aluminium has low melting point etc and can easily start to solidify before completely filling the mould.
it is also cheaper than aluminium, reduced melting temp (iirc), and (as mentioned) reduces thermal expansion...
however, nowadays it is an integral part of designing an alloy for a given application... alloy design is complicated, and not as simple as just Hypo, or Hyper eutectic


contrary to the wiki article, the silicon does completely melt in the molten aluminium, but in a hypereutectic alloy, the silicon solidifies first as primary silicon particles (att he liquidus temp)... and then the aluminium/silicon eutectic mixture (which is whats left after the primary silicon forms) will solidify around the primary silicon.. (at the solidus temp, at the eutectic composition)

like this picture

there are many alloys that could be used for pistons and their properties and structure come largely from (or are significantly produced by) processing....]

edit: and for coffee table talk, the term "hyper eutectic" can be used for any alloy system that has a eutectic point.... if you want to be really fancy, you can drop in "hyper-eutectoid" when talking about high carbon steels, since the transition from austenite to pearlite is a eutectoid transformation (solid to solid.. whereas eutectic is liquid to solid), and higher carbon than the eutectoid composition makes it hyper-eutectoid

[30psi 4agte]

Stew you are welcome at my tea parties any time

[oldcorollas]

Stew you are welcome at my tea parties any time

to discuss the finer points of 18/8 and 18/10 stainless for coffee spoons?

[The Witzl]

to discuss the finer points of 18/8 and 18/10 stainless for coffee spoons?

Yes, and which one is easier to bend and thus inferior.
Also, how they make those funny brassy-gold looking stainless spoons.
And why does metal taste funny?

[6BOOST]

Thanks yellorolla, yes, that exactly what I meant. The stock pistons have a slot behind the oil rings in the piston groove. This helps the oil drain back from where it is scraped off the bores, however the slots weaken the piston, as there is less material/strength around the skirt. Pistons such as ACL cast pistons have grooves with no holes at all for the oil to drain back down, which seems to work well, and most forged pistons have small holes drilled.

Anyway, I'd keep your RPM limit to around 8800 if long term piston survival a goal. Having said that, after I pulled out and inspected my 1G on the weekend, I can now say that the oiling system mods we have worked out while retaining the stock pump have worked flawlessly. I have cut open 5 filters, changed the oil 6 times, and visually inspected 2 big ends while the sump was off, and my engine is spotless, can't fault it, and its copped a 9600rpm bashing a few times Glad its going to a good home, although it won't be the fastest 1G on earth for long hopefully

6BOOST

[30psi 4agte]

Yeah the slots behind the oil rings in pistons are a no-no on a forced induction engine.

They are a big weakness.



6boost: 9600 rpm ....... Shit thats some rpm. What rods are in it ?

[stradlater]

Who bought your engine?

You building another one to be faster?

[love ke70]

Yeah the slots behind the oil rings in pistons are a no-no on a forced induction engine.

They are a big weakness.



6boost: 9600 rpm ....... Shit thats some rpm. What rods are in it ?

standard pistons rods and crank if i am correct

[twentyEight]

and its copped a 9600rpm bashing a few times

9600rpm... Nice!

strad, maybe we should re-consider doing the 1J for mine... 9600rpm out of a 1G with std pistons, crank, and rods speaks volumes to me...