Pistons - Cast vs Forged vs Hypereutectic

[The Witzl]

lets not forget about the completely excessive level of engineering design and specification that goes into a toyota engine.....

example no.1 -> factory 1UZ-FE

[psychofox]

Pistons are not made of mild steel in any modern engine. They are almost all made of alloys of aluminium.

The tolerance of pistons is almost always proportional to the tune - cast/hypereutectic/forged pistons will all suffer from failures (damaged ring lands, etc.) from prolonged detonation. Forged pistons will just take the punishment for a bit longer due to the extra tensile & compressive strength induced from the grain elongations of the forging process.

I think when they say that, they are talking about 11:1 when tuned to within an inch of it's life.

Toyotas generally run rich everywhere as a precation against detonation.

I believe the 20v pistons would be a Cast eutectic alloy not mild steel cast.

[kemicalx]

I'll be using hypereutectic pistons in my current 7m rebuild, so I'll get to find out first hand what they're like, I'm going to investigate into getting them T6 heat treated and also will look into getting the crowns coated as once it's all up and running again it will be getting more boost (10-12psi to begin, but I’d like to be able to venture up to the limits of the ct26 at 14-16psi yer?).
However it really is a case of cost, no point getting all this treatment done to hypereutectic pistons if it's going to put them only a couple of hundred dollars under forged ones

[Lambolica]

Tell em the price son.......

[kemicalx]

Well, i just rang the engine reco place to find out about heat treatment and coating. The bloke there wasn't a whole lot of help... Though he did say it can cost up to $400 to get the crowns coated, which really kills the value of the pistons which only cost a bit over $200 a set. Here are all the prices for my bottom end rebuild:

Bored/Honed - $160+GST
Decked - $60+GST
King (should I trust em?) Main and rod bearings - $130+GST
Pistons - $228+GST
Rings - $103+GST

[oldcorollas]

HPC for coating was only abotu $20 a piston (iirc.. i might be totally wrong)

[atomic rob]

gd post. piston materials and manufacturing techniques such as high presure isostatic prosesing : extream pressure injection casting :eg 1j 2j pistons i think vertion 8+ subaru sti aswell is used to make the best comprimise betrween stengh and small bore clearances these pistons will often have 90/110% the strenght of a forged piston whilst only weighing 70/90% of the wieght also 1j pistons seem to have a donut of metal they r caste around not sure wat metal is be very intressed to find out if any one has info. ive personally run my 1st 1jz engine standard internals at a ev day boost setting of 23-24psi plus 300hp nitrous fogger ocationally and earlier on had several prob 5-7 cases of 40psi plus due to wastegate failier and only lost 10psi of compression on cyl 5. i thought htat was really amazing! a friend of mine not knwn 4 his tuning finesse or mechanicle sympathy has managed to smash a few engine through the most brutal (stupid treament) and even then the damaged pistons seemed to have bent and crushed rather than shattering they were covered with det craters. ultimately stronger pistons allow u to tune a engine with more background noise u can push the fuel u r using a bit harder but even engines with glass pistons :2.5subaru sti can run big boost if engine tuned well and kept quiet

[YelloRolla]

I wont attempt to argue out of my depth here; the choice of piston type should come down to what the engine builder/owner is comfortable with.
I like the idea of the Hyper-Eutectic piston, and if the engine can handle it, then run them. The benefits are there and the down sides neglible.

As far as "how much boost will they handle?" I will throw in my own example. With the stock 3T GTE and CT20, I used to clamp the wastegate actuator for drag purposes and see about 23psi (no IC). In it's stock guise that engine copped a flogging everyday. The only time that I broke a piston (to date) is when we added the CT26 and it pinged during tuning. This is with the fabled "cast glass piston" that these engines are renowned for. This highlites that if the tune is correct, then the pistons will live a happy life.

[Talasas]

Also, concerning the different material types of the pistons and heat expansion, it should be noted that cast pistons have steel bands placed in the mould during casting to help control the expansion of the skirt area making it expand parallel to the wrist pin. The upshot is that the wall clearance is smaller and thus less slap. Hypereutectic pistons also have steel expansion bands, forged pistons do not (thus they are louder when cold, think 4AGE vs GZE).

[RT104GT]

In 1988 I had a Harry Firth/ Shuckey SS 308 engine built up for me $4500.
It had roller rockers, dual bolt crank caps, forged race (HDT) pistons, extractors, head job the works. Pusher electric s/s pump and 3/4 inch fuel lines inside the chassis rails. 5 speed T series box (direct 5th).
140 litre tank and would go at 8 miles per gallon with the speedo vertically down over the odometer 275 km/h.
It was as fast as a GTHO falcon and could outbrake it with the F series brakes.

The engine bell bottomed as some dickhead left metal pieces in the block when rebuilding.

HF told me to piss off it was the way I drove towing trailers with satellite dishes on. Overheated he engine from the inside. Forged pistons melted down skirts collapsed.

$2500 later with GINSING pistons (Flat tops) I lost 40 kph.

So as they say from 200 kph up its $1000 per 10 kmh.

and vice versa.


You pay for performance.

There are no long term short cuts.


And it costs as much to run as 260 kph road racer as a small aircraft per annum.

2 cents.