Piston Specifications and Extras

[Mark Halligan]

And what about the Accumulator grooves? Does it increase wear?

Vasilis

Accumulator grooves shouldn't increase bore wear. They are basically a groove machined into the ringland between the top and second rings.

The idea of this groove is to act as a 'reservoir' for any gases that leak past the top ring and get stopped/slowed down at the second ring.

A build up of these combustion gasses can cause the top ring to flutter at high rpm and lose even more seal.

The only obvious possible downside (I can think of) is that because material is removed from the middle ringland this could compromise its strength and cause it to collapse in extreme stress conditions. But that would be extreme, just watch your ring gaps....

I set my JE's to 0.004" (0.10mm) and I get light slapping when the motor is cold, Darius is probably right if you are not going to run big boost and want longevity along with tighter tolerances and quieter running go for the 4032 alloy pistons.

Cheers

[Billman]

Hi, thanks for the reply.
The question is what is big boost and how much can these 4032 handle? People say with stock pistons you can go to over 500 bhp. Then if the 4032 are better than this it means over 550 or 600 bhp in the 5 Cyl engine?
What can be used as a measure on piston strength. I read somewhere in the net that the 2618 pistons are 10-15% stronger than 4032.


cheers,

Vasilis

What meterial are the stock ones?

[Mark Halligan]

The question is what is big boost and how much can these 4032 handle? People say with stock pistons you can go to over 500 bhp. Then if the 4032 are better than this it means over 550 or 600 bhp in the 5 Cyl engine?

Thats a question for the piston manufacturer, or you could try a forum like Speedtalk

[Billman]

Here some more infos found in the web:

2618

Quote:
Pistons using 2618 are best suited to nitrous, blowers, or higher end race applications where frequent inspection and replacement are not a problem.

(http://www.carcraft.com/techarticles...ng_technology/)

Quote:
may wear a bit faster but provide better strength and durability. In the rare case of a crack in a 2618 piston, the crack will migrate to an area of lower stress and stop. 2618-alloy pistons keep their shape under extreme pressures and high RPM's.
(http://www.stealth316.com/2-pistonguide.htm)

Quote:
The “2618” performance piston alloy has less than 2% Silicon and could be described as Hypo (under) eutectic. This alloy is capable of experiencing the most detonation and abuse while suffering the least amount of damage. Pistons made of this alloy are also typically made thicker and heavier because of their most common applications. Because of the higher than normal temperatures these pistons experience in their usual application, and also the low-Silicon content allowing the maximum possible Aluminum heat-expansion, these pistons have their cylinders bored to a very loose cold-fit. This leads to a condition known as “piston slap” which is when the piston rocks in the cylinder, and it causes an audible tapping noise that continues until the engine has warmed to operational temperatures. These engines should not be revved when cold, or excessive scuffing can occur
(http://en.wikipedia.org/wiki/Hypereutectic_piston)

4032

Quote:
These are the best choice for applications expected to have decent longevity, such as street vehicles and entry-level bracket racing and oval track combos.
(http://www.carcraft.com/techarticles...ng_technology/)

Quote:
have great wear characteristics because the silicon particulate hardens the alloy and reduces the thermal coefficient of expansion. However, silicon-aluminum alloys can turn brittle and become prone to fracturing when subjected to extreme stress. With a piston made of a silicon alloy once a crack starts, it doesn't stop until the piston suffers a catastrophic failure
.
(http://www.stealth316.com/2-pistonguide.htm)

Quote:
The “4032” performance piston alloy has an approximate Silicon content of 11%. This means that it expands from heat less than a piston with no Silicon, but since its eutectic level of Silicon is fully alloyed on a molecular level, this alloy is less brittle and more flexible than a stock Hypereutectic “smog” piston. These pistons can survive mild detonation with less damage than stock pistons.
(http://en.wikipedia.org/wiki/Hypereutectic_piston)

Quote:
Another option for a daily driven vehicle that isn’t going to see over 10 psi, is MAHLE. They are a well known german manufacturer that makes piston for Ferrari and F1 teams. Very well designed and quality made piston, but unfortunately they are made from 4032 alloy, which isn’t as strong as the 2618 that the other brands are made from.
(http://www.svtperformance.com/forums...d.php?t=181225)

[caterpillar]

very intr read: but WHAT to use , for me and the others street/strip users.....??

[Billman]

I know. The question is Mahle motorsport cost double the price of JE.

Does anyone know of an engine without rebuilt that lasted with JE pistons i.e. over 100000 kms?

[caterpillar]

i will NOT have the outcut for oilsquirters in the pistonscurt..... the piston WILL crack there, and the crack will go to the oilringgroove or to the xpin hole( spec for the 3.rd syl.... even on a std engine)

[Billman]

I dont really understand what are you saying now.

[caterpillar]

some audi pistons have the outcut for the oilsquirter in the lower pistonpart....the custom piston i will order, wil NOT have this. the piston will crack there..

[Jamo]

When i asked about a set that will last longer in time i got this answer, what do you think?

"For the longest life between rebuilds I would suggest you use a 4032 alloy. It is not as strong as the normal 2618 we use, but expands much less and the ring grooves don’t wear as fast. However, it is much stronger than the factory piston."

Me thinks that's a generic quote about the factory pistons.

All I'll say if it's possible to melt 2618 pistons in a stroker ( Aronmatic for example ) with aggresive mapping then what chance has 4032.

It's all very well saying you want 4032 because it's wear rate is better but if it can't take the sustained abuse of a turbo application then it's going to fail before it wears out.

You can't build a performance car and then expect it to last 200k

I'm hoping for a long life out of my build but I won't risk using a lower grade alloy as i'll be running 2bar or more.

My 0.02

[Billman]

Is an S2 with 500+ bhp with stock pistons not a performance car? these engine lasted over 100K kms without rebuild.

Thats what i am searching for but in the custom dimentions i need.

What meterial are the stock pistons? What material are the Mahle motorsport pistons?

[HPmuirt]

Is an S2 with 500+ bhp with stock pistons not a performance car? these engine lasted over 100K kms without rebuild.

Thats what i am searching for but in the custom dimentions i need.

What meterial are the stock pistons? What material are the Mahle motorsport pistons?

As a complete novice in this area with the IL5, might I ask an obvious question..... why is no one talking about weights in all this? When we used to tune old 6cyl Triumph engines (which admittedly are agricultural at best) we used to shorten the skirts and lighten the pistons (as well as the rods) considerably.

Are modern pistons already shortened and lightened?

Am I gonna get links thrown at me by our resident jamillionaire?

Cheers n

Si

[Jamo]

The average aftermarket piston is between 300-310 grams I don't know how heavy the OEM is? I heard it was 500-600 grams

I'm sure 4wheeldrifter knows.

[4WheelDrifter]

The average aftermarket piston is between 300-310 grams I don't know how heavy the OEM is? I heard it was 500-600 grams

I'm sure 4wheeldrifter knows.

Stock KS piston with gudgeon pin and rings is ~500g.

[Mark Halligan]

some audi pistons have the outcut for the oilsquirter in the lower pistonpart....the custom piston i will order, wil NOT have this. the piston will crack there..

This is not a concern with JE's as the piston skirt is shorter than stock and the piston clears the squirter, therefore negating the need for the oil squirter cut out.