JE versus OEM

[Allen Henderson]

Hotrodders,

J & E Pistons certainly have a good reputation. However, my understanding is that the wrist pin is not offset like on OEM Mahle pistons. So, does this make a difference? Is an engine more noisy without an offset? Any other untoward issues...with either? All opinions welcome. Thanks.'

-Allen-

[Flieger]

My understanding is that the reason they are noisy when used in MAHLE cylinders is that the forged MAHLE Aluminum alloy is high in silicon and has a lesser coefficient of thermal expansion than does the lower silicon Aluminum JE uses for the pistons. For the clearances to be right at operating temperature, the JE must be smaller cold than the MAHLE forged, high-silicon Aluminum alloy piston would be.

"Nickies" from LN Engineering are matched to the properties of JE pistons and work best with them.

[chris_seven]

Interesting debate.

Pins that are offset to the thrust side are typically used on road engines to reduce piston slap and hence make the engine run more quietly. At higher rpm central pins seem to be preferred and it would be interesting to know why.


The choice of alloy for piston manufacture has also been going on for some time.

Most modern forged pistons seem to be using 2618 alloys, which I think were developed by Alcoa.

As Max says this alloy has a very low Silicon content which means it will expand more than a typical piston material.

It seems to have two main benefits

1. The crown softening temperature is higher than alloys such as 4032-T6

2, It doesn't suffer from any silicon migration which can affect strength over time.

I think the other major benefit to the piston manufacturer is that it is easier to forge.

It does have other disadvantages.

As Max says it expands much more than a more convention alloy so whn used in cast Iron Barrels it can allow piston slap until the engine warms up.

It is also much less resistant to wear in the ring groove regions of the piston.

I have come to the conclusion that for early road cars running cast iron or Biral cylinders i would prefer to sue a 4032-T6 piston as they are quieter when cold and give better life from a groove wear point of view. I don't think piston crown temps are anything to worry about in this type of engine.

For race engines I think the 2618 is a better option as it will take more high temp abuse and long term wear of ring grooves is not such an issue.

Any Aluminium Cylinder will be more closely matched to the 2618 than a cast iron part and cold slap will be less of an issue.

Any help with the offset pin issue?

[jameshtaylor]

I worried about this a bit when building my motor but settled on JE pistons. Among other advantages is a substantial price difference. Frankly I've never noticed any unusual noise.

[304065]

Here is everything I know about this subject: http://forums.pelicanparts.com/911-e...in-offset.html

[Flieger]

I think the other major benefit to the piston manufacturer is that it is easier to forge.

This is what I heard as the main reason for the differences in alloys. MAHLE had already invested in the stronger forging equipment so companies wanting to start making aftermarket pistons would prefer the softer alloy. I am sure JE has passed that start-up stage by now, though.

[advtracing]

so what if you are building a 2.5ltr high comp engine but will be using mostly on the road with a few track days etc... thrown in ? what would be the preferred brand mahle or je?

[BBausser]

I don't think JE is an option for a short stroke 2.5. You need a 89 or 90mm Piston for the 66 crank

[gled49]

Piston pin offset is most recognized in turbo pistons with flywheel marks on the piston top and no valve pockets. The thrust is on the bottom on the 1-2-3 side and on the top on the 4-5-6 side. Pistons that have pin offset and have intake and exhaust valve pockets, are offset correctly only on one side of the engine. Audi V8s have left and right pistons with valve pockets. When I order JE pistons I have them build left and right pistons with the offset up on one side and down on the other. It has worked pretty good. The fit of Mahle pistons will usually produce more power as my last race motor when I changed from JE to Mahle, droped 1/2 point in compression and picked up 5% more power. Gordon

[Scott Clarke]

JE does make 90mm pistons, and in appropriate compression ratios. I have a set in my SS 2.5, 9.7:1 CR. Works pretty well so far. Single plug. John, I will use it just as you describe.