JE Pistons vs. Mahle

[MotoSook]

I found the JE site..and posted this on the JE longevity thread in the general tech forum.

Originally posted by Souk
Well, I think I answered my own question. I found the JE web page. I wonder though...

Wayne posted a picture of the JE piston and their features on a thread in the Engine Rebuild Forum that suggests the pistons available for 911's or through Pelican are made of 2618 alloy (low silicon content). JE also offers pistons in 4032 alloy (12% silicon content, lower coef. of expansion) which they admit can be used to achieve tighter wall clearance.

The Pelican offering confirms the 2618 alloy.

http://www.pelicanparts.com/catalog/shopcart/911M/POR_911M_enginB_pg1.htm#item4

Comparison of JE's wall clearance tables for the two piston types shows the difference in tolerance.

For example:


A 98 mm piston made of 2618 requires 0.0035-0.0045" minimum clearance, while the 4032 piston requires 0.0025-0.0035" minimum clearance.

I don't have my spec book handy, but what is the 3.2 wall clearance? Just as a data point, not that it is comparing apples to apples.

OK, this is a thread about longevity, but I think this applies and is perhaps a factor in the annoyances some may have experienced at some point (loose pistons->piston slap ~>premature wear).

Has anyone used the 4032 JE Pistons? Can you get a 4032 911 piston?

[cnavarro]

I've used both forgings and actually prefer the 2618 forging because of it's strength. It just so happens that I was having a discussion about this same very topic today with JE regarding clearances, since I have been consistantly spec'ing total clearances between .0015-.0025" (depends on bore size, application, n/a vs. forced induction, aircraft, racing, etc). On average, i'm about .0015"-.002" under their "recommended" spec and they were wondering why- well, i'm not under the constraints of a casting and had some choice in the aluminum with which I manufacture my cnc cylinders, and chose an aluminum for both it's strength, thermal conductivity, elongation, and expansion, which just so happens to be closer to the expansion rates of the 2618 forging than mahle's 339-0 casting aluminum is. So I can run tighter clearances...

I prefer to take a set of pistons one at a time and have them made up to the customers spec, not try to fit a customer into a pre-determined configuration. Although this makes for slightly longer lead times, this also allows for changes that really make the difference, including lighter pins and even offset pins, re-enforced skirts, specified minimum crown thicknesses, off-the-wall ring lands, etc. I just designed and ordered a set of pistons today with 1mm top, 1.2mm second and 1.5mm oiling rings for reduced friction, and opted for H-11 tool steel .120" thin-wall lightweight pins, and re-enforced skirts. This kind of freedom and flexibility lets us think outside the box. I have not had a single JE failure in the hundreds of sets used by my customers, but granted i haven't yet had anyone with a fire-breathing 1000 hp 911...But there's always a first time for everything.

Charles Navarro
LN Engineering
http://www.LNengineering.com
Aircooled Precision Performance

[Mookster]

Researching at this time.

I have an '83 SC w/ a 3.0

If I were to use JE pistons, do I need to replace the rods and cylinders (assuming out of spec is not an issue)?

Street car only.

[cnavarro]

As long as your cylinders are Nickasil, just a quick re-honing, and they will be ready for JEs. Rods shouldn't be an issue, since the pistons will be designed (or at least should be) to have the correct pin size, compression height, etc for your engine.

Charles Navarro
LN Engineering
http://www.LNengineering.com
Aircooled Precision Performance

[MotoSook]

In case a reader doesn't find the longevity thread on the main forum:

JE does not and will not offer 911 pistons in 4032 alloy. Also, the values I posted were sampled from a table of Japanese and Chevy applications to illustrate the difference between the two alloy types.

JE specifies 0.0015" wall clearance for their 911 pistons.

[MotoSook]

To minimize confusion, here is the link to the other discussion. Note the discussion of clearance.

JE piston longevity.

[David]

I just posted to the other thread, should we let one of these die?

[911SCfanatic]

These threads have now coverged.

Can a moderator close this thread please?