I'm looking at a 964 with a 3.8 conversion built ~1.5 yrs ago; the engine has approx 15k miles of street and some DE use. It has JE pistons & slip fit cyls.

Consumption and leakdown are good currently according to the owner. A PPI is pending but for the sake of argument let's say it checks out. I've no experience with JEs on these engines. I have heard that early JEs had some slap issues but this engine does not exhibit this.

My main concerns are around the ringpacks & general longevity; blowby, oil control, bore wear etc. I'd hate to buy this thing thinking it's good to go and then have to tear into the engine in 20k miles. Do JEs hold up over the long haul in these engines? Or what's a reasonable expectation of life for a JE piston'd 3.8 in your experience? Hard street/DE use, not racing.

 

Mahle experience only, I see a lot of JE out there but really don't have any experience or knowledge about them.

The only thing I know about is the factory pistons have an offset in the pin location and the JE do not, which some say is what causes the piston slap with JE.

Now, I have also read Steve Weiner recommend replace JE pistons after 100hrs of hard use.

Hi Mark:

Well sir,..the choice of pistons really lies with your expectations of engine life.

JE's are good pistons but they were designed & intended for competition purposes and do not last anywhere near as long as Mahle ones do. JE's are inexpensive and offer greater flexibility for compression choices so thats why they are popular with racing engine builders.

Mahle pistons are far more durable, fit tighter, have less oil consumption, and their cylinders are tapered for less noise and improved top ring life.

If you expect this rebuild to go 100K or more, then the Mahle P/C's should be used. If you simply need this to go 50K or so, then JE's will suffice. We replace them every 100 hours in race applications where RPM's exceed 7500 for periods of time.

IMHO, your engine builder offers you some sound advice.
__________________
Steve Weiner
Rennsport Systems
Portland Oregon
(503) 244-0990
porsche@rennsportsystems.com
www.rennsportsystems.com

 

All of the front running racers here with 3.8 air cooleds only use Mahles.

Then there's the slip-in aspect. I wouldn't build an engine with them unless: 1. they were free, and 2. I was just building a fun "what the hell let's build from the spare parts bin" engine. No way, no how for a customer, or to someone I were gong to sell something to.

Ultimately, the extra 150cc doesn't really mean jack. But if it's an otherwise nice car, priced correctly, and what you're looking for just go in with your eyes open.

 

No experience with the Porsche fit JE's but my mate here in the UK who owns/runs a very well respected tuning shop for Vauxhall, Ford and Suzuki Hayabusa race engines has experience of JE's, for that set of engines. His thoughts were [politically correct mode=on] that they were crude and rather basic by comparison to Omega, and certainly not in the same league as Mahle. I think he used the term "truck" in the sentence!

As I said, no personal experience, so perhaps I'm being a little unfair, but the conversation I had with Steve very much mirrored Kens comments above.

 

You should ask on the Pelican rebuilding forum as well; pretty smart people.

 

Agreed, the +0.2L doesn't actually hold any appeal to me, rather it's that the engine has been completely overhauled (and upgraded everywhere - fancy rods, 993RS valves, springs/retainers, GT3 oilpump, etc).

Oddly enough, it originally had Mahles when the 3.8 conversion was first done. Very shortly afterward, a rod bearing went south; teardown showed some skirt scuffing too. Seems this second rebuild was when the JEs went in. It's not clear why. Are the Mahle P/Cs only sold as a set or something?

 

Yeah, all fitted, balanced as a set. Not something you want to mix and match.

 

Mahle pistons and cylinders are generally sold only in sets of six so its difficult to get singles when one has a problem and for that reason, they are not often considered for racing engines. This is likely why the PO used JE's instead of spending big money on a new set of Mahle RSR P/C's.

JE has improved their 102mm race pistons over the past few years by using a dedicated forging to make a lighter 2618 piston in a "box" design. When these are ordered to one's specifications, they work OK in the context of competition engines where 100 hours is acceptable. Further, the ability to order whatever compression height, ring configuration, and pin height you want is critical for a race engine builder.

2618 pistons are much lighter than the high-density Mahle forgings which, once again, is a big advantage for racing engines that see well north of 7K RPM. This makes a big difference in rod bearing loads.

For people who require engine life beyond 200 hours and or 50K, IMHO, Mahle's are a better long-term choice.

We use Mahle and custom JE, CP and Omega pistons for various applications.


Ultimately, we are all the sum of our experiences so that's likely to vary among the folks who do this for a living,....

 

BTW, back to back dyno testing shows that our 3.6l CP piston makes approximately 10hp more than the Mahle 3.8l RS piston on the same engine under the same conditions.

Also, as mentioned, the Mahle pistons have a deaxised wrist pin, but all of the pistons are identical. This means that upon installation in the engine, one side is offset to the top of the engine and the other side is offset to the bottom of the engine. This acutally causes an air fuel ratio difference between banks due to a slight VE difference between the sides. For longevity, no one can argue with Mahle pistons (see my pictures after 100hrs of race usage on my RSR), however, we've been using a custom designed piston (not JE) with excellent results, both from reliability / longevity and performance. In the street engines we use a factory GT3 ring package which has similar durability as the larger (thicker) 964 ring package.

As for JE, we found that another manufacturer has better tolerances and better design capability.

 

That's a big disparity in usable life. What aspect of the JEs are crapping out so (relatively) early -- oil control, top ring wear, the slug itself is fatigued beyond use, something else?

 

Yessir, that sure is and due to all the variables at work here: max RPM, CR, clearances, etc.

Again, to maintain context & perspective, 100-200 hours is a long time for a race engine so replacing pistons and rings at those intervals is quite acceptable. Some race engines operated to 8K with high compression ratios need replacement between 25 and 50 hours!

The main wear points we see with 2618 pistons are at the top ring lands.