Steve Weiner-Rennsport Systems

Stephen:

LOL,...Jeff & I work together every day and all of the JE's that we use are made to our specification, otherwise we wouldn't use them. Indeed, the newest box-type ones using their latest forgings are better, especially the CNC'ed ones.

They do not have their latest forgings in all sizes so in some applications, thats a limitation.

True enough, its not a "one-size-fits- all" sort of proposition and using a new piston in a marginal or worn cylinder never works.

Its not always accurate to compare apples-to-apples, and one should remember that Mahle cylinders are taper bored from the factory, unlike some others. This helps maintain ring sealing and prevents piston rock which is prevalent in these engines with less-than-ideal rod ratios.

Good point about the occasional differences in ignition timing; I'll dig up some RSR heads I did back in the late 70's and shoot you some pictures to show you what can be done to improve squish when using very high compression (over 14:1) ratios. These heads and pistons are far from ideal in that regard.

My main point was not to denigrate one product or another; both makers are just fine for what they were intended for. My point was only to mention that one must choose wisely when one's engine life expectation is going to be a long-term relationship and avail oneself of ALL the facts.

PorschePhD

As my post, but to also educate that there is more than meets the eye when choosing what piston to use. Too many things are taken for granted and when a Package is bought it is hardly checked. Everything always should be checked.

There are plenty of manufactures that can make pistons to spec. When I order a set they have to make it my way or no it will not make it in my motors. The other aspect of this though is to ensure the rest of the package. Some of the companies above listed in your post have also gone and still going through some growing pains. Doesn’t mean they should not be used. They should be sent the specs and asked to make them “this” way.

PT

Steve, any more info you can share?

Stephen, from what you said, it means that bore-&-replate is ok but the most important part is to check the replate tolerance then to have the the piston done to match that? But what about integrity of cylinder as you said - starting with a used cylinder is good/bad/very bad idea?

Thanks!

Geoffrey

There are two major design challenges with the Porsche piston and cylinders. First is overcomming the excessively short rod/stroke ratio which coupled with the large bore causes the pistons to rock significantly in their bores. The second challenge is the expansion due to heat of the air cooled design. The top of the cylinder expands more than the bottom of the cylinder due to the heat differences. As Steve mentions, the Mahle cylinders are tapered with the top of the cylinder smaller in diameter than the bottom of the cylinder. Why is this important? Sevaral reasons. When the cylinder is at operating temperature, the cylinder is now the same diameter top to bottom and the piston has the same piston to wall clearance (although the piston skirts are also wider than the top). This helps keep things uniform. Also, for every .001" of diameter change in the bore, the piston ring gaps expand .003", which increases leakdown. When you use a non Mahle cylinder, or a Mahle cylinder that has been bored and replated, you loose this taper. Once the cylinder is heated, the extra clearance due to heat opens the ring gaps and it also exposes the top compression ring to more heat. Both bad.

Specific to JE pistons, they are machined out of generic blanks. This means the same blank may be used for Porsche, Honda, Ford, etc. While past issues of piston the cylinder clearance has been largely solved, the wrist pin boss area is not designed specific for Porsche rods and I'd guess it is in this area where Steve is working with JE on a better design. The largest issue I have with JE pistons is in their N/A application in that they do not have optimized squish area and are very inefficient pistons. With EFI and tuning an a good dyno that can load and hold the engine properly I find that a JE pistion needs MORE timing than a properly designed Mahle. This means you are putting more force on the piston on its way up to TDC and are not making as much power as an engine which requires LESS timing for optimum spark angle.

Neil at Perfrormance developments has some pistons from Omega in England that have a nicely designed dome, however, I've never used them so cannot comment on the quality of them.

Colin at Ninemeister in England also has some replacement pistons, mainly for N/A engines and I have a preproduction copy of one of them and will be switching to his piston next winter. Not only does it have a proper squish area, but the piston to head clearance is also controlled very tightly. The wrist pin boss is also extremely sturdy which is a problem I've seen in turbo 911s over the 800hp level where the Mahle pistons crack the wrist pin bosses after about 30 hours.

Since a turbo engine piston does not have much of a dome (net dome volume of a Mahle 7.5:1 is less than 10cc) the squish area and reverse dome to concentrate the air/fuel mixture at the spark plugs is not present. Functionally speaking, the JE pistons require about the same timing as a Mahle in a turbo application. It is not until you start using a piston which has a dome will you see differences in timing between JE and Mahle.

sand_man

I'm glad this discussion is taking place! These are all good points...these are all points that I came accross in one way or another as I was figuring out what direction to take. I know that I've indicated "that I've rolled the dice" on my P&C purchase. However, having Neil Harvey of Performace Developments in my court as the shop going through EVERY aspect of my engine including the inspection and measuremnent of the "new" Supertec Ps&Cs allows me to sleep at night. If they're not right, Neil WILL NOT hesitate to tell me! Plus Henry offers a pretty stout warranty on the engines that he builds and I know he uses these. I wanted so desperatley to use the Mahles...however after sinking several thousand $$$$ into the engine for the machine repairs alone (Neil's services), there just wasn't any money left when I factor in the other things that I still MUST HAVE. Though I haven't run them yet, I'm happy with my descision. And, yes, engine reliability and longevity was at the top of my list! We could beat this to death, I think I'll be fine! If not, then 2002 or 2003 BMW M3 in Leguna Seca Blue...HERE I COME!!!!!!!!!!!!!!!!!!!!!!!

PorschePhD

You will find that there is always another choice, some better, some worse. If you go into the build knowing the information and what the trade offs are then you are 90% ahead of most. The end result is what you are looking for and even with all the info sighted above some boostaholic or a engine builder who is too aggressive with timing will make all this a moot point.

I think you will be fine, will you get 200K miles out of the build, no. Would you with the others, maybe, maybe not. At the end of the day you can bet you will be in there before then anyway because of guides and the other inherent issues with these motors.

sand_man

You also have to remember that I'm rocking twin plug ignition...I'm hoping that will help. Depending on how things go after break-in, I might also be using the IA modified fuel head.

PT

Based upon some of the facts discussed, it definitely sounds like re-plating is not the best way (or even a fairly good way) to go. And I thank everyone for sharing their expertise & experience.

Sandman, I might end up going the same route you are, though mine will be twin plug & EFI to start with While I agree (as others) that Mahle is probably the "best" choice out there, I just can't justify the premium for what I use it for. Time to make some compromise & hopefully an edcuated decision...

E-man930

Thanks everyon fo posting their knowledge and info. I have learned alot and altered my original plans based on my new founded knowledge.
E-man930

DonE

Your assumption on replated cylinders is not accurate. There are quite a few motors out there with bored and plated 3.2L cylinders making high HP without issues. Although I don't know for sure, I would bet Imagine Auto has more than a couple of cars out there with replated 3.2L cylinders with big HP and respectable mileage on them.

I use JE Pistons because they make good pistons and I wanted 8.0:1 CR. Do I care about longevity? Yes, but I doubt I will be looking for another 100,000 miles out my engine. Hell, I hope its sold long before that at 5-10,000 miles per year. For 95% of us on this list, I seriously doubt whether we could tell a difference between JE's or Mahle's over the next 100,000 miles anyway, and I doubt we ever have our motors tuned that well where we could tell the difference. My JE's already survived severe detonation without a scratch, so they get my recommendation.

And Mahle's are not always the obvious best choice out there. Most likely, they are if you plan to use stock cylinders that retain the taper Geoffrey explains. However, there are lots of race teams that don't use Mahles for different reasons. I don't use them because the are over-priced, don't come in 8.0:1 CR and I don't use the stock cylinders. There are a lot of builders out there that use JE's because they work and they are a good value.

I would not loose one moments sleep whether I had JE's or Mahle's going into my engine. That's not exactly true. I would loose some sleep knowing I spent too much on Mahle pistons for my application.

PT - Please know that I am not picking on you specifically. There are lots of opinions out there and you need to make a decision based on application, cost and the product's reputation in the marketplace (i.e., the application you've chosen). Hell, most of us DIY guys will have a $5 part fail due to improper installation before a major part (like a piston) fails. That same $5 part will most likely skew the performance of the $15,000 engine too.

Sorry - rant over.

PT

Don, all good comments! And believe it or not, yes, I think your ranting is good (for me & probably many of us DIY-ers). We all try to make educated decisions and many time without all the professional knowledge/experience.

On this specific topic, one of my local trusted mechanic had also used many re-plated Mahle cylinders with JE for years without any issues. And I haven't heard any of his engines blew up yet & most of them are for track use. What raised my doubts were replate with "stock" JE, taper issue & availability of potentially more cost effective alternative (Supertec).

PorschePhD

The key is simply spec them when you get them. You wouldn't have a motor pop, it would have slap or poor ring seating. Holes are from other issues generally associated with not enough fuel and or too much timing.

m42racer

DonE,

You never ran a 993 3.8LRSR engine with JE Pistons, I must asume? I did for 2 times for a total of 55 Laps. Practice and Race. Both times the Piston failed. The Pin Boss broke, and trashed the complete BTM end. I switched on advice to another Piston make and never had the problem again. The change was not Mahle, but Mahle Pistons never failed like the JE Pistons either. As stated before, you get what you pay for.

Someone who has been named here, has upon hi oggice wall the following quote, "Long after the sweetness of a low cost is forgotten, the bitterness of poor quality remains".

"Sleep tight".

sand_man

HAHAHA! I like this quote. However "low cost" is often a relative term. $2,100 on JUST pistons and cylinders is really not low cost. Of all the cars I've owened over the years, this is the one that's really caused me to lose touch with financial reality and perspective. Don't laugh, there are plenty of cars capable of putting a smile on face for what I paid for these Ps&Cs. Of course this car does more than make me smile...but you get where I'm coming from.

Geoffrey

Mahle pistons are not the end all answer either. Any choice is a matter deciding what works for your given set of goals. Mahle pistons are heavy, they don't have a wide range of compression ratios, and they never mesure out to the advertised compression ratio. 8.0:1 compression seems to me about right for the 3.3 Turbo engine with EFI which is what I mentioned to Don when he was building his engine, and they are expnesive. However, they do last and are reliable.

In a 102mm bore they have the wrist pin deaxised to help with piston rock, however, they are all deaxised the same way, so it helps 3 cylinders and hurts 3 cylinders. There isn't enough net dome volume to machine the exhaust pockets as intake pockets and still retain a reasonable compression ratio. Further, the piston is not high enough so there is too much deck height clearance which affects squish area and cylinder burn. However, if you machine the cylinders down, then the piston to head clearance becomes an issue. So, even Mahle has their compromizes.

I'm really excited about the pistons from 9M and hope that he will begin to produce some turbo pistons in the future. They are even more expensive than the Mahles.