JE Pistons
06-14-2010, 10:40 PM
#1
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JE Pistons
I am still struggling with the decision about upping my displacement to 3.8L while in the process of a rebuild, so I wonder if there is current information available that could help me (to spend wisely or just not spend more money). I am a non-racer with nominal AX and DE activity. I've been confined to Toyota sedans and Dodge minivans for far too long, so I'm consequently moved to bump up the performance of my recently purchased 964 (2 years ago) - first sports car ever. I think this will be it for me in toys (no trading up, etc), so I'm anxious to get the most bang for my rebuild buck. BTW, I have combed the RL and PP forums for this information, and have come away thinking it may not all be currently applicable.
1) The JE pistons I see are 494 grams, which seem like about 150 grams lighter than OEM. Is that correct?
2) The CR for these JE's is listed at 11.5:1 and I believe that the stock spec is 11.3:1. I also think I have seen where the actual CR for stock NA 964's really comes down to around 10.5:1. Is that correct? Does this switch to 11.5:1 represent a jump that cannot be accommodated well with a tuned ship and 93 oct gas?
3) Is there enough of a thermal expansion difference between the material in a stock sleeve and a new JE piston such that boring/replating a stock sleeve to mate with a new piston is a bad idea? Thus, is a complete change (new sleeves and new pistons) advisable?
4) I have heard from a supplier that the new JE pistons / sleeves have approximately the same clearance as OEM versions. I have read in RL about noise and “slap” associated with “excess” clearance in the JE pistons, but other information tells me those references are dated. Any current spec's to compare?
5) Strictly by displacement proportion, it looks like the 3.8L conversion (really only 4% increase for the 102 mm size) would get you about 10 more hp or ft-lbs torque, with no other changes. Is that about right or not?
If anyone has close experience with current design JE pistons and matched cylinders (new or rebored/plated) I would surely appreciate your input. Thanks for your time!
1) The JE pistons I see are 494 grams, which seem like about 150 grams lighter than OEM. Is that correct?
2) The CR for these JE's is listed at 11.5:1 and I believe that the stock spec is 11.3:1. I also think I have seen where the actual CR for stock NA 964's really comes down to around 10.5:1. Is that correct? Does this switch to 11.5:1 represent a jump that cannot be accommodated well with a tuned ship and 93 oct gas?
3) Is there enough of a thermal expansion difference between the material in a stock sleeve and a new JE piston such that boring/replating a stock sleeve to mate with a new piston is a bad idea? Thus, is a complete change (new sleeves and new pistons) advisable?
4) I have heard from a supplier that the new JE pistons / sleeves have approximately the same clearance as OEM versions. I have read in RL about noise and “slap” associated with “excess” clearance in the JE pistons, but other information tells me those references are dated. Any current spec's to compare?
5) Strictly by displacement proportion, it looks like the 3.8L conversion (really only 4% increase for the 102 mm size) would get you about 10 more hp or ft-lbs torque, with no other changes. Is that about right or not?
If anyone has close experience with current design JE pistons and matched cylinders (new or rebored/plated) I would surely appreciate your input. Thanks for your time!
06-15-2010, 07:45 AM
#2
Nordschleife Master
1) The stock pistons are in the neighborhood of 625g depending on the weight group.
2) I've found the compression ratio of 964 engines to be in the 10.8:1 range and have run engines with as much as 12:1 on 93 octane pump fuel (aftermarket ECU)
3) You can run a 2618 alloy piston in a stock cylinder that has been reconditioned and replated provided the proper clearances are met.
4) There is no way a JE piston will utilize the same tolerances a stock Mahle piston uses. The noise and slap reputation from JE is from a long time ago and they generally don't make noise. However, unless something has changed recently, JE does not use a specific Porsche blank to manufacture the pistons and they have had structural issues and do not have an efficient "dome profile" which makes the piston inefficient. When mapping an engine, I can usually tell if it has a JE piston because the engine requires more ignition timing than a Mahle, or other custom aftermarket piston.
5) For what you are doing, I'd suggest staying with 3.6l displacement. To do 3.8 properly, with longevity, you really need to use the bore in barrels. With a good aftermarket piston with a proper design in 3.6l displacement, the engine will generally make more power than a factory 3.8RS piston equipped engine.
I'm not a fan of JE pistons.
2) I've found the compression ratio of 964 engines to be in the 10.8:1 range and have run engines with as much as 12:1 on 93 octane pump fuel (aftermarket ECU)
3) You can run a 2618 alloy piston in a stock cylinder that has been reconditioned and replated provided the proper clearances are met.
4) There is no way a JE piston will utilize the same tolerances a stock Mahle piston uses. The noise and slap reputation from JE is from a long time ago and they generally don't make noise. However, unless something has changed recently, JE does not use a specific Porsche blank to manufacture the pistons and they have had structural issues and do not have an efficient "dome profile" which makes the piston inefficient. When mapping an engine, I can usually tell if it has a JE piston because the engine requires more ignition timing than a Mahle, or other custom aftermarket piston.
5) For what you are doing, I'd suggest staying with 3.6l displacement. To do 3.8 properly, with longevity, you really need to use the bore in barrels. With a good aftermarket piston with a proper design in 3.6l displacement, the engine will generally make more power than a factory 3.8RS piston equipped engine.
I'm not a fan of JE pistons.
06-15-2010, 11:27 AM
#3
Thanks for this info Geoffrey. Given that Mahle won't sell their pistons without a set of cylinders, are you aware of any alternatives to JEs for someone looking for the additional clearance to fit a wild cam?
I am looking for something reasonable from a cost perspective - does not have to be the absolute best.
Thanks in advance.
I am looking for something reasonable from a cost perspective - does not have to be the absolute best.
Thanks in advance.
06-16-2010, 01:11 PM
#5
Rennlist Member
For the ultimate piston/cylinder set, take a look at http://www.capricorngroup.net/. Capricorn is the leading European P/C manufacturer (in addition to Mahle) for Porsche. The winner of Nurburgring 24H race, the 997 RSR from Manthey Racing (among others...) is using P/C from Capricorn. I also believe that 9M are using Capricorn in some of their race engines. The 3.8L (102mm) 11.5 CR piston weighs 422 grams!
06-16-2010, 01:23 PM
#6
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For the ultimate piston/cylinder set, take a look at http://www.capricorngroup.net/. Capricorn is the leading European P/C manufacturer (in addition to Mahle) for Porsche. The winner of Nurburgring 24H race, the 997 RSR from Manthey Racing (among others...) is using P/C from Capricorn. I also believe that 9M are using Capricorn in some of their race engines. The 3.8L (102mm) 11.5 CR piston weighs 422 grams!
Disclaimer: I've no personal experience with Perfect Bore P&Cs.
06-16-2010, 10:34 PM
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1) The stock pistons are in the neighborhood of 625g depending on the weight group.
2) I've found the compression ratio of 964 engines to be in the 10.8:1 range and have run engines with as much as 12:1 on 93 octane pump fuel (aftermarket ECU)
3) You can run a 2618 alloy piston in a stock cylinder that has been reconditioned and replated provided the proper clearances are met.
4) There is no way a JE piston will utilize the same tolerances a stock Mahle piston uses. The noise and slap reputation from JE is from a long time ago and they generally don't make noise. However, unless something has changed recently, JE does not use a specific Porsche blank to manufacture the pistons and they have had structural issues and do not have an efficient "dome profile" which makes the piston inefficient. When mapping an engine, I can usually tell if it has a JE piston because the engine requires more ignition timing than a Mahle, or other custom aftermarket piston.
5) For what you are doing, I'd suggest staying with 3.6l displacement. To do 3.8 properly, with longevity, you really need to use the bore in barrels. With a good aftermarket piston with a proper design in 3.6l displacement, the engine will generally make more power than a factory 3.8RS piston equipped engine.
I'm not a fan of JE pistons.
2) I've found the compression ratio of 964 engines to be in the 10.8:1 range and have run engines with as much as 12:1 on 93 octane pump fuel (aftermarket ECU)
3) You can run a 2618 alloy piston in a stock cylinder that has been reconditioned and replated provided the proper clearances are met.
4) There is no way a JE piston will utilize the same tolerances a stock Mahle piston uses. The noise and slap reputation from JE is from a long time ago and they generally don't make noise. However, unless something has changed recently, JE does not use a specific Porsche blank to manufacture the pistons and they have had structural issues and do not have an efficient "dome profile" which makes the piston inefficient. When mapping an engine, I can usually tell if it has a JE piston because the engine requires more ignition timing than a Mahle, or other custom aftermarket piston.
5) For what you are doing, I'd suggest staying with 3.6l displacement. To do 3.8 properly, with longevity, you really need to use the bore in barrels. With a good aftermarket piston with a proper design in 3.6l displacement, the engine will generally make more power than a factory 3.8RS piston equipped engine.
I'm not a fan of JE pistons.
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06-17-2010, 11:23 PM
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06-17-2010, 11:25 PM
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06-18-2010, 12:15 AM
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And my builder insisted on Mahle. 10.5:1 I believe
'93rsa 3.8
06-18-2010, 10:37 PM
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As I have been doing a good bit of research into 3.8L P/C upgrades, it seems like there are a bit of personal preferences in the reactions about JE pistons. Most things about these cars are not black-and-white, so it's natural that some people are dead set in one direction while others are more open.
Cheers.
06-19-2010, 07:36 PM
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Pistons
Geoffrey,
Whose pistons do you like best for street and occasional DE/AX use? I too am considering a displacement increase. Probably something in the range of true 3.8L or greater displacement. In California, we are limited to less aggressive cam profiles so displacement is one of the few HP variables remaining. Other than J&E who do you recommend?
Thanks Mark
Whose pistons do you like best for street and occasional DE/AX use? I too am considering a displacement increase. Probably something in the range of true 3.8L or greater displacement. In California, we are limited to less aggressive cam profiles so displacement is one of the few HP variables remaining. Other than J&E who do you recommend?
Thanks Mark