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You have to be careful when machining high compression pistons for lower compression. It can cause some distortion in the ring lands based on forging stresses that may be relieved by the machining process. I know there isn't a lot of quench in our engines, but just throwing spacers under the cylinders to lower the compression ratio can make detonation and pre-ignition worse. A careful study of the piston shape and its interaction with the combustion chamber should be done to ensure optimal combustion chamber shape.
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Old 02-07-2008, 01:56 PM
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Quote:
Originally Posted by polizei View Post
What would the C2T gaskets lower the compression to on stock Carrera?

It sounds like the preferred solution is install lower compression pistons. Have you guys found it more cost effective to get your existing, high-compression pistons machined or to purchase lower compression pistons? How much does it typically cost in either case?
for example supertec does both but I would suggest new JE pistons over machining unless you have delusions of 200k engine then go MAhle's..
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Current project 73 914-6 Gt project rusteration 2.4
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Old 02-07-2008, 02:31 PM
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Originally Posted by mb911 View Post
for example supertec does both but I would suggest new JE pistons over machining unless you have delusions of 200k engine then go MAhle's..
Could you send me a link to the pistons you'd recommend? I can't seem to find any lower compression pistons for a 3.2. Is it advisable to do the C2T head gaskets in addition to the pistons, even if I'm not planning on building a monster machine?
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Andy - 1987 911 Carrera Coupe
Old 02-07-2008, 02:51 PM
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Originally Posted by polizei View Post
Could you send me a link to the pistons you'd recommend? I can't seem to find any lower compression pistons for a 3.2. Is it advisable to do the C2T head gaskets in addition to the pistons, even if I'm not planning on building a monster machine?
Call Henry@supertecperformance 760-728-3062 for correct pistons/cylinder combos.. I personally did not use c2 head gaskets
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Ben

Current project 73 914-6 Gt project rusteration 2.4
Reproduction 914-6 oil tanks, 1-5/8" 914-6 heat exchangers source call 2623647426 or email mbconsulting21 @gmail.com
Old 02-07-2008, 03:52 PM
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If I were to swap out to 3.3 or 3.4 L pistons & cylinders, would I have to get my heads machined and purchase new head gaskets? If so, how much would I be looking at to get the heads machined?
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Old 02-10-2008, 05:00 AM
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Originally Posted by polizei View Post
If I were to swap out to 3.3 or 3.4 L pistons & cylinders, would I have to get my heads machined and purchase new head gaskets? If so, how much would I be looking at to get the heads machined?

No head gaskets on the 3.2 to begin with but you would have to chamfer the heads to prevent detonation.. not sure on cost be fairly inexpensive
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Current project 73 914-6 Gt project rusteration 2.4
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Old 02-10-2008, 06:00 AM
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Hmmm,you seem set on using the high-comp pistons for some reason. l`m guessing you hope your off-boost performance will be better with the 10.5`s? On paper that may be true but the reality is that your car will be much faster when you can dial the boost up and that will only happen running a lower compression ratio. My 3.2 running stock pistons gets full boost before 2000rpm, l seriously doubt l could expect noticably better performance with the euro-pistons. l had a chance to buy a set of the 10.5`s and l passed for one reason- l intended to boost the car. lf you truly intend to turbo your car the bottom line is that 10.5 pistons are the worst choice you could make for the pistons.The stock pistons will work but why bother? you`ve got the motor apart ,do what any experienced builder would do when building a turbo motor: install FORGED turbo pistons with a lower compression ratio. The 3.2stock cast pistons tend to break the ring lands under excessive boost, a far greater fear with the euro 10.5`s. While you have pistons out send them to Swain-tech for coatings
http://www.swaintech.com/ you`ll be glad you did. l realize not everyone has $10-k laying around to spend on a motor which is probably the best reason yet not to use high-comp pistons in a turbo build. Some people report detonation using the euro slugs with our gas,imagine how they are under boost...
Old 02-10-2008, 11:26 AM
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I'm sorry for the confusion. I have 9.5:1 pistons in my car currently. I was just initially inquiring about "what if you had 10.5:1 pistons".

I'm trying to decide whether to purchase new pistons & cylinders or to get my 9.5:1 pistons machined to a lower compression. I'm just considering all of the costs if I made the jump to turbo pistons & cylinders.
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Old 02-10-2008, 07:07 PM
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Ok, so if I were to get new P & C's for my 3.2L, it sounds like I should go with the fully finned cylinders from the 3.3L C2 Turbo. If I were to keep the heads from my 3.2L, I believe I need the following:

1. "chamfer the heads to prevent detonation" ~ Ben
2. 0.5mm head sealing gasket
3. o-ring that goes at the base of the cylinder

Am I correct about #2 and #3? If so, anybody have any idea on the cost for those parts? Please chime in if I need anything else. Thanks!
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Old 02-11-2008, 07:41 AM
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Originally Posted by WydRyd View Post
AHHHH, that's a different story! I thought you were referring to the 3.2 CARRERA motor!

Anyway, yes, it can be done on a 993 with the right changes to engine management. I believe the system running on that 993 is a Protomotive system. Protomotive have built their reputation on developing aftermarket kits for the naturally aspirated platforms and know their ***** when it comes to aftermarket turbocharging. Send Todd Knighton an e-mail... top guy

Hello, the project referred to in that post is in fact mine, here is a working link:
http://www.6speedonline.com/forums/showthread.php?t=93992

Todd K certainly does know his stuff, but there are no Protomotive parts on my car. It is a completely custom setup I built myself, including an aftermarket ECU that is completely programmable (which I also tuned myself).

To the thread starter: As others have already said, having full control of ignition timing is key to keeping detonation at bay when running boost and higher CR. I am only running 6 psi on my setup, and I have to keep timing relatively low to run normal pump gas. If I run 110 leaded I can of course run more timing (and make a bit more power) without seeing any knock. Also, using an ECU that has knock feedback controls (such as the AEM I am running) can save you in case you have a bad tank of gas.

If you have any questions feel free to send me a PM. Good luck with your project.
Brett
Old 02-11-2008, 01:40 PM
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I really like the extra large single turbo with stock C.R. When does your boost start coming on?
Old 02-11-2008, 03:00 PM
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