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Old 09-27-2010, 10:52 PM   #1
Aceyduce
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Default Reduced Piston to Wall Clearances

I've been doing as much research as I can on this topic, but I've hit my limit of knowledge. After asking a few sources for opinions, I figured I'd open up the flood gates on my not so new idea.

Shortly I'll begin the process of building my 08's 257 using CP pistons. I understand that the recommended tolerance for piston to wall is 0.0030". Would reducing that tolerance to 0.0028" provide an added benefit that will not be outweighed by other factors? The block will see at most 380-400whp (20g/10cm^2) at the largest turbo. The primary goal of the motor is to be used in a daily driver that averages around 50,000 miles a year, while seeing several tracks days of hard use during that year. (side note- the stock block lasted 78,000 miles for those keeping track of blown 08's)

My thoughts and reasons on reducing the P-W clearance was to reduce the movement of the piston laterally, decreasing the potential for wear on the block itself. This should increase block life at the expense of the rings. What are your opinions and concerns? Am I off my rocker in considering this for my application? In theory it seems sound, but we all know how far theory gets and how much it leaves to be desired. I know there have a been a few users who have done just this and have reported back, to them thank you for the idea, and I hope they can provide further insight.

Thanks.
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Old 09-27-2010, 11:20 PM   #2
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50k miles a year is a lot..

the piston alloy of the CP 2618, is not a longevity piston. iirc most pistons/motors of that alloy are "suppose" to be refreshed every 50k or after a certain period.

4032 is a harder alloy and wont expand as much and will allow you to run much tighter clearances, i think someone on here is attempting to run them at .0020", that may be your better choice if longevity is your priority.

Also side note, look into piston skirt coatings, this will help wear & tear, as well as noise. And as far as being accurate to the .0000X" it may be hard, the clearances will most likely be a range.. ranging from .00027" to .00032", etc for example.. I've never really seen a build dead on .0030" on all 4.
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Old 09-27-2010, 11:23 PM   #3
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Several threads on this subject exist.
I have been a part of 2 of them for sure.

The general "consensus" is that if you use 4032 alloy pistons, you can reduce p/w a fair amount.

Using 2618 alloy pistons most people seem to stay on the looser side for safety.

Here is a great thread on the subject: http://forums.nasioc.com/forums/show....php?t=1061799

Here is another good thread.
Make sure you read down to where I dispute the claim that Mahle 4032 piston engines were not reliable for the reason stated.
http://forums.nasioc.com/forums/show....php?t=1926294

I built my new engine using Mahle 4032 pistons and .002" p/w clearance.

The engine is not yet in the car, but will be shortly.
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Old 09-28-2010, 02:50 AM   #4
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+1 on piston skirt coatings.

Btw, 50,000 miles in 1 year? Are you living in this car or something?
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Old 09-28-2010, 08:08 AM   #5
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I appreciate all the replies. I was considering 4032 as most of you had mentioned for that specific reasoning. Team Scream, thank you for the further links. The pistons will be coated certainly.

As to the miles, I am a service engineer that travels rather frequently. Let's say my average daily commute is in the 200+ mile a day range.... Not ideal for certain, but those are the boundaries I have to be constrained in.

Thanks again for the replies, and by all means I welcome more!
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Old 09-28-2010, 01:30 PM   #6
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If you get the Mahle pistons, the skirts come coated out of the box. No need for an additional $30.00++ per piston to get it done.
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Old 09-28-2010, 01:37 PM   #7
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I'm leaning toward Mahle 4032 as well since I want longevity. Team Scream...it sounds like you have some positive experiences with them? I talked to Outfront and they recommended them for a street car as well.
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Old 09-29-2010, 02:07 AM   #8
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Yes, speak to Ron at Outfront, he is a super nice guy to deal with and my opinion is you cannot go wrong with Outfront.

Ron built my shortblock.
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Old 09-29-2010, 02:46 PM   #9
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Quote:
Originally Posted by chongl View Post
I'm leaning toward Mahle 4032 as well since I want longevity. Team Scream...it sounds like you have some positive experiences with them? I talked to Outfront and they recommended them for a street car as well.
I put a set of Mahle 4032 stroker pistons in the 2.12L stroker I built of my bugeye. I am extremely happy with them so far. I am running near stock power levels with a .0025" PTW clearance. The pistons are as quiet as stock and I have no oil consumption issues whatsoever after close to 16,700 miles. The rings they included seated very quickly and seem to be better than the stock set as far as sealing goes. 1700 miles into my 6th oil change the oil is still more of a transparent gold in color than black.
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Old 09-30-2010, 03:44 PM   #10
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Quote:
Originally Posted by MartinSTi05 View Post
I put a set of Mahle 4032 stroker pistons in the 2.12L stroker I built of my bugeye. I am extremely happy with them so far. I am running near stock power levels with a .0025" PTW clearance. The pistons are as quiet as stock and I have no oil consumption issues whatsoever after close to 16,700 miles. The rings they included seated very quickly and seem to be better than the stock set as far as sealing goes. 1700 miles into my 6th oil change the oil is still more of a transparent gold in color than black.
+1 on that the Mahle's are superb pistons. Mine were set up at .0024. Plasma-moly rings seat super fast.
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