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Old 08-06-2007, 08:42 PM   #1
fishheadback
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Default Which pistons are you running, 4032 or 2618?

Well, just lost a piston in my RSTi hybrid.

Been doin a lot of research but Im still up in the air. They say the 2618 alloy (i.e. JE, Wiseco) pistons are better for boosted and higher hp applications, but they are more prone to scorring piston walls and piston slap. On the other hand the 4032 alloy (i.e. Mahle) pistons have a lower thermal expansion rate, thus resulting in tighter tolerances lowering the chances of cylinder scorring and piston slap. But are not quite as strong.

So basically I just want to hear from other people about what they have done.

P.S.- I want to order these things asap so I can get this beast done this weekend. Any help would be greatly appreciated.


Thanks!
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Last edited by fishheadback; 08-06-2007 at 08:49 PM.
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Old 08-06-2007, 09:16 PM   #2
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2618 cp pistons... .0030 p/w clearence... they are not as loud as I expected.

I have seen a couple cracked mahle pistons on here, but have never seen somebody who had problems with a 2618 alloy piston tearing up their cylinder bores.
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Old 08-08-2007, 08:35 PM   #3
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If they score the piston walls, they were spec'ed too tight to begin with.

Yes, they expand a lot. On the other hand, I've bent them into banana shapes while trying to remove scrap pistons from scrap rods "the easy way". They don't shatter.
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Old 08-08-2007, 09:01 PM   #4
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It's not so much that the 2618 alloy slugs are "stronger" as they are "less brittle." Properly toleranced, the 2618 alloy pistons are almost bombproof. In high power and boost motors, they are definitely the way to go. OTOH, if you're not going for big power or a really aggressive tune, the 4032 slugs, such as Mahle, are arguably the better choice since they will probably last longer - the harder the piston, the slower the wear rate.

Either way, the expansion rate for both is very high. Proper warm-up is critical with any forged piston.
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Old 08-09-2007, 09:14 AM   #5
fishheadback
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Good things to know. Since Im keeping it a daily driver with moderate power levels I went with the Mahle's.

Thanks for the input!
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Old 08-09-2007, 03:01 PM   #6
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Sounds like you made the right choice. Just stay out of knock, and make sure to warm it up thoroughly before you put the hammer down. Enjoy.
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Old 08-09-2007, 11:34 PM   #7
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I've used both and here is the bottom line for me. You have more choice and the ability to make custom pistons in 2618.

My custom CPs don't slap at all. They are a little more dough, but I have higher compression (more responsive, more power, less lag, careful tuning), and they are quiet.
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Old 08-10-2007, 02:53 AM   #8
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I'm running Supertech pistons which are 4032. They are shockingly quiet. The fully built motor in my LGT is actually more quiet than the completely stock N/A 2.5 in my 07 Outback company car. Don't know about strength quite yet since I've only got about 200 miles on it and I'm still breaking it in but I plan on getting around 500-520whp out of it, so we'll see. My personal feeling is that if the tune is good, the "weaker" 4032 pistons are fine and will wear better and run smoother/quieter.
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Old 08-10-2007, 09:36 AM   #9
fishheadback
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Quote:
Originally Posted by socalLGT View Post
I'm still breaking it in but I plan on getting round 500-520whp out of it, so we'll see.

HOLY SMOKES! Thats gonna be one mean Legacy.

I looked at Supertech pistons but I had never heard anything about them. They were very reasonably priced too.

Well my pistons should be here today. Then surgery begins this weekend.

Wish me luck!!
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Old 08-10-2007, 10:27 AM   #10
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2618 Je's
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Old 08-12-2007, 03:30 AM   #11
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Quote:
Originally Posted by fishheadback View Post
HOLY SMOKES! Thats gonna be one mean Legacy.

I looked at Supertech pistons but I had never heard anything about them. They were very reasonably priced too.

Well my pistons should be here today. Then surgery begins this weekend.

Wish me luck!!
The Supertech pistons have an offset wrist pin. So make sure you put them in the right way. I had a buddy use them in his car, not knowing they had an offset pin. Statistically he had a 50/50 chance to get each of them in right. He got 2 right, 2 wrong. Ain't math a b!tch!
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Old 08-12-2007, 07:11 AM   #12
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Quote:
Originally Posted by flycaster View Post
It's not so much that the 2618 alloy slugs are "stronger" as they are "less brittle." Properly toleranced, the 2618 alloy pistons are almost bombproof. In high power and boost motors, they are definitely the way to go. OTOH, if you're not going for big power or a really aggressive tune, the 4032 slugs, such as Mahle, are arguably the better choice since they will probably last longer - the harder the piston, the slower the wear rate.

Either way, the expansion rate for both is very high. Proper warm-up is critical with any forged piston.
That's not entirely accurate. The forging process only marginally increases the thermal expansion parallel to the grain. Cast equivalents of 4032 and 2618 expand almost exactly as much. It has more to do with the alloy than the fact that they are forged. High strength alloys typically expand more thermally.

Also, Mahle's 124 alloy has a Brinell Hardness of only 100, whilst 2618 has one of 115 ... and the elongation before break of the 2618 is 5 times more than the 124 Alloy. Bear in mind, Mahle 124 is NOT 4032.

Standard 4032 T6 has a Brinell Hardness of 120, Elongation At Break of 9%, thermal expansion at room temp of 19.4 um/M-*C, Young's Modulus of 78.6 GPa, and Yield Strength of 317 MPa. However, some proprietary (non-melt-spun) grades make those figures to 120, 4%, 19.4 um/M-*C, 79 GPa, and, more importantly, 331 MPa.

2618 T6 has the same measurements figured at 115, 10%, 22.3 um/M-*C, 74.5 GPa, and 372 MPa .... making 2618 only marginally stronger/tougher, significantly higher expanding, a little less rigid, and slightly softer and quicker to wear. Coatings tend to fix the latter.

To each his/her own ... 4026 T651 is actually stronger than 2618 T6, though it's argued that almost all aluminum pistons, due to combustion temperatures, revert to about a T5 temper after any significant use.

-Adrian
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Old 08-12-2007, 10:01 AM   #13
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Having held both Wisecos and Mahles in my hand side by side, I would "say" the Wiscos would be tougher simply because they look, feel and appear "tougher". The Mahles look like 100% OEM STI pistons, wheas the Wisecos were obviously aftermarket. But....... Thats just the look and feel they have...... No proof coming from me yet.
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Old 08-12-2007, 11:35 PM   #14
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OK, I have now installed stock, wisecos, and Mahle pistons......

The Mahles rings SUCK for ease of installation. ESPECIALLY the 3layer oil rings. They can be installed, but Jesus on a Cracker, what a bitch. You know how OEM rings have the little metal wire that keeps the center piece together once you install it? Mahle decide it wasnt neccesarry... Well it IS!!!!! PITA!!!!

But anyway, they are installed now..... Lets hope nothing jumped out.
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Old 08-13-2007, 12:27 AM   #15
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Quote:
Originally Posted by reddevil View Post
The Mahles rings SUCK for ease of installation. ESPECIALLY the 3layer oil rings...Lets hope nothing jumped out.
If you have ANY doubts about one of the Mahle oil rings jumping its groove, stop, and check it. We went down that ugly road and it cost us a motor.

And you're right, they are a complete bitch to install.
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Old 08-13-2007, 01:09 AM   #16
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And I spoke too soon.

I retracted the damn ring compressor too far, and it whacked out, so I need to buy another ring compressor.....

FLYCASTER.... you make me paranoid.... great....
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Old 08-13-2007, 08:31 AM   #17
fishheadback
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Hmmm. Well the morons at the place I bought my pistons from dont know how to read.

I paid to have them shipped overnight, and they shipped them ground. I paid for them weds morning and they still arent here.

So now the project is pushed back till next weekend.
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Old 08-13-2007, 03:06 PM   #18
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Quote:
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...FLYCASTER.... you make me paranoid.... great....
Sorry, amigo. Much better safe than sorry on this one....
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Old 08-13-2007, 08:17 PM   #19
fishheadback
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Quote:
Originally Posted by reddevil View Post
OK, I have now installed stock, wisecos, and Mahle pistons......

The Mahles rings SUCK for ease of installation. ESPECIALLY the 3layer oil rings.
Edit: Purchased the Mahle pistons.

Question, on the oil rings, the upper and lower rings of the oil set are diff.
One set is flat all the way around, the other set on one end has part bent slightly up. Which goes on top and on bottom?

Also, what about the placement of the rings on the pistons? I heard just place the gaps 180 degrees from each other. Any opinions?
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Old 08-13-2007, 08:44 PM   #20
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Oil rings......

The one with the tab goes on the bottom, and the tab fits into the SINGLE hole that is drill out but DOES NOT GO THROUGH. But you have to place the separator first, because it has a back piece that the upper and lower ring go OVER.

Here is the damn trick I learned though with the middle piece. As far as I could tell, it was TOO BIG. Everytime I tried to get it to compress, it would pop out and try to overlap itself. So I cut off one section of it. How much is a section you ask? Press the ends together. Its like they butt up, out of sequence, right? I remove enough material via a grinder so that they once again butt up out of sequence. Should you do this? I really cannot see it making a difference. MY OPINION! And at least they fit now. What happens if you try to fit the piston, and the lower oil rings pop out is they get bent. Then you get bent and start swearing.....

The middle ring has a notch in it. It goes down (with the piston facing you.) The top ring, as far as I could tell, had no markings, so I just installed them.

The rings are SO FREAKING LOOSE, that I installed them, then did the 180% thing, and hoped for the best as I bet they move around a tad before they settle in.
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Old 08-14-2007, 09:15 AM   #21
fishheadback
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Thanks for the info reddevil. Good stuff to know.

I also came to the conclusion that the middle section of the oil rings is to big.

Any other opinions on this approach?

Quote:
Originally Posted by reddevil View Post
Oil rings......


Here is the damn trick I learned though with the middle piece. As far as I could tell, it was TOO BIG. Everytime I tried to get it to compress, it would pop out and try to overlap itself. So I cut off one section of it. How much is a section you ask? Press the ends together. Its like they butt up, out of sequence, right? I remove enough material via a grinder so that they once again butt up out of sequence. Should you do this? I really cannot see it making a difference. MY OPINION! And at least they fit now. What happens if you try to fit the piston, and the lower oil rings pop out is they get bent. Then you get bent and start swearing.....
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Old 08-14-2007, 12:50 PM   #22
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Originally Posted by reddevil View Post
...What happens if you try to fit the piston, and the lower oil rings pop out is they get bent...
Better still is when you fire it up that way. They make these nice, deep cylinder gouges, turning your air-pump motor into an oil-pump motor. I'm tellin ya', James Bond had nothing on me. No one within 1/2 mile could see a damn thing.
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Old 12-03-2007, 12:49 PM   #23
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Quote:
Originally Posted by reddevil View Post
Oil rings......

The one with the tab goes on the bottom, and the tab fits into the SINGLE hole that is drill out but DOES NOT GO THROUGH. But you have to place the separator first, because it has a back piece that the upper and lower ring go OVER.

Here is the damn trick I learned though with the middle piece. As far as I could tell, it was TOO BIG. Everytime I tried to get it to compress, it would pop out and try to overlap itself. So I cut off one section of it. How much is a section you ask? Press the ends together. Its like they butt up, out of sequence, right? I remove enough material via a grinder so that they once again butt up out of sequence. Should you do this? I really cannot see it making a difference. MY OPINION! And at least they fit now. What happens if you try to fit the piston, and the lower oil rings pop out is they get bent. Then you get bent and start swearing.....

The middle ring has a notch in it. It goes down (with the piston facing you.) The top ring, as far as I could tell, had no markings, so I just installed them.

The rings are SO FREAKING LOOSE, that I installed them, then did the 180% thing, and hoped for the best as I bet they move around a tad before they settle in.
Quote:
Originally Posted by fishheadback View Post
Thanks for the info reddevil. Good stuff to know.

I also came to the conclusion that the middle section of the oil rings is to big.

Any other opinions on this approach?
No, the middle section is too big when uncompressed. If you align it correctly, and compress it slowly, it compresses and fits. There is a lot of load on it, but once compressed (correctly) it seals up really nicely. It pops out if you do it wrong.

And yes I tried cutting out a section, but then the folks@godspeed talked me out of it and I bought a new set of rings (I have a ring set for 3 pistons taking up space if anyone wants them). When I pushed the pistons in the cylinder with the cut ring and the uncut ring, the compression/suction/resistance difference was big.

IMO, if you cut the ring, you will have oil burning issues. Mine had none even from day 1.

hth,

-C
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Old 12-03-2007, 08:33 PM   #24
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FYI, Mahle now makes 2618 pistons.
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