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Old 03-15-2006, 02:29 PM   #1
sonic rx
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Default clearance. Clarence

what is the min and max piston clearance on a new 2.5l sti motor with cp forged pistons. stock bore,or over bore?
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Old 03-15-2006, 03:18 PM   #2
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Quote:
Originally Posted by sonic rx
what is the min and max piston clearance on a new 2.5l sti motor with cp forged pistons. stock bore,or over bore?

.0035" regardless of bore. Better to go .0005" larger than too tight.

Next time, use the search key...this issue has been beat to death.

S.
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Old 03-15-2006, 03:22 PM   #3
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What about contacting CP to see what they recommend?
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Old 03-15-2006, 03:24 PM   #4
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Quote:
Originally Posted by 8Complex
What about contacting CP to see what they recommend?

Or THAT.

S.
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Old 03-15-2006, 04:04 PM   #5
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I thought it was .004 per inch of bore!!! Check the spec sheet that came with the pistons!!!
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Old 03-15-2006, 05:04 PM   #6
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Quote:
Originally Posted by Pacobeagle1
I thought it was .004 per inch of bore!!! Check the spec sheet that came with the pistons!!!

I believe you're thinking of ring gap, which is still, a rule of thumb

S.
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Old 03-15-2006, 05:25 PM   #7
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On standard piston rings a high boost engine should have .006" per inch of bore.
On our Subarus using factory subaru rings (these rings expand alot less) .004" is a good multiplyer to use.
Pistons have nothing to do with ring gaps.

If you are talking about piston to sidewall clearance .0035" - .004" should apply to CP pistons. Depending on the power level, boost, cylinder pressure, nitrous, etc. etc. all these things add heat.
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Old 03-15-2006, 08:09 PM   #8
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Run what the piston manufacturer recomends unless you are Phil of Element Tuning and then you can do the impossible

Based on my experience .0035 for CP Pistons is generous up to 550 whp. If you have a bad tuner .0050 is still to tight

Phil
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Old 03-15-2006, 08:16 PM   #9
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Quote:
Originally Posted by n2xlr8n
.0035" regardless of bore. Better to go .0005" larger than too tight.

Next time, use the search key...this issue has been beat to death.

S.
that it has ,but i am doing this to my car now,and thus most of the posts are a bit older,and i want a current answer. so there is no doubt

the cp pistons recommend .003 -.0035. just seeing what other people have had luck with thanks for all the replies
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Old 03-17-2006, 04:11 PM   #10
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I went with the minimum clearance from what Wiseco told me to use. I used the .0035" min and they're just a little noisey for like the first minute on a cold start and then they get quiet quickly.

If CP says .0030 as minimum then don't go any lower than that for sure - unless you're looking for problems down the road
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Old 03-17-2006, 10:23 PM   #11
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Quote:
Originally Posted by sonic rx
what is the min and max piston clearance on a new 2.5l sti motor with cp forged pistons. stock bore,or over bore?
.0035" for the minimum and .0045" for the maximum

For what its worth, CP pistons are designed to run .0035" of clearance

Quirt Crawford
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Old 03-18-2006, 12:39 AM   #12
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Quote:
Originally Posted by tmarcel
I went with the minimum clearance from what Wiseco told me to use. I used the .0035" min and they're just a little noisey for like the first minute on a cold start and then they get quiet quickly.
Wiseco told me .0030" for my coated pistons Are yours coated?

I had CP's for a few weeks in my motor at .0035" and they were noisy. If I used them again I would go .0030".
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Old 03-18-2006, 08:59 AM   #13
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no they are not coated. i just dont want a ton of slap thats all


quirt

i am sure you have used these on several occasions. what is you input on the amount of slap you get with cp pistons,and how long do they last?last question ... do these pistons have alot of blow by?
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Old 03-18-2006, 09:36 AM   #14
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Quote:
Originally Posted by Javier
Wiseco told me .0030" for my coated pistons Are yours coated?

I had CP's for a few weeks in my motor at .0035" and they were noisy. If I used them again I would go .0030".

I don't think I mentioned above that these are custom, not off-the-shelf pistons. They had it on the spec card stating min. PW cler @ .0035". I asked them if I could go .0030 and they said that it wasn't recommended for my particular piston. Not sure why though as the design is nearly the same as their regular piston except this one is 40 over stock (100.5mm) and the dish was changed to reflect a 2L WRX cyl head and CR @ 8.4:1. Go firgure huh!
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Old 03-18-2006, 12:19 PM   #15
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Tmarcel, mine aren't off-the-shellf either... 100.5mm with 8.7:1 CR dish with 2.0L heads (V7 sti heads). Not too different from yours. I'm gonna have to call wiseco and confirm everything.
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Old 03-18-2006, 01:42 PM   #16
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Quote:
Originally Posted by sonic rx
no they are not coated. i just dont want a ton of slap thats all


quirt

i am sure you have used these on several occasions. what is you input on the amount of slap you get with cp pistons,and how long do they last?last question ... do these pistons have alot of blow by?
Sonic,

The amount of slap you will get from your CP pistons will depend on where you purchased them from, how long ago they were made (what revision), your final bore size and how they are installed. Properly installed forged pistons will last longer than the rings or the bearings in your motor

As for blow by, when forged pistons are up to temp, the increase in blow by will be minimal as long as they fit the bore properly.

For what it's worth, the pistons we sell at Crawford Performance are not dimensionally the same as the pistons that CP sells. Our latest version has so little slap that we no longer get any complaints from our customers

Quirt Crawford
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Old 03-18-2006, 04:34 PM   #17
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Default

Quote:
Originally Posted by Crawford Performance
Sonic,

The amount of slap you will get from your CP pistons will depend on where you purchased them from, how long ago they were made (what revision), your final bore size and how they are installed. Properly installed forged pistons will last longer than the rings or the bearings in your motor

As for blow by, when forged pistons are up to temp, the increase in blow by will be minimal as long as they fit the bore properly.

For what it's worth, the pistons we sell at Crawford Performance are not dimensionally the same as the pistons that CP sells. Our latest version has so little slap that we no longer get any complaints from our customers

Quirt Crawford
Crawford Performance
i believe everything is current ( new sti short block from subaru,and new pistons from cp). it is a new sti short block from subaru with forged cp sc7420 stock bore forged pistons installed. they said clearence is what is called for by cp.
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Old 03-18-2006, 07:04 PM   #18
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Quote:
Originally Posted by Javier
Tmarcel, mine aren't off-the-shellf either... 100.5mm with 8.7:1 CR dish with 2.0L heads (V7 sti heads). Not too different from yours. I'm gonna have to call wiseco and confirm everything.

Very odd and I remember our conversation now Definitely call them to confirm though. I'll be pissed if I could've gone with .0030 vs the .0035 that I went with. Honestly, I am happy with the .0035 except for the first couple or so minutes until they expand/heat up. They very quite once warm.
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Old 03-18-2006, 08:01 PM   #19
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tmarcel - what turbo are you using? is it a twinscroll gt32?
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Old 03-25-2006, 06:02 PM   #20
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tmarcel, I got the pistons from wiseco and they came with a spec sheet specifying .0030" clearance...
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Old 03-25-2006, 06:55 PM   #21
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Quote:
Originally Posted by Crawford Performance
For what it's worth, the pistons we sell at Crawford Performance are not dimensionally the same as the pistons that CP sells. Our latest version has so little slap that we no longer get any complaints from our customers

Quirt Crawford
Crawford Performance
Quirt what clearance do you run on your pistons??
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Old 03-25-2006, 08:58 PM   #22
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Quote:
Originally Posted by Crawford Performance

Our latest version has so little slap that we no longer get any complaints from our customers

Quirt Crawford
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LIES!!!! You'll have to send me some to prove it!
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Old 03-27-2006, 11:33 AM   #23
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Quote:
Originally Posted by nxttruck2002
Quirt what clearance do you run on your pistons??
We run .0035" clearance on the 3.9175" bore pistons

Quirt Crawford
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Old 04-07-2006, 11:44 AM   #24
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Would you say the same for a 3.8155" bore?
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Old 04-07-2006, 12:10 PM   #25
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Quote:
Originally Posted by TyranosaurusWRX
Would you say the same for a 3.8155" bore?
Three and a half thousands are very safe for the 2.2 bore, although you could run them a tad tighter.

Quirt Crawford

Crawford / I-Speed
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