what is the min and max piston clearance on a new 2.5l sti motor with cp forged pistons. stock bore,or over bore?

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.

What about contacting CP to see what they recommend?

What about contacting CP to see what they recommend?


Or THAT. :lol:

S.

I thought it was .004 per inch of bore!!! Check the spec sheet that came with the pistons!!!

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.

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.

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 :lol:

Phil
www.elementtuning.com

.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 :D

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 :lol:

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
www.crawfordperformance.com

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 :confused: 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".

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?

Wiseco told me .0030" for my coated pistons :confused: 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!

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.

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 :D

Quirt Crawford
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 :D

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.

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.

tmarcel - what turbo are you using? is it a twinscroll gt32?

tmarcel, I got the pistons from wiseco and they came with a spec sheet specifying .0030" clearance...

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 :D

Quirt Crawford
Crawford Performance
Quirt what clearance do you run on your pistons??

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

Quirt Crawford
Crawford Performance

LIES!!!! :furious: You'll have to send me some to prove it! ;)

Quirt what clearance do you run on your pistons??

We run .0035" clearance on the 3.9175" bore pistons :)

Quirt Crawford
www.crawfordperformance.com

Would you say the same for a 3.8155" bore?

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

Alright, thanks.