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b18c_ferio
01-09-2006, 09:31 PM
i have 86.5 cp pistons waiting to be installed in to my sr20.. cp recomends a bore of 3.406 with piston to bore clearance being .0035. here's the problem, im measuring 3.4055 in one cylinder all the others come to 3.406. do i need to go out to 87mm or is the 3.4055 cyl safe (im thinking NOT)

b18c_ferio
01-09-2006, 09:34 PM
what im asking is is running a clearance of .0030 going to make a big difference?

hybridynamics
01-09-2006, 10:34 PM
i have 86.5 cp pistons waiting to be installed in to my sr20.. cp recomends a bore of 3.406 with piston to bore clearance being .0035. here's the problem, im measuring 3.4055 in one cylinder all the others come to 3.406. do i need to go out to 87mm or is the 3.4055 cyl safe (im thinking NOT)



you wouldn't need to go to 87MM, only need to hone it a slight bit to 3.406

ItzGenX
01-09-2006, 11:48 PM
what im asking is is running a clearance of .0030 going to make a big difference?





I am running .0030 on mine with no problems with piston slapping etc. The engine on a cold start actually sounds like a regular stock piston SR. I find the CP's don't expand as much as the Wiseco units. I forgot the clearance that Wiseco called for, but my friend's motor definitely isn't quiet on cold start. On one of my previous inspection tear downs of my motor to monitor breakin of the motor, the pistons didn't show any real signs of skirt scrapes or anything. That was about 6k miles ago. I also run CP pistons, but they are 87mm instead of 86.5.

SRFiveTen
01-09-2006, 11:58 PM
On one of my previous inspection tear downs of my motor to monitor breakin of the motor, the pistons didn't show any real signs of skirt scrapes or anything.


dear estevan,
quality in their workmanship was main reason for recommending cp.
i'm pretty sure scott felt the clover-leaf design in the skirts!

b18c_ferio
01-16-2006, 06:38 PM
something interesting i found on another web site....

WHY DID MY TURBO MOTOR BLOW UP?

-You boosted for more than like 15-20 second straight in high gear at high boost. Well, you might say your air/fuel ratio is good, but that means nothing over the long haul. Every second you boost that motor, the motor gets hotter and the cylinders get way hotter. After a certain amount of seconds, the piston will start expanding because that’s what aluminum does when it gets hot. Why do you think the piston companies have a little thing in the box that says something like this “Suggested clearance .003, but certain applications like forced induction might require .0035 or greater” Something like that. So you install your turbo pistons at .003. That’s ok with Wiseco at low boost levels, and if your not going to boost for long periods of time. I have used that, its ok with the proper care. But it’s a good idea, to add a little more clearance to the motor for safety. That way it can take more time in boost without hitting and scuffing the walls. If you start burning oil all of a sudden and are adding a quart a week or something, you probably scuffed the walls and are burning oil. You overheated the pistons.

ItzGenX
01-16-2006, 07:36 PM
I've boosted the living sh!t out of my motor on long interstate runs and countless drags. Correct tuning and supporting mods help the engine stay alive at high performance levels. If you use a stock cooling system with 500whp, then yes, that statement stands absolutely true. However, if you have everything required to handle such thermal stress and cool things down efficiently, you shouldn't run into many problems to begin with.

That little Q&A is only right to a certain extent. Different piston manufacturers make their pistons out of different alloys and silicon content. This calls for different expansion rates. Even so, they give certain clearance specs in general. They don't know if this piston is going to be in a aluminum block with 8mm thick iron sleeves. A aluminum block with 3mm steel sleeves will expand differently with the heat then the one with 8mm iron. The clearance spec sheet is more of a neutral number that should still have clearance under heat with various different block materials. The point all comes down to if the manufacturer counted in this factor and calculated based upon different engine configurations or just plain copied a stock piston out of X alloy. The best thing for them to do is find the best balance between a high strength alloy and a low expansion rate. When the low expansion rate is found, it is possible to have the piston barely expand faster then the block/bore expands so that the clearance almost stays the same the whole time or grows into the perfect clearance.

Scuffing can be caused by more then just too low of a clearance. It can be caused by a fractured piston ring, oiling problems, overheating, bore wash, too high of a clearance, and probably a few others I can't think of right now.

b18c_ferio
01-16-2006, 10:18 PM
this was pertaining to a honda engine b20/18/17/16..just found
it interesting