CP Pistons Bore Finish, Ring Gap, & Other Specs

[Stinger]

Bore finish, Ring Gap, & Ring Installation for our CP pistons with Gas Nitrided rings is here:
www.stinger-performance.com/Pics/cp_instructionsheet.pdf

Specifically:
GAS NITRIDED, CPN, CPN2 AND R8GNHD PISTON RINGS
To identify a gas nitrided top ring the entire ring will be a light gray. These instructions must be followed for maximum ring seal. A torque plate must be used unless the bolt holes are not part of the cylinder. The first stone is a 525 (220 grit) stone, done until there is .001” left from final bore. The bore must be round to .0002”, checked 360 degrees from the bottom to the top of the bore. Then switch to a 625 (280 grit) stone, 50% load until .0002” is left from final bore. Then use the 625 stone at 20% load to final bore size.

ALL RINGS
The honing must be done slow to minimize heat build-up. No hand honing. Final bore needs to be less than plus or minus .0002” out of round,
checked 360 degrees around the bore from the bottom to the top of the cylinder. This should be checked with a dial bore gauge. The expertise of
your machine shop is critical to the proper finish on your block bore. When you receive the block back from the machine shop it will appear clean,
the block still needs to be cleaned. There could be material trapped in the honing grooves of the block that are not visible. Failure to clean the block could lead to premature ring wear and blow-by.

For use with our CPN and CPN2 piston rings, we recommend plateau honing with a cylinder bore cross hatch angle of 30-40 degrees.



30-40 degrees

To reach this roughness, the manufacturers of honing machines and accessories recommend using for a gray cast iron engine block and Nikasil cylinders.
• Conventional stones #220 - #280 grit or
• Diamond stones #325 - #550 grit

After honing with either the conventional or diamond stone, the same manufacturers suggest to finish your honing by smoothing the surface with a fine grit conventional abrasive (#400 - #600 grit) or to sweep the bores with a flexible brush or a nylon bristle plateau honing tool. This is necessary to get rid of jagged peaks and folded or torn material.


Important Note:
Be sure to confirm with your honing equipment manufacturer that the recommended stone grit will produce the following Rz and Ra roughness recommendations.

Rz = 59 - 138 µ in [=1.5 – 3.5 µm] or
Ra = 15 - 35 µ in [=0.4 – 0.9 µm]

RING GAP:
CP recommends a turbo/nitrous top ring gap of .0055" x (bore size in inches). Example for a 2.3T: .0055 x 3.800 = .0209". Since 2.3T's run higher boost than most engines, CP recommends a bit larger than normal ring gap for 2.3T's that run high boost. They suggest .024" on the upper ring and .030 on second ring for a typical 2.3 bore size (.010 to .030" overbore).

RING ORIENTATION:


CP PISTON/RING FAQ:
www.cp-carrillo.com/Tech/FAQ/tabid/107/Default.aspx

PDF Version of info:
www.cp-carrillo.com/files/1-Landing%20Pages/Hardware/pdfs/cpcylinderhoning.pdf

www.cp-carrillo.com/ft-2468-rings.html

[antrep3]

hey i just put my engine together and when i was filing all the piston rings i did the math and chose .19 on the top and .20 on the bottom is that ok?

[Stinger]

Sounds pretty tight to me unless it's a real mild build.

[antrep3]

what do you consider high boost? i have my engine apart right now and i want to order a new set of rings. i want to run about 18 psi of boost. what ring end gap would be best ? also cant a larger ring end gap create blow by issues?

[Stinger]

Typically north of 20psi is high boost. Slightly more ring gap won't cause any extra blowby but will allow a safety margin if you want to bump up the boost in the future. Too little ring gap will end in disaster.

[antrep3]

ohh ok. have you ever heard of anyone having issuss with pistons rings in a cyl where the head gasket popped? i have some xtra rings just dont want to get this thing back together and find out the rings are worn down

[Stinger]

If there is a ring issue after a headgasket failure, it would either be from letting the water sit in the cylinder for weeks and rusting the ring to the bore, or from the detonation that killed the gasket also breaking the ring or lifting the ring land. It's rare though.

[antrep3]

ok. i have everything apart im gonna pull the piston out and make sure everything is ok

[sfish]

Since these pistons run tighter clearances and not standard "turbo clearance " do you know what the piston skirt to cylinder clearance recommendation is?

[Stinger]

I don't have any pistons sets here to view the spec sheet they come with currently. Every set comes with the sheet that covers ring gap and cylinder bore info.