CP Pistons and rings. 84mm bore = 3.307"
Earl (RIP) recommends .006 x bore = top ring gap and .0065 x bore for the second ring gap. That works out to be .020" top and .022" for the second ring.

Top rings had to be filed a bit which is good. But the second rings UNFILED are all .026"! Ring set is CPN3307 which is the right size. I checked the clearance of my old CP rings and the 2nd ring has a much smaller gap .022" like it should be - so its not a bore issue. I called CP and they said its "within tolerance". Thats comforting, why even have gap formulas then?

So whats the deal with these new rings? Should I reuse my old rings (1,000 miles on them) that have the proper gap or ask for new rings or just bite the bullet and use these rings with extra large gap?

 

I would get CP to send new rings....

Has the block been honed since the last run?

 

yes it was honed. i thought maybe it was honed too much so I put the old rings back in to measure and they still have their original gap.

 

Then you don't want to reuse your old rings....

I think a new full set of CP rings is like $90. Might want to save up to get new ones or have CP send you them since they are **** from the box.

 

CP is trying to tell me its because my bore is bigger than 3.307" which is probably true since I had it honed. But that would mean all the rings would be too big. And the top rings are within spec. Its only the second ring thats too big.

 

Recently, a lot of the 2nd ring CP's come .024"-.028" out of the box. I had a detailed discussion about this with earl months ago and the conclusion is this is just fine. The new designs allow for less pressure to accumulate between the two rings. I've used 5 or 6 sets since the new 'design' and they have all worked out just fine. Try out a .022"-.023" on your top instead of the .020"

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by PrecisionH23a &raquo;</TD></TR><TR><TD CLASS="quote">Try out a .022"-.023" on your top instead of the .020"</TD></TR></TABLE>

Just curious what your reasoning is behind this. I have a set of the newer (redesigned) CP's as well.

 

You want somewhat of a 'uniformity' in relation to the .006 and .0065 that you were using as a multiplier. In this case you'll be around .007 and .0075". I have some information reguarding this matter saved on my computer at home. I got into an extensive discussion reguarding this with John over at Race Engineering, Sean at ERL, as well as Earl. When I first got the rings I thought I was screwed as well, lol.

It's been so long ago the reasoning is not fresh in my head. I want to say something with emissions comes into play and something else I am forgetting... I've actually had them as wide as .0028x on a 88mm H23a motor. Again, piston to wall clearance can come into play as well. Sometimes you can mix and match between cylinders if you are off .000x according to your final cylinder bore.

 

Interesting Anthony....

Could you please share the info that you have at home regarding this matter?

I am curious on the emissions impact if there is one....

 

I have a little bit of information but nothing excessive like I thought I had.

From what I wrote down, basically the 2nd ring you want looser due to the pressure in between the two rings. Higher pressures will 'rattle' the top ring off the 'seat'. When going with a larger 2nd ring gap it will allow more pressure to divert downwards towards the crankcase area. Going with a larger 2nd ring-end gap will reduce blowby and in new cars they are running looser 2nd ring-end gaps for better emmissions.

Date on file 7/13/04 Much older than I thought, lol. But if I recall correctly, it was sometime early last year when I noticed the CP 2nd rings being on the looser side.

 

when I did my ring gap calculations, I used CP's recommendation, which was .0065 to .007 multiplier on the top ring and .007 to .008 on the bottom ring.

I just averaged the high and low and ended up with .0223 on the top ring and .0248 on the bottom ring with my bore (81.5) Most people think that's too big of a gap, but I haven't had any problems, plus I feel safer with a bigger gap since I'm boosting on stock sleeves.

I plugged in your bore (3.307) and if you use .008 as a multiplier, the gap comes out to .026456, so technically CP is right..it is within spec.

Honestly, I wouldn't worry about it.

 

Its "barely" in spec for a high boost motor. What would I do if it was a NA motor? The ring would be way out of spec.

Ive been talking with CP about this matter. They told me the out of the box tolerance for the top ring is from .010"-.014", the 2nd .018-.022" UNFILED. They want me to believe my bore is larger than 3.307" to explain why my second rings are larger than the tolerance. But the same would be true for the top rings and it is not. My top rings are all .014" unfiled.

I also asked CP about the "ratio" between the top and second ring gaps and they didn't give me a good answer. I know the second ring gap is supposed to be larger than the top ring but how much larger? And if my second rings are bigger than I want does that mean I should open up the top ring gaps to keep a similar ratio?

 

Up until about six or seven years ago the accepted way of gapping ring was to gap the second ring about half of the top ring.The thought was that the second ring saw alot less heat than the top.Then some clever builder found more power opening up the second ring gap.Now that's the accepted way.
Piston manufactures follow the advice and trends of builders,they are not innovators.If builders said tomorrow that four rings were better than the pistons would all have four rings.Like I've said before don't beat yourself up over a little more ring gap.Other wise try another ring supplier and sell off or return the ones you have.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Muckman &raquo;</TD></TR><TR><TD CLASS="quote">Its "barely" in spec for a high boost motor. What would I do if it was a NA motor? The ring would be way out of spec.

Ive been talking with CP about this matter. They told me the out of the box tolerance for the top ring is from .010"-.014", the 2nd .018-.022" UNFILED. They want me to believe my bore is larger than 3.307" to explain why my second rings are larger than the tolerance. But the same would be true for the top rings and it is not. My top rings are all .014" unfiled.

I also asked CP about the "ratio" between the top and second ring gaps and they didn't give me a good answer. I know the second ring gap is supposed to be larger than the top ring but how much larger? And if my second rings are bigger than I want does that mean I should open up the top ring gaps to keep a similar ratio?

</TD></TR></TABLE>

Maybe as a sanity check you should check your bores with a bore-mic. I ended up buying my own bore mic and high accuracy (.0001") micrometer just to make sure my bore is what I intended it to be.

I think that the reason CP is being vague about the gap ratios is because they haven't done enough research to quantify what ratio is acceptable...it's a 'dark' science..and we are the frontiers

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Muckman &raquo;</TD></TR><TR><TD CLASS="quote">Its "barely" in spec for a high boost motor. What would I do if it was a NA motor? The ring would be way out of spec.
</TD></TR></TABLE>

Very true. I'll let you know when I get a block back from ERL in the next few weeks. We went with custom 90mm CP 12.5:1 pistons and rings. So... we'll see if there is a difference between NA and turbl0w.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Mr. Helsinki &raquo;</TD></TR><TR><TD CLASS="quote">when I did my ring gap calculations, I used CP's recommendation, which was .0065 to .007 multiplier on the top ring and .007 to .008 on the bottom ring.

I just averaged the high and low and ended up with .0223 on the top ring and .0248 on the bottom ring with my bore (81.5) Most people think that's too big of a gap, but I haven't had any problems, plus I feel safer with a bigger gap since I'm boosting on stock sleeves.

I plugged in your bore (3.307) and if you use .008 as a multiplier, the gap comes out to .026456, so technically CP is right..it is within spec.

Honestly, I wouldn't worry about it. </TD></TR></TABLE>

so would this be a good gap to run on my 81.5mm bore with ross rings aswell?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by snowbunny &raquo;</TD></TR><TR><TD CLASS="quote">

so would this be a good gap to run on my 81.5mm bore with ross rings aswell?</TD></TR></TABLE>

I did some research when I was shopping for pistons. According to Ross, they show .004" multiplier for the top ring and .005" for the second ring. (funny that they don't show a range..i.e. high and low like CP does.)

So with an 81.5mm bore (3.209") that would give you a top ring gap of .0168" and second ring gap of .0200"

What that tells me is 2 things?:
1.) Ross rings (whatever brand they use) don't expand as much as CP rings (whatever brand they use)
2.) Ross pistons don't expand as much as CP pistons

or that both companies have their heads up their asses and just give you random multipliers

I went with CP strictly based on reading Earl's threads and the information on CP's website.

Muckman..sorry for drifting a bit off topic on this.

 

ok so would it be a big deal if i run lil bigger gaps then what ross tells me?...what would this cause? oil burning? alot of blow by?

 

NP Jan. This is all good ring gapping info.

My next question is gap consistency. Say 3 of my second rings measure .026 and one is .025. Should I make them all the same at 26?

 

I set all of mine to uniform. If you are off by .001 it's not going to be the end of the world though.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Muckman &raquo;</TD></TR><TR><TD CLASS="quote">NP Jan. This is all good ring gapping info.

My next question is gap consistency. Say 3 of my second rings measure .026 and one is .025. Should I make them all the same at 26?</TD></TR></TABLE>

I would make them all the same. That way no cylinder has a chance to see anything different while running. It makes the motor uniform.

 

If you were to go looser on any cylinder, go looser on numero 3.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by PrecisionH23a &raquo;</TD></TR><TR><TD CLASS="quote">If you were to go looser on any cylinder, go looser on numero 3.</TD></TR></TABLE>

I don't think that is necessary in todays world. Tuning individual cylinders is possible with the right EMS so you would want them all the same.

 

I know... I'm just saying. With individual cylinder trim for fuel you can increase fueling to 3 so that theoretically you can cool it down a bit.

 

Has anybody actually built or tuned a motor that had too small of a ring gap where the ring ends touched? I suspect that CP's ring gap recommendations are very converative and thats why Earl recommended .006 (top) and .0065 (2nd) x bore. Anymore being safe but not nessecary?