Just wanted to hear engine builders thoughts are on gapping CP rings. Theres a million archived threads about this but they are using old ideas where the 2nd rings had a smaller gap than the top ring. Now the reverse is common.

For F/I CP recommends bore x .0065/.007 for the top ring and bore x .007/.008 for the 2nd ring. Those seem very conservative to me.

 

The original thought on second ring gaps was since they are exposed to less heat they will expand less.But after years of testing it was discovered that the pressure build up between the top and second ring lifted the top ring off the ring land.This allowed compression to get around the back of the top ring and loose ring seal.A larger second ring gap allowed the pressure to equalize and allow the top ring to seal better.The second ring is designed more as an oil scraper ring than a compression ring nowadays.Power loss of a slightly wide gap is almost undetectable.But if the gaps touch because of heat will usually break the piston and ruin the cylinder walls.I go a little big on the gaps if I feel there is a chance the engine may be run on the lean side (high cylinder temps).
Glenn

 

That was very informative thank you. What formula do you use for gapping?

 

I went .018 top and .020 2nd on my 84mm gsr and it is perfect...doesnt burn a drop of oil or smoke at all and made over 600 hp

 

Wow thats really tight! Ive never seen anyone use less than bore x .006 and your even tighter than that.
3.307 x .006 = .0198 ring gap"

Have you ever removed the head and inspected the cylinder walls?

 

no i havent but im sure it would smoke if they were damaged...as long as it has the proper piston to wall clearence and is tuned I dont see a problem....your talking about extremely small amounts ...

 

I built an 82.5mm b18c1 with CPs and went really big on both top and 2nd. I think it was like .023" and .026". The motor has about 10k on it now and I re-tuned it to 370whp a month ago. No oil consumption and perfect compression so far.

 

Mike is in Detroit at GM/Rouch Racing taking a class in building Ecotec race engines and transmissions. He told me that GM runs .005-6" piston to wall clearance and .0026" on all their bearing clearances. Ring gaps were quite large also. I guess there is more than one way to build these things and still be right

 

For conservative builds (around 400whp) I typically use .017 top and .019 on the middle for the H series that I do.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by earl &raquo;</TD></TR><TR><TD CLASS="quote">I guess there is more than one way to build these things and still be right </TD></TR></TABLE>

Im starting to believe that too. Im going to run a .022" top and .025" bottom on my 84mm motor.

Im curious to find out how large ring gaps will affect compression test results, blow by and oil consumption.

Earl do you have any pics of butted rings? I think the scuffing in my previous motor was caused by the rings butting together. CP thinks it was caused by fuel wash but I know that was impossible.

 

its interesting also to look at the allowable range of end gap on stock honda rings. Its pretty large if I remember correctly. For turbo hondas it seems like if it starts with a .02 then it cant really not work

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Muckman &raquo;</TD></TR><TR><TD CLASS="quote">Earl do you have any pics of butted rings? I think the scuffing in my previous motor was caused by the rings butting together. CP thinks it was caused by fuel wash but I know that was impossible. </TD></TR></TABLE>Did you send your rings to CP also? They normally check the ring ends for butting with a microscope. However, in either case you get the same results...not enough oil on the cylinders to keep the pistons lubricated.

 

Yeah but he doesnt remember if they butted or not. I asked him after the fact.
My rings were gapped rather tight for an 84mm motor (.019" top, .021" bottom).
You have to run insanely rich to wash out rings and I run a full time wideband and the motor never saw richer than 11.8:1 AFR.

 

I doubt you butted ring ends with a .019" upper gap.
My problem is I do not believe a/f gages when the results show something different.

 

earl what gap you think is good for a street motor 82 mm cp pistons and like 450whp..

 

I use .019" upper and .021" middle

 

Earl what ring gaps would you recommend for a 81.5 Bore CP 9:1?

 

^^^^ bump cause i would like to know since i am having problems with my pistons... they seem to have some play which i dont like... and i am goign to measure the clearance......

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by EK_GSR &raquo;</TD></TR><TR><TD CLASS="quote">^^^^ bump cause i would like to know since i am having problems with my pistons... they seem to have some play which i dont like... and i am goign to measure the clearance......</TD></TR></TABLE>

who did the bor e and hone on your motor? i hope it wasnt street and strip

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by earl &raquo;</TD></TR><TR><TD CLASS="quote">Mike is in Detroit at GM/Rouch Racing taking a class in building Ecotec race engines and transmissions. He told me that GM runs .005-6" piston to wall clearance and .0026" on all their bearing clearances. Ring gaps were quite large also. I guess there is more than one way to build these things and still be right </TD></TR></TABLE>

I'm sure that works on a big sloppy american motor in which case the looser the motor the stronger. that's according to my V8 builder buddies. however our motors have so much precision throughout...

hmm I wonder how a honda motor will work if it's built loose like a V8?

 

The rings that I got were all the same part number but not consistent at all. some were way bigger unfiled than the recommended gaps are. Wtf? Is consistency important? Id assume so.

For instance they call for a minimum of .015" on the oil rings. 3 sets are .017" which is perfect but 1 set of oil rings are .026" unfiled!! thats huge! so should I make them all .026 or what?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Muckman &raquo;</TD></TR><TR><TD CLASS="quote">The rings that I got were all the same part number but not consistent at all. some were way bigger unfiled than the recommended gaps are. Wtf? Is consistency important? Id assume so.

For instance they call for a minimum of .015" on the oil rings. 3 sets are .017" which is perfect but 1 set of oil rings are .026" unfiled!! thats huge! so should I make them all .026 or what?</TD></TR></TABLE>

thats weird. I would check your bore size/taper/round.

 

I did. Engine shop said it was perfect. Its these gay rings.

My middle rings were huge too unfiled. Recommended gap for middle ring on my bore 3.307" is .0231 - .0264" and this is their most conservative F/I recommendation. 3 of the middle rings were .024" unfiled and one was .025" so I made them all .025. If this was a NA motor, it would be way out of spec.

 

Gap not critical for oil rings, just as long as they don't overlap. Don't file them ever. You will wreck them.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by turbosi03 &raquo;</TD></TR><TR><TD CLASS="quote">

I'm sure that works on a big sloppy american motor in which case the looser the motor the stronger. that's according to my V8 builder buddies. however our motors have so much precision throughout...

hmm I wonder how a honda motor will work if it's built loose like a V8? </TD></TR></TABLE>

The Roush Ecotec Earl is referring to is far from a sloppy american engine.Don't confuse precision with tight.Proper clearance is not a matter of loose or tight,just correct.

And Muckman... The oil ring sees little heat and does not expand much.Anywhere from .010 to .040" is fine.