I have a set of Sealed Power file fits for my .060 454(4.310)and as this is a street-strip weekend basher I was going to run a 150 hit of spray thru it.
I have seen the new trend toward a larger second ring gap and it make sense to go there IMO but the recomendations on the ring gaps are so conflicting that I thought I would toss it out here and see what comes up!
Thanks all.

One of the primary reasons builder's use a larger gap on the secondary ring is to control/reduce ring flutter. Ring flutter happens when the top compression ring releases from the ring land near TDC as the piston reverses directions. By gapping the second ring larger you help to reduce the gas pressure that is built up between the compression rings during the compression/power stroke. These gasses get behind the top ring and through the ring gap and work their way toward the second compression ring and seal the second ring to the bore. As pressure builds at the second compression ring gasses are redirected towards the top ring causing the ring to be lifted off the ring land. There is some evidence that a wider second ring gap also helps to keep oil in the crankcase of an engine. Some leakage at the second ring helps to push oil back down the cylinder and helps keep the air/fuel mixture cleaner. In addition to a wider second ring gap, some race engine builders use gas ports either in the cylinder bore or in the piston ring land. These are small holes (.050-.060) that are drilled to allow the gas to collect relieving pressure from the top ring. Another option is what's called an accumulator groove. This is a groove that is cut in the piston between the compression ring lands that provides the same benefit. These options are prolly only useful on max effort racing engines.

There are other factors that can cause ring flutter including too much vertical ring gap and/or excessive ring mass. Many builders are using smaller rings to reduce ring mass. Factory BBC rings are 5/32. Most aftermarket piston manufacturers sell performance pistons which use 1/8" compression rings. Dyno testing has proven that lighter rings make more power but may not provide as much longevity. I think some engine builders have even gone to a .043" compression ring.

I'm in the process of rebuilding my engine. Previously the rings were gapped at .020 top and .018 bottom. I plan to use a wider second ring gap this time. One thing with nitrous engines is to make sure there is adequate ring gap as the cylinder pressure/temps are higher and not having adequate ring gap will cause the ends of the ring to butt against one another resulting in engine failure. A general rule of thumb is to allow .004" end gap per inch of bore diameter for N/A engines. Looser is generally better/safer for max effort racing engines (including bearing clearances). Nitrous engines will require much more gap due to the cylinder pressure/temperature created by the incoming mixture (.030 or more). Check with your ring manufacturer for specific recommendations smile.gif

HTH...

Haha, I see I'm not the only one confused on ring gap recomendations. I've seen many top engine builders going back to the old rule on tighter second ring gaps. If both gaps were set at equal wouldn't it just make sense that the top one will be much smaller under actual running conditions because it is subjected to more heat? The last engine I assembled we gapped them tight- smallblock .014 top .012 second. Another engine I built with .018 top and .022 second and it seems to pollute the oil fast. Good seal though 180psi with no oil burning issues but the extra blow by through the end gaps pollutes the oil. ??????????????????????????????

Originally posted by baddbob71:
Haha, I see I'm not the only one confused on ring gap recomendations. I've seen many top engine builders going back to the old rule on tighter second ring gaps. If both gaps were set at equal wouldn't it just make sense that the top one will be much smaller under actual running conditions because it is subjected to more heat? The last engine I assembled we gapped them tight- smallblock .014 top .012 second. Another engine I built with .018 top and .022 second and it seems to pollute the oil fast. Good seal though 180psi with no oil burning issues but the extra blow by through the end gaps pollutes the oil. ?????????????????????????????? BadBob,

This is interesting... When you say "Good seal though 180psi" I assume you did a leakdown test/cranking compression test? If so, as you know that doesn't really help tell us what's happening when the engine is under load. What conditions (RPM/application) was this engine ran under? How was the tune up on the engine (rich/lean)? Do you run an airfilter on the engine? There are a number of things that affect ring seal including type/material of ring, ring gap, bore finish, roundness of the bore, etc... (in addition to what I pointed out earler). Did you measure the piston/skirt/bore when assembling the engine? What were the other tolerances (piston/bore)? What type of pistons? There are sooooo many variables that come into play smile.gif

When ring manufactures such as Speed Pro and others suggest a change in gaps you can rest assured it`s due to extensive research all across the board.
Be it a 4 cyl or 12 cyl.
They have the corporate $$$ and time, I`d take their word for it.

BadBob,

This is interesting... When you say "Good seal though 180psi" I assume you did a leakdown test/cranking compression test? If so, as you know that doesn't really help tell us what's happening when the engine is under load. What conditions (RPM/application) was this engine ran under? How was the tune up on the engine (rich/lean)? Do you run an airfilter on the engine? There are a number of things that affect ring seal including type/material of ring, ring gap, bore finish, roundness of the bore, etc... (in addition to what I pointed out earler). Did you measure the piston/skirt/bore when assembling the engine? What were the other tolerances (piston/bore)? What type of pistons? There are sooooo many variables that come into play
The cranking test provided 180psi, no leakdown test was done. The engine sees a variety of loads at different rpms to 6500. The tune was good according to what my plugs say :D , I always run an airfilter, speedpro moly rings, honed with deckplate with 400 grit finish, .0025 piston to wall clearance-speedpro hypertectic pistons all were measured. Cylinders measured perfect with a dial bore gauge.

Have you seen the tests speedpro did? The graphs show no improvement untill well over 7000 rpms. I just don't think the wide second gap is a proven deal yet, I think the best setup will have the top ring at .001 in running conditions (hot) with second ring gap just large enough to easily bleed off any pressure that gets past the top ring. Gaps that are excessively large are just pissing contaminants into your oil and costing power. Hell, open them up to .030 top and .040 second and see how much power is made. JMO

Thinking on piston ring gaps has also changed. In the OLD days, second ring gap specs were tighter than those for top rings because they didn’t see as much heat. But this didn’t account for inter-ring gas-pressure buildup between the top and second rings. If the pressure between these rings equals or exceeds the pressure above the top ring, it can cause the top ring to lift off the bottom of the piston ring groove and lose contact with the sealing surfaces. It also inhibits the ring’s ability to transfer heat from the piston. To keep inter-ring pressure from becoming a problem, the current trend is to create an easy escape path for the built-up pressure by gapping the second ring larger than the top ring. Another benefit is that because gas pressure is now directed downward towards the sump, any oil that has collected in the ring pack areas will go with it. (FOUND THIS WRITE UP FROM SPPED PRO) this is new to me i always put the second ring smaller...mike


:eek:

This is getting interesting folks but I still dont see a clear answer! Oil contamination versus mixture contamination....well I know every big overlap cam I have used has always been prone to gassing up the oil fast so I just change the oil more often. As Kjett mentioned leakage at the second ring helps to push oil back down the cylinder and keeps the air/fuel mixture cleaner and that is a prime consideration!
I think the equall gap/more heat related top ring expansion thus leading to a tighter top gap theory justfies looking into as it seem possible although hard to confirm.
Keep it comming. I have wondered also if anyone has checked thier ring gaps after they have had a season on the motor and if so how much more gap was seen from wear?
Thanks all!

Then, of course, there are the marketing claims of MORE POWER from special "gapless" second rings. But now that company is selling "gapless" top rings, too.

Beats me. I'm mighty curious about the whole deal.

To my way of thinking, if the top ring is gapped properly, it'll expand so there's almost no gap at max power. Considering the heavy gas pressure loading of the top ring, you'd think there'd be little leakage. Even a conventionally gapped second ring "should" leak enough to relieve any inter-ring pressure.

But then, I don't have a zillion dollar research department, either.

Vertical ring gap is often overlooked and is a source for leakage in addition to ring end gap.

We just pulled a friends 5.0 litre factory forged piston mustang motor down over the weekend and as it had 50 thousand miles on it.
I thought I would check the ring gaps and see where they were now.
Quite a suprise to see .031 thou on the top ring on average and .028 thou on the second ring.
I am assuming that most of this large ring gap came from wear as I dont think the factory gap would be anywhere near that large!
This has again made me question the large recomended ring gap installation numbers(for steet srtrip use) as I think there could be a .005 gap gain after running it for a season.
Has anyone put a feeler guage on a used set of rings that they had installed at a "known" gap to see how much gap was gained over a season due to wear?
Thanks all!

I think you need to take ring gap suggestions into consideration based on the fact the piston and ring manufacturer's do not want you to have any failures if the engine sees some use at above normal operating temps. You can bet the top nascar teams and top performance engine builders have done some deep testing on what works for a given combination, Maybe they experiment gapping them tighter and tighter till the rings butt and power falls off- then increase the gaps by .002 or so? One of the mags did a test in the exact same way and the engine made more power every time they closed the gap till the ring ends butted. I'm sure ring height in relation to piston top and also piston materials also factor into what gap works best. One of my Smokey Unick books states-don't go less than .003 per inch of cylinder bore- which translates to .012 for a 4 inch bore- .004 tighter than the general recomendation of .004 per inch of bore. Interesting stuff for sure, I wonder how much power is left on the table in most people's combos.

baddbob- I was trying to co-relate the .028 suggested ring gap that the manufacturer suggests for N2O use and the increase in gap that I may see with normal break-in and wear.
I would hate to think I would end up with a .034 ring gap or more by the end of the cruising season!
I am hoping to hear what works well for a 10,000 mile a year type muscle car.
Thanks.

in my bbc's i run gaps between .019" and .022" no matter what i have built. i have ran 150 hp nitrous on a regular basis on a few of my bbc with no ill effect. no sign of butting or breakage. and just in case your wondering this goes for both top and second ring.

i dont get into the "it has to be this" ordeal. i build them and run the **** out of them and it works.

engines have sealed very well and even with my 468 it pushes the compression gauge to 270 psi with 13.5 to 1 compression.

so thats what i run and dont think twice about it. because it works for me.

How bout ring widths with NOS? One of my books suggests running the standard width 5/64" rings with NOS, not 1/16 or .043, to better cope with the heat generated.

Baddbob-The increased frictional losses with the thicker ring just does not appeal to me.
What about the gapless rings for N2O?
A bit pricey but they seem to be a best of both worlds solution.
Has anyone tryed them out?

Originally posted by 67johnny:
Baddbob-The increased frictional losses with the thicker ring just does not appeal to me.
What about the gapless rings for N2O?
A bit pricey but they seem to be a best of both worlds solution.
Has anyone tryed them out? =
I do not use or recommend gapless rings at all any more.
As for the Total Seal ones, every engine I have ever taken apart that had them had at least one & usually more of the gaps lined up.
Every performance engine builder I know advises against them.
I advise against them.
I have seen absolutely no gains except for the static leakdown numbers which don't tell you crap about what's going on under a load at RPM.
I have personally seen more crankcase pressure (blowby) at higher RPM's in the same basic engines with the 2nd gapless rings.
When you read magazine articles citing great gains with the newest widget try to remember who is paying for the article or the advertising in the magazine.
Even the OEM's are going to larger 2nd ring end gaps & most major ring manufacturers are recommending a wider gap also.
Just a few of my thoughts on crapless 2nd rings :D

As for gaps in general, as I said almost all performance engine builders are running more 2nd ring gap.
What kind of piston are you using? How much N2O?
With any piston except the KB's you do not need .028 on a mild N2O deal unless you screw up on the tune-up in which case the extra gap MIGHT save you removing the top of the piston :D

150-200HP shots of N2O are not a big deal & are generally very safe as long as you have enough fuel.

If you are building a mild street 6500 deal you do not need to have the trick of the week end gaps.
On a this type engine .004-.0045/ inch top & the same on the second will work just fine.

For higher RPM stuff we open up the second ring to about .005/inch, sometimes a little more.

Wolfplace-
Thanks for the reply re;the gapless queary! I will stay away from them.
The pistons are 4.310 bore Sealed power forged with a 1/16 ring package and I will not exceed the 200 shot of N2O on this engine. Do you think a .022 thou top/second gap is overkill?
I see that using the 4.5 per inch ratio comes in at just shy of .020 thou.end gap and .005 thou per inch comes in at just under .022 thou.
Just sweating the details!
Thanks again.

Originally posted by 67johnny:
Wolfplace-
Thanks for the reply re;the gapless queary! I will stay away from them.
The pistons are 4.310 bore Sealed power forged with a 1/16 ring package and I will not exceed the 200 shot of N2O on this engine. Do you think a .022 thou top/second gap is overkill?
I see that using the 4.5 per inch ratio comes in at just shy of .020 thou.end gap and .005 thou per inch comes in at just under .022 thou.
Just sweating the details!
Thanks again. =
For 200 or less with those pistons I wouldn't increase the gap.
Just be sure you have enough fuel :D