Ask Sarah: Is gapless good?


Stock rings in modern engines are already typically thin, low tension rings used to reduce their mass and inertia, and when properly seated, they don't float at high rpm and conform well to the shape of the cylinder bore.  Piston rings naturally wear over time which causes poor ring seal so some of the benefit given to using gapless rings could be from comparing them to old worn out ones. Comparing new gapped and gapless rings, you may still see about a 1-2% improvement in both average leakdown and horsepower which isn't that noticeable unless you're trying to extract every last bit of power from the engine.  

Total Seal gapless clearances

Always use the recommended gap provided by the manufacturer.  These are the recommended Total Seal clearances.  

There's also some discussion around using a gapless top ring versus a gapless 2nd ring.  The top ring is exposed to the highest operating temperatures and can run as hot as 600 degrees Fahrenheit, while the 2nd ring may only see temperatures of 300 degrees Fahrenheit.  Since the 2nd rings aren't subjected to as high of temperatures as the top ring and won't expand as much, conventional wisdom has been to run a tighter end gap on the 2nd ring.  Some manufacturers are now moving towards using a wider gap for the 2nd ring, thinking that providing a larger area for the leaking gases to go will keep from lifting the top ring and causing a flutter at high rpm.  You could also machine an accumulator groove in the piston between the two rings to allow extra volume for any gas that escapes past the first ring.  This will also keep cylinder pressures in check and improve ring seal at high rpm.
Naturally aspirated motors experience lower cylinder pressures and less violent detonation, but turbocharged or nitrous injected motors are exposed to higher pressures and more heat and the rings need wider clearances to accommodate for the greater expansion.  High boost pressures could create a destructive thermal expansion situation.  If you want to go with gapless rings on a forced induction motor, make it the 2nd ring that is gapless.  Also be cognizant of the bore finish and follow the recommended assembly instructions.  Too rough a finish will cause increased wear, a poor seal, and excessive oil burning.  Total Seal will recommend how your cylinder should be honed to work well with their rings.  Like everything else, screwing up the engine build process could cause boom chicka boom!  

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