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The Importance of Rings and Gap
Lets discuss ring gaps. First though we must dive into the properties of rings and what is there mission first.
Pistons rings, commonly referred to as just rings are what they sound like, rings. They are rings what surround the piston. Obviously if you had a 4.000" bore and put exactly a 4.000" piston into you will run into problems. The problem is when any material is subjected to heat it expands. If you had exactly the same size piston as the bore when the piston is heated it will expand against the walls and not move. So even though you call it a 4.000" piston it is really slightly smaller.
So this brings up if the piston is slightly smaller than the bore how do you create a seal? This is where the rings come in. There are generally 3 rings on each piston. The top ring is the Compression ring, followed by Secondary Compression Ring, then the Oil Control Ring. All rings dissipate the piston heat into the block.
Top Compression Ring:
The Top Compression ring is your first ring which creates the compression. I am not going to break down the shapes and materials of the rings for this discussion but will explain how they work. When the cylinder creates pressure the pressure forces the ring down against the ring land (which is the groove in the piston where the rings sit). The pressure fills in behind the ring and also forces the ring against the cylinder wall creating the seal.
Second Compression Ring:
The Second Compression ring is the second ring aiding in compression and stopping combustion gases from entering the crankcase. (Blow by). It also scrapes oil from the cylinder walls.
Oil Control Ring:
The oil control ring coats the cylinder wall in oil to lubricate the walls as the piston travels and down. It allows just enough oil to pass to lubricate the top rings. The excess oil is forced through the piston drain back holes and back into the crankcase. There is little to no combustion gasses in this area, so the ring relies on its radial tension to keep it snug against the wall.
What this means for Horsepower
So you may be asking what does all this mean for horsepower? Well its simple, the top two rings create compression and contain the combustion gases. Obviously the combustion process is what creates power. If you have improper ring seal or wrong gap you will lose power by creating blow by and having the combustion gasses escape around the piston. Ring Gaps
Ring gaps are important. This is the gap between the two ends of ring. If you had one solid ring, the ring wouldn't be able to expand to fill in the voids. Ring gaps are determined by a number of things. I don't feel like getting into recommended ring gaps for applications because a search on Google can find you this information.Sealed Power did a study and showed on a typical 350 SBC reducing the ring gap from .024" to .016" gained ~30bhp, thats ~25rwhp just from reducing the ring gap. They further reduced the ring gap to .010" and it hurt power due to the ring ends butting.
I hope you have found this information slightly helpful.
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