![]() ![]() To achieve proper ring clearance, especially where the compression ring is concerned, the ring grooves must be smooth. The vast majority of race pistons are constructed with drilled drain back holes as slotted drain back holes can allow more flex in the piston skirt.Īnother consideration is the actual ring clearance within the groove. Drilled drain back holes make for a stronger piston in most cases, but they do allow more heat to enter the skirt area. When examining piston grooves, you’ll find a couple of different types of oil drain back holes are regularly used: drilled and slotted. This is called an “accumulator groove,” and it’s designed to reduce pressure buildup between the pairs of rings and maximize ring seal. This means the land area between the top and second rings is slightly smaller in diameter when compared to the area between the second and oil rings. Other high performance and race pistons are manufactured with a groove milled into the land area between the top and second ring. For example, some pistons have “stepped” lands. This is narrower than the first ring land, but combustion pressures aren’t present (at least they shouldn’t be) and overall temperatures these rings see are much lower.ĭepending on the manufacturer, some ring lands have special designs. As far as the land area between the second and third ring is concerned, many high performance and race pistons incorporate a width of between. 180-inch in a high performance piston and often much larger in a stock application. Because of this, the width of the first land area is usually between. The second ring doesn’t encounter temperatures anywhere close to those witnessed by the top ring, but the ring land area between the top two rings must also support the combustion pressure exerted upon the top ring. While the location of the second ring isn’t as critical as the distance from the deck down to the top ring, it is still important. While pondering the location of the rings, we also need to consider how much material is found between the rings. The combustion process is cleaned up considerably and power is increased as the rings are moved upward. As the amount of “dead air” space between the top ring land and piston deck is reduced, the amount of trapped combustion gasses is also reduced. There are good reasons for moving the top ring closer to the piston deck. And in heavily modified race engines, top ring location can vary from. In an endurance racing application, the top ring is typically. ![]() 300 to .400 inches down from the deck surface. Most Detroit-built engines have the top ring from. The locations of the ring lands and grooves in the piston are dictated by the compression height of the piston, the size and depth of the valve notches, and the overall dimensions of the ring package. This will hurt performance more than it will help.) (FYI, some pistons of questionable quality can actually incorporate a negative tilt. We should also point out that the tilt is included in all of the ring grooves - top, second, and oil. Something else you’ll hear about in relation to ring lands is “tilt.” Some (but not all) manufacturers machine the actual ring grooves with a positive “tilt.” This tilts the ring package upwards by a very small amount to help with ring seating. The job of handling thrust loads is best left up to the piston skirt. If the piston ring land were the same diameter as the skirt, the rings would be required to handle the thrust load. The reason for this size differential is that once the piston reaches top dead center, it rocks in the bore. The overall diameter of the ring land in a common piston is smaller than the overall diameter of the piston, and in many cases, there is a small vertical taper. Most ring lands are round, although there have been some exceptions over the years. Piston ring lands are the areas of the piston between the piston rings. When it comes to pistons, the most common arrangement you’ll encounter makes use of three piston rings - compression, second, and oil. Today, we’re turning our focus to the areas of the piston most associated with the rings: the ring lands and grooves.
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