Competition piston rings and what the OEMs taught us

Competition piston rings and what the OEMs taught us

By Sam Logan:   In our racing world we tend to think of ourselves as the elite corps. But in pistons and more particularly piston ring design, it is not our racing brains that are the driving force but those of the Original Equipment Manufacturers. It would be a glum glimpse of the US racing industry if nothing changed. But it has and nothing could be more illustrative of change than ring development. In fact, if we’re not careful our tow vehicles will operate with 1 x 1 x 2mm ring packs before our race cars. And it’s not just skinny rings that’s been pioneered by the OEMs, the enduring cast iron top and second rings have been replaced by stronger and lighter steel types. Furthermore, thermal face coatings are being applied to top rings by high-velocity oxygen-fueled spray guns at supersonic speed. The force of the collision causes the face coating to become embedded in the rings. What are they seeking? Well, with regard to the thermal face coating, they are pursuing bond-integrity. Second, they are also constantly looking for improvements in overall strength and toughness of the top ring. And third they seek to lower the ring’s coefficient of friction; that is the ratio between the force necessary to move one surface over another and the pressure between the two surfaces. The high-velocity oxygen-fuel technique that applies the thermal face coatings allows the OEMs to run high-tech rings in their latest turbo applications. These are subjected to countless detonation incidents. Tod Richards, a ring specialist at MAHLE, a racer and a race engine builder marveled, “The rings...
Deck wave: What is it and how is it checked?

Deck wave: What is it and how is it checked?

By Titus Bloom: Research of racing parts invariably includes discussions with race engine builders and manufacturers. During their course, jewels of information can emerge, as was the case when we were developing a story following JE’s announcement of their advanced Pro Series head gaskets. Sometimes the gems are universally known sometimes not – still, these recent comments on surface flatness by Dick Boyer, designer of the latest engine blocks from World Products, seem noteworthy. “The profilometer is useful,” says Boyer, “but measuring the scratch depth in a deck surface is usually of less consequence than wave finish. What would be the point of having a beautifully smooth surface with a potentially threatening wave depth of 0.002in or 0.003in? Some builders probably put too much emphasis on profilometer readings and maybe not enough on surface flatness.” How do you check wave finish? “We lay a granite plate with 300-grit sandpaper on the deck of the block and stroke it five times front to rear—you’ll see the high spots, you’ll see the wave, which we measure with an indicator. We aim to limit variations in wave depth to 0.001in. It’s easy to control the prolifometer readings; it’s less easy to control the wave. I’ve seen waves measuring 0.002in which introduce sealing problems.” Boyer on torque-to-yield fasteners “When installed, torque-to-yield fasteners, which are common on road-going vehicles, are stretched to their maximum limit and discarded after use. If the bolts are not stretched to their full extent when the engine reaches normal operating temperature, they stretch a little more and the gasket gets loose. Torque-to-yield fasteners are not common in racing engines.”...
Gibtec Pistons: Guide to top ring placement from Pro Stock to Street

Gibtec Pistons: Guide to top ring placement from Pro Stock to Street

By Sam Logan: Denver, Colorado: Though piston maker Gibtec was established a mere two and a half years ago, the individuals behind it have specialized in Pro Stock billet piston development since 2003. Notably, during this period their skills contributed to approximately 80 percent of the championship-winning Pro Stock engines. Recently, Tom Prock, the general manager of Venolia Pistons for thirty years said, “Currently, Gibtec is making some of the best Pro Stock pistons I’ve seen.” On the subject of top ring placement, Gibtec Pistons’ head, Rob Giebas explains, “On forced induction and on nitrous applications, which encounter extreme shock loads, we move the top ring down from the piston crown to around 0.300in. However, the top ring could be moved down by as much as 0.450in, depending upon valve size and configuration, as well as the positioning of the valve pockets, the radial width of the top ring and the piston pin height, “Often it’s the intake valve pocket, which is always bigger than the exhaust that determines the position of the top ring. Compact rings and therefore small ring grooves provide more potential for variation in ring placement than larger ring grooves. For example, a naturally aspirated engine with a top ring of 0.6mm (0.0236in) axial depth and 0.110in radial width, which requires a ring groove width of 0.115in, offers more pocket clearance than the top ring spec of a nitrous engine, which might measure 0.043in axial depth and 0.173in radial width. “But on most small-block applications with a standard in-line valve pattern and a power adder, lowering the top ring to around 0.300in protects it and...
Flatness: How gas ports and flat ring grooves succeed with lightweight racing rings

Flatness: How gas ports and flat ring grooves succeed with lightweight racing rings

By Sam Logan: A great many modern drag racing engines are equipped with lightweight piston rings. These rings require combustion pressures delivered through gas ports to achieve complete ring seal. Horizontal gas ports are used in oval track racing pistons to avoid carbon ingress while vertical gas ports are the preserve of the drag racing engine. In either case, the gas ports direct pressure downward and behind the ring to seal the ring to the bottom surface of the ring groove and also to force it outward and seal its thin outer perimeter face to the cylinder wall. To achieve this, it is essential to decide the correct diameter of gas port and to allocate the correct number of gas ports and to equally space them around the piston. Harnessing gas volume and evenness of pressure to a flat ring groove and flat piston ring accomplishes cylinder seal. “So, the number of gas ports, times their diameter creates a volume number,” explains Gibtec’s Robbie Giebas. “On smaller pistons we reduce the diameter of the gas ports and increase their number. To prevent flutter, pressure must be evenly dispersed around the ring. “Also the advent of flatter rings and ring grooves means you can run tighter ring-to-groove tolerances—often as close as 0.0004in to 0.0005in. A decade ago tolerances were significantly greater, probably twice this amount.” Having functional gas ports and perfectly flat rings and ring grooves—with tolerances of 0.00005in to 0.0001in—promote effective ring sealing. But also this sequence of events relies on the fact that every action is the product of a previous action.   Gibtec Pistons (PRI Booth #501)...
Camshaft lobe separation angle: what does it mean?

Camshaft lobe separation angle: what does it mean?

By Freddie Heaney: The lobe separation angle of a camshaft is typically determined by the engine’s purpose, its displacement and its compression ratio. A 350cu in oval track racing engine, for example, often runs on a narrow lobe separation angle of 106 degrees. In contrast, a smooth-running high-performance street engine might use a lobe separation angle of 112 to 114 degrees. Five-hundred cubic inch NHRA Pro Stock engines that rev to 11,000rpm operate on 116 degrees and 800-plus cu in Pro Stock Mountain Motors 120 to 122. The lobe separation angle or LSA is the angle in camshaft degrees between the maximum lift points, or centerlines, of the intake and exhaust lobes. It affects the amount of valve overlap; that is the brief period of time when both the intake and exhaust valves are open. A narrower LSA adopts more overlap and with it a lumpier idle and a narrower more specific power band. The narrower separation makes the engine sound choppier. Some engine specialists refer to it as that 106 sound—the NASCAR and short track oval sound where preferred lobe separation is usually specified between 104 and 106 degrees. The primary function of narrow lobe separation is to impel urgent acceleration off the turns when the throttle is opened. A wider LSA, on the other hand, reduces valve overlap, offering better idle and cruising qualities. Supercharged engines typically benefit from a wider LSA because they don’t require as much overlap for exhaust scavenging as does the naturally aspirated engine. “Changing the lobe separation angle,” says Doug Patton of Pro Line Race Engines, “changes the amount of overlap that...
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