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 in 2015 that revved to 11,000rpm operated on 116 degrees LSA and 800-plus cu in Pro Stock Mountain Motors 120 to 122.   The lobe separation angle 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...
Wild Wilfred: Racing rocker arm virtuoso goes home

Wild Wilfred: Racing rocker arm virtuoso goes home

By Sam Logan Photography by Moore Good Ink, April 15, 2014 Dawsonville, Georgia: How is it that the man who makes the finest racing rocker arms—five to six hundred sets per year—is virtually unknown? His valve train parts, which are shipped in unmarked boxes, flow from his modest manufacturing facility in north Georgia about fifty miles north of Atlanta. They carry the promise of winning. The shop, which is not open to the public is also unmarked and sits among the evergreen scenery and the burnished magnolia at the end of a neat concrete drive behind a gated entrance. In the shop, customers’ names are rarely mentioned. Indeed this policy of discretion is understandable as professional racing teams work hard to gain an advantage and it’s in their interests and those who serve them to remain tight-lipped. Racing, particularly the kind where engine power predominates, requires secrecy and Wilfred Boutilier of WW Engineering knows how to play the game. In nineteen-sixty-five Wild Wilfred Boutilier now 76-years-old left his Nova Scotia homeland, pursuing an ardor for NHRA drag racing. In the nineteen-seventies he competed in Pro Comp Alcohol Funny car, winning at Englishtown in 1974 and again at the Fall Nationals in Seattle, Washington a year later. Boutilier continued racing though not from the confines of a Funny Car. He was the first to create billet heads for Donovan blocks. He also produced them for Lamar Walden’s Chevrolet 409s. The finest rocker arms you’ve never heard of: Almost thirty years ago Boutilier began developing competition rocker arms from billet aluminum. Why would he do that? Why would he not use...
Competition cylinder heads: How would you know if air-fuel movement is good or bad?

Competition cylinder heads: How would you know if air-fuel movement is good or bad?

By Ben Mozart: The race engine requires a precise mixture of air and fuel, approximately 13.0:1 by weight ratio.   But the power it makes depends upon how well the mixture is emulsified and atomized. How well it is delivered through the intake manifold runners and cylinder head ports. And it’s ability to negotiate the intake valves and to swirl in the combustion chambers, which are an extension of the ports, and to occupy the cylinders.   For most of us, arranging and controlling the movements of the gases in the cylinder head ports are beyond our imaginings. Is the air-fuel mixture moving efficiently in the intake tracts or clinging, vexingly, to its sides? If so, how could it be reintroduced into the air stream? And further downstream, how is it negotiating the short turn, the five valve-angles in the throat, and does it demonstrate swirl as it moves into the combustion chamber? Read...