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
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...
Big plug gaps mean big power?
“The best way to ground for the benefit of the ignition,” explains Brock, “is to run an 18g or 14g wire from one cylinder head to the other and from there to a good chassis ground.
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)...
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