The Essential Craft of Keeping Pro Stock Mountain Motors Running

February 9th, 2011

Text and Photos by Sam Moore

Pro Stock Mountain Motors have cubic inch displacements of 820 to 825. Their capacities began much smaller, deriving from original equipment big-block engines of the ‘60s. But gradually the dimensions between their pan rails grew, allowing longer throw cranks to appear with connecting rods measuring 7.750 inches center to center and 5-inch bore centers with 4.770-inch-diameter pistons, all functioning within a deck height of 12 inches. Today’s Pro Stock engines operate on compression ratios of around 18:1, run on VP Race Fuel grade Q16, and generate in the region of 1,900 hp. Depending on weather conditions, they run quarter-mile elapsed times in 6.25 seconds at speeds close to 225 mph.

Jon Kaase Racing Engines has been a driving force in the development of these engines for as long as most can remember. From the beginning, when he worked with Dyno Don Nicholson, Kaase imposed uncompromising standards in race engine building. And his record of success has been impressive: He and his team have produced Pro Stock engines for 12 IHRA national championship winners, plus an NHRA Pro Stock title. Though their business now includes engine part sales to hot rodders, including the supply of the remarkable Boss Nine engine, the Winder, Georgia, firm still maintains about 20 Mountain Motor customers, refurbishing these formidable power plants after every 25 to 30 runs.

When reciprocating engine parts collide (usually pistons and valves) and a connecting rod or rods explode through the engine walls or the oil pan or both, foreign particles are immediately released into the oil stream to be sucked into the oil pump rotors. Rod bearings are often first to disintegrate, showering the pump with brass, copper and aluminum. Seasoned start-line observers will regale you with stories of inexperienced drivers breaking connecting rods at the starting lights and driving the entire length of the track, unaware that the vibration from the engine compartment was a signal of terminal distress. If the camshaft can still operate, usually the engine will continue to keep running—tearing itself apart all the way!

The chief concern about engine durability is the limited life of the connecting rods and also the condition of the skinny top pistons rings. The life cycle of these critical parts and others must be strictly observed in the rarified air of Mountain Motor Pro Stock racing.

In Kaase’s dynamometer cell, before this engine was tested, ace builder Chuck Lawrence leaned across to a visitor and said, “Have you ever heard one of these on a dyno before?” The visitor shook his head. “It’s pretty cool,” Lawrence insisted, “I never get tired of it.” He was right: that sound resides indelibly in the memory. Captured in the following images is the rebuilding process of a Mountain Motor Pro Stock engine.

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