Tech Talk #7 – Dyno Dividends

DavidTechArticlesBy David Reher, Reher-Morrison Racing Engines

“Dynamometers have dramatically expanded the pool of knowledge in drag racing – and knowledge is power in our sport.”

In my view of the world, three discoveries changed the course of human development: fire, which ultimately led to the invention of internal combustion; the wheel, which evolved into the drag racing slick; and the engine dynamometer, which has been the great equalizer in drag racing.

We have two dynamometers at Reher-Morrison Racing, and it’s a rare day indeed when they are not in use. Whether we are testing one of our own Pro Stock engines, a customer’s Comp eliminator small-block, or a Super Series bracket racing big-block, the knowledge we gain in the dyno cells ultimately finds its way into every engine we build.

We may be testing a new honing procedure on a Pro Stock truck engine; if the rings seal faster and the crankcase vacuum increases, we’ll apply that same technique to our other motors. When we determine the piston-to-wall clearance that produces the best combination of skirt life and power, we’ll use that same dimension in other applications that use a similar forging.

Automobile manufacturers frequently talk about “technology transfer” between their racing programs and production cars. I’m not an expert on that end of the business, but I do know about technology transfer between our Pro Stock and Super Series engines. It’s no secret that reducing parasitic losses is a top priority in Pro Stock, and like many engine builders we are cutting down the bearings to reduce friction. We use a coating on the bearings in our race motors to extend the life of these narrow bearings. We are now using the same coating on our 555ci Super Series engine bearings because many of our customers use alcohol in these engines. We’ve seen some signs of bearing distress in alcohol engines because the volume of methanol that washes down into the crankcase on initial start-up impairs the oil’s lubricating qualities. We had already proven the effectiveness of this bearing coating in our Pro Stock engines, so it was logical to use the same treatment on our most powerful bracket racing big-blocks.

We have also learned a tremendous amount about the behavior of camshafts and valvetrain components on the dyno and on our spin fixture. Obviously I would never recommend a Pro Stock-style camshaft with an inch of valve lift for a bracket engine – but I would recommend a profile from a similar camshaft “family” that I know has smooth acceleration and good valvetrain stability. We’ve also learned a great deal about oil systems on the dyno; we now know what it takes to maintain steady oil pressure over a wide range of engine speeds.

Our dyno testing procedure for a drag racing engine is to accelerate the engine at 600 rpm per second under load. We decided on this acceleration rate because it simulates what the engine experiences in high gear on a quarter-mile run. By running a 1500 rpm sweep with an acceleration of 600 rpm per second, the duration of the test is 2.5 seconds, which is about the time required for a Pro Stock to run the “back half” of the quarter-mile. When we test a circle track or an endurance racing engine, we use an acceleration rate of 100 rpm per second, which more accurately duplicates an engine’s typical duty cycle on a speedway.

When Buddy Morrison and I started our business 27 years ago, virtually no one who built drag racing engines had access of a dynamometer. Now they are almost universal. Like flow benches and onboard computers, the proliferation of dynamometers has intensified the competition in the sport. Before the advent of dynos and data recorders, a driver who had a good “feel” for the car or a builder who had an innate understanding of engines had an advantage. Dynos, flow benches, and data loggers have dramatically expanded the pool of knowledge in drag racing – and knowledge is power in our sport.

Dynamometers that were once used exclusively for power development are now used routinely for reliability testing as well. When I go to a weekend bracket race at Kennedale Raceway, I’m amazed by how many racers know exactly how much power their engines make. That’s because the majority of racers in the fast brackets have had their engines on a dyno. Even the guys who build their own engines recognize the importance of dyno testing. Dyno testing gives them the reassurance that the ignition timing is set correctly, the oil pressure is adequate, and the engine doesn’t leak or overheat.

Ten years ago, a bracket racer might have to make four or five fruitless trips to the track to diagnose an engine problem. Now if an engine that ran perfectly on the dyno suddenly develops a misfire, a racer can concentrate on fixing the car’s fuel and electrical systems instead of the motor.

The cost of professional dyno testing is about the same as a pair of tires. That’s a small price to pay for the peace of mind that comes with knowing that the engine is in good operating condition.

Dyno testing has become an integral part of our engine business. We test every customer motor we build. We know that before an engine goes into its shipping container, all of its pushrod cups are seated, its valves are adjusted properly, its leakage has been tested, and its compression checked. Dyno testing confirms that we’ve built a good engine. And on the rare occasions when an engine doesn’t make the power we expect, we tear it down and find out what the problem is. I’d rather discover what’s wrong on the dyno than have a customer find a problem at the drag strip.

Like laptop computers and televisions, it’s hard to imagine what life would be like in the ’90s without a dyno.