A very good friend of mine, noted engine guru, and PHR contributor David Vizard, was once being queried about some aspect of engine theory. The interesting part of the exchange was when the fellow asking the questions summed up the discussion with the words, "So, in your opinion..." Vizard interrupted, "I don't have an opinion, I have a dyno." The point was that the information being presented was not based upon conjecture or opinion, but rather was derived from empirical testing on one of an engine builder's most important tools: the dynamometer. In those days, facilities equipped with engine dynos were few and far between, and some of the widely accepted engine building practices were based as much on wives' tales and hearsay as on fact. In more recent years, the accessibility of the engine dyno has expanded to the point where dyno testing has become a relatively routine punctuation to a performance engine build-and for good reason.
Why Dyno Test?
The reasons here can be varied, depending upon the final objective, be it an involved development program, or a one-off test of a completed engine, but the underlying objective is to get the most from an engine package. Building an engine without testing is somewhat like playing baseball without keeping score. You'll likely have some fun in the process, but it's going to be impossible to evaluate the stats. A dyno test will provide a wealth of information that will sharpen both the engine's performance, and the builder's skill. What are some of the things the dyno can tell you?
The absorption unit, shown here with twin starters, is what determines the power rating of the system. The absorber's name is derived from its ability to absorb the engine's torque production, holding the engine to a set rpm or acceleration rate, and the force applied here is what determines how much power the engine is making.
Horsepower and torque
Oil and water temps
Oil pressure
Mechanical efficiency
Brake mean effective cylinder pressure
Brake specific fuel consumption
Exhaust gas temps
Fuel pressure
Fuel flow
Manifold pressure or vacuum
Air temp for best power
Engine airflow
Volumetric efficiency
Fuel efficiency
RPM range
Besides the detailed information on the numerous running parameters of the engine, the test will also allow the builder to find the optimal tuning setting for best power and/or economy. This can be as simple as finding the basic timing and jetting requirements, or it may be more involved, including detailed tuning of the fuel and spark curves to really dial-in a combination. The dyno makes it possible, providing instant feedback to various changes. Running the engine on the dyno will also provide an opportunity for more basic adjustments and checks of the engine's operation. The cam and rings can be broken-in, and the valves given a final adjustment on the dyno, and running the engine under load can assure there are no mechanical problems or leaks before the engine is bolted into a car. This alone can be worth the cost of a test.