By Greg Banish

Having tuned lots of cars over the years, I've had the opportunity to do so many different ways. When I first started, my only choice was to drive the car on the street and make an attempt watch the wideband in between glimpses at lane lines, traffic and pedestrians in some cases. While this worked great for confirming the "real world" performance of the vehicles I was testing, the conditions (and safety) were less than ideal.

Enter the chassis dynamometer, that wonderful piece of equipment that every tuning shop must have these days to be "state of the art." The chassis dyno allows for easy recording of actual WOT power and usually incorporates wideband air/fuel, engine speed, and a host of other measurements into the data array for the calibrator. The ability to record and later look back upon the data makes WOT tuning a snap once the tuner is no longer preoccupied with the prospect of jail time or worse resulting from his testing.

Today's performance enthusiasts are becoming even savvier though. They want good horsepower and street manners out of their cars. Luckily, most EFI systems have the capability to deliver this IF they are properly calibrated. The real trick is to build not just a wide open throttle characteristic of the engine, but an entire map of engine performance accurately. This means that at any given speed and load point for the engine, the ECU must know how to properly control things.

Building this map for an engine is a lot like driving from Detroit to St. Louis. Along the way, we might need to stop in Chicago or Indianapolis (even if it's just to top off the tank!) before reaching our final destination. Without a road map, this journey is more difficult and we might even get lost. But if we read a map that shows us exactly where to turn and how far it will be until the next landmark, our travels are much smoother.

EFI Engines operate the same way. They use maps to tell them where to go on their way to WOT or redline. The more accurate these maps are, the smoother the journey.

So where does the dynamometer come in? A load bearing dyno gives the calibrator the ability to hold the engine at one location while he refines the map of the surrounding area. Inertia only dynamometers freely accelerate as the engine makes more power. This makes it difficult to hold the engine steady at all the necessary map locations and build a detailed map. Load bearing dynos have the ability to hold the engine steadily in a much wider range or map locations in order to properly tune these areas. The more accurate these measurements can be at each point, the smoother the engine will run. So a dynamometer that can allow the tuner to make accurate measurements at each individual point on the map gives him the potential to make the engine run smoother in these areas as well. Keep in mind that this applies not only to fuel delivery, but the spark map as well. Finding MBT timing at part throttle requires instantaneous torque feedback at steady state that can only be done with a properly load controlled and instrumented dynamometer.

The added benefit to a load bearing dynamometer is that when it comes time to test dynamic conditions, the rate at which the engine sweeps across the RPM range can be adjusted to match exactly what happens in the real world. This means that the amount of time it takes to complete a run is the same between the track and the dyno. We have a better idea of just how much heat and load the engine will see on the street or track. In today's world of handheld flash tuning devices and "canned" tunes designed to fit a wide array of cars, testing under these real world conditions can make difference between "That should have been fine, I don't know why it broke at the track," and "Everything performed just like we expected" when the car comes off the dyno.