Dyno Tuning

Larry Strangfeld

What is a Dyno and what can it do for me?

A dyno-short for dynamometer, is simply a machine that we strap your motorcycle or ATV on so that your drive wheel(s) spin a drum on the Dyno. One of the functions of the dyno is to read horsepower; it does this by measuring how fast the dyno drum accelerates, then calculates horsepower, taking into account the atmospheric conditions. To get good data, this should be done as close to a 1 to 1 ratio as possible. (Example: a motorcycle with a 6-speed transmission, with 6^th being overdrive, we would use 5^th gear for dyno runs.) Having said that, as long as you consistently use the same gear for all dyno runs, the data gathered will be consistent and reliable, and therefore, very useable for tuning.

Horsepower numbers usually get all the attention, buy in my opinion, the most important function of our dyno is the exhaust gas analyzer.  This tells us air/fuel ratios, and more important, at any RPM and percentage of throttle opening. Yes, it is normal for a unit to have rich and lean areas of the fuel map, depending on RPM’s and how far the throttle is open. The dyno tells us exactly where we need to make changes in the fuel delivery to give us an optimum air/fuel ratio under all conditions. Once we get the air/fuel ratio right, your engine will be happy and produce as much power as it is capable of. A street bike can be tuned to run a little leaner in cruise mode, let’s say 50-70 MPH in high gear to optimize fuel mileage and then tuned for maximum power at wide open throttle settings. Our dyno is an EDDY-current model, which means it has a powerful electronic brake to hold the engine at any RPM, no matter how far the throttle is open, for tuning fuel injection units. All data gathered is stored in the Dyno computer, so we can access any previous run data at any time in the future.

Another important function of our dyno is to put a load on your unit to simulate normal riding conditions (usually 20-25% load) and monitor air/fuel ratios. We do this while running it up through the gears at different speeds to see how close the fuel map is under actual riding conditions.

What is a Power Commander and What Does it do for me?

A power commander is a tuning device that we can install on an electronic fuel injected unit to optimize air/fuel ratios. There are less expensive fuel modules on the market, but they can generally only add fuel, (only in low, mid, and high throttle ranges). Power commanders can add or take fuel away in a much more precise manner. If you can picture a grid with RPMs along the left-hand side, and percent of throttle opening along the top, there is a box where any two lines will intersect on the fuel map. (example pictured below-Figure 1) We can go right to the trouble spot and fix the problem. If your unit has a lean area, let’s say at 3,000 RPMs at 40-60% throttle opening, I can set the Dyno to hold the engine at 3,000 RPMs, run until 40-60% throttle opening, monitor air/fuel rations at these points, and make fuel map adjustments to get the correct air/fuel ratio.

Example of Power Commander Screen. (Figure 1)

Power Commander F.I. models can only change fuel mapping, and they are the least expensive power commander model. For many units, this is all you need. Power Commander 5 models have a lot more bells and whistles; some models allow adjustments to IGN timing, mapping individual cylinders, and easy addition of accessories to the power commander system (quick shifters, data displays, multiple maps, auto tuners, and more).

The auto tune system works well for a touring rider that rides in a variety of atmospheric conditions like mountains/low elevations/cold/warm/etc. This system has a separate oxygen (O₂) sensor installed, so it can monitor air/fuel ratios while riding down the highway and make adjustments on the fly to your fuel map. Snowmobiles and belt drive UTVs also work well with an auto tune system.

Since most units come with a less-than-perfect fuel map, when you buy a power commander we can load a custom map onto it ranging from “zero” (no changes, an improved stock map) to a map that works with popular modifications to your unit. Once we get an appropriate map loaded, we can put the unit on the Dyno and make some adjustments to the map (optimizing your air/fuel ratios). Now you have a sweet running ride, with usually and improvement in fuel mileage and overall power.

Power Commanders are available for nearly all motorcycles, ATVs, UTVs, and snowmobiles equipped with electronic fuel injection.

Is a Dyno only for Racers?

Simply put, NO. We probably use our Dyno most often for non-racing applications. A very common problem we see is with riders that have installed an aftermarket exhaust system on their motorcycle, ATV, or UTV. Their unit suddenly develops a run-ability issue; usually a “popping” out of the exhaust when slowing down. This indicates a lean condition at let’s say, under 3,000 RPMs at 0-2% throttle opening. This is easily corrected with a Power Commander.

Another issue may be fuel mileage. Believe it or not, most new machines are programmed to run a little on the rich side for most of the map. We can clean it out a little in the wide-open throttle area. Still keeping things safe, and usually will see an increase in horsepower. Then we go to the cruise mode area of the fuel map where you do most of your riding (high gear at/around the speed limit) and lean it out for maximum mileage without compromising W.O.T performance. Kind of like getting your cake and eating it too!!

We have also checked speedometer calibration on the Dyno. As long as your unit reads off the rear wheel (which most newer units do).

Engine and drive train vibrations/noises can be troubleshot a lot easier and safer when strapped onto the dyno instead of trying to troubleshoot these issues while riding on the street.

The longer we use this Dyno, the more uses we find for it.

What is the 1^st Step in Using our Dyno Services?

The 1^st step for anyone bringing in a unit for a Dyno run, is simply getting a diagnostic run. Whether it is carbureted or fuel injected, we start out with a wide-open throttle roll on run. This gives us air/fuel ratio data and a horsepower graph at W.O.T. The results of this run will tell us if your unit has any fuel delivery issues along with a pretty good idea of the overall condition of the engine.  Next, we will load the dyno 20-25%, to stimulate normal driving conditions. We then run it through the gears at various RPMs, concentrating on low and mid-range while monitoring the air/fuel ratio. This tells us how the engine is running on the low-end and if any fuel delivery problems exist. We can do this inside, regardless of weather conditions outside and at speeds that would get you arrested on the highway.

If needed, we can also do a negative horsepower run, which measures how much drive train drag your unit has. For example, a rusty chain not turning freely, brakes dragging, bad read differential bearings, etc. Once we have completed a diagnostic run on your unit, we can tell you what issues your unit has (if any), and what we can do to correct them.

Also, you are welcome to watch us run your machine on the Dyno. It can be very educational.

Are all Dyno’s the Same? & Do all Dyno Shops Work the Same?

Most of the dynos you see in a shop like ours at Power Pac will be a rear wheel drive type. This style of Dyno measures how much power your machine is getting to the ground.

An engine building shop is more likely to have a Dyno Driven Direct by an engine. These generally read horsepower numbers at/around 20% higher than a rear wheel driven dyno, since there are no drive train power losses to eat into the horsepower numbers.

All Dynos still have a variance in horsepower calculations, but at the end of the day the most important function of an Dyno is to provide good, solid, reliable, repeatable data. It is easy to get caught up in the “how much power does it have” mentality, but a Dyno is primarily a tuning tool and it will measure changes in power output as tune up changes are made. It is important that you are getting good, reliable, repeatable data to make the correct tuning changes.

Our Dyno can read and calculate up to 750 ___ horsepower, and we haven’t come close to that yet. Got close to 400 horsepower once, don’t expect to see much past that.

When you bring your machine in here for Dyno work, you can expect us to keep your results confidential.

Last but not least, we work on all makes and models of machines that will fit on our Dyno, including Harley-Davidsons.

Larry Strangfeld
Power Pac Technician

This is before & after on a Harley-Davidson. Machine was running very lean at beginning. Ended up with 20 horsepower improvement! This is an extreme example.

Bottom two lines show air/fuel ratio. The lower blue line is the initial, the lower red line is after mapping. Note the red line stays close to the horizontal dotted red line (which is our goal).

Top two lines show horsepower. The upper blue line is before, the upper red line is after mapping. Notice the red line is much smoother, which indicates a happy engine.  It also is higher than the blue, indicating a rise in horsepower.

New Yamaha Bolt. Installed different air intake and different exhaust. Also, did some fuel mapping. Picked up 11 horsepower. Was really rich with stock fuel map. The bulk of this horsepower increase was due to fuel mapping, not intake and exhaust modifications.

Bottom two lines show air/fuel ratio. The lower blue line is before, the lower red line is after mapping. Note the red line stays close to the horizontal dotted red line (which is our goal).

Top two lines show horsepower. The upper blue line is before, the upper red line is after mapping. Notice the red line is much smoother, which indicates a happy engine.  It also is higher than the blue, indicating a rise in horsepower.