Dyno discipline: 10 tips for consistent results

Publish Date: 
Feb 24, 2014
By Dave Koshollek

TIP #6: Find Your Center
When setting the motorcycle up on the dyno, adjust the carriage so the center of the rear tire is positioned a little behind the center of the dyno roller. When you apply power during the test, the bike’s front suspension will compress, and the rear tire will move forward to center of the roller where it belongs for an accurate and consistent test. Have a helper check the tire’s position under load because front ends compress a varying amount. Remember, a tire too far forward will dig into the roller, causing excessive friction. A tire too far rearward may slip on the roller.

Daniels adds: Due to the soft suspension on some cruiser-style bikes, you'll need to check for tire contact against the dyno unit's top cover under hard load and throttle release. The best way to minimize this problem is by tying down the front suspension to compress it and then readjusting the dyno carriage to get the rear tire positioned correctly on the dyno roller.

TIP #7:  Fuel for Thought

If your dyno results don’t match the horsepower or torque that the performance product manufacturer advertises, don’t automatically blame the manufacturer.

Changing fuel brands or fuel octane or testing the bike with varying fuel tank levels can make for inconsistent test results. Always run the bike on the same octane fuel from the same fuel manufacturer. Buy shop fuel from a station that has a pump with a dedicated hose for each octane. Single source hoses that pump three different types of gas can push over a gallon of one type of octane before the selected octane starts flowing. Always maintain the bike’s fuel tank level at half full or higher.

Daniels adds: When dyno testing, many people think higher octane equals higher power when just the opposite is true. Over the years we have swapped high-octane race fuel for 85-octane regular and made more power on the dyno. However, this is a different scenario on the race track where engine temp and loads aren't as controllable as on the dyno. When racing, high performance/high compression engines may experience engine damage due to detonation that's exacerbated by low octane fuel.

I've also had customers show up for their dyno tune with 100-octane low lead fuel from their local airport, or leaded racing fuel in the gas tank. I can assure you that leaded fuel is very bad for engines built to the tight tolerances of today’s engines. Additionally, leaded fuel will drastically shorten the life of the oxygen sensors on EFI-equipped motorcycles.

TIP #8: Operator Omissions
Full-power tests should be run with the throttle wide open and with the weight of the rider on the bike. Check that the throttle opens 100 percent when twisted to stop and make sure the bike is set up correctly on the dyno. When setting the rear safety straps the tech should sit on the bike and cinch the straps taught, not pull them down tighter. If the straps are too tight the rear tire will be overloaded, which can cause the tire to overheat, leading to tire damage and lower power readings. On the flipside, if the rider doesn’t sit on the bike, there may be insufficient tire-to-roller friction and the tire may slip during the test.

Wong adds: Spikes can also appear at the end of the graph if the rider chops the throttle or pulls in the clutch while still sampling. This may give an artificial “max” number since the spike registers as data. Eliminate this problem by stopping the sample (pressing the red button) while still in full throttle mode. The same applies to the beginning of the run. Start sampling after rolling the throttle wide-open. Note that our WinPEP software does have the ability to set a start and stop RPM to make this process even easier. 

TIP #9: Deadman's Booth Hill
Some dyno booths move air so poorly that the booth heats up excessively during testing. And some booths extract exhaust gases so poorly that they allow exhaust gas to re-circulate and contaminate the air supply. That ruins test consistency, and it’s unhealthy for those working in the booth. If you smell like an exhaust pipe after an hour of dyno testing, you need to check the air supply and exhaust extraction performance of the booth. Install a carbon-monoxide (CO) sensor so you know if the air quality gets unhealthy. If you think the booth isn’t working properly, call the booth or dyno manufacturer for assistance.

Daniels adds: I've found that shops think it's OK to purchase the lowest priced CO meter and then install it next to the fresh air intake so the thing never goes off. All dyno booths have dirty and clean areas, depending on air flow turbulence. I use a personal CO monitor like a coal miner might wear. You can get one for about $200. They clip to the operator and vibrate or sound an audible alert if dangerous levels are measured.

We have to keep in mind that CO is a dangerous, even lethal gas in large amounts. It's a gas that will absorb into your pores. You are probably more likely to get CO poisoning from absorption than by breathing it into your lungs. Fresh Air respirators don’t work. The test booth needs to exchange all of the air in the booth at a rate of 10 times per minute. Even at that we recommend catch hoses be placed about one foot behind the exhaust pipes to direct most of the exhaust to the extraction system and keep it from circulating throughout the booth.

TIP #10: Confounding Configurations
If your dyno results don’t match the horsepower or torque that the performance product manufacturer advertises, don’t automatically blame the manufacturer. Start by reviewing the engine configuration you’re testing. Any departure from the configuration advertised will alter the results, including something as simple as a different exhaust system. The exhaust system (full system or muffler change) has a huge effect on engine performance. Pipe length, pipe diameter and muffler design all affect the way gases flow out of – and back into – the engine. Open pipes can allow gases to revert back into the engine, lowering midrange performance. Restrictive mufflers reduce exhaust flow out of the pipes, lowering top end performance.

Ask the manufacturer of a performance product what the exact engine configuration was that produced the dyno test numbers they advertise. That includes which intake system, cams, heads, compression ratio, ignition timing, exhaust system, carburetor jetting or EFI program was used. Don’t expect your power output to match the advertised numbers perfectly unless your engine configuration is a perfect match.

Wong adds: Record as much available data as possible during the dyno test, such as ignition advance, lambda/AFR, intake air temp, etc. This will help determine if another factor is limiting performance rather than the actual product itself.

For more assistance in obtaining consistent, accurate dyno test results using a Dynojet dyno contact Dynojet's motorcycle dynamometer team at 800-992-3525. For dynamometer operations training contact Dynojet Research at 800-992-3525 or Daniels Performance at 702-283-3781.