Recently I was asked for some information and suggestions for adjusting the timing while tuning a bike on a dynamometer.
In our classes we teach that in most cases if you pick a good calibration the ignition table should be great as far as peak power goes. The most critical component of chasing peak power numbers on a dyno is doing the runs correctly. Engine temp, oil temp, tire temp,… are some of the things that can change peak power numbers run. Which can easily be confused with an adjustment made by a tech to timing or some other table. More on this in a future post. You can learn more about Horsepower and Torque on a dyno here: http://harleytuner.com/horsepower-torque
Before adjusting timing you need to understand what you are doing.
The simplest way to explain it is timing is temperature management.
When you ignite a specific volume of air/fuel it makes a specific amount of heat. Changing (timing) when you ignite it changes what you do with the heat. As an example. Near the end of the power stroke the exhaust valve starts to open. The later you ignite it (less timing) the more of the heat you send out the exhaust.
“Increasing the timing heats the engine and cools the exhaust”
“Decreasing the timing Cools the engine and heats the exhaust”
Most important thing to remember with chasing numbers using timing on the dyno is that advancing timing (heats engine) to make power can be a bad call.
On the Dyno we control the head temp and if we are chasing a pretty HP graph heads should be near 200F. When the customer rides his bike head temps can be near 400F.
Advancing the timing in the peak power areas increases the the chance the bike will ping when ridden by the customer. I have seen several pistons with holes in them over the years.
- Decreasing timing helps with pinging
- You can increase timing in the decel column (lowest kpa) to help with decel popping. Low load area no risk of ping
- you can change timing in the lowest rpm row to help with start up. I.E. decreasing timing can help with kickback.
- Increasing the timing in the wild-man area can help the bike feel better leaving a stop.
Obviously there is no hard rule “If you do this you will get this”. every bike and situation is different.
Until next time.