View Single Post
Speedy Squirrel Speedy Squirrel is offline
Rocket Scientist
Join Date: Jun 2008
Location: Detroit
Posts: 824
Here is an example of the charts using the EURO timing spec. Remember these rules:

1. The RPM shown is cam RPM. Engine RPM is twice that.
2. ATDC is After Top Dead Center. That means Retarded timing.
3. BTDC is Before Top Dead Center. That means Advanced timing.
4. Vacuum means the pressure is below atmospheric pressure. It is meant to be a measure of load. When the throttle is closed vacuum is high, that means a big number. When the throttle is at Wide Open Throttle (WOT), the vacuum is low, that means a small number.

For the Euro example below, the procedure states to set the ignition timing at 0 degrees crank with the vacuum hose connected and at 1000 RPM. For the centrifugal diagram we divide the crank RPM by 2 to get cam RPM. At 500 cam RPM we see on the chart that there is 0 degrees of advance. We are setting the timing at idle, so the vacuum is high, and is taking out 10 cam degrees, or 10 x 2 = 20 crank degrees. In other words, if we pulled the hose at idle, we sould see 20 crank degrees of advance.

Now, if we button everything back up and go out and stomp the throttle, at 6000 crank RPM (or 3000 cam RPM) we will get the 10 crank degrees (5 cam degrees) of centrifugal advance, and 20 crank degrees as the vacuum decreases due to the open throttle. 10 + 20 = 30 crank degrees of nominal timing at 6000 RPM and WOT.

Last edited by Speedy Squirrel; 07-01-2017 at 08:19 PM..
Old 06-30-2017, 12:32 PM
  Pelican Parts Technical Article Directory    Reply With Quote #9 (permalink)