Ryan wrote:WTF is with the hole in disty idea - what a moronic idea.
Thats what ignition timing is for
How do you get a strobe to fire with spark anyway, without using a timing light?
Since you've got your timing light out, just point it at the crank like a normal person. That will give you a freakin' degree scale to measure it on....
Perhaps I misunderstand... I'm really educated about ignition back from the points and condenser days. Back then, to adjust timing, you would rotate the disty a few degrees, thereby changing when the spark is released as compared to the angle of the crank shaft. Moving the disty, meant that the relative position of the rotor to the terminals remained the same. However, other timing affects position of rotor to terminals, as follows.
I know that you already know this stuff, but in order to explain, I have to recap some bacics. At high RPM, and open throttle, the vacuum advance is meaningless, instead the mechanical advance modifies the timing in relation to the angular position of the timing sensor shaft. That is, it is modifying when the spark is released in relation to the the position of the rotor to the terminals in the cap. If the mechanical advance is set to achieve a total maximum advance of 36 degrees BTDC, then the rotor is 18 degrees from being in line with the position of the terminal. Add to that half the angular coverage of the rotor arm (half = about 10 degrees on some rotors (this is a guestimate, I didn't measure)), and you have 28 degrees. At 6000 RPM, the rotor is moving at 3000 RPM = 50 RPSecond, or 18000 angular degrees per second. One angular degree takes 55 micro seconds.
Estimating 100 Microseconds for spark duration, a spark lasts for approximately 2 degrees of rotor rotation at 6000 RPM engine speed. Magically, 28 degrees plus 2 degrees of spark, and you are at 30 degrees -- a magic number of 6 cylinder engines. Since the spark plug wires terminals are evenly spaced around the disty cap, they are separated by 60 degrees, of which half is 30. Get it? It is possible for part of the rotor's conductive surface to <= to half the distance between terminals. If this were to happen, then the spark might be split between the two terminals -- the one it just fired previously, and the one it is going to fire this time. The charge that gets sent to the plug previously fired will harmlessly fire through mostly burned fuel/air mixture. However, that also means that the spark isn't as powerful for the cylinder that was intended to be ignited. This can only be visually seen if you use a disty cap with holes drilled in it, and then capture it with a timing light.
Now, this is applicable to this topic because we're talking about stutter at high RPM. High RPM is when the throttle is wide open, and vacuum advance is meaningless. At high RPM mechanical advance takes over. Mechanical advance affects timing in relation to angle of timing sensor. The problem Fragz was writing about happens at high RPM. This may be relevant to his situation. Or, it could be the plug wires, or the coil. None the less, checking the position of the rotor when the plug fires at high RPM is not a moronic idea.
Thank you for your comments.
