9YaTaH wrote:
simon k wrote:
simon k wrote:
could the little increase in RPM be due to the lack of resistance in the lead causing the charge to arrive at the plug earlier therefore advancing the timing?
after testing one of my Bosch leads @ 1.75Kohm, I consulted my radio/electronics guru at work - he agreed that the resistance is only there for radio interference, and that the (substantially) lower resistance would give a better spark because the "rise time" of the charge reaching the end of the lead is a lot quicker - electricity isn't ON and OFF - putting a charge on a piece of wire will build up (really f*cking fast of course) - higher resistance means the build up will be slower, and I guess that the whole charge mightn't reach the end of the lead before the spark jumps, lower resistance means that the whole charge is likelier to hit the end of the lead before the spark jumps.... or something
Yes but...what does the pulse look like from the coil when it hits the plug...if you don't allow sufficient time for a nice square wave to form or there is an impedance mismatch that is less than optimum...you could be fueling yourself
I've had a long think about this since the last time it was raised, and learnt a few extra things about traveling waves as well...it's interesting to me, but I don't know if it will interest anyone else...
The velocity of the pulse isn't really an issue, it's in the order of 1 to 1.5 x 10^8 ( 100 to 150 million meters per second). So for our puny earthling needs, it is a casual pace of about 3 nano seconds from one end of the lead to the other or (to really put it to bed) .0015
pico degrees degrees of crank rotation @ 5000rpm.
The square wave pulse is a really nasty signal which produces infinite harmonics across the frequency range. The inductance caused by the coiled carbon rounds conductor and the capacitance caused by the dielectric in the insulation rounds off the leading edge of the waveform. This energy is not lost but is stored as a magnetic field around the wire. When the square pulse passes, the collapsing magnetic field is fed back into the tail end of the square pulse. The traveling waveform now looks like a breaking wave at the beach moving backwards as the inductance acts on the square wave. No energy is lost and the pulse duration may be lengthened slightly, without exact values for inductance in the lead, I have no idea if this extra duration is of any benifit or so small it doesn't matter..
The rounding off of the leading and the tailing off of the trailing edge removes (suppresses) the vast majority of harmonic frequencies which normally carry right on through the FM and AM radio bands.
