cdi timing advance

[yardog]

Does racing cdi advance timing @ idle? Are they really better than stock?

[yosemite]

If it doesn't say advanceing it is just a fixed advanced cdi from start to finish.
Advanced timing produces a little more power because it is igniting the fuel mixture earlier than near top dead center.
Sam

[yardog]

Since timing will be advanced at idle will idle not be as smooth as a stock cdi?

[tvnacman]

I have a hp cdi that will advance over 3k rpm .

John

[skuttadawg]

I have a 2T with racing CDI with advanced timing and I had to raise up the idle speed a lil bit

[tvnacman]

Feb 1, 2013 22:58:56 GMT -5 skuttadawg said:

I have a 2T with racing CDI with advanced timing and I had to raise up the idle speed a lil bit

Skuttadawg , have you taken a look at the timing curve with a timing light ? Is the the timing the same at idle as say 5k ?

John

[woowilly]

Several years back I looked at the electronics and microcontroller programming for a few electronic ignitions. The simplest and cheapest used fixed timing. usually about 20-25 degrees before top dead center as best compromise. drawbacks: slightly rough idle, a bit of kickback when starting (too advanced), more advance at higher rpm when not under heavy load would be better performancewise. Older mechanical systems had base timing set at idle with centrifical advance when rpm increased and addition advance added under high manifold vaccumm conditions. ie:lightly loaded. Nearly all modern electronic versions set base timing at maximum ever needed then feed in a delay that varies as needed between pickup trigger and firing off the coil primary. here's an example with made up numbers ( I don't remember the exact numbers and don't feel like crunching numbers unless I'm getting paid for it... : 20 milisec delay while cranking to start, then 10ms delay below 1k rpm decreasing to zero delay at 3k rpm. add more delay with decreases in vaccum sensed by map sensor to prevent pinging under load. as a additional means to keep from going too advanced under load or crappy gas, a knock sensor can by used to detect when to add more delay.
The custom ignition on my weedeater engine converted for rc airplane use only has a cranking delay then rpm based decreasing delay once running. it runs best at 28-32 degrees advanced at 6k rpm.
(all timing delay is out by 3k rpm)
I looked at a schematic for a scooter AC CDI, it was just a simple fixed timing setup.
No suprises there, China is the land of how cheap can we make it...
I suspect the "performance" CDIs just add a varying delay for lower rpms.
It costs a bit more to design and produce a CDI to go from that to one that"s fast enough to
calculate when to fire the coil based on the trigger signal from 355 degrees ago to have the coil fire off at the best time instead of the compromise timing choosen for a fixed timing setup. That's in addition to the rpm advance curve timing changes. ( exact timing needed before trigger signal depends on where fixed timing signal is.)
If so, adding an offset flywheel key or relocating the pickup more advanced might help performance. That could be too much advance under load. A way to have the performance and not ping would add a power commander module between the ingition pickup and coil and a map sensor to back off advance under load. Expensive though...

[tvnacman]

Yes , the hp cdi acts like the old vac advance system . It is retarded at start up , once you hit 3k it advances . I had a light on it and you can see the timing move when you increase the rpm .

John