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Need to Understand CDI Timing for Project
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Posted by: slant64
I will apologize in advance if any of this seems vague but I will do my best to make it understandable. Me and a buddy of mine are trying to take a 50cc Dirt Bike engine and convert it to run on Hydrogen (no we are not environmentalists, were just trying to see what we can do).
Now, because of how Hydrogen combusts as a fuel it is necessary to drastically retard the timing on our engine so that the piston and crankshaft are in the correct position during time of fuel combustion. So, the question becomes, how do we retard the timing of the CDI so that the spark plug fires at the correct time and we don't end up damaging our engine?
*I did try to do some research on my own online and searching your forums but I couldn't really seem to find my answer.
Thanks for any help you guys can provide!
Slant64
Posted by: blackduc98
How many degrees of retard do you need, and at what rpm? Do you want just a simple shift relative to the timing curve of your petrol engine, or do you need a whole different curve?
If it is just a shift, then you should be able to accomplish what you want using the traditional method of rotating the stator plate (assuming your project has typical magneto ignition) but if the amount of retard desired is extreme then you may need to hack the stator plate a little to allow it to rotate that far.
If you require a totally different curve, then it will depend on your analog circuit design abilities. There are some DIY-CDI projects out there which you could adapt to your needs: http://www.molla.org/DIY-CDI/
Another option is a programmable ignition module, e.g. megasquirt:
http://megasquirt.sourceforge.net/
Posted by: slant64
To give an idea, typically you need to retard the timing roughly 8 degrees at idle. the idea being that you just need the piston to be well clear of TDC on its normal rotation pattern so that when the Hydrogen/Oxygen mixture cumbusts it doesn't force the piston to try and rotate in the opposite rotational direction.
In any case, thanks for the links and the help so far, I'll check out the links and see what I can come up with.
Slant64
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