Advancing CDI units

[collinsda]

Just wondering if anyone here has advanced a CDI unit. I was thinking of mapping the peak cylinder pressure against crank angle for a race engine I am developing and then tweaking the ignition timing so that I am achieving peak pressure at the optimum angle for a particular RPM range. I was thinking of modifing the CDI some way however I thought a simpler way would be to simply move the position of the hall-effect sensor relative to the blade wheel/magnet. I could do this easily by slotting the sensor mounting holes or by slotting the wheel itself.
Has anyone ever done this?

Thanks,

Dave

 

[patprimmer]

Yes

The principle of moving the trigger relative to it's activator has been around since the early 20th century. Initially controlled by levers on the steering wheel or nearby the driver, to a bob weight device in the distributor.

More recently electronic sensors and computers have done it.

Most early to mid 80's models will have a "Hall Effect" trigger inside a distributor. A two way advance system will have the sensor on a plate that is advanced by bob weights and a diaphragm connected to inlet manifold pressure.

You should be able to see examples at any second hand parts yard or swap meet.

I believe GM called theirs their HEI or high energy ignition.

Regards

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[mburgess]

Can do it by a slotted tone wheel or why not use a programmable CDI so you can write your own advance curve.
There are a few on the market.
Regards,
MB

 

[collinsda]

Cheers lads! Thanks Michael, I'll have a look out for one.

Dave