Retarding timing on a nonadjustable CDI

Ummm...

I'll get pictures at work tomorrow. I always thought that there was a diode acting like a half wave rectifier in the CDI box so that you don't have to deal with the negative signal. I'm not sure though. I'll try to scan in the wiring diargram tomorrow too.

Becker wrote:

Ummm...

I'll get pictures at work tomorrow. I always thought that there was a diode acting like a half wave rectifier in the CDI box so that you don't have to deal with the negative signal. I'm not sure though. I'll try to scan in the wiring diargram tomorrow too.

The 1/2 wave rectifier is used on the charging coil which charges the main capacitor.

The firing sensor, which is what controls the SCR, is a separate pickup entirely. It may or may not have a simple diode. That is the part of the circuit which does the timing so it often has other circuit elements. If there is some sort of active circuit applying a bias voltage to the pickup, we probably don't want to interfere with that, or at least not until know what it does.

Fig 1 will allow current to flow through the pickup coil which results in a delay. The higher the RPM, the longer the delay (in crank degrees). This also attenuates the signal's amplitude at the output, which will further cause a delay, but this secondary delay effect may or may not increase with RPM.

Fig 2 may slightly reduce the current in the pickup coil, but that won't create much difference in the ignition timing. However, the voltage will be reduced by .5 to .8 volt for each pair of diodes in the circuit. (Add more as necessary.) The reduced voltage will cause a delay since the amplitude of the signal will be lower. This delay will be prominent at the initial RPM where this pickup takes over the triggering duty. At higher RPMs, it will have negligible affect.

Notice how FIG 1 affects higher RPMs more and FIG 2 affects lower RPMs more. That's why I think it may take a combination of the two.

Also notice, these amplitude reducers work with the polarity of the signal in either direction.

FIG 3 and FIG 4 are the two ways to implement the combinations. I gave both because in one, the potentiometer will attenuate the effect of the diodes, and in the other it won't.

This should give you some ideas to tinker with. Unfortunately, without knowing the actual schematic of the ignition, these have a chance of not working at all. I'll keep my fingers crossed.

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Pending the diode design, dual in series Diodes will produce ~= 1.4Vdc voltage drop....

The voltage out of the Pickup, +12Vdc?

Interesting concept, look forward to the results no doubt...

Wow, this is awesme. Thanks so much loudhvx. I owe you one. If I can ever return the favor just let me know. Until then some pics!!

Ok, so I can't figure out how to copy and paste them but here is the web page. Oh, and the website is still a work in progress.

www.dakotaperformanceinc.com/

Go to turbo performance and then click the button at the bottom.

Hmmm. 400 hp on a snowmobile? :woohoo: That'll help outrun the avalanche caused by the screaming exhaust!! :woohoo:

Haha, ya it'll outrun a few things. And those exhausts are loud. They pretty much are straight piped from the turbo.

Ok, just finished the first night of testing. No serious progress to result we just firgured outr a bunch of ways to not do things.

We also found out the limits of the little black box. It turns out that there is an exhaust temp sensor that retards the timing curve in order to heat up the exhaust pipe. Heating the exhaust pipe changes the resonance in the pipe. So as it turns out there is 12 timing curves that advances the timing as the pipe gets hotter until the pipe reaches 650 degrees F and then it stays constant after that.

Thats it for tonight. I'll try to post more on results as we test. Once again thanks for all of the advice guys.

Oh and the ECU reads both the positive and negative voltage that comes from the reluctor in the alternator. And I douple and triple checked that it is a reluctor.

"I double and triple checked that it is a reluctor. "...
:huh: :dry: :blink: :S ...

I'm no electrical wizard, but you said something that triggered my brain. If the black box retards timing based on a reading from the exhaust temp sensor, would it be possible to control the ouput from that sensor to trick the black box into retarding the timing. Basically making it think that it still needs to warm the pipe. I don't know that this won't have un-intended consequences. Is the temp sensor a 0-5 Vdc output?