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Randy - I was thinking about the XJ tci again, wondering how I could make a replacment for it. Wondering how, if I were yamaha, I might do it.
If yamaha did it the way I am thinking it might not be as hard to replace the TCI as I thought...
Ok - no mechanical advance, all done with the black box. If you are yamaha, how do you implement the advance? You use timing, miliseconds, and fire the coil a predetermined amount of time before or after the pulse from the pickup coil.
All this time I was thinking that the pickup coil is positioned so that when top dead center passes, the key on the crank is aligned with the pickup coil. I then thought that in order to advance the timing curve, the box would measure the rpm and then fire on the NEXT REVOLUTION in advance of the key passing pickup coil, hence getting your ignition advance.
What if yamaha did it a different way, a simpler way?
What if the key on the crank and the pickup coil align at the engine's maximum advance and not at TDC? Now all the TCI has to do is insert a delay, x number of miliseconds, based on rpm, and fire the spark. The closer the bike gets to maximum spark advance, the shorter the delay gets until it reaches 0, then full advance is reached! When the bike is at low RPM's, the delay is larger.
Instant advance computer! it would be a relatively simple circuit compared to some crazy prediction scheme based on how quickly the engine is capable of revving, etc!
The vaccum sensor must modify the delay, probably subtracting from the final delay derived from the RPM derived delay.
Is this possible?
An alternative would be that the the delay is calculated from the point that the crank key passes the opposite cylinder's pickup coil. Basically the same idea as above but a little reversed.
Now if you could easily seperate the coil driver circuit from the VR sensor circuit inside an HEI you'd have a cheap, assembled, available building block. You'd just need to put the a timer connected to an rpm counter in between and figure out the best ratio.
Does anyone have the actually curve of the XJ ignition advance, minus the vaccum?
Dan
If yamaha did it the way I am thinking it might not be as hard to replace the TCI as I thought...
Ok - no mechanical advance, all done with the black box. If you are yamaha, how do you implement the advance? You use timing, miliseconds, and fire the coil a predetermined amount of time before or after the pulse from the pickup coil.
All this time I was thinking that the pickup coil is positioned so that when top dead center passes, the key on the crank is aligned with the pickup coil. I then thought that in order to advance the timing curve, the box would measure the rpm and then fire on the NEXT REVOLUTION in advance of the key passing pickup coil, hence getting your ignition advance.
What if yamaha did it a different way, a simpler way?
What if the key on the crank and the pickup coil align at the engine's maximum advance and not at TDC? Now all the TCI has to do is insert a delay, x number of miliseconds, based on rpm, and fire the spark. The closer the bike gets to maximum spark advance, the shorter the delay gets until it reaches 0, then full advance is reached! When the bike is at low RPM's, the delay is larger.
Instant advance computer! it would be a relatively simple circuit compared to some crazy prediction scheme based on how quickly the engine is capable of revving, etc!
The vaccum sensor must modify the delay, probably subtracting from the final delay derived from the RPM derived delay.
Is this possible?
An alternative would be that the the delay is calculated from the point that the crank key passes the opposite cylinder's pickup coil. Basically the same idea as above but a little reversed.
Now if you could easily seperate the coil driver circuit from the VR sensor circuit inside an HEI you'd have a cheap, assembled, available building block. You'd just need to put the a timer connected to an rpm counter in between and figure out the best ratio.
Does anyone have the actually curve of the XJ ignition advance, minus the vaccum?
Dan
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