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Old 06-10-2014, 05:45 AM
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Davezilla Davezilla is offline
Motorized Bicycle Elite Member
Join Date: Mar 2014
Location: San Antonio Texas
Posts: 2,710
Default Re: MY CDI comparison results are posted in swap and shop..

I do have some electronics experience and I also have an associates degree in electronics, but I hadn't workid in the electronics industry in over 20 years so I'd need to really read up on stuff to remember exactly what to do if I was to make my own from scratch, but buying one that's easy to modify like the Rocket cdi, I can find out which caps and resistors control the timing advance and swap them out.

The biggest problem with any aftermarket CDI is that you can't change teh timing curve to match your engine and tehy won't perform if they don't match the engine they're on fairly closely. I'm sure tehy do perform on the engines they were designed around, but once we change something about the engine like port timing or duration etc, the timing curve needs to be modified to match the engine's new mods in order to get the most power from the engine without detonation.

As far as using a bigger coil goes, the magneto only puts out a certain amount of energy that can be converted to higher voltage, but as voltage goes up, current goes down, so to really get a hotter spark you'd need an external power supply like a small battery or stronger magneto to create more energy. And so far, like mentioned, even the stock coil is up to the task at the higher compression ratios some of us are running.

Of course, having a separate coil and CDI box can have some advantages for custom builds where the builder wants a really clean looking install or wants to locate the CDI in a better location, and the dual fire version of the HD lightning setup does have an advantage of detonation prevention since running 2 plugs at opposite sides of the combustion chamber burns the fuel quicker, it does mimick higher timing but since the spark doesn't actually happen sooner, there's no further risk of detonation... If you or anyone remembers the Nissan NAPS-Z engines, they were 4 bangers with dual plug hemi heads and their initial timing was set at only 3 degrees BTDC because of this effect of mimicking higher timing by burning the fuel twice as quickly, they were able to reduce emissions by retarding the timing without killing the performance too badly, and advancing the timing to normal settings while still firing both plugs has little effect, but the advantage was less risk of detonation at low rpm where both plugs were firing, and better emissions by retarding the timing back... as for performance tho, they were dawgs... really good bottom end torque but very lacking on the top end, but the engines were also designed to redline at around 5500 rpm.
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