I had a conversation with Kerry Wittig (some of the long timers here will remember him. He designed the RingR and other products for adapting Toy parts onto the Kicks.) shortly after he put a Jacobs multi spark ignition, he was raving about the difference it made in his truck. I purchased a used single spark Jacob ignition for lil Suzy and found it increased performance noticeably. The trick is to open up the gap on the plugs to take advantage of the increased performance of the higher voltage coil. This produces a stronger spark and potentially better ignition burn. The multi spark continues to relight the mixture during the ignition stroke. In theory this helps achieve full combustion. I have been told that the multi spark works best under low RPM high torque conditions.
My '85 Corvette (w/ automatic) had a Jacobs box installed when I got it used. As far as I *knew*, nothing else except the exhaust was changed from stock. But, the original owner was a mechanic with an IndyLights team, so, who knows. Plus, as far as I could figure, the thing was making around 300hp. When I didn't have mufflers on it, it popped off 5.2 second 0-60 runs (after slooowly squeezing the throttle down to prevent wheelspin), and it would beat my sister's Camaro SS, which was rated around 320 hp, until somewhere around 110 mph, when the ram-air Camaro would begin to walk away.
I just kinda figured the damned thing was just some sort of anti-lemon, and that the Jacobs box
worked. Later, I did more research on the Jacobs Engineering box and couldn't find anything to scientifically substantiate the claims and, moreover, found a bunch of folks calling it hocus pocus.
But it sure as hell didn't slow that Corvette down any.