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Originally Posted by Aurora40
Wouldn't this be about the same? Whether it's a plug wire or a regular electrical system wire, there's going to be about the same length either way. I don't think electricity travels more slowly in plug wires vs harness wires?
Anyway, I agree coil on plug (or coil near plug on the LSx motors) is definitely better. But 25hp better on a ~400hp motor? That just seems unlikely to me.
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Inductive reactance (resistance) to current flow is a function of changing current over time (t) - the shorter the time, the higher the "resistance". Not quite that simple, actually. Induction tends to resist changes in current; either to initial current flow, or current stopping - the key to ignition coil operation.
The two halves of the ignition coil is the primary side and the secondary side. Of course inductive reactance applies to both sides, but there is a difference in the time each circuit half is "operating".
On the primary side, the inductance is not an issue as there is ample time (between spark signals) to overcome initial inductive reactance of the primary wiring and the primary side of the coil and "saturate" the primary winding - "cocking" it and then waiting, if you will.
The spark command comes as a sudden interruption of the charging current on the primary side; "sudden" is the key. The magnetic field in the primary collapses almost instantaneously, cutting thru the much bigger secondary coil in the process. The result is a tremendous (compared to the battery voltage that initiated it) voltage spike that is exacerbated like flood water behind a dam. The "dam" is in the form of the spark plug(s). Voltage builds up to the point it overcomes the combined resistance of the spark gap and the compressed air/fuel mix.
Once the current jumps the gap, it is like the dam broke. However, the current must first flow thru the plug wires and when current flows, the law of inductive reactance cannot be denied. The longer the plug wires, the more induction takes place, and the current flow will be impeded more.
So, due to the very short nature of the plug-side current, induction plays the bigger role on the plug side of the ignition circuit. Reducing the plug side conductors to zero would be the ideal situation.
I don't know how much hp this will make in the case of the LSx vs. the LT5. But, it couldn't hoit!!
Gotta take the dogs to the vet. Mo later!
P.