MomsDuster
Well-Known Member
I’ve got a tuning question. I’ve always just gone to the book when gapping spark plugs. But then I’ve always had stock cars. So what factors in to the proper spark plug gap on performance engines?
Spark plug gap is conditional on how much total energy the ignition coil puts out. Energy, not voltage. The wider the spark plug gap the higher voltage needs to build up to ionize the fuel-air mixture in the spark plug gap. Once the mixture is ionized current can flow across the plug gap. The time the current is flowing across the plug gap is the burn time. Typically, 1 to 1-1/2 milli-seconds.I’ve got a tuning question. I’ve always just gone to the book when gapping spark plugs. But then I’ve always had stock cars. So what factors in to the proper spark plug gap on performance engines?
Spark plug gap is conditional on how much total energy the ignition coil puts out. Energy, not voltage. The wider the spark plug gap the higher voltage needs to build up to ionize the fuel-air mixture in the spark plug gap. Once the mixture is ionized current can flow across the plug gap. The time the current is flowing across the plug gap is the burn time. Typically, 1 to 1-1/2 milli-seconds.
All else being equal, the more voltage it takes to ionize the fuel mixture the less energy is available to sustain the burn time, and vice versa. The less voltage required to ionizer the mixture the more is available for burn time. You want enough burn time that the fuel-air mixture in the combustion chamber is exhausted.
Obviously, the fuel-air mixture plays into this as well. A richer mixture in the plug gap is easier to ionize. You can see that there are multiple variables involved. So, it depends.
Running an MSD system plugs gapped at .045..
I did the Jacobs stufff. Bought their adverting hook,line, and sinker. Got me one of their topline CDI multistrikes and matching E-core coil. Ran it with the same .042 gaps as the Orange box had been blasting (RN12YC Coppers). It didn't seem to run any different, and then one day about a month later,when the CDI box crapped out 20 miles from home, I was glad I had left the old system on standby. Ten minutes later I was rolling. But the Orange box was not happy with the Ecore coil.If you get the book written Jacobs he covers quite a bit on plug gap. If you have enough ignition and if you have good enough wires and the cap and rotor are in shape, you can open the gap and help with combustion.
As I've said since I was still in my late teens...most cars are ignition defficent, unless they are dead stock. It's easy to tell. Especially if you are on the dyno. Just open the gap until power falls off. If you can't get much over .040 without losing power you can use more ignition. An MSD 6 is notoriously weak. The Crane when you could get it and the Mallory 685 box were much better. Neither one understood advertising very well.
Wish I would have done some testing on the Jacobs stuff.