Plug gap for electronic dizzys

[Ozdunc]

Quick lunchtime question

Has anyone using an electronic dizzy gone to using a bigger plug gap?

I've seem recommendations to go from 0.8mm to 1.0mm (0.032" to 0.038-0.042")
Does it make a difference?

Cheers

[bee utey]

Dissys on vehicles designed to run 1.0mm gaps and upwards tend to be taller and bigger in diameter at the cap to prevent arcing out. I'd stick with 0.7 - 0.8mm myself on an old design dissy.

[Ozdunc]

I'm not sure I understand.

Having a bigger gap at the spark plug can cause arcing across the contact inside the dizzy?

I thought you could have a bigger spark plug gap because there's no points delay. To be honest I've only read this and haven't gone into the dynamics of why this would be the case.

Can anyone point me to a good reference of how and why the sparking system work as they do?

[PhilipA]

Has anyone using an electronic dizzy gone to using a bigger plug gap?

If when you talk of an "electronic dizzy" you mean an aftermarket transistorised ignition then there is no more energy than with points. Its just that it is more reliable. If you have the original or aftermarket points type coil with current limiting that is what you have.

If you are talking about a "high energy ignition" which includes a complete dizzy, amplifier , coil , leads then you can maybe increase the gaps. An electronic coil is non current limiting and will fry a transistorised ignition in less than a minute. Ask me how I know. I was young once.

I am sure if you google car ignition or similar there will be lots of explanations etc.
Regards Philip A

[bee utey]

I'm not sure I understand.

Having a bigger gap at the spark plug can cause arcing across the contact inside the dizzy?

I thought you could have a bigger spark plug gap because there's no points delay. To be honest I've only read this and haven't gone into the dynamics of why this would be the case.

Can anyone point me to a good reference of how and why the sparking system work as they do?

Never heard of a "points delay", what's that? The rate of voltage rise on the primary side of the coil is set by the condensor.

The voltage required to create a decent spark at the plug gap depends on a number of factors.

1. Plug gap, voltage is directly related to the size of the gap.
2. Electrode sharpness, rounded electrodes need higher voltage. Sharp edges concentrate the electric field at that edge.
3. Air pressure in the combustion chamber, due to compression ratio, throttle setting, ignition timing. Higher pressure at firing point = higher voltage needed.
4. Fuel mixture. Richer mixtures need a lower voltage to initiate a spark as fuel molecules aid ionisation.

Now the voltage needed to spark has to be initiated at the coil, travel down the coil lead, down the carbon brush, along the rotor, across the air gap to the electrode, up the terminal and along the lead, and through the plug body to the gap. Anywhere that the open air gap is sufficiently small there is a potential for the voltage to arc out to a close but incorrect point. Increasing the gap by 25-30% will increase the chance of the current arcing out somewhere else that the plug gap.

So that is why manufacturers in the 80's made ignitions capable of 1.5mm gaps with large distributor caps. Example:

http://www.ebay.com.au/itm/Holden-St...-/400529931118

Oh and keeping all lead boots tight and clean also reduces the chance of arcing out across dissy caps.

[Ozdunc]

Whoa! Did that come off a dustbin! Its massive.

Thanks guys.
I'm pretty happy with the way everythings running on the truck. I have a 45D electronic distributor and looking at the S2 club servicing specs - it mentioned running a plug gap of ~1.0mm, and I'd read somewhere that it was something to do with the points opening/closing that was a limiting factor in providing voltage to the spark plugs.

if thats complete rubbish, thats good to know. I wasn't looking for extra grunt, just wanted to make sure I was setting up the ignition to run correctly having removed the points

Cheers