Plug Gap - Modified

[chrisryder]

I'm aware that the plug gap should be 25 thou.

I'm also aware that with electronic ignition, a 'sports' coil, and lumenition silicon leads, i can run a bigger gap for fatter sparks.

trouble is...

how big a gap? 30 thou? 35? 40? suck it and see?

[bmcecosse]

25 thou..... Why would you want to change it?

[chrisryder]

fatter sparks!

[linearaudio]

Yep-run it at 70 thou and the sparks will be so fat there won't be any room for the fuel
Seriously, an electronic set up will easily spark 30 thou (some people wouldn't know about these new-fangled things ) which can help firing an indifferent mixture, ie when you are juggling the choke, or labouring at certain revs.

[bmcecosse]

No need for bigger/fatter sparks- the slightest spark will ignite the explosive mixture - size is not important......

[linearaudio]

No need for bigger/fatter sparks- the slightest spark will ignite the explosive mixture - size is not important......

The whole point is when the mixture is indifferent, as above, then a "fatter spark" will fire more effectively. But of course, for those who just toodle around once in a blue moon on a sunday, to annoy real he road-users out there, it wouldn't make any difference at all.

[bmcecosse]

Naturally my engine's mixture and timing is always perfect - so no indifferent mixture to be ignited...... Seriously - for a wee simple A series engine, none of this applies........Points are fine.

[Alec]

Hello LA,

"indifferent mixture,"

it would need to be so far from ideal that whether it gets a better spark is irrelevant, the car will be running badly anyway.
High specific power engines with high cylinder pressures need a higher voltage, but the average classic doesn't.

Alec

[bmcecosse]

Exactly......

[chrisryder]

well i'm pleased to have provoked a discussion if nothing else!

[ASL642]

......and sucking spark plugs is definitely not recommended!

[lambrettalad]

hi ASL642
I live in yardley,have i seen you about?

[bmcecosse]

Feel free to open up the gap if you wish - it won't run any better, and when it won't start some cold/damp morning you will know why!

[Neil MG]

Read this for more detailed information on spark plug gaps and more:
http://mgaguru.com/mgtech/ignition/ig101.htm

[Alec]

Hello Neil,

although he dismisses the older type plug they do have some advantage on worn engines. The N series Champion plugs had the electrode inside the nose and would actually last longer than the more modern extended nose plugs (NY series)and would cope with oil in the chambers better.
The gain with the long reach plugs was it extended the heat range and so fewer plugs are required for a variety of engines, in other words the manufacturer benefits.

Another point is that high voltage ignition systems do not necessarily give a higher voltage at the plug, once the voltage is high enough the plug fires and that's it. It is an advantage to have higher H.T. voltage on engines that stress the plugs but it is not an automatic benefit. (And an MGA certainly does not need it unless extenively modified)

Alec