Spark Plugs...

"Richard Parkin" wrote in news: snipped-for-privacy@bt.com:

Yes there's differing gaps according to plug make, yes 0.3mm can make a difference and no, I haven't seen yer feeler gauge :-)

Stu

Thanks for that Stu ;)

Bigger the gap the better the fuel ecomnomy make it massive!

How big would the gap have to be before it used no fuel at all?

Chris

Well, current late cars with coil-on-plug HT systems are capable of generating at least 80,000v, which at atmospheric pressure will fire a plug with an 8-10mm (if not more) gap....

Tim. .

But plugs don't spark at the *begining* of the compression stroke. Surely it's going to be much higher than atmospheric. (Not that I have any idea of the effects of pressure on sparks...)

Tim

Chris Whelan ( snipped-for-privacy@prejudicentlworld.com) gurgled happily, sounding much like they were saying :

IME about 3mm+ is the point at which the damn thing won't start, and thereby uses no fuel...

The further apart the electrodes (within limits) are, the better the fuel economy. What is the explanation for that? Any one?

:-)

Chris

Fancy a carrot?

"Lin Chung" wrote in news:nA5Bh.13400 $ snipped-for-privacy@newsfe3-gui.ntli.net:

Bigger spark over a bigger distance? More fuel ignited quicker?

Tunku wrote in news:Xns98D9B6C4961Cstuartggraydslpipexc@216.196.109.145:

Big gap = no spark = no fuel burnt = 100% economy ;-)

Stu

Stu wrote in news:1171658861 snipped-for-privacy@sp6iad.superfeed.net:

Must be a fine point between the two then ;-)

Actually setting the gap different from the car manufacturer's specification is unwise.

As a thought experiment, imagine increasing the gap steadily, the combustion will progressively become:

1) more efficient > increased power, can be interpreted as MORE mpg (keep the speed as before, so travel a bit farther) ; and 2) more complete > less exhaust O2, but ECM in response to the lambda sensor promptly injects more fuel to make up for the 'deficit' > more fuel used > so LESS mpg.

It is at the 'sweet spot' that the two are optimally compromised (the crossing of the two graphs on a mpg-verses-gap plot), and that must also be the plug gap the car manufacturer specifies for best economy and power.

Hence, my contention that deviation from the manufacturer's specified gap value (for a specific recommended spark plug model) is counterproductive.

Sorry, more O2, ie leaner mixture, not "less" O2.

If it's a Mk 2 Mondeo Zetec, the reason for the different gaps is down to time. Up until 1999 (or so) the gap was 1.3mm. After that, it was 1.0mm.

This is because the voltage (spark) is so high, it finds it easier to track down the side of plug lead 1 (shortest lead, closest to gearbox), rather than jump the gap.

This means lunched plug leads, uneven idle, and many postings on the internet.

Pete.

Ignore my last two posts. On second thought, there is an unresolved problem! The reasoning was sound but the facts on which the reasoning was based might not be!