I found this site yesterday
http://www.btinternet.com/~madmole/
the bloke talks about changing the gap on the spark plugs on his mondeo from 1.3mm to 1.1mm, Says it makes the car idle better. I seemed to me an odd
thing to do given the manufacturer (ford) has obviously done the research to come up with the optimal gap of 1.3mm. Question is how does the spark
plug gap affect the performance and running of the engine. Does reducing the gap to improve lower speed running will affect the top end to some degree
as well ?
The Ford coil-pack uses a higher voltage than most, can't remember the details exactly.
With plugs set to 1.3mm Ford found there were problems with the plug leads breaking down, causing misfiring.
Cheap plug leads break down within days, the original Ford items are the only ones worth getting. Expensive but less hassle than changing them a few
days down the line.
Closing the plug gap to 1.0mm allows the leads to last much longer.
Ford now specify 1.0mm plug gap for Zetecs.
HTH
Tony
as above, in very simple terms, the bigger the plug gap the better the spark will set fire to the mixture, but the harder it will be to make the
spark.
Ultimately the biggest gap will give the best performance, but only if the mechanism that supplies the spark is up to the job. If it isn't,
performance will not be very good at all!
Thanks all makes sense now. So do new spark plugs come already set with the correct gap or do they need adjusting ? I fitted a set of NGK plugs to my zetec ages ago. Never thought to check the gap on them. Car seems to run without any problems though.
plugs usually have the right gap set, i asked the other day.
The spark plug gap determines the voltage that the HT system needs to be able to cope with ("spark gaps" are used as HV protection systems
in electronics) Note that gas at higher pressure has higher dielectric strength so it takes more volts to create a spark with a higher compression
ratio of if forced induction is used. This is why spark gaps are smaller on high pressure turbo systems; you still want as big a spark as possible,
but the volts required would be too much for the rest of the HT system (leads, coils etc).
High power microwave systems frequently pressurise waveguides to prevent internal arcing.
Bob
A manager at my company once wrote a reply to a report. It went something like "I understand every word used in this report but not in the
context used".
quote:
Originally posted by Bob C
High power microwave systems frequently pressurise waveguides to prevent internal arcing.
Bob
sorry - just another example of increase gas pressure then the sparks stop..... Waveguides are wacky things - peice of pipe that electricity goes down
- how can that work . ? . ? . For satellite comms the ground stations churn out up to a few kilowatts & it's piped down waveguides to the
big dish.
Bob
For what? Lots of different engines use the same plugs with different ignition systems and settings. All plugs come with a nominal setting and should be checked before you put them in.
sorry, my last post wasn't supposed to come across like it did. I just read what you wrote and didn't understand a word. Reminded me of the
reply on the report
Still not 100% what you wrote even after you explained it - i'll blame the organic cider 
I think that bloody stuff could be blamed for a lot of things!!!!!!!!
hee hee - serves you right for drinking a whole jar of scrumpy (and that wasn't organic). Found some lovely stuff though, looking into setting up a little brewery!
does the organic stuff give you less of a headache!!!!
well i didn't have a headache after the bbq! Found a single variety one that is just soooooo smooth, sweet, tasty, hmmmmm although its not
7.5%!
(think we're doing a thread hijack again, oh, someone was asking about where you're getting your drive shafts from on another post)
Everytime I improve anything on my Calibra turbo engine I've got to close down the plug gap to avoid misfire. I'm down to 0.58mm now, with
Denso Iridiums.
A stronger coil would allow me to run bigger gaps probably with a bit more power.