spark plug gap vs lean mixtures

[NewbVetteGuy]

Any updates?

You've got a little bit of a challenge in that the LS1 coils are significantly weaker than any of the later LS coils. 40 mA peak secondary current; LS1 coils reach peak saturation @ 8ms but spark energy stops increasing after 6ms. You could crank up your max dwell time before you go in to do your emissions testing as it won't significantly decrease the life of the coil for the small duration of getting to the testing site, testing, and getting home.

I also tend to agree with going with an Iridium tipped fire wire plug to help your poor coils out and to support that larger gap that you want.

I'm trying to remember your engine, but if I remember right it's an individual runner sequential injected, very finely tuned SBC?

If so, I think NGK Laser Iridium IZFR6K11 6994 fits the bill:
14mm thread, 1.25mm pitch, 3/4" reach, extended projection tip, comes with a gap of .043".

They're $11.46 each here in the US; I don't want to know in Belgium, but they're 100k mile plugs; obviously Iridium center electrode and the ground strap has a small embedded disk of platinum on the other side -> this is what makes them last longer than the NGK Iridium IX. These are the choice of MANY OEMs.



I wish someone had a rule-of-thumb for how much you can increase the gap when running with a thin wire electrode Iridium spark plug but I haven't come across one yet.

The MicroSquirt site has some great info on your LS1 coils: http://www.megamanual.com/seq/coils.htm
AND a handy-dandy Paschen's Law calculator tool at the bottom with constants built from being fitted to a curve of coil data that the Microsquirt folks had, but I'm guessing it was done using traditional electrode spark plugs.

I'm also interested in running some lean AFRs at cruise so I've been looking into this and settled on the NGK 6994 plugs myself. I don't have to get emissions tested though so NOX isn't a concern of mine.

Adam

[FredWinterburn]

Paschen's law really doesn't apply to ignition systems because the voltage rise is so fast that there is always a voltage overshoot that exceeds the nominal gap breakdown voltage. It can easily be 1.5 times the voltage predicted by Paschen's law. Weak ignition systems have a higher voltage overshoot. For Paschen's law to work properly the voltage needs to be sneaked up slowly to the point of breakdown which is uncharacteristic of any ignition system. I could run an experiment to determine how much wider a fine wire centre electrode spark plug gap can be to maintain the same breakdown voltage but with my equipment it would be done cold, not hot so the results might not be representative. Generally speaking, adding 4 or 5 thousands of an inch gap to a fine wire plug over a conventional plug of the same resistance seems to work. That's in practice without any real laboratory testing. One could probably go even wider. Fred

Any updates?

You've got a little bit of a challenge in that the LS1 coils are significantly weaker than any of the later LS coils. 40 mA peak secondary current; LS1 coils reach peak saturation @ 8ms but spark energy stops increasing after 6ms. You could crank up your max dwell time before you go in to do your emissions testing as it won't significantly decrease the life of the coil for the small duration of getting to the testing site, testing, and getting home.

I also tend to agree with going with an Iridium tipped fire wire plug to help your poor coils out and to support that larger gap that you want.

I'm trying to remember your engine, but if I remember right it's an individual runner sequential injected, very finely tuned SBC?

If so, I think NGK Laser Iridium IZFR6K11 6994 fits the bill:
14mm thread, 1.25mm pitch, 3/4" reach, extended projection tip, comes with a gap of .043".

They're $11.46 each here in the US; I don't want to know in Belgium, but they're 100k mile plugs; obviously Iridium center electrode and the ground strap has a small embedded disk of platinum on the other side -> this is what makes them last longer than the NGK Iridium IX. These are the choice of MANY OEMs.



I wish someone had a rule-of-thumb for how much you can increase the gap when running with a thin wire electrode Iridium spark plug but I haven't come across one yet.

The MicroSquirt site has some great info on your LS1 coils: http://www.megamanual.com/seq/coils.htm
AND a handy-dandy Paschen's Law calculator tool at the bottom with constants built from being fitted to a curve of coil data that the Microsquirt folks had, but I'm guessing it was done using traditional electrode spark plugs.

I'm also interested in running some lean AFRs at cruise so I've been looking into this and settled on the NGK 6994 plugs myself. I don't have to get emissions tested though so NOX isn't a concern of mine.

Adam

[NewbVetteGuy]

Paschen's law really doesn't apply to ignition systems because the voltage rise is so fast that there is always a voltage overshoot that exceeds the nominal gap breakdown voltage. It can easily be 1.5 times the voltage predicted by Paschen's law. Weak ignition systems have a higher voltage overshoot. For Paschen's law to work properly the voltage needs to be sneaked up slowly to the point of breakdown which is uncharacteristic of any ignition system. I could run an experiment to determine how much wider a fine wire centre electrode spark plug gap can be to maintain the same breakdown voltage but with my equipment it would be done cold, not hot so the results might not be representative. Generally speaking, adding 4 or 5 thousands of an inch gap to a fine wire plug over a conventional plug of the same resistance seems to work. That's in practice without any real laboratory testing. One could probably go even wider. Fred

Any updates?

You've got a little bit of a challenge in that the LS1 coils are significantly weaker than any of the later LS coils. 40 mA peak secondary current; LS1 coils reach peak saturation @ 8ms but spark energy stops increasing after 6ms. You could crank up your max dwell time before you go in to do your emissions testing as it won't significantly decrease the life of the coil for the small duration of getting to the testing site, testing, and getting home.

I also tend to agree with going with an Iridium tipped fire wire plug to help your poor coils out and to support that larger gap that you want.

I'm trying to remember your engine, but if I remember right it's an individual runner sequential injected, very finely tuned SBC?

If so, I think NGK Laser Iridium IZFR6K11 6994 fits the bill:
14mm thread, 1.25mm pitch, 3/4" reach, extended projection tip, comes with a gap of .043".

They're $11.46 each here in the US; I don't want to know in Belgium, but they're 100k mile plugs; obviously Iridium center electrode and the ground strap has a small embedded disk of platinum on the other side -> this is what makes them last longer than the NGK Iridium IX. These are the choice of MANY OEMs.



I wish someone had a rule-of-thumb for how much you can increase the gap when running with a thin wire electrode Iridium spark plug but I haven't come across one yet.

The MicroSquirt site has some great info on your LS1 coils: http://www.megamanual.com/seq/coils.htm
AND a handy-dandy Paschen's Law calculator tool at the bottom with constants built from being fitted to a curve of coil data that the Microsquirt folks had, but I'm guessing it was done using traditional electrode spark plugs.

I'm also interested in running some lean AFRs at cruise so I've been looking into this and settled on the NGK 6994 plugs myself. I don't have to get emissions tested though so NOX isn't a concern of mine.

Adam

Thanks Fred. That's the first time I've even heard someone make a guesstimate.

Adam

[Truckedup]

Recently a friend's vintage race bike was misfiring at higher rpm on one cylinder. We dicked around for awhile with new plugs,substitute parts, but the problem persisted. So I took a pair of used NGK G plugs,fine wire gold electrode, and screwed them into his engine. The miss cleared up and he said the bike started and idled better. The gold electrode plugs was masking the problem and I believe this shows the gold plug fires with less energy than a copper NGK

[Geoff2]

What this shows is a weak ign system. System was able to produce enough firing voltage for fine wire plugs [ which require less voltage, all else being equal ] but not enough for conventional plugs.