Electronic ignition - spark plug gap ?

Bertonemorten · #1 (**permalink**) 01-18-2008, 03:10 PM

Hello fellow BB's

I have just finished installation of a 123 distributor and a 1.5 Ohm Flame Thrower coil to the Junior. Unfortunately I cant tell you if it has improved performance, because the kids are sound a sleep and therefore no noise is allowed in the garage (Its 23:10 here in Denmark), but it was very easy to install. I was wondering what spark plug gap to use with this setup ? The coil should be much stonger than a normal 3 Ohm, and the quick "breaker" in the new ignition system should also give increased output to the spark plugs. I use NGK B7ES plugs and solid core copper leads with 1 KOhm NGK resistors. The gap is set to 0.7 mm, should I continue to use that, or can the cap be increased ? I have heard about engines utilising gaps of 0.9 - 1.1 mm but I dont why it is advantagous ?

PiperYelloGTV2k · #2 (**permalink**) 10-20-2008, 06:52 AM

Does anyone have views on widening the plug gap? I use a new 123 distributor although with standard Bosch coil.
I did wonder if opening the gap would put any more strain on the 123?

**Tifosi** · #3 (**permalink**) 10-20-2008, 07:20 AM

Bigger gap makes a physically bigger spark, but the wider you go, the harder it is for a coil to push across that gap. (it becomes a coil voltage thing)

At the extreme end of things, a large change in gap like say .025" being opened up to .032" can actually change the way the engine runs by a little, but noticable, amount. (the biggest effect it can have is on ignition timing in electronic stuff, as the gap change effectively changes what would be dwell on a normal points type ignition)

Wide gap, narrow gap :shrug: I've always gone close to what stock called for pre-ignition change. Like if it called for .025" before, I'll go for .025" ~ .027" unless the swap involved putting in a really hot coil. (going from a 20k volt coil to a 30k volt coil isn't all that much of a change, or at least not enough to consider changing gaps, but going from a 20k coil to a 45k coil, now that's something you can work with....)

However, I make sure the ground electrode on the plug has nice sharp, crisp corners and edges by getting after it with a small file rather than the somewhat rounded stamped bit they have from out of the box.

Sharp edges make for better spark as it's MUCH easier for the electricity to make the jump when compared to a not so sharp edge. easier jump = more consistant spark quality.

PiperYelloGTV2k · #4 (**permalink**) 10-20-2008, 07:23 AM

Thanks Darren.
Further reading around eg NGK Fast Tech Tips for Street or Strip Vehicles indicates that Alfas with electronic ignition can use 0.030 in. rather than the standard 0.025 in.
I am looking for smoother pickup under 2000 RPM (standard 2L, Euro with 123 dizzy)

**Tifosi** · #5 (**permalink**) 10-20-2008, 07:25 AM

:nod:

.030" is what's actually called for on the L-jet (depending on what source you look anyway. I've also seen .025" and .027", but .030" is the most commonly quoted figure)

Bertonemorten · #6 (**permalink**) 10-21-2008, 02:32 PM

I have set my NGK's to 0,9 mm (0,035") and it runs fine with a 1,5 Ohm Flamethrower coil.

**alfaparticle** · #7 (**permalink**) 10-21-2008, 08:11 PM

I have a 123 distributor with a Bosch Blue coil. The NGK BP7ES plugs are gapped at .030". I have Weber 40DCOE's and RJ racing cams. The motor idles at 700 rpm and makes good power to 7000rpm. It is a nice setup.

maxbg · #8 (**permalink**) 10-13-2009, 09:07 AM

Sorry to dig out old thread...

I took a picture to compare 3 diff plug manufacturer.. NGK, Lodge and Autolite

The Autolite plug seem to have a longer reach. I wonder if it will do any damage to the piston?

**alfaparticle** · #9 (**permalink**) 10-13-2009, 10:07 AM

You could have problems with extended nose plugs if you have oversize valves. Piston clearance should not be a issue.

**Tifosi** · #10 (**permalink**) 10-13-2009, 12:00 PM

:nod:
What Ed said.

Using a dial indicator or piston stop will show that even when at TDC there's better than 1/2~3/4" clearance from the bottom of the plug hole to the crown.

My druther is for the protruding tip actually as it's less prone to spark masking compared to a recessed tip. (NGK BP7ES if you want a #)

maxbg · #11 (**permalink**) 10-13-2009, 06:23 PM

I see.... do you guys know what is the recommended gap setting for autolite plugs for nord engines? the default gap seemed more than 1mm.

**alfaparticle** · #12 (**permalink**) 10-13-2009, 07:01 PM

It depends upon your coil. A Bosch Blue coil or similar needs .025". Mine are at .040" but I have a Milano coil and MSD spark box. You should set them to .025" with a 123ignition dizzy and a standard coil.