ArKay99

iTrader: (1)

This is something I hadn't thought about, but I have strarted to wonder. As I understand it, the narrower the gap, the slower the burn. I am running AFR heads milled .030", mounted on Cometic .040" gaskets, pistons out the hole .004", pistons cut .065", Comp XER 224/228 .581"/.588" on a 112 installed 112 ICL. I also am running Kooks LT's, ported LSX90mm Intake and Nick Williams 90mm TB. I had NGK TR55 IX's and had occasional KR up to 2 degrees with the CR at 10.7:1. Now at 11.2:1 and with NGK TR6IX's I get no KR at all. Using Sunoco 94 Octane. I have them gapped at .035" (factory setting). Should I open them up? I will probably be putting ~450rwhp.
What is the accepted way to find the ideal spark gap? Is there one? My timing table is at 28 degrees @WOT.

AsianIce25

iTrader: (2)

just leave it stock gap or if you really want to...open em up a lil. stock gap will be fine though.

PREDATOR-Z

If you're staying NA at 11.2:1, I would gap .038>.042, myself I would do .042

oange ss

iTrader: (50)

general rule of thumb, reduce gap .20 from stock for every 50 horsepower added

777

iTrader: (21)

umm no. That would mean I would be running like a .20 gap I feel bad for your "thumb." I believe the rule of thumb is .05 for every 50rwhp.

oange ss

iTrader: (50)

uh yeah..swap the 2 and the 0 around

777

iTrader: (21)

I figured it was a type-o.

ArKay99

iTrader: (1)

That makes sense, but also confuses me a little. Stock gap for TR55's is .050" (higher heat range). Stock gap for TR6's is .035" (1 heat range colder than stock). So does the 'rule of thumb' apply to stock gap (.050") and does the heat range play a part in altering the 'rule of thumb'? It seems to me that compression ratio coupled with quench area and height would be a determining factor also. Whoa! Maybe I'm getting too deep for this!
I've added ~150rwhp so by the 'rule of thumb' I should be running a .035" gap.
Should I start opening the gap until I get KR and then back it off a little? This is starting to sound like I'm playing with optimum timing. See J-Rods thread. https://ls1tech.com/forums/advanced-engineering-tech/254868-ignition-timing-101-a.html

oange ss

iTrader: (50)

stock gap for LS1 is .060 from the factory, the rule of thumb is just that, and it's because of higher cylinder pressure that it is used, but was also the standard for older ignition systems that had trouble keepin up with the demands of highly modified vehicles,..... has nothing to do with detonation , only keepin the flame kernel from the plug "hot"

ArKay99

iTrader: (1)

Ok. Thanks for the clarification. That makes sense. Looks like I should open the gap to ~.045".

Adrenaline_Z

Since the LS1 uses individual coils for each cylinder, the coil energy between
power strokes is much higher than a single coil motor.

That extra voltage charge allows for a wider gap when compared to a single
coil system under the same circumstances.

Cylinder pressure, static compression, RPM and fuel type play a big role in the
gap setting as well. I don't know if there is a cross reference chart, but I would
imagine manufacturer sites like NGK, or MSD would have good info.

As for burn rate being affected by spark plug gap, that's news to me.
I'd like to read more about that.

JZ'sTA

iTrader: (23)

I have always used NGK plugs and I have always called them and asked what gap I should be at.
I very rarely change it that much.
From what I was told thy try and gap it where thay believe it should be gaped.
Kinda like how Yank has a converter guide on their web page, it's not always exact for every car but is close for most setup's.
I would probally gap the plugs for your setup around .040

Brandon Boomhauer

iTrader: (10)

So I should run a .050 on mine?
with tr55s?? or are the 6s better for a cam car?

I'm runnin 55s at stock gap right now...

JZ'sTA

iTrader: (23)

55's at stock gap are .050 I believe.
The 6's are a bit colder plug. Most Nitrous/FI cars require a colder plug. I run the TR8xi's in my car as I spray A LOT.
I tried the 6's and in one nitrous pass a few plugs were garbage.
I would say that somewhere between .048 and .045 would be a good area for a cam only car.

oange ss

iTrader: (50)

not burn rate, that's affected by timing, combustion chamber design, yada, yada, yada..... flame kernel of the spark...in older ignition systems in highly modified vehicles , the flame could all but be blown out , hence the smaller spark gap..but as stated earlier this is on older, less effecient ignition systems..also the reason for reducing spark gap for lots of nitrous

777

iTrader: (21)

both sets of my tr55's are gapped at .055. Not .050 like everyone is telling me. I should probably run a .050 gap but I'm not into bending the plugs and what not. Plus they are hard to bend haha. .055 should be good enough.

PREDATOR-Z

Let us not forget to account for his compression. Like it is said above .042 (my preference) and .045 being max.
It has to do with the increased pressures in order not to "blow out" the spark and have increased missfires.
Plugs are a PIA to put in, otherwise the proper thing to do is to run different gaps and datalog your missfires. The one that gives you the least and is the widest, is the gap you want to run.

Brandon Boomhauer

iTrader: (10)

So I take it I should run a 50 on my TR55s?
or should i setup to the TR6?

VSGLS1

iTrader: (8)

Anyone considering he is using Iridium plugs??? Leave them at the gap the came in.

Adrenaline_Z

That's exactly what I thought, hence the slight sarcasm.

As for finding the perfect gap, there's another trick (but not many have
the resource):

Increase the primary coil voltage in 0.010 mV steps until the misfires cease
under the most extreme engine conditions.

From that voltage figure, you can determine the plug gap needed at the
'standard' system voltage.

It's a good alternative to trying different gaps which is time consuming.

You would have to consider the coil winding ratio to prevent excessive
secondary side voltage which could damage the plug and wires.