can we talk plug gaps?

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pjc360

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I'm trying to determine what the best gap would be for my set up and figured you guys would know as much as anyone, I know alot of people here run cd ignitions and hei conversions and have expierence with trying different gap sizes.
My engine is a 300hp crate 360 magnum, compression is 9:0.1 i run 91 octane fuel i live 4000 feet above sea level. My initial timing is 15 degrees and total timing is 33 degrees and i have another 10 degrees of timing added to idle from vaccum advance on manifold vaccum, so accually have 25 degrees timing at idle. I have a crane cams hi-6 cd ignition and a crane cams lx91 coil and i'm running champion rc12yc plugs and i have all my plugs indexed. Crane says .045 is a good gap to run with a good ignition, so when i installed it i gapped up to .045 from .035 and didnt have any misses thru out the rpm range.
A guy i work with said he runs a .060 gap in his small block 350 chevy with a mallory hyfire cd ignition, he told me to go up .5 in gap size untill i have a miss and then back down .5 and run that as my gap, so i gapped my plugs to .050 from .045 and still dont have a miss. But i am skeptical in going any larger then .050, in fact i was skeptical even going to .050. But as far as i can tell i dont have any misses. So my question is can a cd ignition light off a .050 gap with no problem? Or should i go back down to .045 just to be safe? or should i keep going up in gap size untill i get a miss and then back it down? What do you guys run for gaps that are running cd ignitions and hei ignitions?
 
I run .045 just to be safe.
Running a GM HEI conversion that can go larger but think about this.
If you gap it larger till you get a miss then that spark is very likely to go somewhere you dont want it going.
It can burn right through a plug wire, or rotor ruining them.
It can even burn/short the coil internally.

.045 - .050 would be the max I'd go for safety.


OH, also some plugs are really close to the pistons already and opening the gap too much can cause it to touch the piston.

Just my own experience and oppinion.
 
I pretty much agree with TrailBeast on this. Ignition systems are a "funny thing." The conditions of combustion and the spark gap determine the voltage at the plug, which is loading down the "open circuit" voltage which that particular system can output

So as you open this gap, and as the voltage goes up, the STRESS on the entire secondary system--- coil, rotor/ cap, wires and plugs, gets worse. This of course is the very reason that OEM went to larger plug wires---better insulation.
 
So should i just leave them alone gapped at .050? or should i back them back down to .045? My distributer is brand new and i have a good cap with copper inserts instead of brass (better conductor) and I have a good rotor. I am in need of some better plug wires i'm sure, i currently have borg warner selects 7mm wires that test out around 450 to 500 ohms of resistance per foot. I'm thinking about getting some taylor wires or some crane fire wire in a 8mm or 8.5mm.
I know the plugs wear over time and .055 might be too much of a gap, so i am leaning towords dropping them back down to .045. But my plugs are indexed and are brand new. But still i wanna be safe from miss fires. so what would you guys do? call it good at .050 or pull em back out and go back to .045?
 
I would wait until it has worn a bit (20K miles) before removing to re-gap. A few mis-fires shouldn't hurt anything, and will tell you if you need to re-gap sooner. You will first notice a mis-fire at low rpm, WOT, like accelerating on a freeway ramp. I had that in my 2.4L engine and fixed by lowering the gap from the factory setting. Took me a while to figure out the problem, and it was a bad miss. A Mopar TSB for the 2.4L turbo engines suggested that.
 
BillGrissom said:
I would wait until it has worn a bit (20K miles) before removing to re-gap. A few mis-fires shouldn't hurt anything, and will tell you if you need to re-gap sooner. You will first notice a mis-fire at low rpm, WOT, like accelerating on a freeway ramp. I had that in my 2.4L engine and fixed by lowering the gap from the factory setting. Took me a while to figure out the problem, and it was a bad miss. A Mopar TSB for the 2.4L turbo engines suggested that.
Click to expand...

Hey Bill,
Once the spark escapes the system through one of it's components it will get worse fast. because every time it will encounter less resistance than the last time.
The issue isn't the misfire, but more where the spark goes to find a ground.
 
I'll probly just drop them down to .045 and call it good. Even tho i'm sure this crane box and crane coil is more then capable of firing a .050 gap consistently. The crane coils have a lower turns ratio to keep the spark gap current stronger. does a lower turns ratio mean the coil fires the plugs faster or does it mean it gets a more powerfull spark?
 
i believe the turns ratio of my coil is 54.4 or something like that? i just remember the lower turns ratio makes for the best possible spark gap, whatever that means? thats why im asking because i'm not sure what that means?
 
The more windings/turns there are in the secondary windings of the coil, the higher the output of the spark.

Higher voltage = hotter spark, and therefore quicker and more efficient ignition of the air/fuel mixture.

Here is a really good article from Hod Rod magazine on coils.
http://www.hotrod.com/techarticles/ignition_coil_tech/
 
so with my crane coil having a 54.5 turns ratio or whatever, what does that mean? a powerfull spark? more spark? faster spark? i'm confused....
 
thats funny trailbeast, i was just reading that article right before you posted that lol
 
still dont really understand what the lower turns ratio does, crane claims the lower turns ratio gives better spark gap current, wich means what?
 
The more windings/turns there are in the secondary windings of the coil, the higher the output of the spark.

Higher voltage = hotter spark, and therefore quicker and more efficient ignition of the air/fuel mixture.
Click to expand...

Yup, more windings = higher voltage and lower current.

still dont really understand what the lower turns ratio does, crane claims the lower turns ratio gives better spark gap current,
Click to expand...
Current is flow of electrons. Voltage is potential, or in a water pipe analogy pressure. It is a tradeoff in ignitions which is optimal.

Voltage is what makes a spark jump. Current is what eats up contacts.
 
well i took the plugs out and gapped them back down to .045, they all looked golden brown and non of them were fouled. It may just be in my head, but i think it idles a little better with the .050 gap vs the .045 gap. And since all of them were golden brown that must mean the crane box was firing the plugs just fine.
 
my coil has a turn ratio of 54.1, does this mean it can fire a plug with a slightly larger gap?
 
Dude, please just leave them at 45 and be done with it. As previously stated increasing your gap just adds strain to all the components in the ignition system. You should be able to run fine on .045 and if it doesn't you have something else to worry about.
 
I am leaving the gaps at .045, i'm just trying to learn about my coil and its strengths and weaknesses, i purchased a performance ignition rotor made by Echlin part number Mo-3000. The end of the rotor is just a little bit longer i guess and it helps reduce scattered spark inside the cap and helps get more voltage to the plugs because it gets more thru the wire then to the plug from my understanding. Anyone else here running this rotor? you can get it from napa for about 7 to 8 bucks.
 
The 7,8,8.5,8.8 plug wire you get are the diameter of the insulation, nothing to do with the inner carbon filament size. 8.8 is a big wire that can handle lots of juice, like multi strike CD and magneto. .050 is usually what MSD recommends. Nothing to gain by going bigger if you use Crane Hi-6 multi strike as the CD coil output is pretty big with a 300V input from the box.
 
ya i have left my gaps at .045 and my plugs are indexed. I put the echlin mo-3000 rotor on it. I really want new plug wires, i would have to have a custom set made for me or get universal set that you make.
My coil takes the hei type plug in but then the other end takes the female mopar distributer cap type plug in, and i like keeping my coil wire real short, right now my coil wire is only about a foot long if that.
 
i just dont know wich brand to go with, thinking ether taylor thundervolt 8.2mm or taylor spiro pro 8mm or crane's 8.5mm fire wire or some black msd 8.5 mm super conductors. the msd's are around 80 bucks the thundervolts are around 60 to 65 the spiro pro's are 50 to 60 and the crane fire wire is 50 to 60.
 
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