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Old 11-28-2012, 11:49 AM
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coil and plug gap question's

I'm trying to learn a little more about ignition coils, I recently purchased a brand new crane cams hi-6 cd ignition and a crane cams lx91 coil wich is the recomended coil to run with the hi-6 on the street. I have a 300hp crate 360 magnum engine with my initial timing set at 15 degrees and total timing set at 33 degrees and i have an additional 10 degrees of timing added to the 15 degrees of initial timing at idle from my vaccum advance being on manifold vaccum.
I run 91 octane fuel and i live 4000 feet above sea level and the plugs i am running are champion rc12yc factory plugs for the 360 magnums from 94 to 98 i believe, anyways i am trying to determine what gap to run, i tried .045 and it ran better then it did with the stock .035 gap, then i tried .050 and i think it ran even better at .050, but i have been told .050 may be too large.
So i decided to do some research on my coil to try and find out whats going on with my spark and got confused... i dont know if i have a hotter spark or a faster spark or what but here is what i was able to find out about my coil. Primary resistance is 0.420 ohms, secondary resistance is 3.5k ohms, turns ratio is 54:1, inductance is 5.6mh, peak current is 100ma and spark duration is 2,800 us. So with this information, does this mean i have a coil that puts hot a good hot spark? or faster sparks? Crane claims the 54:1 turns ratio brings great spark gap current? Does that mean this coil can fire a plug with a bigger gap? And with my set up would .050 be an ok gap with my ignition and coil and engine? I forgot to add the compression ratio of my engine is 9:0.1. I'm just trying to determine the best gap to run, i have tried .045 and .050 and .050 felt the best to me, but others tell me thats too big of a gap. So please help me figure out if .045 is where i need to be or if .050 would be fine.

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Old 11-28-2012, 12:42 PM
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Quote:
Originally Posted by pjc360 View Post
but i have been told .050 may be too large.
There's your problem right there, listening to others who may not have a clue. I'm no electronic genius and the numbers you posted mean nothing to me, but I have been hot rodding for over 50 years and if there's one thing I've found out it is "do your own thing", no matter what it may be. If it works, great. If it doesn't work, try something else. If this were my motor, I'd open the gap to 0.055", then 0.060", then 0.065", then 0.070". At some point, the gap will offer more resistance than the system can overcome and you will get misfire. It is your job to find that point.
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Old 11-28-2012, 01:09 PM
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so run the .050 gap and dont worry about it? I guess i will try opening them up to .055 but that seems a little large... .050 seemed to be pretty large, but it worked without any issues. I wish somone could tell me how powerfull this coil of mine is and what its strengths and weaknesses are
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Old 11-28-2012, 02:16 PM
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Back in th "day" Im talking 80's, some gaps were as large as .080. This was due to 100,000 volt ignition systems and the need to lower emissions. My personal experience, and using an HEI, I find I can run a .040 or even a .045 gap in a plug that calls for .035. Bigger gap, bigger spark, BUT too much gap puts a strain on the cap and rotor and the coil itself. I do find my motor starts easier and runs fine with the .040 gap I m using now.
And personal preference, I will NEVER use a Champion plug, old design, old technology. I ve been doing this too long. This may start some flack but like I said, its my opinion.
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Old 11-28-2012, 04:53 PM
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well i'm just a believer in running whatever the factory put in it, so thats why i am running champs in it, never have had a problem with the champs so far. i have had problems with autolites tho, ngk and champs are my two favorite plugs to run.
But back to the gap size, i wasnt just listening to some random jerk off on the internet, a friend of mine who lives in oregon spends alot of time at a dyno near portland and they also have a suncoast distributer machine, he says you can put the plug in and adjust pressure on it similiar to cylinder pressure and he said with an msd ignition at higher rpms a .050 gap was miss firing. He told me .045 is maximum i should go. And he said since i live 4000 feet above sea level a .045 gap should be just fine because there is less density in the air or something. He said a .045 gap would assure that i'm not ever miss firing thru out the entire rpm range.
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Old 11-28-2012, 05:51 PM
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different gaps and different brands react differently. Did you index your plugs?

If you runa large gap and you have a powerful coil,then a spark will occur,,,,,,somewhere? the spark can jump through the wire to the valve cover or header,the spark will go somewhere. Your job is to make the spark jump at the plugs electrode and to do it at the correct time,the fuel will take over from there
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Old 11-28-2012, 08:05 PM
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Here is something to remember. Wider gap = higher resistance. Higher resistance = higher temps. Higher temps = higher resistance. Higher resistance =........ you get the idea. Wider gaps raise coil temps. Contact the mfg and ask about maximum recommended gap for that ignition
system, and the stay safely below it.
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Old 11-28-2012, 11:20 PM
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Quote:
Originally Posted by pjc360 View Post
And he said since i live 4000 feet above sea level a .045 gap should be just fine because there is less density in the air or something.
A motor that's built with a 9.0:1 static compression ratio and generates cylinder pressure of 160 psi at sea level will still have the same static compression ratio at 4000 ft elevation, but the cylinder pressure will be somewhat less because there is less air density to fill the cylinder during the time the intake valve is open than there is at sea level.

I seem to remember that we used 3% loss for each 1,000 ft. above sea level when I was working at Caterpillar many years ago. So, for instance, if you had 160 psi at sea level, then 160 x 0.88 would mean you would have a pressure of 140 at 4000 ft. Therefore, there will be less resistance across the plug gap at 4000 ft than there would at sea level. Therefore, you should be able to crank up the gap. Crane says the Hi-6 will fire a plug at 14.5:1 static compression ratio. If you want the straight skinny on this, call and talk to one of the techs at Crane, ask 'em what the limit would be. I've called them with questions before and they're nice guys.......
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Old 11-28-2012, 11:31 PM
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tech? is that 3% loss of power per 1000 feet a constant,or does the adiabatic lapse rate also make a difference?
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Old 11-29-2012, 08:31 AM
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I e-mailed crane and gave them my engine combination and asked them if a .050 gap would be acceptable and there reply was "our technicians claim to see no gain in performance going above a .045 gap with our ignitions".
But maybe i can ge away with a .050 being in higher elavation, and if i remember correctly my friend told me that cylinder pressure that was 180-200 can blow out a .050 flame at higher rpm from what he seen on a distributer machine...
And yes i do have all of my plugs indexed. I have a pretty solid ignition, everything is brand new except for the plug wires, and i am going to get new plug wires soon as i can.
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Old 11-29-2012, 10:04 AM
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so what does the lower turns ratio mean on my crane coil? its got a turns ratio of 54.1. Does that mean a higher voltage output to the plugs vs a coil with say 100.1 turns ratio?
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Old 11-29-2012, 12:29 PM
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Quote:
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tech? is that 3% loss of power per 1000 feet a constant,or does the adiabatic lapse rate also make a difference?
Vinnie, I'll have to admit that I had to google adiabatic lapse rate, so no, the 3% would have been a rule of thumb constant that we used. Thank you for contributing to my education, I'm a sponge for knowledge.....
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Old 11-29-2012, 03:47 PM
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Im just messing with ya Tech. I used to have an airplane so I know what you were talking about when it comes to altitude and power. For a pre flight plan we had to make sure we had enough fuel on board to get to our destination. Of course power determines speed and we dont have a lot of gas stations to just pull over get get topped up.
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