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post #1 of 11 Old 11-30-2012, 07:24 PM Thread Starter
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What spark plug for 20psi boost?

Apologies for having to bring up this "old as dirt" subject but I cannot find any info with the crappy search engine on this website

What spark plug do y'all prefer in a high boost 2.2 / 2.5?

I used to run NGK GR5 spark plugs per the general consensus (and Ed Peters if I recall correctly) for high boost engines but cannot find them in town unless I special order and wait a week. One store sold me a Champion RN14YC as an equivalent but I don't believe it, 14 is a bit hot and a cross reference at the Champion home page shows the heat level of an eleven or twelve being equivalent to the GR5 heat level. I remember running Champion RN9YC in years past but maybe that was when I was sinking my automotive education monies into that '69 Dodge 340 engine.

My recollection is to ignore all Platinum coated plugs in our applications. Would we want to go cooler or hotter?
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post #2 of 11 Old 11-30-2012, 07:30 PM Thread Starter
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Re: What spark plug for 20psi boost?

Here is a link to a Spark plug heat cross reference:
Heat Range Conversion Chart
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post #3 of 11 Old 11-30-2012, 07:40 PM
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Re: What spark plug for 20psi boost?

Most everyone uses Champion RN9YC, colder than the RN14YC. I only run 24 psi but have had no problems with them.

Thanks
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post #4 of 11 Old 11-30-2012, 07:41 PM
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Re: What spark plug for 20psi boost?

if the 9's are too hot you can run the coldest plug the AR51 Autolights too
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post #5 of 11 Old 11-30-2012, 07:44 PM
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Re: What spark plug for 20psi boost?

Yeah stock most what I've seen over the years myself, we're, RN12's the Rn9's I liked better just ran cooler, with a slightly bigger gap at 40 that's how I used to roll.



Hey Super Pope, what are AR51's?
And how would they affect EGT, if installed?

Last edited by GhostDaytona; 11-30-2012 at 07:55 PM. Reason: asked question
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post #6 of 11 Old 11-30-2012, 11:30 PM
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Re: What spark plug for 20psi boost?

I use RN9YC's with stock gap. This is stock timing at 28 psi, and the plugs always look perfect. My intercooler is near 100% efficient though, and I have water injection, plenty of fuel, and a wideband, so I think I have zero detonation issues.
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post #7 of 11 Old 11-30-2012, 11:51 PM
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Re: What spark plug for 20psi boost?

I run RN9YC's also, but with a slightly tighter gap than stock. I'm at 20 psi, with stock stuff at the moment (other than the basic 3 bar requirements, of course). I tuned it to not set off the knock light without water/meth, but I run a little bit for added insurance. The plugs look fine when I check them periodically. It has been my daily driver for the last several years also if that helps.
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post #8 of 11 Old 12-01-2012, 06:29 PM Thread Starter
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Smile Re: What spark plug for 20psi boost?

OK thank you all for your comments! I found another long tread on this website about plugs and have adjusted a set of RN9YC to .035 inch gap, installed them, and am very satisfied that the 2.5TII in my omni now runs fine.
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post #9 of 11 Old 12-01-2012, 11:03 PM
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Re: What spark plug for 20psi boost?

BTW people running real high boost also like 28 for the gap, to keep the boost from snuffing the spark..
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post #10 of 11 Old 12-02-2012, 12:02 AM Thread Starter
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Re: What spark plug for 20psi boost?

Thanks for that Mr. Pope- i understand orienting the gap in special orientation with respect to the intake valve but hadn't considered modifying the gap to accommodate extra high velocities in the combustion chamber. We have family in Colfax if you are near there.
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post #11 of 11 Old 12-02-2012, 01:57 AM
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Re: What spark plug for 20psi boost?

yeah been through Colfax a lot. They all come up here to the "big city" to shop lol.

I don't know that turning the plug matters much with boost, the AR plugs though have a shorter electrode though for a better fire path.
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