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10-27-2012, 08:49 PM
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Join Date: Aug 2009
Location: Goodyear, Arizona
Posts: 877
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What spark plug gap for NGK BR8ES?
I am using automotive spark plugs in my IO-375 with dual P-Mags. Just wondering what gap I should be using for the NGK BR8ES plugs. They come out of the box with .025 gaps, so I installed them as is with no change. They seem to run fine after a couple of test flights. But I'm wondering if anybody has actual data showing how/why it would be better to use a different gap. Thanks!
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Karl, Goodyear, Arizona (KGYR) ATP, CFII
RV-14A, Flying
Extra 330LX, Flying
RV-8, Sold
RV-7, Sold
Bearhawk 4-Place, Sold
=VAF= donor 2020
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10-27-2012, 08:53 PM
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Join Date: Jan 2005
Location: SC
Posts: 12,887
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Always check the gap of plugs before installing them. I have seen them come out of the box and be all over the place.
To answer your question, I have mine set at .032.
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Bill R.
RV-9 (Yes, it's a dragon tail)
O-360 w/ dual P-mags
Build the plane you want, not the plane others want you to build!
SC86 - Easley, SC
www.repucci.com/bill/baf.html
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10-27-2012, 08:57 PM
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Join Date: Nov 2007
Location: NJ
Posts: 1,747
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IIRC, the range is .030-.035
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My ATC opinion is NOT an official FAA recognized opinion, so any advice you get from me is ONLY my opinion.
Track my RV7A!!
Bought my flying -7A
Building an -8! (Fuse)
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10-27-2012, 09:31 PM
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Join Date: Feb 2006
Location: George West, TX
Posts: 567
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Quote:
Originally Posted by tkatc
IIRC, the range is .030-.035
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Correct, right from the manual. 
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Deal Fair
RV-4 (N34CB)
George West, TX (8T6)
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10-27-2012, 10:34 PM
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Join Date: Aug 2009
Location: Goodyear, Arizona
Posts: 877
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Okay guys, thanks. I did measure the plugs individually, and they were very consistent at .025 right out of the box. The plane seems to run fine (no CHT anomalies, etc.) at that gap.
But...
You say that "the manual" says the range is .030 to .035. Which manual is that please? I've been digging around in my manuals and haven't been able to find that yet. If you could tell me which one to look in, that would help greatly.
Finally, what might be the consequences of running these automotive plugs at .025?
__________________
Karl, Goodyear, Arizona (KGYR) ATP, CFII
RV-14A, Flying
Extra 330LX, Flying
RV-8, Sold
RV-7, Sold
Bearhawk 4-Place, Sold
=VAF= donor 2020
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10-27-2012, 10:54 PM
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Join Date: Jan 2005
Location: SC
Posts: 12,887
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Look at page 8 of the E-mag manual. As for your 2nd question. No consequences that Iknow can thimk of.
__________________
Bill R.
RV-9 (Yes, it's a dragon tail)
O-360 w/ dual P-mags
Build the plane you want, not the plane others want you to build!
SC86 - Easley, SC
www.repucci.com/bill/baf.html
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10-28-2012, 04:54 AM
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Join Date: Feb 2006
Location: George West, TX
Posts: 567
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E-mag/P-mag Manual
Oops, sorry Karl, thought you could read my mind  Bill has it right. You can go to the Emag website for a quick download of the manual.
Cheers,
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Deal Fair
RV-4 (N34CB)
George West, TX (8T6)
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10-28-2012, 05:29 AM
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Join Date: Sep 2010
Location: Charlotte NC
Posts: 1,166
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I don't know if Emag is different from lightspeed however they recommend you gap the plugs based on timing which normally is a function of compression.
Engines normally timed at 25 degrees BTDC:
These are normally engines with compression ratios less than 8.7:1. Gap spark plugs fired by the CDI to .032"-.040".
Engines normally timed at 20 degrees BTDC:
These are usually engines with compression ratios of 8.7:1 or higher. Gap spark
plugs fired by the CDI to .026"-.035".
George
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10-28-2012, 10:52 AM
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Join Date: Aug 2009
Location: Goodyear, Arizona
Posts: 877
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This is some great information. Thanks very much guys!
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Karl, Goodyear, Arizona (KGYR) ATP, CFII
RV-14A, Flying
Extra 330LX, Flying
RV-8, Sold
RV-7, Sold
Bearhawk 4-Place, Sold
=VAF= donor 2020
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10-28-2012, 01:48 PM
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Join Date: Mar 2007
Location: Sonoma County
Posts: 3,821
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Gap to the low side so it can wear to the high side. An oversize gap will stress the coils.
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VAF #897 Warren Moretti
2019 =VAF= Dues PAID
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