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Non Aviation Spark Plugs -- Interesting Data

bjdecker

Well Known Member
Ambassador
The setup --

My RV-7 (2018) has stock Lycoming YIO-360-A1B6, Avstar Fuel Injection, Dual Lightspeed Plasma III ignitions with "mini-sensor" option.

As mentioned on another thread I was doing some work getting fuel flows a little more predictable. Since the cowling was off, I decided to change out my spark plugs because I had noticed a little stumble at idle when the engine was warm.

Iridiums baby --

I started out with NGK BR8EIX's kind of by accident -- I used them as a replacement for the DENSO W24's from way back when. They happened to be on the shelf, and I didn't want to continue using or trying to find DENSO plugs. So, in the BR8EIX's went and ran and ran and ran for 200 hours.

New plugs --

In preparation for this exercise, I sourced NGK BKR9EIX's -- 5/8" hex, colder heat range, other than that, it's the same plug.

Initial flight testing, using same fuel flow, LOP °, altitude (5500MSL, 30.02InHg altimeter, OAT 20°C, 2500RPM, 24.7" MAP, 10.5 GPH,) etc. , showed a reduction of CHT's.

BR8EIX CHT 1: 305°F, CHT 2: 327°F, CHT 3: 305°F CHT 4: 282°F
BKR9EIX CHT 1: 299°F, CHT 2: 318°F, CHT 3: 303°F, CHT 4: 281°F

FWIW, the BR8EIXs looked fine, aside from the gap being a little more open after 200 hours...

Oh, and the stumble is gone -- so that's nice.
 
Interesting info regarding the CHT's.

Iridium vs copper electrode is always an interesting point of discussion. Supposedly the BR8-EIX will have less tendency to foul and may last a little longer, and rumor is that the spark is a little more robust. Downside is that the iridium electrode version can be 3-4x more expensive.

One thing to watch out for in ordering these NGK plugs is that they often come in two versions...solid tip vs scew-on tip. I'd recommend strongly against the screw-on tip for sure.
 
I've tried Denso with a couple of heat ranges, the Iridiums and the most basic $2 BR8ES with the solid tips from Rock Auto, and the last seem to work the best for me. Here is about 100 hours on the bottom set, as an example, swapped out at my last CI. IO-360/pmags/FM-200/Mogas&UL91&100LL(20% of the time)

IMG_7704.jpg
 
From a pure data collection standpoint I'm suspicious of the accuracy of "consumer grade" CHT probes - especially in a non labratory environment.

That said, its been a long standing drag race tip to throw brand new plugs into an engine if you want that little "extra". The plug performance is typically best right out of the box and then degrades a bit until it normalizes.

See if this behavior remains for the next 20 hours.
 
I've tried Denso with a couple of heat ranges, the Iridiums and the most basic $2 BR8ES with the solid tips from Rock Auto, and the last seem to work the best for me. Here is about 100 hours on the bottom set, as an example, swapped out at my last CI. IO-360/pmags/FM-200/Mogas&UL91&100LL(20% of the time)

View attachment 33719

+1 - my experience as well over three RVs (two IO-360 and one IO-540).

Carl
 
I've tried Denso with a couple of heat ranges, the Iridiums and the most basic $2 BR8ES with the solid tips from Rock Auto, and the last seem to work the best for me. Here is about 100 hours on the bottom set, as an example, swapped out at my last CI. IO-360/pmags/FM-200/Mogas&UL91&100LL(20% of the time)

View attachment 33719

I use the non-iridium BR8-ES plugs too and completely change them out for new ones with each oil change. My A&P thinks it's unnecessary and I don't disagree. He did my last oil change and just re-gapped them and re-installed. All is working fine, as expected.

Looking forward to G100UL being available someday.
 
I don't claim to know anything about plugs but in my recent class to get my LS Repairman-Inspection rating it was explained that a colder plug achieves that lower temp by transferring more heat to the head. If that is true then shouldn't a colder plug raise the CHT at least a little (rather than lowering it)?

So I that's correct, then perhaps something else happened. My first guess would be lower combustion temps but I've no idea how that would happen.

Anyone should feel free to correct me on any of these points.
 
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