Spark Plug Adapters
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Ralph "Trapper" Trapaga
Aug 5, 2025, 5:04:55 PMAug 5
to FalconRV-List
Hey guys,
I noticed some text traffic about Iridium spark plug adapters, used of course to increase the auto plug diameter so it'll fit the bigger holes meant for aviation plugs. I did this for a while, and found it was a pain in the posterior to change out the plugs, having to use a vice in order to twist the soft adapters.
As I may have shared with our group, I've gone the way of what many do at Mallard's Landing. For my PMag ignition, instead of Iridium plugs I switched to Autolite 386 plugs that have the same diameter as aviation plugs and replace them every year with new ones. They're widely available at car parts stores (I've even bought them at Walmart). I've had no fouling and overall good performance from them.
And as also done by many at Mallard's, I did a G3i ignition cable conversion on my Slick Mag side, allowing me to use the Autolite plugs throughout. No need to buy/borrow a spark plug cleaner and pick the lead out. Just toss the used plugs into the trash every year and replace with new. No cleaning, no adapters...just gap and install.
Here's the website for G3i, which was a pretty easy conversion:
Some might throw stones at this, but I just wanted to provide an option to consider that's employed by many in the Experimental world. Do your due diligence and I think you'll agree that this option works like a champ.
Best,
vic syracuse
Aug 6, 2025, 6:59:52 AMAug 6
to Ralph "Trapper" Trapaga, FalconRV-List
Make sure you are using the spark plug anti-seize when using the adapters. Sometimes the 386 style plugs will cause radio noise.
Vic
Sent from Gmail Mobile
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Ralph "Trapper" Trapaga
Aug 6, 2025, 11:23:16 AMAug 6
to vic syracuse, FalconRV-List
So far I've had no radio noise at all with the 386's...
Ralph "Trapper" Trapaga
Aug 6, 2025, 11:30:57 AMAug 6
to Alton, FalconRV-List
No worries, Alton. As I told Hollywood last night, G3i recommends a .026" gap on the Slick side. For the PMag side, I use the gap specified on Page 9 of their manual at .030-.035". We're talking only a .004-.009" difference so you could just set to .030" give or take and call it a day.
On Wed, Aug 6, 2025 at 10:36 AM Alton <adew...@comcast.net> wrote:
Screwed that up, my apologies for two emails.Trapper, your email was forwarded to our Dawg Flight list.RV7A, IO360 here. Curious what gap you are using?I am going to swap over to these.AltonN526RVGet Outlook for iOSFrom: Alton <adew...@comcast.net>
Sent: Wednesday, August 6, 2025 9:34 AM
To: trapp...@gmail.com <trapp...@gmail.com>
Subject: Fw: [falconrv-list] Spark Plug AdaptersGet Outlook for iOSFrom: Alton <adew...@comcast.net>
Sent: Wednesday, August 6, 2025 9:29 AM
To: Carl Wood <cwoo...@gmail.com>
Subject: Re: [falconrv-list] Spark Plug AdaptersI’ll give them a try. 50,000 ohm plug seems like a lot. The end is screw on.Get Outlook for iOSFrom: Carl Wood <cwoo...@gmail.com>
Sent: Wednesday, August 6, 2025 5:23 AM
To:
Subject: Fwd: [falconrv-list] Spark Plug AdaptersTrapper, your email was forwarded to our Dawg Flight list.RV7A, IO360 here. Curious what gap you are using?I am going to swap over to these.AltonN526RV
Jim Faber
Aug 6, 2025, 1:31:15 PMAug 6
to Ralph "Trapper" Trapaga, FalconRV-List
I have dual electronic ignition on my RV 10. And I use the iridium plugs with adapters top and bottom. I get them for about $7 bucks apeice (rock auto) and I replace them every year. I use anti seize on them and have had no issues getting them out. I like the idea of not needing the adapters with the champion plugs, but I think the Iridium plugs are better. Given the relatively small amount money saved, I think I'll stick with the Iridium plugs.
Good to know though.
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Ralph "Trapper" Trapaga
Aug 6, 2025, 11:14:27 PMAug 6
to Jim Faber, FalconRV-List
All good, Jim. The cost difference is really not a factor ($2.50-$3 vs. $7 per plug). But for me, the adapters are separate parts added to a high pressure point on the engine. They've been used for years and I'm not aware of any data showing cracking and/or failure, but I don't want to deal with that possibility regardless of how remote it might be.I also have to wonder about having 2 torque points: one for the plug into the adapter and another for the adapter into the cylinder. You're not supposed to torque the adapters without the plugs in them or they can collapse.
As for the iridium plugs being better: they're designed to last longer (100,000 miles in a car) because the electrodes are made of iridium, but that's about it. I maintain that the 386's I use are every bit as good (and I've been using them for years), they just don't last as long because they're not made of iridium. By replacing the plugs with new ones every conditional, this is a non-issue in my book. Just the same, I fully respect your choice and merely wanted to respond for the benefit of our discussion.
Jim Faber
Aug 7, 2025, 8:26:05 AMAug 7
to Ralph "Trapper" Trapaga, FalconRV-List
I believe the Iridium plugs offer a better spark, more focused and stronger spark After all isn't that what a spark plugs all about?
Jon Fitzsimmons
Aug 7, 2025, 9:39:02 PMAug 7
to Jim Faber, Ralph Trapper Trapaga, FalconRV-List
To add an extreme data point, after 285hrs in 12 months the BR8ES plugs were running just fine on my PMags (although they did show a wider gap and definite wear), however one plug did manage to work loose and was starting to leak which I picked up on and changed
them at OSH. I may start electively doing a 100-150ish hr inspection just to check plug torque and couple other odds and ends, the 18lb torque for the adapters always seemed low and it was in this case. May try those 386's.
I believe the Iridium plugs offer a better spark, more focused and stronger spark After all isn't that what a spark plugs all about?
On Wed, Aug 6, 2025, 11:14 PM Ralph "Trapper" Trapaga <trapp...@gmail.com> wrote:
All good, Jim. The cost difference is really not a factor ($2.50-$3 vs. $7 per plug). But for me, the adapters are separate parts added to a high pressure point on the engine. They've been used for years and I'm not aware of any data showing cracking and/or failure, but I don't want to deal with that possibility regardless of how remote it might be.I also have to wonder about having 2 torque points: one for the plug into the adapter and another for the adapter into the cylinder. You're not supposed to torque the adapters without the plugs in them or they can collapse.
As for the iridium plugs being better: they're designed to last longer (100,000 miles in a car) because the electrodes are made of iridium, but that's about it. I maintain that the 386's I use are every bit as good (and I've been using them for years), they just don't last as long because they're not made of iridium. By replacing the plugs with new ones every conditional, this is a non-issue in my book. Just the same, I fully respect your choice and merely wanted to respond for the benefit of our discussion.
Best,
On Wed, Aug 6, 2025 at 1:31 PM Jim Faber <james...@gmail.com> wrote:
I have dual electronic ignition on my RV 10. And I use the iridium plugs with adapters top and bottom. I get them for about $7 bucks apeice (rock auto) and I replace them every year. I use anti seize on them and have had no issues getting them out. I like the idea of not needing the adapters with the champion plugs, but I think the Iridium plugs are better. Given the relatively small amount money saved, I think I'll stick with the Iridium plugs.
Good to know though.
On Tue, Aug 5, 2025, 5:04 PM Ralph "Trapper" Trapaga <trapp...@gmail.com> wrote:
Hey guys,
I noticed some text traffic about Iridium spark plug adapters, used of course to increase the auto plug diameter so it'll fit the bigger holes meant for aviation plugs. I did this for a while, and found it was a pain in the posterior to change out the plugs, having to use a vice in order to twist the soft adapters.
As I may have shared with our group, I've gone the way of what many do at Mallard's Landing. For my PMag ignition, instead of Iridium plugs I switched to Autolite 386 plugs that have the same diameter as aviation plugs and replace them every year with new ones. They're widely available at car parts stores (I've even bought them at Walmart). I've had no fouling and overall good performance from them.
<image.png>
And as also done by many at Mallard's, I did a G3i ignition cable conversion on my Slick Mag side, allowing me to use the Autolite plugs throughout. No need to buy/borrow a spark plug cleaner and pick the lead out. Just toss the used plugs into the trash every year and replace with new. No cleaning, no adapters...just gap and install.
Here's the website for G3i, which was a pretty easy conversion:
Some might throw stones at this, but I just wanted to provide an option to consider that's employed by many in the Experimental world. Do your due diligence and I think you'll agree that this option works like a champ.
Best,
--
Visit our website: https://sites.google.com/view/falcon-rv-squadron/home
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Dean M.
Aug 7, 2025, 9:52:01 PMAug 7
to Jon Fitzsimmons, Jim Faber, Ralph Trapper Trapaga, FalconRV-List
Those NGK BR8ES are the same plugs on my 1988 jetski, and subsequent skis, two strokes. I'm dating myself, but they were considered expensive at $1.75 each.
Darryl Hudec
Aug 8, 2025, 8:22:38 AMAug 8
to Dean M., Jon Fitzsimmons, Jim Faber, Ralph Trapper Trapaga, FalconRV-List
Blonds, brunettes, red heads. Camels, Lucky Strikes, Salems. Bud, Bud light, Bush. It kinda boils down to what you like. I tried 2 dollar plugs, 8 dollar plugs and some in between . Fancy grounds, tiny electrodes, bla, bla, bla. In the end the NGK’s turned out to be the most reliable. The adapters are a bit of a distraction but, work fine. I used to get all wrapped up on torques for the adapters but, when removing the plugs, some of the adapters would unscrew with the plug. Now , I gotta separate the plug from the adapter; PITA. Now I just tighten plug with or without adapter until my elbow cracks . Oh I know, some of you are aghast at the idea of not using a torque wrench. I borescope every 50 hrs so the plugs are checked often. Never had one fallout or get loose. Personally, I like blonds but, they all work.
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Martin Walker
Aug 8, 2025, 6:08:37 PMAug 8
to Darryl Hudec, Dean M., Jon Fitzsimmons, Jim Faber, Ralph Trapper Trapaga, FalconRV-List
Are the 386 the right heat range? 8 is what I’m using on my lowers with efi ignition
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vic syracuse
Aug 9, 2025, 6:04:19 AMAug 9
to Martin Walker, Darryl Hudec, Dean M., Jon Fitzsimmons, Jim Faber, Ralph Trapper Trapaga, FalconRV-List
Some have luck with them, as noted here. Personally, I stick with the Denso iridium IK27 or IHK27(long reach like on the IO-390). The trick is to place the spark plug into the adapter and then insert the assembly into the spark plug hole. Tighten the spark plug and then use a 7/8” deep well (aircraft spark plug socket) and tighten the adapter just a little bi more. Then the plugs will always come out leaving the adapter in the cylinder.
Vic
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Ralph "Trapper" Trapaga
Aug 12, 2025, 4:31:48 PMAug 12
to Jim Faber, FalconRV-List
Jim, pardon the delayed response but we’ve been in CO.
Regarding the performance of iridiums vs. the copper 386’s, I’ve read about the “focused spark” that the former offers, but that the benefit is more for racing engines operating at very high RPM’s. For our engines, running between a nominal range of 2200 and 2700 RPM, I’ve read that the copper plugs actually offer better performance. There are many opinions on this but I found that this article lays it all out pretty well and is from an objective source: Copper Vs Iridium Spark Plugs (With Pros & Cons) Briefly, the comparison states that:
“Iridium plugs are stronger and tougher than Copper, nonetheless, when it comes to performance, iridium plugs perform lower than its counterpart.”
Moreover, the argument for “focused spark” is based on automobile engines with a single plug per cylinder. I’d say that having 2 coppers firing together will offer all the spark (regardless of “focus”) as needed for optimal performance. Based on the comparison above, this should be better than iridiums, not to mention no need for adapters with the 386 plugs.
Speaking of the 386, here’s a summary of the benefits that they offer according to Autolite (which I recognize as being possibly biased):
Autolite Copper spark plugs are engineered to deliver quick starts and the power your vehicle or applications needs to meet performance expectations.
- The copper core center electrode aids in thermal control and improves resistance to fouling.
- Its specially engineered high nickel alloy center and ground electrode provides extended life.
- The high alumina multi-rib ceramic insulator provides thermal conductivity and superior insulation for increased strength.
- Designed with a nickel-plated shell that is corrosion resistant to provide increased durability for extended periods.
There may be other arguments but for me personally, I ran the iridiums for several years and found that after switching to the 386’s I had as least as the same performance as with the iridiums. Performance took a noticeable improvement after my engine overhaul at Penn Yan. It runs as smooth as a turbine and pulls harder than ever. I couldn’t recommend them more highly.
Ralph "Trapper" Trapaga
Aug 12, 2025, 4:56:15 PMAug 12
to Martin Walker, Darryl Hudec, Dean M., Jon Fitzsimmons, Jim Faber, FalconRV-List
Flameout, this is an excellent question that I was remiss in discussing.
Correct that the IO-360 has an "8" heat range. I believe that the IO-540's have a "6" heat range but I haven't verified it. The last number on the Autolite plugs denote this, with the 386 being in the "6" heat range. This is what they've been using at Mallard's so I thought I'd start with them. At my next Condition Inspection, the insulators all looked perfect so I've been using them ever since (too cold a heat range and you'll see dark residue, too hot and you'll see a yellowish, blistered appearance). If you'd prefer the 8 heat range, you can install Autolite 388 plugs. Like the 386's, they have the 18mm thread diameter that fits directly into the hole without the need for an adapter. They're readily available and can be had for $1.75 apiece. I'd appreciate knowing your results if you use them.
Again, I'd consider these plugs disposable because the electrodes will wear quicker than the iridiums. The good news is that they'll save you from having to buy/borrow an $800 plug cleaner, not to mention a lead picker.
I've gotta see your Jaguar XKR. Hoping you'll bring it to our Kill the Keg event.
On Fri, Aug 8, 2025 at 6:08 PM Martin Walker <martinw...@gmail.com> wrote:
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