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NGK BR8ES 3961 replacement

Well, for $2.72 (providing you purchased 8 and got free shipping, you will find out..........:D
 
To get rid of adapters, I just changed to Denso L14-U from 14mm plugs. Here is my recent experience:


I have about 5 hours on new auto plugs: Denso L14-U recommended by many on VAF. (18mm plugs, no more adapters) After 4 hours on plugs I pulled one. It was very clean, hard to read tip color. Yesterday while climbing through 7,000 feet at full throttle I leaned to about 1200 EGT. Thought full rich (EGT around 1000) was too rich. Shortly after that the engine ran very rough. It was scary rough, thought it was failing. Oil temp & oil pressure were normal. CHT normal. It smoothed out as I reduced power. About 1700 RPM was normal/smooth. Put mixture full rich and put power back to 2350 rpm, ran normally. Eventually leaned a little after level at 9,500 ft. (I don't have manifold pressure or fuel flow indications). Did a full power run up after landing, was normal. What do you think? I have good idea, but want to hear others.
 
I have about 5 hours on new auto plugs: Denso L14-U. (18mm plugs, no more adapters) After 4 hours on plugs I pulled one. It was very clean, hard to read. Yesterday while climbing through 7,000 feet at full throttle I leaned to about 1200 EGT. Thought full rich (EGT around 1000) was too rich. Shortly after that the engine ran very rough. It was scary rough, thought it was failing. Oil temp & oil pressure were normal. CHT normal. It smoothed out as I reduced power. About 1700 RPM was normal. Put mixture full rich and put power back to 2350 rpm, ran normally. Eventually leaned a little after level at 9,500 ft. (I don't have manifold pressure or fuel flow indications). Did a full power run up after landing, was normal. What do you think? I have good idea, but want to hear all.
 
To get rid of adapters, I just changed to Denso L14-U from 14mm plugs. Here is my recent experience:


I have about 5 hours on new auto plugs: Denso L14-U recommended by many on VAF. (18mm plugs, no more adapters) After 4 hours on plugs I pulled one. It was very clean, hard to read tip color. Yesterday while climbing through 7,000 feet at full throttle I leaned to about 1200 EGT. Thought full rich (EGT around 1000) was too rich. Shortly after that the engine ran very rough. It was scary rough, thought it was failing. Oil temp & oil pressure were normal. CHT normal. It smoothed out as I reduced power. About 1700 RPM was normal/smooth. Put mixture full rich and put power back to 2350 rpm, ran normally. Eventually leaned a little after level at 9,500 ft. (I don't have manifold pressure or fuel flow indications). Did a full power run up after landing, was normal. What do you think? I have good idea, but want to hear others.

To really make a good guess we would need to know your normal EGT’s at Takeoff , cruise EGT’s, EGT spread from full rich to lean and if carbed or injected. Normally as you lean a engine becomes rough because one cylinder becomes to lean to fire. 1200 would not normally be near that point but the 1000 full rich EGT is very low and might make it possible especially if you have a high fuel flow spread where each cylinder peaks. How far down your exhaust are the probes?
The other possibility was you were getting detonation. 2350 on the RPM is a bit lower than most would use in a full power climb. Fixed pitch prop? Lower RPM deceases your detonation margin. Still I think that’s unlikely and at 7000 feet you are way down on the power already and detonation margins should be large.
 
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I have about 5 hours on new auto plugs: Denso L14-U. (18mm plugs, no more adapters) After 4 hours on plugs I pulled one. It was very clean, hard to read. Yesterday while climbing through 7,000 feet at full throttle I leaned to about 1200 EGT. Thought full rich (EGT around 1000) was too rich. Shortly after that the engine ran very rough. It was scary rough, thought it was failing. Oil temp & oil pressure were normal. CHT normal. It smoothed out as I reduced power. About 1700 RPM was normal. Put mixture full rich and put power back to 2350 rpm, ran normally. Eventually leaned a little after level at 9,500 ft. (I don't have manifold pressure or fuel flow indications). Did a full power run up after landing, was normal. What do you think? I have good idea, but want to hear all.

Isn't a 14 a bit hot?

https://www.densoproducts.com/heat-range-conversion-chart-2

Denso Heat Range Chart.png
 
The Denso 5003 M22 is a colder plug with the same dimensional specs as the L14-U that might serve as an alternative if you were concerned about the plug temp.
 
How do you decipher the heat range for this particular plug part #?


Here is the Denso chart of heat ranges.
https://www.densoproducts.com/heat-range-conversion-chart-2

Here is the spec for the 5000 L14-U. Click on the "Product Specification" tab for the physical characteristics including heat range.
https://www.densoproducts.com/denso-5000-l14-u-nickel-u-groove-spark-plug

Here is the 5003 M22. Do the same as above for the specs.
https://www.densoproducts.com/denso-5003-m22-nickel-spark-plug

The heat range is actually in the part number of most plugs. You just need the decoder table. Here is a cross-reference table for multiple manufacturers.
https://www.sparkplugs.com/heat-range-conversion-chart-2

It's probably worth noting that there are counterfeit plug manufacturers(crooks!) out there, so buy from a reputable supplier.
https://www.denso-am.eu/media/1374174/identify-counterfeit-denso-spark-plugs-white-paper-_pk3.pdf
 
Here is the 5003 M22. Do the same as above for the specs.
https://www.densoproducts.com/denso-5003-m22-nickel-spark-plug

The heat range is actually in the part number of most plugs. You just need the decoder table. Here is a cross-reference table for multiple manufacturers.
https://www.sparkplugs.com/heat-range-conversion-chart-2

Yes this one wasn't decipherable by the part #. I ran Autolite 386's which were a little bit too hot but they worked. If I recall the L14U cross references to the 386. These should be better. The BR9ES plugs worked the best, but require adapters.
 
IO-360, 9.5:1 compression ratio, Denso L14Us and dual Pmag Emags.

Got very pronounced detonation while climbing through 7,500ft with full power.

Throttled back considerably and mixture full rich solved detonation immediately. Max CHT temp was 405.

Thinking I'll retard Pmag timing a few degrees, and get colder plugs (maybe AUTOLITE 376s???)

Thoughts?
 
IO-360, 9.5:1 compression ratio, Denso L14Us and dual Pmag Emags.

Got very pronounced detonation while climbing through 7,500ft with full power.

Throttled back considerably and mixture full rich solved detonation immediately. Max CHT temp was 405.

Thinking I'll retard Pmag timing a few degrees, and get colder plugs (maybe AUTOLITE 376s???)

Thoughts?
The timing will help - are you running on the A curve or the B curve? Do you have an enginebridge or eicommander? They can tell you the pmag timing while flying. Our engines don't seem to be as sensitive to spark plug heat as the 2-cycle engines I played with as a kid, but it can't hurt to use a colder plug like the Denso IK24 5311 Iridium or the basic NGK BR8ES as recommended by Brad/Emagair. They require the 14mm-18mm adapter, and some seem to not like that, but doesn't seem to be an issue to me. The 14mm plugs are much more modern than the 18mm, and there is a lot more choice.
 
I am betting you were getting preignition not detonation. As some mentioned that’s a hot plug. If you ordered them from Amazon they may also be counterfeit not real Denso plugs.
The detonation margin would have been quite large at that altitude. You would also have noted CHT’s rising very rapidly. I think 1 degree per second has been mentioned.
 
Yes this one wasn't decipherable by the part #. I ran Autolite 386's which were a little bit too hot but they worked. If I recall the L14U cross references to the 386. These should be better. The BR9ES plugs worked the best, but require adapters.

Autolite sort of admits their part number scheme is less than perfect for determining the heat range. Here is a quote from their website.

Where is Autolite?
Autolite's numbering system does not have a standardized heat range identifier. The last digit in an Autolite part number represents the heat range within a plug family. For example, take the 254x plug series. Autolite has 2544, 2545 and 2546 available. 2544 is the coldest plug in that plug family, and 2546 is the hotest. However, according to an Autolite reference chart, Autolite 86 has the same heat range as 2244 and Autolite 303 is a hotter plug than 2974. Therefore, it is impossible to chart an Autolite heat range hierarchy, let alone a standardized comparison to other spark plug brands.


Autolite 386's are comparable to the the Denso 5000 L14-U and both are on the "hotter" side. I know some on this forum run the L14Us on the top and 386's on the bottom. I'm inclined to try the Denso 5003 M22s for my next change as the temp range is closer to NGK BR8ES 3961 (8 for the the NGK and 22 for the Denso).
 

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I read every one of these 14 vs 18 mm plug threads and I've yet to find reference to an 18mm plug with a resistor. Does one exist?

I was bitten pretty hard when NGK non resistor plugs scrambled the brains of both Pmags in my -8 some years ago, so I'm not trying that again.
 
I was bitten pretty hard when NGK non resistor plugs scrambled the brains of both Pmags in my -8 some years ago, so I'm not trying that again.

I can't name a single modern automotive ignition system that places the coil and ignitor next to the electronics controlling it. They are separated for EMI/RFI immunity. That's not the case with the PMag.
 
I read every one of these 14 vs 18 mm plug threads and I've yet to find reference to an 18mm plug with a resistor. Does one exist?

I was bitten pretty hard when NGK non resistor plugs scrambled the brains of both Pmags in my -8 some years ago, so I'm not trying that again.

The Autolite 386 is a resistor plug. There are other resistor plugs like the 18mm Champion RD16 (comparable to the 386 in heat range). I've not heard of any issues with Pmags and the Denso plugs (non-resistor), but that's a reasonable caution.
 
The Autolite 386 is a resistor plug. There are other resistor plugs like the 18mm Champion RD16 (comparable to the 386 in heat range). I've not heard of any issues with Pmags and the Denso plugs (non-resistor), but that's a reasonable caution.
The Denso website says that the IK24 plugs have the 5k ohm resistor, and I confirmed this when checking both the IK24 and IK27 Iridium plugs. I have not yet put the IK24 plugs in - will probably do so next change.
 
The Autolite 386 is a resistor plug. There are other resistor plugs like the 18mm Champion RD16 (comparable to the 386 in heat range).

Geeeez... You're right. How did I miss that?

This old age thing really sucks!

....I've not heard of any issues with Pmags and the Denso plugs (non-resistor), but that's a reasonable caution.

NGK B8ES... I know some are getting away with it, but I was punished immediately with misfiring, crazy EGT's and CHT's indicative of "lost timing" events. Pmags sent home but no malfuntion found, boards replaced... Only fix was installation of proper resistor plugs. Installed old plugs just for repeatability and yep, problem came back. I'm convinced.
 
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Maybe I experience preignition, not detonation, with my possibly counterfeit Denso L14Us, and my 9.5:1 compression IO360, but engine was really rough, was afraid of engine damage.

Which 18mm, resistor, cooler plug, has been used successfully?

Any experience with Autolite 376?
 
Maybe I experience preignition, not detonation, with my possibly counterfeit Denso L14Us, and my 9.5:1 compression IO360, but engine was really rough, was afraid of engine damage.

Which 18mm, resistor, cooler plug, has been used successfully?

Any experience with Autolite 376?

I think the Autolite 376 18mm may be a taper seat, so won’t work. Can’t find the exact spec. The Denso 5003 M22 has a temp range close to the NGK BR8ES 3961 (8 for the the NGK and 22 for the Denso). Different scales, but use the cross reference heat chart and you will see they are close.
 
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Maybe I experience preignition, not detonation, with my possibly counterfeit Denso L14Us, and my 9.5:1 compression IO360, but engine was really rough, was afraid of engine damage.

Which 18mm, resistor, cooler plug, has been used successfully?

Any experience with Autolite 376?

BTW, I find this site to be an excellent source to look for plug alternatives. You can filter by size (18mm), reach (12.7mm or 1/2in), gasket or taper seat, and resister/no resister, etc. The Autolite brand is missing, but you can see many others. https://us.gsparkplug.com/ignition/spark-plugs/18mm-diameter?reach=55558&sealtype=17
 
!4mm Plugs for your RV

NGK BR8ES is equivalent to Denso 24 Heat Range. the Denso IK 27 is a bit colder , it will work well . Standard Engines will work well with a 24 heat Range if run at high power a 27 is a good heat range .
many plugs are available in this range . Lightspeed has spent years investigating heat Ranges for Safe operation , ask and you will get good info
Peter
 
Just a quick update to this thread - RockAuto has the 3961 back in stock - I just bought four dozen ($1.57 each) to restock because I have four airplanes using them…..

That should hold me for a few years!
 
Just a quick update to this thread - RockAuto has the 3961 back in stock - I just bought four dozen ($1.57 each) to restock because I have four airplanes using them…..

That should hold me for a few years!

Thanks Paul - looks like everyone is trying snag these plugs - their website is struggling:

RockAuto Adding Part to Cart.png
 
Not familiar with RockAuto but be careful out there.
 

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I’ve been buying these plugs from RockAuto for over ten years - big name. Mine arrived yesterday, so they are definitely shipping. Or were…..;)

Good to hear it Paul! Interesting thing how many people couldn't find these plugs, must be somewhat regional based on a car fleet. My Napa was never out of stock on them. But then again I'm guessing the coal rollers that are so prevalent around here don't use them. :D
 
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