What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

P-mag using NGK BR9ES Plugs

RV8R999

Well Known Member
Screen shot using BR9ES Plugs: Vmax, full rich, ~5200DA

zn31v.jpg


Very difficult to say if CHTs are any cooler running these plugs as the variables are difficult to isolate. I'm digging through my older data to see if I have comparable environmental and configuration (bad test pilot - should have reviewed this first!!)

I can say I've never had such balanced temps - especially EGT but I'm not willing to say it has anything to do with these plugs yet.

I ran through a bunch of tests: rapid throttle response, slow idle, WOT, hot starts, etc... nothing bad to report so far.

I'll try some leaning tests later today.
 
Ken,

What is your goal in changing plugs? It sounds like you are trying to drive combustion behavior.

The temperature ranges on plugs should be selected to make sure the firing tip operates within it's self cleaning temperature range. Too cold and it will carbon foul, too hot and it will melt. Plug heat ranges are about keeping the plug alive.
 
Was using NGK BR8ES

Goal was to learn something new as I'd never thought much about spark plug heat range before Paul started his thread on P-mag plugs and was curious if CHTs would be affected as is implied by the manufacturer. Specifically I thought it would be interesting if CHT balancing could be accomplished using a mix of plug heat ratings but first wanted to determine what happens when they are all changed. My #2 has always been the hottest. It isn't bad at all and I'm not trying to "fix" anything just experimenting for fun :)

I read the NGK tutorial on heat range during my research the other day and it was clear they suggest when a timing advance is made a switch to a "colder" plug may be in order (I pasted the verbiage on Paul's P-mag thread). Since P-Mags advance timing (in certain regimes) and the plug manufacturer thinks it is a good idea, I thought I'd check it out. For $10.99 at auto zone and 30 minutes of work swapping plugs it was a reasonable endeavor. I ran the engine at idle for 30 minutes, shut down and pulled two plugs to check for fouling. They looked clean as a whistle. According to NGK the optimum combustion temp is between 500-800ish and 1 heat rating change results in 75-100 deg delta in combustion temp (not CHT obviously) unless the BR8ES were already running on the low side of the 500-800 range, changing to BR9ES wasn't likely to be an issue especially going to a colder plug.

No EIC for me..not required as I'm not trying to accomplish anything other than understanding what effect plug heat range ratings have on aircraft engine operation, if any. Maybe once I have established a baseline with various plugs the EIC would be interesting to play with - when will it interface with my iPhone/Ipad?
 
... According to NGK the optimum combustion temp is between 500-800ish and 1 heat rating change results in 75-100 deg delta in combustion temp (not CHT obviously)...

I think you read that too fast... They are talking about firing tip temperature (of the plug) not combustion temperature.

"As a general guideline, among identical spark plug types, the difference in tip temperature from one heat range to the next is approximately 70?C to 100?C"

What I think they are trying to say is that the "tip cleaning temperature" is a composite of the temperature of the spark energy itself combined with whatever the environment is within the engine. If the engine runs "cold", then you want a hot plug to ensure the tip can stay clean. Use that same hot plug in a hot engine and the tip temperature will shoot right above the optimal cleaning temperature and may even start to act as a glow plug.

I don't think that a plug heat range selection has any appreciable effect on combustion temperature unless it is way outside the normal range and causing a misfire (fouled or glowing white hot).
 
nope - read it below:

Heat range

The term spark plug heat range refers to the speed with which the plug can transfer heat from the combustion chamber to the engine head. Whether the plug is to be installed in a boat, lawnmower or racecar, it has been found the optimum combustion chamber temperature for gasoline engines is between 500?C?850?C. When it is within that range it is cool enough to avoid pre-ignition and plug tip overheating (which can cause engine damage), while still hot enough to burn off combustion deposits which cause fouling.

The spark plug can help maintain the optimum combustion chamber temperature. The primary method used to do this is by altering the internal length of the core nose, in addition, the alloy compositions in the electrodes can be changed. This means you may not be able to visually tell a difference between heat ranges. When a spark plug is referred to as a ?cold plug?, it is one that transfers heat rapidly from the firing tip into the engine head, which keeps the firing tip cooler. A ?hot plug? has a much slower rate of heat transfer, which keeps the firing tip hotter.

An unaltered engine will run within the optimum operating range straight from the manufacturer, but if you make modifications such as a turbo, supercharger, increase compression, timing changes, use of alternate racing fuels, or sustained use of nitrous oxide, these can alter the plug tip temperature and may necessitate a colder plug. A rule of thumb is, one heat range colder per modification or one heat range colder for every 75?100hp you increase. In identical spark plug types, the difference from one full heat range to the next is the ability to remove 70?C to 100?C from the combustion chamber.

The heat range numbers used by spark plug manufacturers are not universal, by that we mean, a 10 heat range in Champion is not the same as a 10 heat range in NGK. Some manufacturers numbering systems are opposite the other, for domestic manufacturers(Champion, Autolite), the higher the number, the hotter the plug. For NGK, the higher the number, the colder the plug.

Do not make spark plug changes at the same time as another engine modification such as injection, carburetion or timing changes as in the event of poor results, it can lead to misleading and inaccurate conclusions (an exception would be when the alternate plugs came as part of a single pre-calibrated upgrade kit). When making spark plug heat range changes, it is better to err on the side of too cold a plug. The worst thing that can happen from too cold a plug is a fouled spark plug, too hot a spark plug can cause severe engine damage

Timing

Advancing the ignition timing will raise the firing end temperature and becomes even more critical when compression ratios are also increased. Adjustment in spark plug heat range is likely necessary.
__________________
 
Ken we're reading the same information and drawing different conclusions. One of us is wrong (and it certainly can be me), so don't take the posts that follow as an argument... Just an opportunity for one of us to learn.

It's my understanding that a properly firing plug does not drive the temperature of the combustion process - it merely handles the results of the combustion (temperature) differently so that it can survive. In a cold running engine, the plug slows the conductive heat path so the tip stays warm enough. The opposite is true - in a hot engine, the plug has to transfer the combustion temperature off the tip quickly so it does not melt.

"...In identical spark plug types, the difference from one full heat range to the next is the ability to remove 70°C to 100°C from the combustion chamber..."

This statement (to me) means that the conduction of heat to the head is rapid, not that the combustion temperature is any different. It's like using a flame torch on an aluminum can - the can will melt rapidly, but if you fill the can with water it survives - yet the flame is the same temperature.

One way to look at it is if your house thermostat is set to 65 in the winter, you can bundle up with enough clothes to be too hot, or strip down to shorts and be shivering, but in no case does your clothing selection effect the temperature of the house. With proper plug selection, you take an engine and its unique combustion temperature and match the plugs to either retain or reject enough heat to live in their happy place.

Now, if I'm off base, I'd certainly welcome the correct information.
 
Last edited:
I'm not arguing at all as I don't have a stake in the results one iota just repeating what the manufacturer wrote. I haven't supported a position one way or another - hence the experiment. We can postulate all day long, doesn't mean a thing unless we try it and verify the findings. I am completely open to it having been a complete waste of time - but then I'll (we) will have learned something.

I posted the info from NGK to address the question of whether I read it too fast or not. Even at half speed it still reads the same... :)
 
Fair enough...

We're reading the same words but different with inflection. I read that the design of the plug allows it to control heat (retain or transfer) from combustion, you read it that the design of the plug controls the heat of combustion. An easily overlooked, but significantly different point.


No doubt the experiment is not going to hurt anything, and at worst, gave you an excuse to fly.

...I do have my guess on the outcome of your flights though....;)
 
For a carb O320 160 hp electronic ign. Try the NGK--9 (cooler) first. If the plug stays clean then that is a good choice. If it won't, then try the --8 (hotter) but look for tip wear at about 100 hours. Too much wear, and it is too hot.
 
Auto Plugs

Not to start anything...BUT, Why are you guys using Auto plugs in the first place? Cost?
I decided to use fine wire plugs with the PMags. Any reason to switch to Auto?
Nordo
 
Some additional stuff

There is a lot of info on the web relative to this most interesting topic (thanks Ken and Michael). Surprisingly the web info is consistent. I like pictures and the following link to a motorcycle maintenance site has lots, over 30 to be exact.

Tutorial
http://www.dansmc.com/sparkplugs1.htm
Lots of good/bad plug pics
http://www.dansmc.com/Spark_Plugs/Spark_Plugs_catalog.html
The site
http://www.dansmc.com/mc_repaircourse.htm

I guess Ken is on the right track in that this seems to be an issue of test-adjust-test.

Don
 
Not to start anything...BUT, Why are you guys using Auto plugs in the first place? Cost?
I decided to use fine wire plugs with the PMags. Any reason to switch to Auto?
Nordo

Cost, pre-made plug wires from Emag, and because that is what Brad at Emag recommended as well as both A&Ps I talked to.

I think fine wire plugs would be a great choice if I was going to fly 200-300 hours a year, but I'll be lucky to get to 100.
 
...I guess Ken is on the right track in that this seems to be an issue of test-adjust-test...

Indeed... The goal is to find the coldest possible plugs that will still get up to self cleaning temperature in your engine. If the 9's work well, then 10's might too...
 
cross-country LOP

With BR8ES plugs in my carb Xp-360 I wasn't ever able to really explore LOP ops as the engine would run rough just past PK.

Now with BR9ES plugs I flew several long cross-country flights in very smooth air and was able to lean to 30-50 deg LOP without running rough - I saw first hand the reduction in CHTs as well as power. I'm not advocating LOP ops just reporting what I found with the cooler plugs. The data is not conclusive only interesting.

Test and Test Conditions:
Mixture: 30-50deg LOP on leanest cyl #2
Throttle: Fixed at 55% when leaned to best power
6,700ft DA

Results:
163mph
Power: 52%
FF: 6.8g/hr
CHT range 329-345deg
EGT range 1450-1485deg

Test and Test Conditions:
Mixture: PK
Throttle: fixed at 55% when leaned to best power
6,700ft DA

Results:
167mph
Power: 54%
FF: 7.7g/hr
CHT range 335-355deg
EGT range 1380-1410deg
 
Thanks for posting. I've been running BR8ES with an Emag in an O-320 E series with 160hp cylinders for 7 years. In that time the plug wear has been higher than I thought it should be (0.050" gap after ~50 hours, starting at 0.035"), but didn't really know what might be the cause. From this discussion it seems that I may be using a plug that is only just cool enough for my engine, and switching to BR9ES may improve matters. I run as lean as I am able all the time as the gas prices are so high (~$13/gal).

Pete
 
the plug wear has been higher than I thought it should be (0.050" gap after ~50 hours, starting at 0.035"), but didn't really know what might be the cause. From this discussion it seems that I may be using a plug that is only just cool enough for my engine, and switching to BR9ES may improve matters. I run as lean as I am able all the time as the gas prices are so high (~$13/gal).

Pete

Pete, That big of a gap will place extra strain on your ign coils. Don't let the gap increase that much......... Yes, try 9's
 
I just removed a set of BR8ES's from my IO-360 after 80 hours (during my condition inspection) and found them to be in very good condition. Not oily, and not white spec'd, but nicely tan in color. The gap had grown a little from the factory gap of .030 to .035.

I've decided to try a set of the 9's and see how they do.

I'm loving the fact that I no longer have to dish out $27 each for aviation plugs anymore.
A set of eight (8) NGK BR9ES R plugs for the price of a single Champion REM40 plug.
 
Last edited:
I just replaced all of mine last week at annual as well. They logged just over 200 flight hours since the 2010 annual - I replace them with new every year. No oil or anything abnormal at all about them. I install them new with an .035 gap, they all opened up to .042 to .045. Since the pMag system uses the "wasted spark" method of firing, they have the equivalent usage of 400+ hrs of sparkage. I'm very happy with the performance.
 
Would the 9 series plug be applicable to a 150 hp Lyc. with one Slick and one P-mag? I can't get close to 400 RPM. About 900 is as low as it will idle smoothly.....:confused:
 
now switching to 10's

restarting this thread...

I've accumulated over 100 hours using the 9's (having switched from 8's).

during my annual this weekend I pulled the plugs and found no signs of wear whatsoever. Gap remains at .035 on all four plugs and they are all clean.

I have lots of data with 8's, and 9's. Once I put a 100 hours on the 10's I'll throw up some charts.
 
Back
Top