scsmith

scsmith

Well Known Member
For several years, I ran the DENSO W27EMR-C plugs that Claus sells with my Light Speed ignition.
The heat range of those looked just about right, the plugs were always pale tan/grey color.

For more availability, I wanted to switch to NGK, and I bought BR8ES plugs that several mentions on the forum seem to be the right ones. But now, the plugs are black with just a very light dusting of soot.

So, it looks like I need a slightly hotter plug. A look at the NGK website says that lower numbers are hotter plugs, suggesting that I should go to a BR7.

However, the cross reference chart for heat range on the DENSO chart shows that NGK BR9 is equivalent to DENSO W27.

I think the confusion is between the nomenclature of 'hotter plug' vs 'higher heat range' plug which I think actually needs to be a colder plug-carries heat away faster for operating at higher temps.

Anyway, the W27's worked well, so I think I want to buy the BR9ES. Is anyone else using BR9ES?

Next is the trick to figure out the right part number to get the solid tip instead of the loose tip. Found it -- p/n 3194 (BR9ES solid) at Advanced Auto parts, same price as the p/n 3961 (BR8ES Solid)
 
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Same here! I switched from densos to NGK BR9ES. I have high comp Pistons so I needed the cooler plug. So far they have been great.

Dan
 
Hi Steve,

I believe the higher NGK number means it can conduct more heat away from the tip. There was also a suggestion that going to the Iridium NGK EIX series was like going up a heat range as well. Not sure but something to consider.

the 8-9 plugs were discussed here...

http://www.vansairforce.com/community/showthread.php?t=76149&highlight=ngk+heat+range&page=3

I chose to use BR8EIX with dual P-mags and they seem to be looking/working good. Will re-evaluate at next annual.

Bevan
 
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A black plug is not necessarily caused by the heat range. The best way to determine whether you have the right heat range is by looking at the heat temper mark on the base electrode (bent metal tab). Once clean, you will see a mark where the heat affected area stops. Similar to the heat marks on steel after welding. You want the mark to stop just past the bend on the way to the tip. You can do some research on-line for learning this method.

When experimenting with heat ranges you DO NOT want to do it based upon plug deposits. A very hot plug will be very clean, but it can also cause pre-ignition. Stick with plugs that have been used successfully by others in your experimentation and do the research on properly evaluating the results.

Larry
 
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thanks Larry and Bevan

While it is true that soot on the spark plug is not necessarily caused by the heat range, in this case it is. Nothing else in the engine has changed except the heat range of the auto plugs on top. The standard aircraft plugs on the bottom, fired by a mag, look exactly the same as they have for the last 300+ hours. Those plugs are effectively my "control" showing that nothing else has changed.

But thanks, I didn't know about the heat range tab...I'll clean a plug and take a look. Its a cool idea, I've just never noticed it before.

The other indication is that the DENSO W27, while running clean and tan/grey, also shows some electrode wear. Not excessive, but probably open 0.005--0.007 in 50 hours. On the other hand, the NGK BR8 shows virtually no electrode wear over the same interval, but runs with a slight soot deposit.

Of course I'm not planning to explore heat ranges beyond the small changes that have been talked about in the past, and if the NGK 9 IS equivalent to the DENSO W27 that I have already run, and recommended by Claus, then I am not really experimenting at all.

Bevan's comments and those in the thread he linked seem consistent with what is written on the NGK website, but disagrees with the DENSO cross reference chart, which shows BR9 = W27. My direct experience with the W27 was that it ran clean, whereas the BR8 has light soot. So now I'm confused again.
 
I have been running Denso IWM27 Iridium plugs in my IO-540

What is the difference between the IWM27 and the IK27?

Both are Denso Iridium plugs..

Rob Hickman
N402RH RV-10
 
Steve,

I'm no expert by any means but NGK 8 vs 9 is not a big change in my limited opinion. One chart may suggest the 8, another may say 9. A numbers guy may then decide to look for an 8.5. :eek: I'm thinking the idea is to "start" with either 8 or 9 and change if you think there's room to improve. Either one may perform at an acceptable level. Too many variables to say for sure which one is the absolute best.

I liked the idea of the fine wire and seems to work well for me. I wonder if the fine wire version picks up less heat having less mass and surface area.

Bevan
 
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