P-Mags and Auto Plugs: Two Questions

[Joe]

If you want to be rid of the whole adapter issue, try 18mm NGK AB-8 plugs.

http://www.sparkplugs.com/results_cross.asp?pid=AB-8

They're heat range 8 (just like the BR8-ES). I have about 100 hours on a set in my O235 Long-EZ (Lightspeed Plasma II) and just picked up a spare set locally (at NAPA) for $4-and-some-change each.

--
Joe

[pmnewlon]

Is there any concern for the 12mm reach versus the typical 19mm reach? That's a little over 1/4" shorter....

[Ironflight]

Thanks to everyone for the great inputs! this thread should add considerable knowledge to the archives - one good reason for asking questions.

Paul

[gpiney]

All the Rotax suppliers carry the plugs with the solid stem. Lockwood Aviation and California Power Systems are 2 that I have dealt with. Here is a link to the page for CPS.

http://www.rotaxparts.net/scripts/pr...idCategory=109

[apkp777]

FWIW, I started out with BR8ES and switched to BR8EIX's. At the time I thought there was a noticeable difference on how smooth the engine ran. Of course the extra $5 per plug may have been skewing my opinion.

[RV8R999]

Has anyone tried NGK plugs with heat index of 9 rather than 8 such as BKR9EIX?

Specs state plug temps of 70-100C cooler with each higher heat index number.

Maybe this would help offset the higher CHTs due to timing advance?

What would happen if you used plug heat index to help balance CHT variances between cyl such as using 9's in hotter cyl? Anyone ever mix spark plug types? Wonder if it would run rough?

[jbDC9]

Originally Posted by pmnewlon

Is there any concern for the 12mm reach versus the typical 19mm reach? That's a little over 1/4" shorter....

True, but... the difference should be made up by the additional length of the adapter unit. Comparing specs of the NGK AB-8 plug to a standard aircraft short reach plug, the reach is very close; a standard short plug has a 1/2" (12.7mm) reach while the NGK AB-8 shows a 12mm reach. Is running an AB-8 that's .7mm shorter enough to make a difference operationally? I dunno, but it'd be nice to ditch the adapters...

[pmnewlon]

Originally Posted by jbDC9

True, but... the difference should be made up by the additional length of the adapter unit. Comparing specs of the NGK AB-8 plug to a standard aircraft short reach plug, the reach is very close; a standard short plug has a 1/2" (12.7mm) reach while the NGK AB-8 shows a 12mm reach. Is running an AB-8 that's .7mm shorter enough to make a difference operationally? I dunno, but it'd be nice to ditch the adapters...

Ah - I hadn't thought of that. The 19mm length is needed to account for the extra depth of the hex on the adapter. 0.7mm is only about .028"

[RV8R999]

Quick trip to Auto-Zone and $10.99 later I have and installed 4 NGK BR9ES spark plugs to the top 4 cyl. I have only one P-mag and a Slick.

Engine starts normally and runs on P-mag alone in the low 400rpm range all day long (although smoother with the other mag on). No discernible difference in temps but sitting on the ramp starting from cold doesn't provide a very stable reference either.

Shut it down after 10 minutes. Let it sit for a few minutes. Re-started on 2nd blade rotation just like the first time. Repeated this drill 3 times total without any issues.

total time at or very near idle was about 30 minutes. Pulled 2 plugs (#1 and #3 - lowest CHT), no fouling.

No roughness, no missing, no temperature issues, no hot restart issues, no fouling.

Next step is run-up and fly.

[RV8R999]

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.