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Motors,

Great question!  And when I went poking around, I (re)learned a few things. Thanks!

Apparently A3's are called No. 6's nowadays. No idea why they needed to be renamed--they had a great reputation, so it wasn't that. I think that they just wanted to reserve all the lettered plug designations for the car guys. Now, all of the so-called "air plugs" have number-only designations.

The available OS plugs show up on this chart, arranged by heat:

     https://www.osengines.com/glowplugs/index.html

I have been running P6 turbos ("hot") in engines that take turbo plugs  (OS 18TZ, etc.), and A3s in engines that don't (OS 15 CVA, etc.). I don't know why P6's don't show up on the chart, unless they have renamed those as well. Perhaps they are RP6's in order to remind us that it is illegal to run these in anything but road vehicles? That does not make sense based on the packaging of the P6's that I have in hand, which says "Hot."

The chart implies that the P3 "Ultrahot" is the same heat as the No. 6---but I wouldn't count on it. Sales brochures mostly fall short of technical accuracy. You could pull out the ancient Wild Bill magazine article where he tested and ranked the available plugs by heat range and repeat his glow plug test methods on the No. 6 vs. P3 and see what you get. I would add a test given today's technology:  connect to a calibrated voltage source and measure with an infrared thermometer. Might take a imaging sensor to be able to resolve just the plug element though.

I have only run OS-made turbo plugs, so don't have a correlation to other brands. Sorry.

McSlow

Steve,

The OS Type F plug is listed under the tab "Specialty Plugs." Take a look at the link provided, then hit the other tab and you can see both the F and the G5. It would be nice to see it positioned on the bar chart relative to its heat range, but since they list the F as a cold plug, it is probably not of much interest to those comparing plugs at the hot to ultrahot range.

I pulled down an engine for someone recently and it had a hose-nose plug in it like an F. I have my doubts that these are a good idea in an engine not designed for them. The "nose" actually sticks down into the combustion chamber on the one I looked at.

Dave

Steve,

I'm curious about your comment that the OS "F" plug might be considered a hot plug in a 2-stroke. Do you believe that because of the coil characteristics or because it is projecting further into the combustion chamber?

Pulling the coil out of the plug (reshaping) should have the effect of advancing the timing which is what a hotter plug should do as well. Having the coil distort due to overheating would screw up the settings too. I assume it is pretty rare in stunt, but not in speed and racing.  Which is where I assumed Motorman was coming from. Conversely, running an OS A3 (now their No. 6) in a Fox, I would expect even a hot plug like that to run cold because it is recessed so far. It would be interesting to know if it was more likely to die from the "Fox burp," or if it actually improved things. I would guess more likely to die, because it probably still isn't protected from a slug of oil/fuel...?

I don't know of a listing of head/plug conversions. The only conversion I actually use is the Galbreath head for the Cox .049 that takes a Nelson plug. Is there a specific glowhead you are looking for? MECOA has a number of new manufacture glowheads for old/ancient engines, and some conversions. You might check them out.

Dave

PS--Yes, for those not familiar with turbo plugs, they will not screw into a "normal" glowplug head. Tapered seat and not the same thread.

What is the hottest turbo plug ever made? Is there anything hotter than the OS A3 ?

Thanks,
Motorman

I guess  you know  the  A3  is  not  a  turbo plug, are you looking for  only Turbo plugs, or  plugs that will fit  normal glow plug heads?

Randy

Yes, I would expect the hose-nose to give an effectively hotter glowplug due to putting the element further into the combustion chamber...all else being equal. I don't know how much the size of the coils, number of turns, wire size or alloy composition would change the heat range, but I'm sure all would also have some sort of 'fluence. I'm really happy with my NOS Thunderbolts.

The old glowheads I have are for a Fox Rocket .09 and Cox TD .09 or .15. I can probably just blow through them and tap them to 1/4-32 and then counterbore to get the glowplug exposure correct.

OS sure screwed things up with their "medium" length glowplugs, tho I fully understand why they'd do it. Making long and short lengths was a bad idea, 60-ish years ago.  Steve

YOu would think that, but I tried them on several engines, and they were not hotter, ran colder  and  did not perform well

Randy