ReMiXeDg

Hey all, Today I am posthing this thread regarding glow plugs.

First off, whats the diffrent of a COLD GLOW PLUG &A HOT GLOW PLUG?

Am I suppose to use a Cold Glow plug when its cold out side and a Hot glow plug when its hot out?

Like Iwan to drive my traxxas truck in the winter what glow plug would Iuse cold or hot?


Thanks..

downunder

Firstly, it's got nothing to do with the actual temperature of the plug coil. Heat range refers to how easily a plug can ignite the mixture so by choosing the right heat range plug for your engine/fuel it helps to set the correct ignition point for best power. A hot plug ignites the mixture more easily (advances the ignition point) than a cold plug so in a way it's like adjusting the distributor in a full size car engine to set the ignition timing. Plugs can be made hotter or colder by a number of different methods (depending on the manufacturer) so generally you can't tell what heat range a plug is just by looking at it. Finding the optimum plug is a matter of trial and error but because there are no standards (unlike car spark plugs) what one manufacturer calls a hot plug could work just as well as another brand medium plug.

pyromatic177

thats helpful, thanks downunder

1QwkSport2.5r

A general rule of thumb I go off of is using the volume of methanol in the fuel to determine the heat range of a glow plug. More methanol/less nitro needs more heat to ignite properly because less nitro retards the ignition point. More nitro needs less heat since the ignition point is more advanced. I use hot McCoy mc59 plugs in all of my engines with nitro content from 5%-20%. Some engines perform better with cooler heat range plugs so it does take some experimentation. Hotter plugs promote a more stable idle but depending on mixture can be too hot on the top end. Leaner fuel mixtures advance the ignition point so a combination of hot plug, high nitro, and hot plug can be a bad combo. A frying egg sound at higher rpm means detonation and needs to be corrected in very short order or engine damage will result.

One brand to another, heat ranges are not equal. A McCoy hot plug may be hotter than an OS hot plug or vice versa. I do not use OS plugs so this is an example only. Experimenting is the only way to find what performs best.

pyromatic177

great explaination

supertib

also colder plugs tend to be more durable...they usually use a heavier coil that can withstand more punishment before they fail....colder plugs can also require a stronger glow ignitor...the heavier coil takes more juice to light up then the thinner coil hotter plug..... Myself i prefer to adjust the compression ratio so the engine is optimized around a colder plug...i find hotter plugs to be quite fragile when you start putting them into high performance engines...

rccheech

+1 ....A hotter plug in a higer performance engine will eat it up fast, all you need is for the coil to fall of in the sleeve and trash the p/s.

downunder

Maybe a few more words on plugs won't go astray. All plugs today use platinum as the working material in the coil but platinum is soft so it's alloyed with other metals like rhodium or iridium to make the coil stronger to withstand the vibrations of a running engine. Very early plugs, like the first Enya plugs, used a coil made from ni-chrome wire which worked quite well because in those days engines weren't throttled so always ran at full revs. Retained heat between firing impulses was enough to keep the coil glowing hot. When engines began to be throttled these plugs wouldn't work at low revs (they lost heat too fast) so platinum coils began to be used. The difference is that platinum reacts with methanol by a catalytic reaction and this reaction puts heat into the coil so keeping it glowing even at low revs. It still loses some heat at low revs so doesn't glow quite as hot but this is a good thing because it retards the ignition point which is just what's needed at low revs and gives something like the advance curve in a car's distributor.

But something else is needed to get this catalytic reaction started without having a plug glowing white hot and on the point of burning out and that's to have enough methanol vapours (molecules) in close contact with the coil. This is done with compression by the piston. The higher the compression the more molecules are packed close to the surface and the easier it is to fire the mixture. Overdo the compression and it fires too soon (ignition advanced too far) and you lose power or it can lead to pre-ignition which can lead to detonation.

Methanol, by itself, can handle compressions up around 17:1 but you'd probably need quite a cold plug for that. Adding nitro gives a complication because, although it doesn't react with platinum, a little heat in the plug will ignite it and it detonates at much lower compressions. Pure nitro can't handle much more than about 6.5:1 compression but because we use a mix of nitro/methanol in various percentages the compression of our engines has to be somewhere in the range between 17:1 and 6.5:1 so they're usually around 9:1 to safeguard against those who like to tip the nitro can . Using a colder plug delays the ignition and reduces the chance of detonation. However there's a balancing act once again. Too cold a plug may give very erratic or non-existent idle or bad transition.

So how to make a hot or cold plug? Given that compression is generally fixed (other than adding or removing a shim or two) we're left with how to pack enough methanol molecules against the coil. One way is by varying the surface area of the coil. This can be done by using a longer length of wire giving more coils in the space available or by using a wire with a larger diameter. Basically the greater the surface area the hotter the plug. Another way is to use the same coil in the whole range of plugs but varying the size of the hole in the plug body. Done this way, a cold plug would have a small cavity to make it harder for the fresh mixture to get around the coil while a hotter plug has a larger cavity to make it easier. Some manufacturers could even use both ways.

The trouble with glow engines and how they work is that they seem to be so very simple but they're actually quite complicated in the details.

supertib

can't forget the body of the plug...hot plugs have a large steel body that stores heat....cold plugs ( or at least the good ones) have a small body that sheds heat !

1QwkSport2.5r

So I see some car guys swear by cold plugs for better performance, whereas others swear by hot plugs for the same reason. What plug will give the best overall performance and what plug gives a better top end? I myself have never used a "cold" plug. Always medium or hot. Any engine I've had hot plugs in had a better idle and topped out nice. The medium plugs gave a decent idle, needed a leaner idle mixture but top end was not as good as with the hot plug. I tried several engines small and big block and had nary a change in behavior. I'll have to dig my spare plugs out and do some testing with a tach.

supertib

i think it depends on the engine and the efficiency of the combustion chamber....i get the best performance from a Werks #6 in my modifieds...the Werks 6 is a medium heat plug that uses a very heavy coil.....its very durable and has great performance characteristics from idle to top end...tho it can be picky on what glow ignitor you use.......... If i try to run a hot plug like a OD 97 or OS P3 the tune needs to be richened up, the top end drops slightly, the idle is more forgiving, but the plugs fail after only a few short runs........I mainly run the colder plugs because they are substantially more durable...........

proanti1

My Feedback: (2)

A plug in a certain heat range isn't going to make your engine perform "better", it will just allow it to run as efficient as it can. It really mostly depends on you the engine itself... you cant just say "hot plugs do this, and cold plugs do this". Each engine (even of the same model) is different. Generally... the hotter the plug the better, but if you are killing hot plugs then you move on to colder plugs.

1QwkSport2.5r

I have my own reasons for the plugs and fuel I use.. I just remember seeing a few guys say "Use cold plugs", "Try an A5", etc. and wanted others opinion on the matter. It was stated in another thread to the effect of "the performance is notably better, especially on the top end, though the idle suffers some". I suppose letting the engine gargle 30-40% nitro I can see the benefit since it would help the engine from melting down. Other than the durability/longevity factor, I dont see any performance benefit to a cold glow plug. I will give hot plugs the delicate award, but I still like 'em.

HerrSavage

I'm the one always saying try an OS A5 in an SH big block engine.. So far I have run three Mach 427's, two Sportwerks 26's, an LRP Spec 3, and a Dynamite Big Red 28(all SH), and experimented with most of the plugs you can run in them, and I really do notice the differences I've mentioned before running a cold OS A5 - noticeably more top end, cooler temps, but a less stable, more gargly idle(need to blip more so it doesn't cut out..) I always just assumed that it was because with a cold plug you can run somewhat leaner.. I don't know - but I've done a bunch of testing, including racing truggy and buggy with a silver Mach and SW 26, including 20 and 30 minute mains.., and that's just what I've noticed. If you have a Mach or LRP or Big Red or whatever, just try an OS A5 and see for yourself. If you don't like it go back to the #8 or McCoy or whatever you prefer... In two identical trucks though, with say an LRP Spec 3, I'm pretty convinced the one with an OS A5 will be faster than the one with the #8.. Not night and day faster or anything, but if like me you like WOT, you should notice the difference..

But who knows, a lot of all this is subjective.. - and dependent on all kinds of variables - local climate, fuel, elevation, even - apparently - quality inconsistency of batches of the various plugs.. Still.., I have read before over the years that this is the case - colder plug means more top end because you can run leaner(AND still have cooler temps..)

I'm actually kind of curious if the same holds true for turbo plugs.. Don't have enough experience with them yet to say.. So far, I feel a vague sense of something not being just right with hot OS P3's and OD 97T's.. Had a P4 in my Caster Grenade though, and it shredded.. Sirio #6 in a Nosram 21RR was also very, very good... Running an Argus A52 now with OD 97T, and it's nice and bottom end is great and all, but somehow I wonder if a cooler plug like a P4 - especially with all the pinch causing extra heat, would make a positive difference...

1QwkSport2.5r

HerrSavage - Just for S&G's I'll grab a long-reach cold plug and try it against my hot plug. I will get a McCoy so its within the same brand. I'll post back somewhere around here with what I find out.. Totally out of curiosity.

supertib

We run 9% oil 30% nitro and we run 20-45 minute races......The tune is spot on due to the fact we need to get mileage from the engine......it can be a huge advantage to be able to run a 20 minute race with only 1 pitstop....So for me the #6 plus we run work very well.....We get good power, good mileage and they are very reliable.... running a nitro hard in race tune for 45 minutes straight can a toll on the engine and glowplug if everything isn't dialed in 100%

Nitrovein

One thing to remember is that the more efficient the combustion is the less advance is needed on the ignition to maintain the same burn rate/pressure curve.
The reason that Mr.supertib gets good overall performance with cold plugs is that he has done a good job, there is nothing more to it than that.

ZeroKelvin

I have 7 nitro's in my garage, engine sizes range from .18 up to .28. I run 20% nitro in all of them and some run better with hot plugs (generally my smaller engines) and some run better with cooler plugs. I haven't replace a glow plug in over a year in any of them. I've run over 2 gallons through an engine and not replaced a plug. I haven't seen any difference in reliability in cold vs. hot. Run a good tune on your motor and the plug will last a long time, that's what has worked for me.
Generally speaking the lower the nitro the hotter the plug, but there are plenty of engines that are an exception to the rule. The best thing to do is try a wide range of plugs in your engine and see what it does best with,.