HI I AM CONSTANTLY DEALING IN NEW AND VERY VERY LOW TIME HIGH PERFORMANCE GLO ENGINES I CAN NOT TELL YOU HOW MANY ENGINES I HAVE PURCHASED THAT HAD THE WRONG GLO PLUG IN THEM-YOU SHOULD RUN A SHORT GLO PLUG -ONLY IN GLO ENGINES THAT ARE SIZE 15 AND SMALLER-A LONG GLO PLUG SHOULD BE RUN IN ANY ENGINE LARGER THAN A 15THE SIZE OF THE GLO PLUG COMPLETELY CHANGES THE TIMING OF THE FIRING OF THE ENGINE SO THEREFORE WILL EFFECT PERFORMANCE AND RELIABILITY VERY MUCHALWAYS SAFE TO GO WITH A MEDIUM HEAT RANGE-THIS INFO MOSTLY APPLIES TO TWO CYCLE GLO ENGINES AS THE FOUR CYCLES LIKE TO RUN ON A LONG OS F PLUG-WHICH I THINK STAYS HOTTER AS THE ENGINE BY DESIGN ONLY FIRES EVER OTHER STROKE THIS INFO IS PRETTY BASIC STUFF-BUT NEED TO GET THE BASICS RIGHT TO ENJOY OUR DAYS OF FLYING-MOVED TO FLOIDA JUST TO FLYTURNING OUT TO BE A GREAT IDEA-WE FLY AND BQ ALL YEAR ROUND IN CITRUS COUNTY - CENTRAL FLORIDAENJOY REGARDS TONY "the omega man " think pink !!

bag of Popcorn in hand............

Hi!
First of all there are 3 sizes of glow plugs! Long, short and the japanese OS and Enya plugs which is in between long and short!
Second.
There is no rule that smaller engines like a .10 or .15 (1,8cc and 2,5cc) should use short plugs!!! For instance all small 1,8 and 2,5cc engines have always been supplied with the OS 8 plug... which works perfectly good for these engines, and most other two stroke engines too.
You can also use long plugs like the Nova Rossi 3-4 or Rossi 3-4 in these engines if you like.

It is important that you choose the right plug but the right plug is more so linked to what fuel you use and not only to what engine you have.
For instance all two stroke engines function perfect on 0-15% nitro and the there is a wide variety of plugs that works well, like the Enya 3 or OS 8 for most sport engines.
But for out most power, in a .40 engine, using a 10x6 or 9x7 APC or RAM prop....like in Q-500 pylon racing running 0-5% nitro; Nova Rossi 4A-5 or Rossi 3-5 are hard to beat. But of course there are others that work good too.

And typing in all capitol letters is considered yelling.

Jan et al, here is a shot of my LA .10 head with an OS #a3 that came in the LA .10 and a Fox #8, the OS #a3 does not come close to being in the optimium location. If I had not converted the LA .10 to Diesel I would run the Fox. It clears the piston top by slightly more than 1/16th inch. Since you're more knowledgeable of two strokes than I am please comment, Thanks, Dave

Hobbsy

Friends don't let friends drive red tractors.

I agree with you guys about the plugs in small engines BUT I think the OP was more refurring to not using short plugs in the larger engines, Figured I'd give my take on his post before he needs his flame gear on...[sm=what_smile.gif]

Dauntae

no one needs a flame suit, but the OP needs to be more accurate on what really determines the proper plug in an engine of any disc. saying that short plugs are for disc. from 0-.15 and long plugs are for anything over .15 is in error.
some racing engines of .40 disc. have required short plugs. normally as a start, the end of the plug should not protrude past the end of the threads in the head..........adjustment to cold,medium, and hot plugs follows.

as has been posted though, variables in fuel, altitude, temp and humidity conditions will rule the requirment of what plug is actually best............very tedious testing will find the end result, but since not many modelers have the equipment or knowledge to measure rpm in an accurate manner, and even more so know what detonation looks like, it's better to just go with what a manufacturer recommends for fuel,prop, and glow plug.
i have a hard time running OS plugs in some larger engines as they really aren't short or long which leaves them short of the threads in heads that are really in need of long plugs. they may do an OK job, but they aren't the ultimate even for their own engines.

Rossi plugs are much better plugs and they do make a difference.

Do any of you know who makes the “Hottest” hot glow plug? I have found that by using the hottest glow plug I can find and running the engine rich produces the most top end power without hurting the engine. So far I have found the Merlin Hot Plug to be the hottest. Is there another that is hotter?

As for the long and short issue, the plug should go into the head so that no threads are showing when fully tightened. Longer is acceptable shorter is not.

Bob

Ihave been told the reason OS plugs are short is to make the expensive filament material shorter and thus cheaper. Iwill take mine full length please.