kitracer

Another BRB set ready for action on a NS12
Who said Speed and durability don't mix

Speedypeterb

iTrader: (16)

hi Edward, i have,nt got the information about oct. 1 2 3 races and i still need to get airline tickets, let me know soon, We have another hurricane coming! Peter

HELLION

Looks good Palm ! Good luck with it

ziggy12345

Hi

This seems to contradict what I understood about glow engines. The plug rating is based on the temp it ignites the mixture.

A Hot plug will ignite the mixture when it is hotter and a cold plug when colder.

Therfore a cold plug will advance timing as it ignites the mixture when the compression is less. this gives you low end power

The fact that Nitromethane is a lot slower burning than Methane means that you would need a cooler plug to ignite the mixture sooner (more advanced) and allow the burning to progress further through the stroke.

Therefor...

for lower head clearance use hotter plug
For higher head clearnace use cooler plug.

Cheers

xtreme888

you got PM !!

EdwardN

iTrader: (1)

Yes my understanding defenetly contradict to yours.
First: Yes it is simple tech properties of Nitromethane that igniting temperature of it is much higher then Methanol. But why would you set up your ignition system based on tech properties of one element of fuel ( content only 30-40 %) and do not set it by other ( 60-70%). So, still in my understanding, we have to concider Methanol as primary igniting element in our fuel.
Now bck to Nitromethane, I am sure you know what is the reason why we use Nitromethane-it is simply "oxidizer" for our fuel ( it has very similar chemical formula as Methanol, just has extra oxigen molecula in addition). So if you have extra oxidizer, you can add extra fuel to the combustion chamber. But in the mean time adding extra fue will increase compression ratio ( more fuel in the same volume-is increasing compression ratio) and this will advance ignition timing. I am sure it is pretty simple that we need only certain amount of compression ratio for normal engine's work and over compressing will icrease chance of preignition which will bring to detonation. Here is two ways to adjust it-decrease compression ratio to normal number or to use plug which will ignite fuel later ( everything in reasonable imits). Which plug ignites fuel later-cold or hot? I think it is cold.
We can go further about power output and idle, life of glow plug etc.
This is basic which I use to tune engines.
More nitro- bigger combustion chamber/colder plug, less nitro-smaller combustion chamber/ hotter plug and it is no based on Nitromethane tech properties, it based on ammount of fuel in combustion chamber. Nitromethae is not ignating by glow plug-Methanol is ignating by glow plug and then Nitromethane burning together with Methanol. Nitromethane is "ALMOST" non flamable chemical.

ziggy12345

Ed

So we are in disagreement.

I thought a HOT plug meant that it ignites the fuel when at a higher temperature = more compression = Ignition advance

Cold plug means it ignites the fuel at a lower temp therfore lower compresion = Ignition retard.

You said it yourself above...More nitro- bigger combustion chamber/colder plug

You know more about this than i do, which might explain why my engines never run properly!!. Does anybody have diffinitive answer?

Cheers

afm

This is what Dennis Richey, renowned engine tuner and noew manufacturer has to say about engine shimming and glow-plugs, which is in concordance with Ed.
Hope it helps.
AFM

"Engine Shim Tuning
A decrease in head shims or an increase in compression ratio will increase torque because as the compression ratio goes higher the actual ignition timing occurs sooner. This is the same effect that happens with a colder plug except in the instance of a colder plug the ignition is slowed until a greater point of compression build occurs. however there is a point of diminishing returns where detonation occurs or engine temps can soar this is where a colder plug can also help.
Consequently the same effect occurs when you increase the head clearance. top end is enhanced as the ignition timing is retarded and occurs later. generally a hotter plug is needed to advance the ignition cycle so the timing does not occur to late in the cycle as at this point you end up over leaning the engine to get it to rev properly and the engine life will suffer dramatically.

On a 12 engine I would only advise going .004 thousandths over or under .018. so that is .014 or .021. I have run as low as .008 but this was with tremendously increased exhaust timing and to regain static compression ratio. To little and the piston can hit the head as you have to take into account rod and piston growth relative to their temperatures.

You can safely use 30% on the stock head clearance. Using an O’Donnell 99 plug you can go to 40%, if you don’t over lean it the engine life will not suffer dramatically.

I should also point that my comments with regards to plugs and head shimming are when both are used together. used alone a hotter plug will rev harder and a colder plug will make more torque.
One last comment. never assume that the head shim that is on the engine is the actual head clearance. in many cases you will find that the engine actually has .006 to.008 without any head shim. Novarossi's are .008 without one and the factory installs an additional .010 giving the engine .018 stock. this has not always been the case but 99% of the time it is. when in doubt measure the head button register and the piston to the top of the liner at top dead center and subtract. this is the only way to really know.
Generally on a 12 engine .004 thousandths will change the Compression ratio about 3/4 to 1 point. I said generally.

Someone asked about plug fatigue the other day, plug fatigue can occur under high sustained RPM's this is where the plug stays shiny and the wire just fractures for no reason. This is why I have always run McCoy MC9 or the new O’Donnell plugs (77 or 99 standard plugs) as they don’t do this. When this happens it is usually not a carb. tuning or head clearance problem. If you see the wire start to pull out of the hole this means that the engine is scavenging really hard and when this occurs the engine is making serious power.

Motorman"

afm

Here is another good article about glow plugs and timing

http://www.rcnitro.com/rn/articles/glowplugs.asp

Hope it helps

AFM

click, dublin

Hi Edward,

What is the head clearence on a .12 Palmaris without head shims?

What thickness are the head shims supplied.


Many Thanks


Kevin

ziggy12345

Jeez. I had it round the wrong way, I was wondering why my engine tuning was suffering.

To clear it up

A HOT plug will ignite sooner in the compression cycle. It glows HOTTER than a COLD plug for the same conditions (pressure, temp, fuel mixture). a COLD plug require more compression to reach the same temp.

That makes sense now!!

Right now to get that JP screaming!! No 7 plug with 0.21 Head clearance and 25% nitro.

Cheers.

The original post from motor man was one I was involved with. I thought i understood everything being said, obviously not

EdwardN

iTrader: (1)

HI Kevin.
Original head clearance without shims is 0.2 mm and we supply every engine with 0.05 head Stainless Steel shims at list 5-6 of them. If you will need more just let me know and I will give them to you.
Edward

EdwardN

iTrader: (1)

Hi Tony. I am realy happy that I was able to some how help you. Any questions, please you are welcome to ask.
Edward

teammpp

I have plenty of shims here. If you need any Kevin send me an email and I'll get them down to you.

EdwardN

iTrader: (1)

Hi Peter.
Check please your PM box.