robertnitro

hi guys ive become pretty good at doing the port and conrod mods in a few engines ive owned.But recently ive been wondering about timing and more specificaly ignition advance.As you will know full size cars use an ignition advance curve via a vacum unit or electronicaly as as the revs rise.
i was wondering as a nitro engines ignition is more or less a set point,is there any way to effectively advance or retard the ignition (apart from using hotter or colder plugs) and can timing mods have any effect on this.Also im surprised nitro engines even reach full rpm as there is no advance curve to compensate for increasing piston speed and so provide the best mechanical advantage on the downstoke,can anyone explain how this process works in a 2storke nitro mill.It all boils down to me wanting to do mods that give the highest possible rpm but without lossing any bottom end torque.

ttoks

the advance in the glow engines comes from the hotter glow plug, as RPM's rise the glow plug get's less time to cool between firing, so each stroke under acceleration it will fire slightly sooner then the last, this is why running an engine with to little head space will cause detonation in a glow engine, not because there is any actual detonation, but because the glow plug get's to optimal temperature before the piston get's time to get to the best firing point, port timing changes will effect the dynamic compression ration so yes port timing changes will effect the "timing" so to speak.

downunder

A glow engine's (I don't know anything about nitro engines ) ignition timing is basically controlled by the plug's heat rating (which is different to whatever temperature it's glowing at) combined with the actual compression pressure in the combustion chamber. Heat range of a plug is like a combination of the temp it works at plus the area of the wire exposed to methanol vapours. The more area the more molecules of methanol can be in contact to set up the catalytic reaction. The more heat, the easier the reaction starts. Compression works by packing more molecules close to the surface of the coil plus there's some extra heat produced just by compressing the air quickly.

Raising compression or using a hotter plug will advance the ignition timing. If for instance the compression gets a bit too high (advancing the timing) then you can try a cooler plug which retards the timing back to something more suitable. It's really quite a complex bit of juggling but luckily for us the engine manages to do it pretty well all by itself from idle up to full throttle. Maximum compression BTW occurs at the point of maximum torque. This is when the engine is pumping air at it's most efficient so there's more air inside to be compressed which generally means when the ignition is advanced about as far as it can go.

JB COMP

modding timing from what everyones telling me, is trail and error, you just have to cut, and of ot works it work and if it doesn't then you have a nice looking paper weight. simple enough right?

slayerphonics

Guy at our track took a axial motor ported the sleeve to an 11 port said it can crack out 60,000 rpms,
Of course it was the night i didn't goto the track so I didn't get to see it myself but my friends said it
was jaw dropping

ziggy12345

The engine timing in a glow or nitro engine is a combination of a few things. these are

Burn time of the fuel (Nitromethane burns slower than methanol)
Head clearance (depending on pressure in the cylinder at TDC)
Glow plug type

To advance your timing you can do a number of things. The main one is to remove head shims. Next is to add Nitromethane and next change the plug to a hotter plug.

Also changing the tuned exhaust length can increase the pressure in the cylinder and also advance the timing. You want to get the max pressure in the cylinder at the useful rev range and then tune the engine for this length.

Its a real balancing act and the trick is to know whats happening so you can adjust the settings.

Cheers

JB COMP

nitro burns faster then methanol, thats why the more nitro the colder the plug.

Pacific Rider

I read somwhere if you advance the exaust timing you'll get higher RPM.