ignition timing's affect on engine temperature

could someone give me some information on the affect ignition timing has on engine temperature ?

Advancing the ignition timing makes the engine more efficient ( providing no knock is occurring) thus generate more heat which is to be observed by engine cooling system. If it is not sufficient the coolant temperature will raise...

i should have mentioned im tuning harley davidsons which are air cooled. so with that being said can you elaborate on air cooled ?

Not really had much to do with other than OEM small air cooled engines, so discussion points.

In basic terms, when the fuel is burned in the engine, it produced heat and gases, with the heat being used to increase the gases' pressure in the cylinder to push down the piston.

Depending on the specific engine's characteristics, approximately 30-35% of the heat energy is lost to the cooling system - including the oil in the engine - this can be significant with some air cooled designs that use a lot of oil flow for internal cooling - not sure about the H-D engine, but good oil cooling may be a very good idea, as there's a fair amount of oil passing through/around the cylinder heads! This is why race engines are normally run as hot as practical - less temperature difference between the burning fuel and cylinder/piston surfaces means less heat loss and better power - doing this while keeping the charge cool is the trick. Same basic principle applies whether the engine uses coolant or direct air cooling.

As you can expect, the earlier the ignition point, the longer the burning/burned gases have to pass heat energy to the cylinder's, and piston, surfaces, so the greater the heat load on the engine.

You may think, "cool, the engine's running hot I'll just retard the ignition a bit", but while this may reduce the heat transfer to the cylinder it increases it around the exhaust opening point and this can result in overheating there, through the valves, ports, and the exhaust sytem - why retarded ignition is often used for building boost - it also means less of the fuel's energy is used to produce power, so more fuel-air is required for the same power and this may rather compromises the whole concept on part throttle. Of course, if it's already at full throttle, and running hot, options may be limited - for a drag engine the temperature rise may be acceptable for a brief period, an over-rich mixture may help, or an alcohol based fuel may reduce combustion temperatures directly or indirectly.

For a street bike it may be restricted to running a bit rich under full load and/or adjusting timing, it may possible to direct air over the fins, or use aftermarket cylinder barrels and/or heads with better fin cooling - there is going to be a limit to just how far you can go with cooling, though, and it's the main reason higher power level engines are almost exclusively liquid cooled - it just does the job better.

If you're trying to run some serious power increases, I'd suggest checking out the H-D tuning forums - heck, do that anyway - as this is something they've been battling for decades and should have it down pat.

Hmmm, thinking on it, with the right oils and oil coolers for the higher temperatures, and piston materials, clearances and coatings, you may be able to run reliably at temperatures a fair bit warmer than normal OEM levels - but that's something to think carefully about first.