Fans /airflow / techies wanted

[rossi46]

sorry guys going back to the fact of removing the hot air from the cylinder cowl, I have noticed that the carbon PM Tuning cylinder cowl has a much larger outlet for the release of the hot air, and is angled differently to the standard cowling, I also noticed while stationary the air being flowed by the fan with the PM Tuning flywheel cover and cylinder cowling is very good at idle and extremly good when the engine is reved, I think if you fit an angled scoop / duct from the splash plate or (Drill it like I did) the floe of air under the footboards would create a vacuum and suck out the hot air, thus you would not have to modify the side panels as the hot air would exit blow the engine.

[156 D]

So on a high revving engine, the heat can either be in the cylinder (say 23 degrees BTC or in the exhaust 15 degrees BTC) and therefore 15 degrees puts the heat into the exhaust and helps the cylinder run cooler.....no?

But my understanding, on our scooters (not turbo car engines) and within the 16-23 degress parameters that most work with, a high revving engine will run cooler at 17 degress and hotter at 23 degrees.

If someone has overheating or pinking issues at 19 degrees BTC, you'd generally back off to say 18 or 17 degrees to reduce heat....not increase to 20 or 21 etc.

Am i wrong?

The 15 degree`s, yes puts the combustion partly in the exhaust port, but does not have the effect of cooling the engine because of conduction... the heat then passes back up through the metals and to the components of the engine to contribute towards a heat seize........

Ignition timing as you know is dictated by technology or age of a design and the degree of tuning of an engine.........the timing of say your 19 degrees may be a favourable amount of advance but if advanced too much in the process the flame front becomes ‘overheated’ or too much heat generally is added to the unburned fuel, then the unburned fuel reaches its spontaneous combustion temperature before the arrival of the flame front, then the whole of the unburned charge in the area will auto-ignite giving rise to huge temperatures and pressures.... the pressure will give a ‘knocking’ sound and the temperatures may melt your piston.....but the thing is the engine in general is not overheating as the raised temperature is kept mainly within the combustable space and therefore burns the hole in the piston because it can still run within that engine temperature.........Yes, too much advance gives heat .......but the excessive heat caused by enough retardation of the ignition will wreck the whole engine in a more severe way.......of course the art is know what the symptoms are as you say .......if it pinks, you retard the spark ...but in turn if your engine runs really hot with less power you advance the spark...........All in all it is heat that causes all the problems but at each end of the spectrum ,so to speak.......the answer is of course to have the ignition correct.......

..................why i mention this in the first place was because the topic was fans and ducting mods... if a new "V" shaped ducting was in place it would also force cool air by the exhaust as well as the flywheel side....the silencer exhaust components would run cooler and would easily due to conduction take more heat away from the cylinder etc. and therefore allow cooler running of the engine..........this is only my thoughts and contribution to the starter of this thread.......

[J1MS]

The 15 degree`s, yes puts the combustion partly in the exhaust port, but does not have the effect of cooling the engine because of conduction... the heat then passes back up through the metals and to the components of the engine to contribute towards a heat seize........

Ignition timing as you know is dictated by technology or age of a design and the degree of tuning of an engine.........the timing of say your 19 degrees may be a favourable amount of advance but if advanced too much in the process the flame front becomes ‘overheated’ or too much heat generally is added to the unburned fuel, then the unburned fuel reaches its spontaneous combustion temperature before the arrival of the flame front, then the whole of the unburned charge in the area will auto-ignite giving rise to huge temperatures and pressures.... the pressure will give a ‘knocking’ sound and the temperatures may melt your piston.....but the thing is the engine in general is not overheating as the raised temperature is kept mainly within the combustable space and therefore burns the hole in the piston because it can still run within that engine temperature.........Yes, too much advance gives heat .......but the excessive heat caused by enough retardation of the ignition will wreck the whole engine in a more severe way.......of course the art is know what the symptoms are as you say .......if it pinks, you retard the spark ...but in turn if your engine runs really hot with less power you advance the spark...........All in all it is heat that causes all the problems but at each end of the spectrum ,so to speak.......the answer is of course to have the ignition correct.......

..................why i mention this in the first place was because the topic was fans and ducting mods... if a new "V" shaped ducting was in place it would also force cool air by the exhaust as well as the flywheel side....the silencer exhaust components would run cooler and would easily due to conduction take more heat away from the cylinder etc. and therefore allow cooler running of the engine..........this is only my thoughts and contribution to the starter of this thread.......

I think he knows what he is talking about...

[drunkmunkey6969]

I think he knows what he is talking about...

Yes he does indeed, he's giving a basic example of pre-ignition/knock/pinking at 19 degrees, all perfectly correct, no dispute

But i'm not sure i concur with the opposing view of a retarded ignition example, but am always willing to learn.

My thought process was that the 15 degrees example would move the heat into the exhaust, which is fine, and if we went further, beyond the point of efficient burning (say 14 or 13 for example) that the power would decrease due to inefficient burning of fuel, and the decrease in power meant LESS heat being created in the first place and the unburnt fuel cooling gasses further.

So in my understanding, it would be: example one....too much advance = heat and preigntion, example two.....accurate timing = efficient burning, example three....too much retard = loss in power (resulting in less heat initially being generated, and unburned fuel cooling gasses further).

And of course all three examples also have levels of overlap.

However 156D doesnt agree with my understanding of example 3, and suggests that even though power is reduced, the heat stays the same and is merely moved into the exhaust pipe, where it then conducts itself back into the cylinder.....i'm not saying he's wrong, i'm just saying i struggle with that concept. Surely less power means less heat to begin with, regardless of where it is moved to (cylinder or exhaust) and unburned fuel aids cooling further?

I like to understand the logic behind any explanation or theory of mechanical scenarios, and if i don't (as people on here well know) i like to try my best to discuss the examples until i do understand. I think it benefits me as well as other forum members.

So as i say, im always willing to learn, so if 156 or anyone else can help me get my head round example 3 i'll gladly take the lesson on board.

[Avantone]

I agree with your point Dan. The principle to remember is that the charge doesn't explode at x-deg BTDC, but burns over something like 40-deg of the stroke. The idea being that you get maximum "push" out of the combustion as the piston moves over TDC. If you detonate too early (too advanced) the combustion is trying to push the piston backwards back down the bore - this is going to produce a lot of heat because all of the energy is being absorbed in the piston crown (and other components) rather than pushing the piston down the way it wants to go. If you detonate too late, you waste all the combustion potential, and on a 2-Stroke, lose a proportion of the unburnt charge out the exhaust port. You may see some combustion in the header, but the heat produced is nothing compared to a motor running too advanced - in short retarded = no power, wasted fuel and high emissions (IMO)

[J1MS]

I like this thread.... its opened a can of worms... Not sure if my theory is right on this... but somthing I read or was told, but now cant remember exactly who by or when... But I was lead to believe that if the Ignition fires at a massive retard ...The heat can cause localised heating of the piston over the exhaust port ( I would assume only at high revs)..... because of the exhaust gasses not being fully burnt as they exit and its possible for the cooling gasses from the squish band adding fuel to this late burn which elevates the front pipe temperatures and furthur raises the piston crown temperature over the exhaust port... I might have this completely wrong as I dont now have a record of where I first heard this and I may just be mistaken... ...

[156 D]

I like this thread.... its opened a can of worms... Not sure if my theory is right on this... but somthing I read or was told, but now cant remember exactly who by or when... But I was lead to believe that if the Ignition fires at a massive retard ...The heat can cause localised heating of the piston over the exhaust port ( I would assume only at high revs)..... because of the exhaust gasses not being fully burnt as they exit and its possible for the cooling gasses from the squish band adding fuel to this late burn which elevates the front pipe temperatures and furthur raises the piston crown temperature over the exhaust port... I might have this completely wrong as I dont now have a record of where I first heard this and I may just be mistaken... ...

...........you have it "J1MS".......i am no good with English explaining things ,that`s why whatever i say comes out with the wrong attitude ,but it is not meant that way........you have said it in a nutshell exactly what i was on about.........engines are engines and rely on combustion......but as you know it has to be at the right time and also take the right time to combust ......a good enough retarded combustion will take longer to complete it`s explosion than an advanced one which also adds to the heat damage as there is more of it happening for a given time .....also the engine just purrs along and that`s also why it`s bad for the engine as you don`t know what is happening until it seizes..........I will be burning some midnight oil later to try and find some examples.......

[156 D]

............to try... and prove the point that the heat in the exhaust manifold conducts back into the cylinder etc. ,...............your EGT`s will be a lot higher in a retarded state than in an advanced one for a given air/fuel ratio, compression ratio...............

........as an example on a four stroke to try and prove it.......with a lean air/fuel ratio which = Higher EGT`s......the burn will be slower and later in the stroke, continuing to burn while exhausting if severe....will cause cycling /snowballing into and causing rising coolant temperatures, preignition, then detonation..........in other words it has done a full cycle off events and will eventually give you the signs of a too advanced timing.............. I know this sounds complicated and it is again in a four stroke but it has the condition of a retarded spark has the same but quicker effect in the 2 stroke as there is no liquid coolant only air so it will seize.

When your next on your Dyno .....if you have the ability to check the EGT`s.....try them at the correct advance then try a fews degrees less and see what the temp`s do?..............

[soulsurfer]

[soulsurfer]

Noticed the new MB cowlings at Lincoln, snug around the flywheel and blowing around the exhaust port area, but bugger all cowling around the inlet area. The idea is cold air in, hot air out as quick as possible.
Also noticed on Mark's bike that expanding foam was used to fill any gaps between the flywheel and standard type flywheel cowl