why are watercooled so much more powerful

[POCKETRACINGBIKES]

Greeny has taken the words right out of my mouth.Well said mate!
With the Polini engines there main A/C 4.2 hp is basically an a/c engine that you cannot fit a w/c setup.The next jump is the Polini 6.2hp a/c and this is one setup that you can apply all w/c cylinders to,etc.
BZM call there engines the 420 and 620 cases.There are alot of reasons for HP outputs.Bigger carbs,different reed boxes,different cranks,different exhausts,etc.The difference that i have noticed that the Italian A/C engines are 40cc 4.2 hp or 6.2 a/c 40cc and now BZM have made a 50cc 5 port a/c engine.With the w/c engines they start from 6.2hp 40cc w/c all the way up to 50cc w/c 6 port engine.So in saying all this they have produced more out of the w/c than the a/c engines.Also what Dazza has said is spot on as well!!! Maybe if they built a 50cc a/c 6 port that might be a bit of a weapon!Hope i havent confused you all!
cheers danny

[minimotorider]

Well as a whole i think a 50cc a/c 6 port would be incredible, i think though at that power the cooling becomes crucial especially with that many rpm to obtain such hp figures.
For a 50cc to be able to do 15-18k rpm it would need substantial cooling to safely sustain these sort of rpm. This would also be a factor in design which limits the a/c to its 12-14k rpm. There is physical attributes which limit it from needing this water cooling i guess.

[greeny]

Being aircooled is not in itself a barrier to revving hard or making power. For example aircooled formula A kart engines (100cc A/C) rev to 20,000+ RPM and produce 40hp. However their engine life is less than an hour. These guys rebuild engines between heats, and have specialist qualifying engines.

The moral of the story is that yes you can get big horsepower from a/c but the reliability and durability of the engine will be severely compromised. Dazza and Danny are right. The more power the more heat you produce. If you fill a balloon with water (try this at home), and hold a cigarette lighter to the balloon it will not pop. Do the same with an airfilled balloon and it will pop almost instantly. This is because water is far more dense than air, and theirfore disperses heat far more efficiently throughout the water in the balloon. An aircooled motor cannot dump heat as well and this has several effects:

1. When an engine is hot, the air going inside is also hot, making it less dense. If the air is less dense, effectively there is less of it and as i have said before, More air = more power. This is the sole role an intercooler plays in a turbo setup, to cool the inlet charge. Similarly, engines will make more power in cold weather at sea level as the air is more dense.

2. Due to the inability to drop heat, A/C barrels distort unevenly, especially around the exhaust port where temperatures are very high. This uneven distortion serves to change the shap of the bore, forming an oval. This opens tolerances, reducing power and secondly increases wear as the piston no longer effectively fits. To take the formula A example again. At the end of a straight you will see the driver choke the engine by putting their hand over the airbox. They do this under brakes before they get off the throttle. The reason they do this is that at the end of a straight the piston is so hot that it actually does not fit in the bore, it is an interference fit. If they came all the way off the throttle, the engine would have no fuel (oil) and would intantly seize. By putting their hand over the inlet, they dump a whole bunch of nice cool fuel onto the piston to cool it, shrinking it just enough to keep going when they get off the throttle. These are the types of lengths you have to go to to get equivalent power from an A/c engine.

Hope that clears up the cooling issue, cheers

[rigma]

Originally Posted by greeny

Being aircooled is not in itself a barrier to revving hard or making power. For example aircooled formula A kart engines (100cc A/C) rev to 20,000+ RPM and produce 40hp. However their engine life is less than an hour. These guys rebuild engines between heats, and have specialist qualifying engines.

The moral of the story is that yes you can get big horsepower from a/c but the reliability and durability of the engine will be severely compromised. Dazza and Danny are right. The more power the more heat you produce. If you fill a balloon with water (try this at home), and hold a cigarette lighter to the balloon it will not pop. Do the same with an airfilled balloon and it will pop almost instantly. This is because water is far more dense than air, and theirfore disperses heat far more efficiently throughout the water in the balloon. An aircooled motor cannot dump heat as well and this has several effects:

1. When an engine is hot, the air going inside is also hot, making it less dense. If the air is less dense, effectively there is less of it and as i have said before, More air = more power. This is the sole role an intercooler plays in a turbo setup, to cool the inlet charge. Similarly, engines will make more power in cold weather at sea level as the air is more dense.

2. Due to the inability to drop heat, A/C barrels distort unevenly, especially around the exhaust port where temperatures are very high. This uneven distortion serves to change the shap of the bore, forming an oval. This opens tolerances, reducing power and secondly increases wear as the piston no longer effectively fits. To take the formula A example again. At the end of a straight you will see the driver choke the engine by putting their hand over the airbox. They do this under brakes before they get off the throttle. The reason they do this is that at the end of a straight the piston is so hot that it actually does not fit in the bore, it is an interference fit. If they came all the way off the throttle, the engine would have no fuel (oil) and would intantly seize. By putting their hand over the inlet, they dump a whole bunch of nice cool fuel onto the piston to cool it, shrinking it just enough to keep going when they get off the throttle. These are the types of lengths you have to go to to get equivalent power from an A/c engine.

Hope that clears up the cooling issue, cheers

nice said

good work

[mac90]

excessive heat is the enemy of all combustion engines & saps power, performance & reliability
so cooler = more power

but you cant compare a aircooled cag with a blata or blata rep they have a totally different internals crankcase transfer ports & exhaust port setup as well as bore & stroke etc..
most wc pocket bike & high reving ac chainsaw engines also only run 1 ring witch reduces heat & friction but wear the ring out faster

[1968falconxt]

Originally Posted by Dazza

A watercooled engine and a aircooled engine made the exactly the same way.
i.e Elite 14R and the Elite 14WR
Have the same power.
But the more power you produce the more heat you produce.
So this is where a watercooled engine can get rid of the heat better.
Optimal temp for a pocket bike to run is around 65 to 75 degrees.
An aircooled bike will not get rid of the heat as quickly as a watercooled.

So a watercooled will produce more power due to it being able to get rid of the heat much more quickly and will be able to continue to run at optimal temperature.

actually dazza, an aircooled with the right design of cooling fins can also get rid of the heat very quickly so long as it has good air flow. they can cool as quickly as W/C engines. cags are poorly designed though

cags have nowhere near the same stroke as a W/C engine either

[minimotorider]

I"m quite suprised how well a Cag goes between weights.
My mate weights 79kg and i weigh 55, the difference is barely anything,
Either his bike goes really well or mine doesn't. hehe
Wonder if running in would have much to do with it, his engines got 6 hours more use than my 1 hour!

[Stellerlicious]

the reason y cars are watercooled?

run more eficiantely, colder, more powerful and all reound better.

think this way, cag motors are like realy small lawnmower motors, crap unles victa made

watercooled are like the audi of the lawnmowers but raced.

god im a wierd one somtimes haha

back to my underground UV lair i go

watercooled for the win!

[mac90]

Originally Posted by 1968falconxt

actually dazza, an aircooled with the right design of cooling fins can also get rid of the heat very quickly so long as it has good air flow. they can cool as quickly as W/C engines. cags are poorly designed though

cags have nowhere near the same stroke as a W/C engine either

but the thing is if its the same design barel on the same aircooled engine but with a watercooled top end it will produce more power
thats why most performance & race engines are liquid cooled

as long as they have a good pump & radiator they will take longer to heat up & run at one consistant temp

unlike a aircooled engine that tend to get hot fast & can only cool as low as the outside air will allow

so most aircooled engines run at higher temps they cant cool to the lower temps most liquid cooled engines run at so oil to fuel ratio is usually 25:1

a example is a outboard engine that alwayse has a fresh supply of cold intake water usually run fine @ 50:1 because of the much lower temps they need less lube in the mix

best way to see is to compare the running temps of a blata aircooled & a blata watercooled engine of the same design like the replicas or the older style blata engines the reps were copyed from,

the aircooled engine will run hotter not only top end but in the crank case where induction takes place this will effect the air density & how much air/fuel can be packed in

lower top end, cylinder & crank case temps will allow you to run less oil & will pack more air fuel mix in to the combustion chamber & give you alot more power than the same engine running at a higher temp
this is why the water cooled will win out almost every time performance & power wise as long as the cooling system is working properly


now a true rotary 2 stroke would be another story all together with 3 power strokes per revoloution compared to 1 powerstroke per revoloution you get with your standard 2 stroke engines but thats another debate

[greeny]

Yes fins can be designed to direct heat very effectively, however they can never do so as evenly. This has implications around the exhaust port. Look at the barrel of a W/c engine and observe the bulge around the exaust port. This is designed so extra water capacity can be realised to direct heat from the exhaust port and stop it from swelling back into the bore. Water is around 20times more dense than air. To air-cool this area you need at least 20times that volume of air come in contact with the barrel. This is possible but not practical, the engine would not fit in your frame.

The other advantage of water cooling is that the cooling can be directed to exactly where it is needed (as per exhaust port). Air cooling introduces more variables, such as air velocity, intereference and ambient temperature none of which can be controlled.

Secondly, air cooling it reactionary. To illustrate: you wind the throttle wide open at the beginning of the straight. The straight lasts 3 seconds. In this time, the inner cylinder temperature has spiked, but it may be another three seconds befre this heat soaks throught to the finns and is dissipated. In this 6-seconds, the exhaust port has swelled, puting pressure on the piston and sucking power. This is made worse if you are slip-streaming another rider. In a water cooled machine, there is a supply of cooled water lasting up to half a lap, and so cylinder temperature does not fluctuate as wildly.

It all comes down to reliability. Aircooled motors will produce similar peak power to water-cooled given optimum conditions. However engine life will be significantly less (formula A motor- 1 hour) compared to a water cooled engine (Rotax- 40 hours).