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Water Cooled vs Air Cooled? Make same hp? ...

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Generally you see the best performance bikes being water cooled. What is the major advantage of water cooling vs being air cooled.

XR400R vs DRZ400

Air Cooled CR500 Vs Water Cooled CR500

so etc.

Is it possible to have such a high performance bike and it be air cooled?

Also why not have bikes water cooled and also have fins on the head to dissipate the heat?

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Water cooling maintains a more steady temperature. Tolerances can be tighter on a water cooled engine. Longevity is increased.

The only disadvantage to water cooling is the peristaltic draw of power to run the pump, the added complexity of the pump/hoses and radiators and the weight. But these are more than offset by the gains.

Sure, it is possible to be air cooled and be high performance. It is just with all else being equal, a water cooled engine is capable of creating more power and lasting longer.

Some do have both but the water still has to transfer the heat.

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Internal combustion engines are heat engines and most of the fuel burned ends up as heat, only a little bit ends up as power. So the limit on power is the ability to remove the excess heat out of the motor to prevent heat damage to the internal parts, that is part of the design process. The old air cooled motors had steel liners in an aluminum cylinder and heat did not transfer from the steel to the aluminum very well, not much power. The next step was to plate the aluminum cylinder for better heat transfer so more fuel could be burned. The last improvement was water cooling a plated aluminum cylinder, this allowed the engine to survive burning more fuel (and more power). Water also absorbs a lot of heat when it boils which adds another level of protection from overheating.

Finally the heat must be transferred to the air and the many small fins on a radiator have much more surface surface area to transfer the heat than the few thick fins on an air cooled cylinder.

Adding antifreeze to the water reduces its ability to absorb and conduct heat but the antifreeze provides corrossion protection, freeze protection, and water pump seal lubrication. The 50/50 rule is from the auto world for freeze protection; if you want better cooling use distilled water (WalMart) and reduce the antifreeze to 25% or less, and change it more often. Wetting agents also help. The pressure cap is important because it raises the boiling point of the coolant and reduces water pump cavitation (cavitation reduces pump efficiancy and life).

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Internal combustion engines are heat engines and most of the fuel burned ends up as heat, only a little bit ends up as power. So the limit on power is the ability to remove the excess heat out of the motor to prevent heat damage to the internal parts, that is part of the design process. The old air cooled motors had steel liners in an aluminum cylinder and heat did not transfer from the steel to the aluminum very well, not much power. The next step was to plate the aluminum cylinder for better heat transfer so more fuel could be burned. The last improvement was water cooling a plated aluminum cylinder, this allowed the engine to survive burning more fuel (and more power). Water also absorbs a lot of heat when it boils which adds another level of protection from overheating.

Finally the heat must be transferred to the air and the many small fins on a radiator have much more surface surface area to transfer the heat than the few thick fins on an air cooled cylinder.

Adding antifreeze to the water reduces its ability to absorb and conduct heat but the antifreeze provides corrossion protection, freeze protection, and water pump seal lubrication. The 50/50 rule is from the auto world for freeze protection; if you want better cooling use distilled water (WalMart) and reduce the antifreeze to 25% or less, and change it more often. Wetting agents also help. The pressure cap is important because it raises the boiling point of the coolant and reduces water pump cavitation (cavitation reduces pump efficiancy and life).

100% spot on! :ride:

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Now what about the 1000+ hp WWII aircraft engines that were air cooled?

Two sayings come to mind here

a) There is no replacement for displacement.

:ride: Quantity has a quality all its own.

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Now what about the 1000+ hp WWII aircraft engines that were air cooled?

Those engines were typically in the 27,000-28,000cc displacement range and 1000-1600hp. Do the math and it's just 59hp/L in a best-case scanario. Spread that over 12 cylinders or more and factor in the high air speed and low air temperature over the cooling fins and it's clear why cooling wasn't a problem. From what I could find, the American, British, and German fighters were actually water-cooled anyway.

Something not mentioned is that water-cooled engines typically have lower cylinder head temperatures than "airheads." This helps reduce octane sensitivity somewhat, which goes further toward making more power with a given fuel.

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Now what about the 1000+ hp WWII aircraft engines that were air cooled?

As others said they were big and most were lucky to produce over 50hp/L. The biggest load on an aircraft engine is during takeoff and they had forced air cooling from the propeller.

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The clearances on air-cooled engines are not necessarily larger than with water cooled. The guy who wrote Guzziology claims the Nickasil (I think) plated cylinders of Guzzis actually had piston tolerances tighter than some water cooled engines (although I can't remember the exact quote, that was the gist of it).

And it's a bit of a stretch to say air-cooled engines can't last long. Think about airhead BMW's; not unusual to see them over 100k miles (who knows what repair history though). Longevity seems to have more to do with oil quality and oil change intervals and oil & air filter quality than anything else.

But yeah, you can probably get more power out of an water-cooled engine. Hard to beat the evenness of cooling and the effect of a radiator fan when the speed is low.

On the other hand, the extra surface area of radiators is only in the ideal case, when it is nice and new. Most radiators I have seen were filled with dead bugs and so forth. Or had many bent fins and sometimes blocked tubes. And it's a hell of a lot harder to clean bugs out of a radiator than out of the cooling fins of an air-head. Often, radiators are very large and look bad on a narrow bike like a thumper or v-twin.

I kinda like the idea Suzuki used for a while: having an air-cooled engine with a small supplemental radiator for the oil (did they have a fan, too?). Kind of a nice compromise, and the thing getting the cooling is the oil, which is the main thing. Also no need to mess with another fluid in the bike; the oil is already there.

I've had both kinds of bikes. I prefer the simplicity and reduced maintenance of an air-cooled bike.

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The difference between air cooled engines and water cooled engines is only in the way to transfer the heat from the engine to the external air.

The way to cool the engine doesn't have any effect to the power and the reliability of the engine.

Just think that my XR is worked to crank out 65hp at the wheel and i used it 4 years without replacing any mechanical component.

We are working now to build an 900cc based on the XR 600 R engine block, keeping it air cooled and making it to crank out about 100hp !!

Isn't true that the water cooled engines does have more power... just see the top fuel dragster, they run without any cooling !!!

Simply the water cooling keep the engine in a more uniform temperature range while air cooled keeps some point very hot and other points colder.

Another reason to the water cooling is the appearance, just look at two bikes in a showroom: the water cooled ones looks more likely than the air cooled. This seems to be an irrilevant factor but it isn't. We have worked on a brake systems and the most powerful brake disc material is ductile iron while all the brake discs used today are made with stainless stell: the last one will never rust but if you try a ductile iron brake you will never come back to stainlesssteel !!!! This is just a sample but it means how the appearance is important today !!!

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I was reading some guy in Germany who raced MZ Skorpions, who changed his bike from water-cooled back to air-cooled (using different cylinders or something, a very big job) just so he could shave some weight off his bike.

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Just think that my XR is worked to crank out 65hp at the wheel and i used it 4 years without replacing any mechanical component. We are working now to build an 900cc based on the XR 600 R engine block, keeping it air cooled and making it to crank out about 100hp !!

You really should start posting in the XR600/650 forum. I'm sure everyone there would love to hear about the project. :ride:

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Those engines were typically in the 27,000-28,000cc displacement range and 1000-1600hp. Do the math and it's just 59hp/L in a best-case scanario. Spread that over 12 cylinders or more and factor in the high air speed and low air temperature over the cooling fins and it's clear why cooling wasn't a problem. From what I could find, the American, British, and German fighters were actually water-cooled anyway.

Something not mentioned is that water-cooled engines typically have lower cylinder head temperatures than "airheads." This helps reduce octane sensitivity somewhat, which goes further toward making more power with a given fuel.

yea considering a crf250 make about 120 hp/l

rossi's gp bike makes almost 300 hp/l

the ams lancers dyno cars make 450 hp/l

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The difference between air cooled engines and water cooled engines is only in the way to transfer the heat from the engine to the external air.

The way to cool the engine doesn't have any effect to the power and the reliability of the engine.

Just think that my XR is worked to crank out 65hp at the wheel and i used it 4 years without replacing any mechanical component.

We are working now to build an 900cc based on the XR 600 R engine block, keeping it air cooled and making it to crank out about 100hp !!

Isn't true that the water cooled engines does have more power... just see the top fuel dragster, they run without any cooling !!!

Simply the water cooling keep the engine in a more uniform temperature range while air cooled keeps some point very hot and other points colder.

Another reason to the water cooling is the appearance, just look at two bikes in a showroom: the water cooled ones looks more likely than the air cooled. This seems to be an irrilevant factor but it isn't. We have worked on a brake systems and the most powerful brake disc material is ductile iron while all the brake discs used today are made with stainless stell: the last one will never rust but if you try a ductile iron brake you will never come back to stainlesssteel !!!! This is just a sample but it means how the appearance is important today !!!

the reason dragsters dont have cooling is because the run on alcohol and it runns really cool

also i think honda make an over 800cc xr based bike in the 80's

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yea considering a crf250 make about 120 hp/l

rossi's gp bike makes almost 300 hp/l

the ams lancers dyno cars make 450 hp/l

Turbo F1 engines were just reaching 1000hp/L in 1986, but the engine only lasted(most of the time) through qualifying. The point is that the WWII plane engine were huge so that power was adequate, yet power density was low for longevity. A CRF250 doesn't have that longevity even 70+ years later.

1.) the reason dragsters dont have cooling is because the run on alcohol and it runns really cool

2.) also i think honda make an over 800cc xr based bike in the 80's

1.) Dragsters don't have cooling systems because they aren't run long enough to need one regardless of fuel. Evaporative cooling is significant with methanol, but it will still burn hot enough melt pistons and cylinder heads.

2.) It wasn't that big and it was in the '90s, not the 80s. The engine also had a tendency to break the cases.

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on alcahol motors don't care if there air or lc'd for instance a "nitro" glow rc motor or a jawa speedway motor.

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on alcahol motors don't care if there air or lc'd for instance a "nitro" glow rc motor or a jawa speedway motor.

Please clarify the point you're trying to make.

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with gasoline a liquid cooled engine is better. alcahol.... air cooled engine is better. when alcahol evaporates it takes heat out of the air its mixed with so liquid cooled + alcahol = lots of warming up.

whats neat is a two stroke will produce more horsepower and gain reliability when ran on alcohol because it cools the bottom end nicely.

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