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I had a discussion with a friend of mine over liquid vs. air cooled at the bar last weekend. I would like to hear some other riders thoughts. My friends qualifications are a B.S. and M.S. in Mechanical Engineering from U of M [xx(] in Heat and Mass Transfer so usually agree with him on these matters. Here goes. He claims on a 2-stroke motor the fan-cooled engine will last as long as the liquid under normal operating conditions. He claims to have seen studies using thermocouples across both engines and the variences were negliable under "Normal Conditions". He also rides an XCF (fan) with about 4000 miles and no rebuilds. He claims the only advantage to liquid cooled is less drag on the motor from the fan resulting in more horsepower. WHAT ARE YOUR THOUGHTS?? I would love to prove him wrong.. The only thing I have on him now is a nicer Lawnmower[:D].
 

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HE is right on the horse power issue. An Arctic cat 440 liquid cooled has 18 more horse power than a 440 fan cooled. If you ride in areas with low snow you will not get the cooling on a liquid cooled with out the snow going across the heat exchanger. If you run in a lot of powder the vents tend to plug up and you do not get the air circulation needed to cool the motor.Hope this helps
 

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Liquid sleds can be pushed to higher power because of it's better cooling ability (ie higher compression, porting, etc), however, a fan will generally last longer from the same reason (lack-of-high compression...).
 

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Liquid cooled sleds generally last longer in between rebuilds. The reason is that there is a more even heat transfer. Also liquids produce more power because of the tighter tolerances inside the engine. They usually have less compression though. As far as the fan stealing power. I think the water pump will turn harder than a fan. 4000 miles isn't all that much for a fan cooled. But if you took two similar sleds, one liquid and one fan, rode them the same after 6000 miles the fan will have a larger drop in compression. However other problems can occur to cause engine failure that are more connected with the increase of power.
 

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I'm inclined to agree with the assumption that the liquids are designed differently to take advantage of the increased cooling ability. I know that a Fugi 500 fan and liquid take the same pistons but most liquids run 38mm carbs as opposed to 34s on the fan. Dont know about the ports. I think that most if not all of the premature fan cooled engine failures are caused by running outside of design parameters. IE. not enough cooling for whatever reason.

I seriously doubt that a fan takes that much more hp to opperate than a pump, if any. If It did I think you would see a significant increase in fuel consumption by running a fan as opposed to a liquid doing the same work. I've not found this to be the case.

Speaking from decades of hands on expirience, if you can keep them cool, they will last. I cant remember any sled I owned before 91 that i didn't make modifications to to get more air to the engine. BTW I made mods to my 96 ski-doo SLE to get more air to the engine, didn't on my 97 Indy Trail.
 

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Originally posted by zackattack
[br] As far as the fan stealing power. I think the water pump will turn harder than a fan.
You are right about tighter tolerances in liquids, better cooling means more power.
but Smokey.. is right about fans sucking power, 18 hp diference with same size engine...where do you think those lost ponies went? A water pump will never draw as much power as a fan will.
 

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the fan is 8" radius

the water pump is 1/2" radius

it's a lever, the farther out you go the faster it's moveing the more drag. sure, water's harder to push that air, but this is an exponential equation guys, snoweek had a big thing on this awhile back, even the aerodynamic clutches, at 8400 and a radius of 5" or so cost you something like 2.5 hp to spin, and they're not designed to push air, they're designed to not push it.

in any case, it takes MUCH more power to spin the fan, the impeller takes very little power to spin. roughly 14hp less on an AC 440 : )

I don't know about the fans being more or les reliable, I know the cylinder away from the fan will be hotter than the other one... if they're the same, but generally compression, porting and jetting are staggered so that the cylinder closer makes more power.
 

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The power difference is NOT NOT NOT because of the fact that one spins a fan, and one spins a water pump.

It is because a water pump/radiator is MUCH MUCH MUCH better at removing heat from a motor. Therefor, the motor can CREATE much more heat, without burning down. This means tolerances can be tighter, compression can be higher, and the motor can run at a consistent temp (thermostat).

-Dean
 

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I was just gonna say that pulling over my friend's indy 500 (488 liq) was one hell of a lot easier to pull over than his indy trail (488 fan) which is the same size engine.
 

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you jst gotta love the fan/liquid cooled debate, i wish i had 10 bucks for everytime ive seen this posted, i could quit working. j.k. guys, this is one debate that will live on forever, some like fans or free air, some like liquids, me, i dont care, i just want to ride
 

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"normal operating conditions"
That's what the liquid will buy you consistantly. Motor's Like to run at the same temp and same conditions. They usually don't care too much to be stressed by excess heat. My experiances with fan's were not all good, always seems like the pto side always ran just a bit hotter. Dad's indy trail is a slug in the spring etc etc.. guess it's just a personal preferance over time.
 

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Originally posted by kevin
[br] Speaking from decades of hands on expirience, if you can keep them cool, they will last. I cant remember any sled I owned before 91 that i didn't make modifications to to get more air to the engine. BTW I made mods to my 96 ski-doo SLE to get more air to the engine, didn't on my 97 Indy Trail.
Er, the ammount of air sucked into the engine doesnt do anything but vary the ammount of gas sucked in. The more air, the les gas, and vise versa. The fresh gas coming over the top of the piston is actually generating the cooling function that your talking about. More air would just lean you out, resulting in a need for larger jets, to conpensate for the fact that it's so much easier to pull air than gas.
 

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Originally posted by RotaxAtax
[br]
Originally posted by kevin
[br] Speaking from decades of hands on expirience, if you can keep them cool, they will last. I cant remember any sled I owned before 91 that i didn't make modifications to to get more air to the engine. BTW I made mods to my 96 ski-doo SLE to get more air to the engine, didn't on my 97 Indy Trail.
Er, the ammount of air sucked into the engine doesnt do anything but vary the ammount of gas sucked in. The more air, the les gas, and vise versa. The fresh gas coming over the top of the piston is actually generating the cooling function that your talking about. More air would just lean you out, resulting in a need for larger jets, to conpensate for the fact that it's so much easier to pull air than gas.
I guess I should have said cooling air. As in air to the fan or cooling fins.
 

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I would say a combonation of what Junior and Ripperd sounds good to me.yuk yuk.
 

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As for the 4000 miles on his sled, if he dont replace his crank seals soon he will be doing a major rebuild. I found out the hard way!
 

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As for the 4000 miles on his sled, if he dont replace his crank seals soon he will be doing a major rebuild. I found out the hard way!
My cousin just turned 11,500 miles on his 1997 Indy Trail. It has never been rebuilt once and runs like new.

Fan cooled sleds are just as reliable if properly maintained and not overheated (by towing heavy things or running hard in mild weather). Liquids do however have a power advantage.
 

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well now here i go! volkswagons stopped at about 75hp because of fan losses. airplanes went way up there in hp (air cooled) because they didnt need a fan! i have never seen a dragster run a air cooled because you cant get rid of that many btus that quick without liquid being the heat transfer medium. im betting the sled companies have came to the same conclusion[:D]
 
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