GBD Approved

Your question is quite confusing & unclear. How does liquid cooled engine works? There is a jacket of coolant which passes through engine absorbing the heat. This means that coolant itself is also getting heated. How do you cool that? Through air only.

The fins are used to distribute the heat generated in the cylinder in an air cooled engine. Here more metal is used to create fins and the contours on them is cooled by wind. In a LC engine there is a sleeve of coolant around the cylinder to keep it cool.. Using fins could help, but then they aren't required all the time especially considering the more usefull lc anyways does that work. Why incur more costs for something that addsto weight, doesn't really help in a covered bike and the utility is minimal!

The cylinder is a chamber where a blast takes place.
A 150 cc engine means 150 cubic capacity of "charge" fuel + air would be sucked in, compressed and blasted inside to generate power. Extrapolate this to a 1000cc engine.. A litre of charge. Bigger the explosion. More the heat.

Cars have huge radiators, they don't rev as high as a motorcycle and so they heat lesser than a bike!

I guess Radiator acts as fins (if you observe the radiator carefully there are fins on them ) to cool the coolant so no point in having fins on the engine. As it further increases the cost .

i guess, you guys didn't understood his question, he was not asking why LC instead of air-cooled. he was asking why not LC + air cooled by adding fins on engine.

well, there are some reasons to it-

• it will add weight to the bike and everybody is trying to reduce weight.
• quite often there is not enough space to provide fins on higher displacement bikes.
• even if fins are provided, there won't be sufficient air-flow because air-path is blocked by radiator.
• and even if some of the air, does manage to reach engine block, the amount of air will be very less and will be pre-heated by radiator so, very less heat exchange will take place.
• and even that very small heat gain may not be too much helpful, as whenever engine cooling is designed, the intention is to cool the internal walls and maintain them at manageable temperatures. keeping the outside walls cool are just a side-effect.
• most importantly these high capacity bikes are primarily not meant to be ridden in bumper to bumper traffic. so, these bikes are not happy to be ridden at ridiculously slow speeds, just as our commuter bikes are not happy when ridden at 100+ speeds.

with regards.

Isnt that pretty much what I wrote sirjee :P

NOTE: I'm just doing some Physics level brainstorming. Have not ridden Sbk's, or anything above a Ninja 250 till now.

I think the main reason why liquid cooled engines mostly don't have air fins is that (according to a source): "Water (or water and antifreeze) offers 1000 times greater thermal conductivity than air and it can be routed much more closely to high temperature areas such as the exhaust valve seat and guide."

It points out that water/ liquids cooling an engine are so effective, that fins may no longer be needed.
As for Litre class sportsbikes generating too much heat, I think it might come from these main reasons:

1. Probably because most of them are not ridden in their optimum powerband range. If you ride them at 1500-2500 rpm, they'll heat anyways. A bike with a 13,750 rpm redline shouldn't be expected to cruise along, near their idle rpms.
But again, in city, one hardly has a choice. In 3rd gear, most superbikes do a 30-40 kmph at around 3000 rpm or so.

2. Their large engine size makes the same heat more "reachable" to our thighs. Otherwise, even Indian bikes heat up, but their tiny engines are spaced away from our thighs and can hardly make the heat spread so far.

In air cooled single-cyl bikes, the closest cylinder parts to our thighs are the head/ fins.
In 4 cylinder imports, its the entire cylinder block next to the thighs.


Lastly, I believe that if fins dissipate the heat from an engine, then they will definitely heat up the air around the thighs EVEN MORE.
After all, the rider feels the engine's dissipated heat only, and nothing else. So, having fins might not help the rider's thighs, in fact, may worsen the situation.

Getting my point?

Reminds me of my child hood days when I used to sit on the engine box near the driver, the bus cabin used to get extremely hot and unbearable, and I always wondered why not fit a huge air conditioner to the engine to keep it cold!

This one too is a similar notion.
The normal fins you are asking to add is like your table fan. Remember the Liquid cooled engine is like Air conditioner. You dont actually need a fan for a room which already has an AC.

what an example sir jee...

You mean there is complete cover around the engine of coolant and I thought there is pipeline for the flow of coolent in liquid form...

Understood very well additionally....

Really, how come the cost

Well explained, thanks...

Got your point very nicely....



Thanks all for explaining me this, After to read all this a thougt cam into my mind that what are these liquid, which we use as coolant

Use an effective tool called GOOGLE - https://www.google.com/search?q=cool...x=&startPage=1

Coolant - Wikipedia, the free encyclopedia

Mostly it contains ethylene glycol ,water and other add on chemicals ..

water?

The water used in an coolant is an anti-freeze mixture or some chemical water.
if we use plain water it leads to corrosion..