Engine Heat

[Constant Mesh]

If a 600cc liquid-cooled bike and a 1300cc liquid-cooled bike both get 40 mpg running at 60 mph does the 1300cc bike generate more engine/radiator heat?

Does the larger engine generate more heat only when you're using the extra power and consuming more fuel?

 

[shuswaper]

...easy. Bigger explosions= more heat. :assassin:

 

[jestal]

In your example they will both reject the same amount of heat.

In most any internal combustion engine (generically speaking) the heat energy from the fuel burning goes three ways: 1/3 makes power pushing the piston down, 1/3 escapes out the exhaust and 1/3 is rejected to the water/oil. Nothing to do with the size of the explosions. So....if the engine are making the same power (using the same amount of fuel and getting the same MPG) then they are going to be similarily rejecting the same amount of heat. The "explosions" are not "bigger" by the way. They are relatively the same. Since the smaller displacement engine will run at a higher throttle opening it will be working a little harder in each cylinder compared to the larger displacement engine. The larger displacement engine will be more heavily throttled so the "explosion" will be a smaller percentage of what it could be at full throttle compared to the smaller displacement engine.

From a practical standpoint I would say there is no difference in the heat rejected. BUT...for the nitpickers....there is no way the larger four cylinder is likely to get the same fuel economy or use the same amount of fuel as the smaller engine all other things being equal. There is simply more friction in the larger engine with more cylinder area, friction in the crank rod journals, etc.... And, with more piston area the larger 4 cylinder there is going to be more pumping loss than the smaller engine since it will be throttled more. All this equates to more fuel being burned in the larger engine for the same effort going down the road as the smaller one. That would make the larger engine reject (a little) more heat. In addition, the larger cylinders and cylinder head area is going to present more area for heat rejection from the cylinder. Shouldn't make much of a difference but it won't help any with putting more heat into the coolant.

I still think that, within reason, they are about the same but theoretically the example as you stated it is slightly flawed thus skewing the results....LOL

Clear as mud??

 

[Constant Mesh]

I was trying to get at the assumption that since the FJR has a larger engine than many sport bikes that it will obviously reject more heat onto the rider.

If both engines at reasonable cruising speeds offer approximately the same mpg then the heat rejected is about the same for both. The deltaT of the air through the FJR radiator would likely be less than the deltaT of the air through the smaller engine's radiator.

 

[jestal]

That is why I say that under practical conditions the bikes in the example would reject the same amount of heat. The larger displacement is not the cause of the "heat" issue. All new engines while in development are subjected to testing to determine "heat rejection" to determine the amount of heat rejected to the coolant. This confirms the engine design does not have a serious flaw and predicts the amount of radiator cooling and air flow will be required in the vehicle. After seeing quite a few engines go thru this testing the basic assumption that a third of the heat energy of the fuel is going into the radiator is always born out. I would see no reason that the FJR would be an exception given the engine's construction and design and high flow cooling system.

I don't think the FJR rejects anymore heat than other motorcycles at all. I think the heat issue is a result of the air flow from the radiator (mis?) directed so that it hits the rider's legs and thighs, not too hot of air or too much hot air.

I haven't changed the heat rejection of my FJR at all but it is plenty cool to ride now with the sealed up airflow behind the radiator and the heat extractor "spoilers" added to the gills to improve air flow in that area. The tank heat is completely eliminated by the sealed up air flow so that the tank stays plenty cool. That seems to confirm my earlier suspicions that the tank heat was from hot air directed on it NOT the fuel being heated by the engine and return fuel flow.

By eliminating the catalytic converter the bike is fine sitting in traffic. This seems to correlate to the extra sealing Yamaha did on the 06 to prevent hot air from the cat from rising around the rider while stopped. That has nothing to do with displacement or engine heat generated. I have also eliminated some exhaust heat generated by the air system by disabling and eliminating it.

I would say riding my 03 FJR in the mid 90's in Michigan lately that it is cooler than my old XS1100 (air cooled) was and is definitely cooler than my CBX is. It is FAR cooler than it was originally. Nothing was done to change the "cooling" or heat rejection per se, just redirecting the air flow and eliminating the secondary heat source of the cat and air system.

 

[twowheelnut]

If a woodchuck could chuck wood, would the woodchuck cut more wood if he had a bigger chuck to cut wood? Well, could he? If he did, would he be burning more calories and shedding more heat?

Then again, no soap radio, right? :dntknw: