Topic: Which is better when hot, high or low rpm?

[smccloud]

I would agree with KNG that given a larger surface area to radiate heat, the oil would act as a cooling medium. I have a K8 and my side covers are solid. In the earlier models they louvers which may have acted to help cool the oil in the tank rather than being just cosmetic. These engiines have a large oil capcity for their size. Roughly 4 quarts for 736 ccs vs 5 Quarts for a 5.0 litre V8.
Having said that, they do not like standing still very long in hot weather.

what earlier bikes are you talking about?  i have a k2 and it has solid side covers.  it is my only motorcycle, and i ride 15 miles one way to work (kinda sucks to have a leaking head gasket when you wear kakhi dress pants to work).  i know my bike is getting to hot when it starts to idle at 2000+ when it normally idles around 1000-1500, and it is jetted rich right now too.  then again, when i first get it out or put it away for the season it can be hovering around 50 degrees (gotta love mn weather).  this winter i plan to pull the engine out, rebuild it (possibly with an 836 kit) and then keep riding the thing.  tonight i got more "nice bike" comments than i ever have in one day.  had a guy on a honda vfr say that i have a nicer bike than he does; although he did admit that his is faster.

I have only seen them in pictures, it looks like louvers to me.

see, the side covers on mine don't look like that.  i have solid ones.

[DaveNTexas]

I agree with twotired up to a point....

and I won't disagree with him but.... this statement:

"The more fuel is fed to the engine, the more heat is generated."

I will do some searching but I am pretty sure that there is a graphed curve showing that any engine's temp (cylinder head temp) is an inverted U, the peak is "Best Power" where the mixture provides the hottest temps.  Either side of that, the temps drop off, as the mixture is progressively leaned or enrichened.  I will look around for that.  Maybe I take his comments out of context, if so I apologize in advance.

Also we talk about in air cooled airplane engines;  Detonation Margin. 
I believe an overheaded engine, among other things such as deformed valves, warped seats, can suffer detonation.  And is it not true that lugging an engine at low speed can result in detonation?  "Lugging" plus "overheated" sounds bad to me but I am no expert.
Not to say 6000rpm is doing it any favors when hot either but 1500rpm when underway seems 'luggish' to me! 

[TwoTired]

I tend to believe that oil does contribute to heat transfer.

I believe this because I've measuered the oil temp with and without an oil cooler.

I've always agreed that oil has a contribution to heat transfer.  And your measurements show that oil coolers lower oil temperature.  I'm not surprised about that. I mean it IS called an oil cooler, after all? Do they have engine cooler labels?  Aren't you still inferring that lowering oil temperature also lowers cylinder head temperature?  Have you isolated lack of oil lubrication quality with temperature rise as a contributing factor?  From an experimental test construct, the data provided lacks connective assumption proof.  Is the oil cooling effect on cylinder temp .1 degree?  2 degrees? 10 Degrees? 50 Degrees? 100 Degrees?

While cooling the oil certainly should have some beneficial effect at removing heat from the engine, no one has yet quantified the magnitude of that effect with either calculations or empirical before/after testing.

If you get a 0.01% increase in salary, yes it is better, but is it significant?  And, are you willing to put in extra work hours to achieve it?

I won't argue that modified engines might benefit from an installed oil cooler.  It's just that no one, not even oil cooler salesmen have quantified the actual benefits they provide.  Data that suggests or shows oil temps lowered, is NOT data that demonstrates engine cooling benefits.

There may well be data that proves it.  I just haven't seen it.  The simple fact that heat conductivity through oil is rated around .15 and heat conductivity through aluminum is 250, certainly suggests that the aluminum cooling fins perform the greatest portion of heat removal from the engine cylinders.  Certainly seems that you will have to lower the temperature of oil a LOT, and circulate lots of it, in order to significantly remove heat from the engine.  But, I can find no data to deny or support the assertion, and am disinclined to perform the necessary calculations, as few here would accept it anyway.  Someday, I'll design a meaningful test with a Lockhart cooler I have around here somewhere.  Until then, I just warn that your hopes and dreams may or may not support reality.  You are certainly free to place your money where you feel it is warranted.

Neither the oil cooler or the cooling fins efficiently transfer heat without air replacement occurring near them.  That's why easy bake ovens work!

Cheers,

[TwoTired]

I agree with twotired up to a point....

and I won't disagree with him but.... this statement:

"The more fuel is fed to the engine, the more heat is generated."

I will do some searching but I am pretty sure that there is a graphed curve showing that any engine's temp (cylinder head temp) is an inverted U, the peak is "Best Power" where the mixture provides the hottest temps.  Either side of that, the temps drop off, as the mixture is progressively leaned or enrichened.  I will look around for that.  Maybe I take his comments out of context, if so I apologize in advance.

Also we talk about in air cooled airplane engines;  Detonation Margin. 
I believe an overheaded engine, among other things such as deformed valves, warped seats, can suffer detonation.  And is it not true that lugging an engine at low speed can result in detonation?  "Lugging" plus "overheated" sounds bad to me but I am no expert.
Not to say 6000rpm is doing it any favors when hot either but 1500rpm when underway seems 'luggish' to me! 

This is why my responses often get so wordy.  Perhaps I should have said "The more fuel/oxygen mixture is fed to the engine, the more heat is generated."  Or, "The higher the fuel flow to the engine, the more heat is generated."

I believe the original question was about throttle setting, not mixture setting. Of course, a mixture ratio makes a difference in combustion temps.  But, as you drive through traffic, or sit waiting at a traffic light, there just isn't a convenient mixture knob on the bike like there is in the airplane.

I was trying to keep it simple.

I do agree that lugging an engine increases the cylinder pressures and can lead to damaging the engine.

Cheers,

[edbikerii]

Keep is really simple:  "all things being equal, low rpm runs cooler".

[summitlt]

I tend to believe that oil does contribute to heat transfer.

I believe this because I've measuered the oil temp with and without an oil cooler.

I've always agreed that oil has a contribution to heat transfer.  And your measurements show that oil coolers lower oil temperature.  I'm not surprised about that. I mean it IS called an oil cooler, after all? Do they have engine cooler labels?  Aren't you still inferring that lowering oil temperature also lowers cylinder head temperature?  Have you isolated lack of oil lubrication quality with temperature rise as a contributing factor?  From an experimental test construct, the data provided lacks connective assumption proof.  Is the oil cooling effect on cylinder temp .1 degree?  2 degrees? 10 Degrees? 50 Degrees? 100 Degrees?

While cooling the oil certainly should have some beneficial effect at removing heat from the engine, no one has yet quantified the magnitude of that effect with either calculations or empirical before/after testing.

If you get a 0.01% increase in salary, yes it is better, but is it significant?  And, are you willing to put in extra work hours to achieve it?

I won't argue that modified engines might benefit from an installed oil cooler.  It's just that no one, not even oil cooler salesmen have quantified the actual benefits they provide.  Data that suggests or shows oil temps lowered, is NOT data that demonstrates engine cooling benefits.

There may well be data that proves it.  I just haven't seen it.  The simple fact that heat conductivity through oil is rated around .15 and heat conductivity through aluminum is 250, certainly suggests that the aluminum cooling fins perform the greatest portion of heat removal from the engine cylinders.  Certainly seems that you will have to lower the temperature of oil a LOT, and circulate lots of it, in order to significantly remove heat from the engine.  But, I can find no data to deny or support the assertion, and am disinclined to perform the necessary calculations, as few here would accept it anyway.  Someday, I'll design a meaningful test with a Lockhart cooler I have around here somewhere.  Until then, I just warn that your hopes and dreams may or may not support reality.  You are certainly free to place your money where you feel it is warranted.

Neither the oil cooler or the cooling fins efficiently transfer heat without air replacement occurring near them.  That's why easy bake ovens work!

Cheers,

Oil coolers help cool oil, that also goes into the tranny. Have you ever gotten a bike hot and felt that it shifts funny and the clutch acts different. An oil cooler should help with that too.

Im not sure how CB's are, but my dirtbike definatly feel different in the tranny when hot.

[eldar]

Cloud, you should not need to worry about any engine work, unless of course you want to bore it out for performance reasons. Try torquing things first, if you have not already done so.  Many times that will clear head leaks. But hey, I do not know the work you have done so I can only suggest.

You never did say why you needed new jets though. Were they drilled or something? It has been known to happen

[smccloud]

Cloud, you should not need to worry about any engine work, unless of course you want to bore it out for performance reasons. Try torquing things first, if you have not already done so.  Many times that will clear head leaks. But hey, I do not know the work you have done so I can only suggest.

You never did say why you needed new jets though. Were they drilled or something? It has been known to happen

it sat for 10 years before i got it, thats why i am going to rebuild.  and i never rejetted when i switched exhaust............

[eldar]

I can see doing a rebuild but these bikes can be odd. They will leak after sitting but when ridden for a while, will sometimes seal back up.  I know my 78 has never had the head or anything off so the gaskets are original and it barely leaks anything. Maybe a drop every couple weeks and that's it.

But if you rebuild, then maybe you might want to contact mreick on this site. He is the resident headmaster. Even if you do not bore, a porting will still help.

But I am confused about the exhaust. What did you put on? I mean most any changes will usually result in leaner running.

[smccloud]

I can see doing a rebuild but these bikes can be odd. They will leak after sitting but when ridden for a while, will sometimes seal back up.  I know my 78 has never had the head or anything off so the gaskets are original and it barely leaks anything. Maybe a drop every couple weeks and that's it.

But if you rebuild, then maybe you might want to contact mreick on this site. He is the resident headmaster. Even if you do not bore, a porting will still help.

But I am confused about the exhaust. What did you put on? I mean most any changes will usually result in leaner running.

i'd love to say what i put on for exhaust, but i have no clue.  i got the bike with the factory exhaust (rusty) and picked up a 4-1 system at a junkyard for $25.

the head leaks bad enough that i can't wear my tan pants to work when i ride it, they have a lot of black spots.  plus i would just feel a lot better knowing the engine was just rebuilt by my dad and i (he used to be an ase certified master tech), also kind of a father/son project.

[eldar]

I can see that. I suppose a leak that bad means the gasket is blown out and since you have to pull the engine, may as well redo it. When you get the gasket sets, check into them thoroughly. Some sets include everything and some do not.

Good luck on the build. From what I hear, it is not hard just take your time.

[johnny-from-bel]

All the heat in the engine is generated by the burning of fuel.
So on the generation part less full consumption is better as less fuel burned means les heat generated. (power generated = weight fuel burnt/second) in popular terms more MPG.

On the cooling side ; the riding wind cools but that is independent of the RPM. Oil flow is dependent on RPM.

Specific heat is in KJ/Kg*°C that is the heat the oil will absorb. Flow does not come into the equasion.

The heat transfert coefficient between a moving fluid and an solid surface is :

    Q=h.A.Delta T

where

    Q = heat lost/ gained
    h = overall heat transfer coefficient
    A = outside solid-fluid contact surface area
    DeltaT = difference in temperature between the solid surface and surrounding fluid area


To work it out would lead me to far. But the equasion works both ways so as long as the oilflow is constant thoughout the whole system equal heat is aborbed at hot places and the same heat is lost at cool places. Of course the engine heats up to the point where delta T with the environment is high enough to dissipate the generated heat.

Conclusion oil cooling is not contribution more or less depending on RPM.
We do generate less heat at low RPM. So  low RPM is better.

Hope I got all the equasions right. It was over 20 years ago when I studied this suff, so I could be competely wrong. I do remember that thermodynamics alows you to calculate all this. So maybe one of the younger academics should do the math.

[HondaMan]

I have only seen them in pictures, it looks like louvers to me.

Yep, the K0 had little vents in the front of the side covers. Honda seemed more worried about oil temps in the beginning than later: like Bob Wessner can tell you, some of the earliest K0 bikes only held 3 quarts of oil. Later it went to 3.7 and even more quarts, and the louvers disappeared on the K1, partly to make the rider's stance narrower and because the oil temps had dropped with the extra volume.

[HondaMan]

This may be a basic question, but as my scientific knowledge is sowmehat lacking I was looking for some advice.

Here in Central Texas it gets very hot in the summer. While this year has been cool by our standards, triple digits are common. I commute to work on my K5 750 (25 miles each way) almost every day when it isn't raining. Traffic in Austin can be a pain and crawling along on the highway at 10 to 15 mph is, sadly, not uncommon. I know that idling my bike is the fastest way to overhead it, but it would seem to me low speed driving with little air flowing over the cooling fins would be a close second.

That leads to my question. Is is better to crawl in a higher gear at a lower rpm to prevent overheating, or to go with a higher rpm and a lower gear.

All moving parts generate friction, no matter how good your lubrication is. So, at first blush, I figured lugging the engine a little would be better, since lower rpm means the parts are moving slower and less friction is generated. At the same time, however, lower rpm moves less air through the engine, and possibly more heat is building up inside. Higher rpm would create more friction, but move more air through the engine.

Or it may make no difference. I have a lot of time to think for 25 miles at 10 mph.

Patrick

Patrick:
I forgot to mention this earlier: the X24ES-U sparkplugs from ND will also let the engine run cooler. Mine sees a solid 10 degrees or more difference in 100 degree traffic with the "X" plugs (oil temperature) instead of the NGK D8E series. There's about 10 reasons why, but I won't go into that now...you can find these on the internet: I just bought a half dozen of the X24 and X22 (for winter riding) last week. My K2 loves these plugs, runs like silk when compared to the NGKs.


...no, I don't want to start a fight, it's just my experience...   

[ofreen]

Traffic in Austin can be a pain and crawling along on the highway at 10 to 15 mph is, sadly, not uncommon. I know that idling my bike is the fastest way to overhead it, but it would seem to me low speed driving with little air flowing over the cooling fins would be a close second.

That leads to my question. Is is better to crawl in a higher gear at a lower rpm to prevent overheating, or to go with a higher rpm and a lower gear.

Here is the question and I think Hondaman addressed it best in his first post.  In this situation, I believe a little more RPM is better on the bike.  I could try to figure out theoretical reasons why, but I'll think I'll rely on empirical evidence.  I live in southern Idaho and we have had our share of triple digit temps this summer, just like evry summer.  If it hasn't been over 100F, it's been in the high 90s.  I ride my 750F daily to work, and run into the situation described above too often.  I can tell the bike is happier with more revs.  It is always bad to lug an engine, but it is especially so when the oil is very hot.

I also agree with Hondaman about the 750's ability to handle hot weather.  If it is stop and go at 100 degrees on my CBR1000F, the damn fan runs continuously and is like sitting on top of a blast furnace.  If I am on the R100GS, it is rattling like it will disintegrate at any time.  (Without any consequence, though.) The old 750 just shrugs it off.

[Bob Wessner]

I have only seen them in pictures, it looks like louvers to me.

Yep, the K0 had little vents in the front of the side covers. Honda seemed more worried about oil temps in the beginning than later: like Bob Wessner can tell you, some of the earliest K0 bikes only held 3 quarts of oil. Later it went to 3.7 and even more quarts, and the louvers disappeared on the K1, partly to make the rider's stance narrower and because the oil temps had dropped with the extra volume.

The louvers look cool with the screen and all, but from a practical standpoint you have to wonder about the left one in particular funneling wind driven rain right at the fuse box.

[HondaMan]

I have only seen them in pictures, it looks like louvers to me.

Yep, the K0 had little vents in the front of the side covers. Honda seemed more worried about oil temps in the beginning than later: like Bob Wessner can tell you, some of the earliest K0 bikes only held 3 quarts of oil. Later it went to 3.7 and even more quarts, and the louvers disappeared on the K1, partly to make the rider's stance narrower and because the oil temps had dropped with the extra volume.

The louvers look cool with the screen and all, but from a practical standpoint you have to wonder about the left one in particular funneling wind driven rain right at the fuse box.

That's why cosmolene spray is waterproof.   

[smccloud]

I have only seen them in pictures, it looks like louvers to me.

Yep, the K0 had little vents in the front of the side covers. Honda seemed more worried about oil temps in the beginning than later: like Bob Wessner can tell you, some of the earliest K0 bikes only held 3 quarts of oil. Later it went to 3.7 and even more quarts, and the louvers disappeared on the K1, partly to make the rider's stance narrower and because the oil temps had dropped with the extra volume.

The louvers look cool with the screen and all, but from a practical standpoint you have to wonder about the left one in particular funneling wind driven rain right at the fuse box.

That's why cosmolene spray is waterproof.   

and if its anything like plain cosmolene, i never want to touch it.  i spent over a week cleaning cosmolene out of a gun stock