| Author | Message | ||
     Ourdee |
I will not be buying either one of them. I don't like them. I was trying to find an attribute that I liked. I can't. | ||
| Blake |
It is absolutely a myth that air cooled engines have difficulty meeting EPA exhaust emissions limits. The combustion chambers of air cooled engines reach operating temperatures much more quickly than water cooled. That is simple fact. NOx emissions increase with combustion chamber compression. An air cooled engine running 10:1 compression produces less NOx than a water cooled engine running 13:1 compression. My '09 Ulysses has no catalytic converter. It didn't need one to handily pass required EPA emissions limits; since probably the mid-1980's, every liquid cooled street bike sold in America did. Exploding popular myth is fun. | ||
| Blake |
Tom, >>> What I do know is that my Triumph will show full temp at a point where I can still put a bare hand on the cooling fins of my XB with no problem. Even if your perception is accurate, which is very tough to accept, what is the flaw with your logic? Question: Is it really true that until a liquid cooled engine reaches normal operating temperature, no coolant is circulating through the engine? | ||
| Ratbuell |
Air versus liquid cooling comes down to one thing: Temperature CONTROL. It is far easier to CONTROL the temperature of a water-cooled engine, than that of an air-cooled engine. Period. End of discussion. Air cooled engines also have far looser tolerances inside, to account for thermal expansion/contraction. Those "gaps", if you will, contribute to poor emissions while the engine is going through its warm-up cycle. Liquid cooled engines are built to much tighter tolerances because there is not the cold/hot variance in size/shape/fit. IF emissions are coming for motorcycles - and I see no reason they won't - liquid cooled is the way to go so the manufacturers can have the CONTROL they need, to meet standards. Back to the topic at hand - liquid cooled Harleys. I think HD is missing the boat BIG TIME by not simply putting a Revolution motor in an FLH frame. "Die-hard" HD owners have been clamoring for that specific combination for years and I, personally, believe it could make for one hell of a motorcycle. It could also be a good marketing tool - young buyers like the VRSC. People who want power, sportiness (yes, I know, the only "sporty" VRSC was the VRSCR in '06...), but they want to have a Harley...go VRSC. A Revolution bagger would be a "natural progression" for those buyers: "here's the powerful motor you love...in a "grown-up" platform...time to trade up!". | ||
| Ratbuell |
Question: Is it really true that until a liquid cooled engine reaches normal operating temperature, no coolant is circulating through the engine? Yes, on an older engine. No, on newer ones. The thermostat is a "dam", and it keeps coolant trapped in the engine block until the coolant is warm enough to open the thermostat. Older engines...the thermostat was the only pathway to the radiator. Newer engines have a bypass hose - a small-diameter passage to allow coolant to circulate a small amount to allow thorough heating, so there's no rush of "cold water" when the thermostat opens. This also allows the water pump to actually pump, instead of simply cavitating in non-moving fluid. | ||
| Sifo |
Blake, Here's the problem with an engineering challenge, and I covered this earlier. When someone says you can't do X this way, someone will find a way to do x that way. The fallacy is that I ever said X can't be done that way though. My point is that when you need to accomplish X, Y and Z, one way is easier than another. It's not just about emissions. It's emissions, reliability, power, noise control, packaging in the vehicle, cost, etc. The ONLY variable I've really gotten into is which type of engine gets to full temp quicker. No doubt, there are a lot of variables in this examination. My perception of my Triumph vs. XB? That's based on a common route away from my house. After a slow putt through my neighborhood, it's about a mile of 45 mph down to a major stop light where I often sit and have scanned my gauges often. It was my surprise at the fact that my Triumph shows full temp at that light, that had me wondering this exact thing with my XB. As fate would have it that intersection has a gas station that is easy in, easy out for me and tends to keep prices low. I often get gas there. This has given me ample opportunity to pull in, shut the bike off, take my gloves off and feel the cylinders and head on the XB. I'm kind of funny that way. what is the flaw with your logic? I would have to say the big flaw here is that neither bike is having the combustion chamber temp measured. Even that wouldn't tell the entire story though if you want to discuss the effects on emissions. The temperature of the entire intake will also affect that. I'm not clear what "myth" you exploded, but it isn't one that I'm discussing here. Question: Is it really true that until a liquid cooled engine reaches normal operating temperature, no coolant is circulating through the engine? I think that may depend on what the definition of is is. In practical terms, with the thermostat closed, coolant will not circulate to the radiator where it can dump heat out of the system though. In contrast, the cooling fins on an air cooled engine will always dump all the heat they can out of the system, even when the engine still need more warm up. There is just no denying the fact that that will slow delay getting to full temperature. As a side note, using the XB design as an example of an air cooled engine is a bit flawed from the get go because it is shrouded by the frame and has a pretty good cooling fan to supplement cooling when hot. This isn't typical and it specifically isn't the case with what started this conversation. It's all good mental gymnastics though. Going to be a nice day around here, probably the last for quite a while. Color me gone! | ||
| Hughlysses |
I think Sifo's points above show we should all be careful in making generalizations, one way or the other, about any engineering design. I'd also say we've got pretty good evidence that air-cooled motorcycle engines won't disappear for a while yet: witness the 2013 Indians. I don't believe Polaris would have invested millions in design and tooling for an all-new air-cooled engine if they knew it would be obsolete almost immediately. | ||
| Cityxslicker |
still trying to wrap my head around the dimensions. a shorter seat height than the iron, but a taller ground clearance, a longer travel, but a shorter wheelbase.... need a demo, need to see it. | ||
| Sifo |
So I took off on the Triumph today with a cold engine, about 50 degrees ambient temperature. I was paying close attention to the temp gauge, and as I was approaching the stop light I described earlier, the temp gauge turned on it's 5th bar which is where it tends to run. I mapped it on Yahoo maps and it claims it to be a 1.02 mile drive taking 3 minutes. No warm up in the driveway either, just hit the start button and putt out of my subdivision. That seems like a pretty fast warm up to me. Feel free to drive an XB 1.02 miles and feel the head. I would stay away from the header though. | ||
| Hughlysses |
So, I wonder how one of these 750's would work (suitably rodded) in an XB frame?  | ||
| 46champ |
I have a feeling that the 750 with a little work mufflers, intake (why is it that something can always be done in the airbox) a remap, and maybe cams. I can't find it now but the bore and stroke ratio was over square not by much but not under square. The lower end is plane bearings and with the OHC I think 11,000 should be doable. At that RPM somewhere above 100 hp should be had. Mark my words we will see the first one in a tracker frame on a mile track by 2015. | ||
| Cyclonedon |
I actually like the idea that Harley-Davidson started making smaller motorcycles with mid controls for the beginners. If I had to start all over riding motorcycles with the forward controls like most of the Harley's have now, I would give up motorcycling. | ||
| Blake |
Thanks Joe. The bypass circuit does allow coolant to circulate, true it is at a much reduced rate, but it indeed does circulate and is being heated and thus removing heat from the engine. All the coolant in a liquid cooled engine is thus part of the engine warm-up transient heat transfer equation. This is true for all engines, new and old. Is it really true that looser piston/cylinder/ring tolerances of an air-cooled engine cause more pollution? Not so much. In properly operating engines, the issue of piston ring sealing and tolerances really has no significant effect on exhaust emissions. How can that be? All such resulting blow-by is sent back to the intake and returned to the combustion chamber via the crankcase breather circuit. No significant amount of the blow-by gasses are expelled to the ambient air. The only pollutants that make it to ambient air must traverse the exhaust tract or escape directly from the fuel tank breather. Tom, The myth exploded is that air-cooled engines will have difficulty meeting exhaust emissions requirements. That is a complete and utter myth. You nailed it. The tip of cooling fin temperature may be a poor indicator of combustion chamber temperature. Another important variable is the amount of fuel being consumed during engine warmup. If for example the cold Triumph is consuming fuel at twice the rate, but warms up to normal operating temperature 20% sooner compared to the Buell, which engine is expelling more hydrocarbons? The only true measure is the actual products of combustion. Someone mentioned the reduced viscosity engine oils and close tolerance journal bearings. That has little to to do with products of combustion from a cold engine, but it's clear that in a cold engine, roller type bearing are more efficient. The advantagse of plain bearings are numerous (reduced mass, improved reliability, and redudec complexity) but better efficiency is not among them. However, the ability to use reduced viscosity engine oil is an indirect benefit to overall engine efficiency. I don't know any motorcycles running W20 grade engine oil. Great discussion! | ||
| Hootowl |
"This is true for all engines, new and old." Yes. Thermostats for older cars without the bypass hose have a small hole in them to allow coolant to flow when the engine is cold. | ||
| Sifo |
Great discussion! It has been. Let's not forget that a very important factor in getting the combustion to produce the desired results has a lot to do with having the engine at the desired temperature. Too cold, or too hot, and you have problems. This is where a liquid cooled engine has an advantage over an air cooled engine. As for the thermostat bypass, let's just do a mental exercise. Which will warm up faster? An engine with a bypass that allows a small percentage of cooling to take place, or an identical engine with the thermostat stuck wide open using 100% of the cooling capacity during warm up? Which most closely resembles how an air cooled engine typically works? One other thing that hasn't been addressed in this discussion. A liquid cooled engine can be engineered to eliminate the cast aluminum cylinder over much of the length of the cylinder having the steel liner exposed directly to the coolant. This reduced a good amount of thermal mass that can't be eliminated from the air cooled variant. You nailed it. The tip of cooling fin temperature may be a poor indicator of combustion chamber temperature. Just as the coolant temperature is a poor indicator of combustion chamber temperature. | ||
| Blake |
If the temperature of slow moving liquid flowing immediately around and exiting the cylinder head is not a pretty good indicator of cylinder head temperature, what is? Liquid cooling has significant advantages. Quicker engine warm up is not one of them. Air cooling is VERY effective. Much of an air cooled engine's cooling is also achieved through radiative heat transfer. It's why we should never chrome our cylinder heads. Chrome finish kills radiative heat transfer. As engine temperature rises, the effectiveness of radiative and convective cooling continues to increase. Once a liquid coolant system reaches its boiling point (~250 F), it becomes less and less effective. Within normal operating conditions, both cooling systems perform well. Crossing Death Valley in the middle of Summer on a lean running (prone to overheating) motorcycle, I'd MUCH rather it be air-cooled. I agree with your observation, but see no relevant point to your thermostat bypass mental exercise. My point concerning all the coolant being part of the heat transfer equation was to refute the notion that in a water cooled engine, the coolant need not be heated until the engine reaches operating temperature. That just wasn't true. All the coolant is being heated right along with the engine. True, it could be MUCH worse if the liquid cooling system were stuck full open right from the start. I hate to name drop, but as it seems my technical credibility is lacking in your mind, no less than Erik Buell himself has stated that one of the big advantages of an air cooled engine is its ability to reach operating temperature significantly more quickly than a comparable liquid cooled engine. No cat on my Ulysses. Cats on ALL liquid cooled road bikes going on for decades now. It's simple physics. In normal operating conditions, it takes more heat and more time to increase the temperature of an engine plus water than it does for engine absent water. The heat capacity of water far exceeds that of aluminum. Again, my point was to dispel the popular mythology that air cooled engines are likely to become obsolete for being unable to meet air pollution emissions requirements. That is just complete nonsense. 1. Because they typically reach operating temperature much more quickly, air cooled engines are generally much better (less polluting) during cold start and warmup compared to liquid cooled engines. 2. Crankcase rebreathing eliminates the otherwise detrimental effects of increased blow-by caused by looser tolerances in air-cooled engines versus liquid-cooled engines. | ||
| Tootal |
I've been enjoying the discussion here but just thought of something that hasn't been mentioned yet. The 2014 Harley dressers have liquid cooling on the head's alone. The lean conditions they run to meet epa standards were causing extremely hot exhaust valve temps. The water jacket in the heads cools only the exhaust side. With this extra cooling they were able to run hotter cams and get more power out of the engine. I can tell you from personal experience that's only a week old that running a Harley Big Twin too lean will warp the exhaust valve on the rear jug. Since mine is carbed, I had it jetted at around 14.3/1 AFR while cruising 70 mph. I took a trip and all was good until the temps dropped. I usually carry extra needles and jets with me just in case but in my haste I had left them on the work bench. I rode home 500 miles in those cooler temps including some rain. I made it but my AFR gauge was showing up to 17/1 occasionally!! I made it home but when I started it three days later it dropped a cylinder. I yanked it apart to find a warped exhaust valve. Thank God it happened in my driveway! Keeping a cooler temp might not help with emissions but it will allow leaner mixtures from destroying exhaust valves! | ||
| Sifo |
If the temperature of slow moving liquid flowing immediately around and exiting the cylinder head is not a pretty good indicator of cylinder head temperature, what is? A temp sensor in the head itself would be better. Isn't that what the XB has? I'll get back to that. True, it could be MUCH worse if the liquid cooling system were stuck full open right from the start. But that essentially is what you get with an air cooled engine. No cat on my Ulysses. Cats on ALL liquid cooled road bikes going on for decades now. Air cooled too for the most part. For reasons that I won't bother to speculate on Buell chose to engineer a system that could manage without the cat. Many seem to believe that this also lead to compromises in the fueling. I've not had the pleasure of discussing these things with Erik, so I really can't say what his primary concerns were. He was certainly outside of what was normal in the industry on this though. I will also say that my '06 Lightning ran quite poorly with no mechanical reasons. Changing the fuel maps has it running MUCH better. I still get an occasional low RPM stumble during warm up though. Interestingly that stumble will go away at about the same time that my Triumph hits normal temp on it's gauge. Is the XB fully warmed up at that point? I have some doubts. It's simple physics. In normal operating conditions, it takes more heat and more time to increase the temperature of an engine plus water than it does for engine absent water. The heat capacity of water far exceeds that of aluminum. Are we talking about getting the combustion chamber up to temperature, or getting the cooling system up to temperature? As you've pointed out, the edge of the cooling fin is a poor indicator of combustion chamber temps. By the same token you don't have to have the water up to temp on a liquid cooled engine either. Getting back to the temp sensor in the XB, I would be curious to see a data log from an XB during warm up after about a mile down the road, like I described on my Triumph. I checked and don't have any data logs from when I was tuning my XB. BTW, as I pointed out earlier too, the XB would have an advantage in this apples to oranges comparison, in that it's not a typical air cooled installation, but is shrouded by the frame with a fan to aid cooling when hot. Certainly not what this conversation started with, but I would still be interested in the results. The XB would have a second advantage in this comparison, in that the temp sensor is right in the head, not in a water jacket where water has to be heated by the head to get a temperature increase. So if anyone is able to produce some data on this from an XB, would you please? Again, my point was to dispel the popular mythology that air cooled engines are likely to become obsolete for being unable to meet air pollution emissions requirements. That is just complete nonsense. Fair enough, it just wasn't something that I was arguing. Can it be done? Sure. Are there better ways to achieve all of your design goals? Well that depends on your design goals. | ||
| Hootowl |
"with the thermostat stuck wide open using 100% of the cooling capacity during warm up" "But that essentially is what you get with an air cooled engine. " You are forgetting, or haven't absorbed, the fact that an air cooled engine simply doesn't give up a significant amount of heat to the air unless the engine is significantly hotter than the surrounding air. In other words, at low temperature deltas, air cooling is nearly 0% efficient, so it doesn't matter if you've got 100% of your cooling capacity available. 100% of nearly zero is still nearly zero. Conversely, a water cooled engine readily gives up its heat to the surrounding water as fast as it can generate it. | ||
| Sifo |
You are forgetting, or haven't absorbed, the fact that an air cooled engine simply doesn't give up a significant amount of heat to the air unless the engine is significantly hotter than the surrounding air. In other words, at low temperature deltas, air cooling is nearly 0% efficient, so it doesn't matter if you've got 100% of your cooling capacity available. 100% of nearly zero is still nearly zero. Conversely, a water cooled engine readily gives up its heat to the surrounding water as fast as it can generate it. I will admit, I'm having some difficulty with that point. Isn't heat transfer from any medium to another dependent on a temperature delta? What is it that makes one fluid different from another? A point that I've made, that doesn't seem to get through is that in both engines you eventually heat the entire cooling system. The liquid cooled version has some control over that though and limits heating in the radiator until more critical areas are up to temperature. The air cooled version however is passing heat into the entire cooling system right away. Even if it isn't passing it to the air right away (which isn't true), it's still a big heat sink. The cooling fins are a huge volume compared to the water jackets on a liquid cooled bike. Especially if you focus on the heads. | ||
| Sifo |
I hate to name drop, but as it seems my technical credibility is lacking in your mind, no less than Erik Buell himself has stated that one of the big advantages of an air cooled engine is its ability to reach operating temperature significantly more quickly than a comparable liquid cooled engine. I hate to say anything derogatory about Erik around here, and that really isn't my intention, but I do wonder, when he made that statement, was this Erik the engineer look at what would meet his needs best, or was that Erik, the marketing person making the best of what he had to work with under HD? I notice that when left to his own devices, he went with a liquid cooled variant. Of course, I'm sure he factored in things beyond fast warm up times. I would still love to see some actual data on this from an air cooled engine. | ||
| Hootowl |
"What is it that makes one fluid different from another?" Water is dense, and absorbs heat rapidly. Air is diffuse, and absorbs heat slowly. | ||
| Sifo |
"What is it that makes one fluid different from another?" Water is dense, and absorbs heat rapidly. Air is diffuse, and absorbs heat slowly. And this relates to the temperature delta issue in what way? | ||
| Hootowl |
"I notice that when left to his own devices, he went with a liquid cooled variant" Because it is easier to cool the heads of a high horsepower engine with water, for all the reasons I've stated above. Air cooled engines require a certain amount of surface area per Watt. There's only so much surface area you can get in an engine that will fit in a bike. Transfer the heat to water, then transfer it to air in a radiator that has lots of surface area in a relatively compact space, and you can dissipate much more heat. | ||
| Hootowl |
"And this relates to the temperature delta issue in what way?" Because of its reduced ability to transfer heat, the air cooled motor must be significantly hotter than the surrounding air to achieve a transfer rate similar to that of a water cooled engine. Heat transfer rate increases with the difference in temperature. | ||
| Sifo |
Because of its reduced ability to transfer heat, the air cooled motor must be significantly hotter than the surrounding air to achieve a transfer rate similar to that of a water cooled engine. Well they make up for that difference by providing much more surface area in the form of cooling fins. Heat transfer rate increases with the difference in temperature. Isn't this true of all fluids? | ||
| Hootowl |
Did you know that the tanks they used in the deserts of northern Africa during WW2 were air cooled? Likewise, the aircraft engines were all air cooled. Heck, modern jet engines are air cooled. There's nothing wrong with air cooling. It's just that water cooling is more practical in a lot of situations, especially where the motor is stuffed inside something, and it would be impractical to duct air to it. Water cooling is also superior when there are banks of cylinders. It isn't possible to cool the inner cylinders as effectively as the outer cylinders with air cooling, as the adjacent cylinder is in the way of where the fins should be. Water cooling makes sense. But air cooled combustion chambers heat up faster  | ||
| Hootowl |
"Isn't this true of all fluids?" It is. But air is less dense than water, and does not absorb heat as rapidly, so to achieve similar rates of heat transfer, the temperature delta must be higher. I feel like I'm repeating myself at this point. | ||
| Sifo |
Did you know that P-51 Mustangs were liquid cooled. Made them vulnerable to small arms fire in a ground attack roll. It wouldn't do to have a tank that could be disabled with a .45 sidearm, now would it? Is the heat transfer rate dependent on a temperature delta for all fluids? | ||
| Tootal |
It was previously mentioned that the Buell did not need a cat since it's air cooled, or even though it's air cooled, where other liquid cooled engines did. I think there is another part of the factor being ignored. It's not the air cooling that made it more efficient it's the long stroke, under square, engine that did it. A long stroke motor is more efficient than than an over square engine. That's why our 1200cc engines get such good fuel mileage. I had an air cooled Cagiva Gran Canyon with it's 904cc Over square engine. It revved higher and had lots of horsepower at high rpm but it only got 39 mpg. It was a V-twin, air cooled and only 904cc. That's the difference in efficiency. |
