| Author | Message | ||
     Djkaplan |
"I cannot see how if that is valid why air-cooled engines would not emit more pollution after they are warmed up too." I'm assuming the (greater) thermal expansion closes up the (larger) clearances, allowing less blow-by and complete combustion after the engine has reached it's (higher) operating temperature. "I'm skeptical of the claim." Okay. | ||
| Spatten1 |
I always understood that the ID of the cylinder expands more than the OD of the piston, with heat. Therefore, the piston/cylinder gap should increase. Is this incorrect? | ||
| Jlnance |
The thermal coefficient of expansion of aluminum is about twice that of iron (source: http://www.supercivilcd.com/THERMAL.htm) I would guess the piston is hotter than the cylinder wall as well. Thus it makes sense that the tolerances would close up as the temperature increased. | ||
| M1combat |
The tolerance certainly closes up. Air cooled engines emit less than water cooled engines during warm up. This is due to the fact that their combustion chamber heats up a LOT faster. Keep in mind that the definition of "warmup" as it pertains to our conversation is defined by the EPA. I don't remember how long it is, but they don't judge warmup by cylinder head temperature. They measure the emissions over a set amount of time from the time the engine starts. Because the air cooled engine warms up so much faster it can spend a chunk of this time running efficiently warmed up. Turbo's are parasitic... | ||
| Ceejay |
how? most use exaust gases to power the turbo-thus the reason they can be failure prone, they continue to spin after the motor is shut down, but the oil pump is already off and thus not pumping oil to those bearings. Superchargers are run usually directly off of the crank, and some require an immense amount of power to do so. Granted the turbos could probably be creating a gas flow problem and thus losing some power because of the interupted exhuast gas flow.... I think up to the 07 models Ford was using a adjustable vane turbo to help with the exhaust flow problem and oiling problem. Plus it allowed them to spin up faster. Now I think they are using a two stage turbo(even though I think they are marketing it as a twin which it is not) | ||
| Spatten1 |
I must either be thinking of aluminum bore small engines, or I've just lost my mind in the past 15 years that I've been on the computer and phone. Probably the latter. | ||
| M1combat |
Because they add back pressure before they spin up. As I recall they are certainly more efficient than a super charger but they do take power to make them work. I've always been of the mindset that a turbo on a sportbike is BAD mojo. You don't want power building in any way other than what is PERFECTLY anticipated when you're on the edge of the traction limit. Super chargers give you that and turbo's have to spool up. Granted, with a modern turbo that's designed correctly for the application you won't have much boost lag but you will have some. It's not good when your pegs are on the ground. Super chargers are more parasitic but they give you a direct boost to HP based on the immediate RPM. Both of them mean a boost to HP so you can call them parasitic, but it's somewhat of a misnomer in this case because you get more HP. | ||
| Blake |
DJ, If the piston expands more than the cylinder, I can see the point. It seems like aluminum cylinders would also run hotter too though, so wouldn't they also expand more due to the air cooling scheme? Don (M1), I wouldn't characterize a turbo as parasitic. Granted if you disconnected the pressurized tubo feed from the intake and left the turbine in the exhaust tract, it would diminish the engine's power, significantly. The increased impediment to exhaust gas flow and the scavenging action of negative pressure wave exhaust tract pulses would compromise peak engine performance. In short, the turbine is diminishing cylinder fill or volumetric efficiency of the engine system as a whole. It would render the engine less powerful. It's not however consuming power that is created by the engine, which is what parasitic loss generally implies. It's akin to the effect of an air filter in impeding cylinder fill. Most importantly, when you restore the turbocharging action via the intake, the turbo provides a bunch of added cylinder filling action thus in effect increasing the volumetric efficiency of the engine, so that the turbine's effect in impeding optimum exhaust tract performance is inconsequential. Bill, A supercharge would probably require significant modification to the engine cases and such, not to mention yet another mechanical drive system that needs maintained and lubricated and... Tubocharging may be a simple add-on and option that can simple be bolted onto an engine with no major revision to the engine itself other than installation of the turbocharger kit and related exhaust and intake system bits. I'm also thinking that turbocharger can be made quiet a lot more easily than could a mechanical supercharger. Superchargers also to contribute inertia to the engine and also parasitic losses, unlike a turbo.  So they would actually hurt engine efficiency. No so with a turbo. | ||
| Anonymous |
This is an excellent thoughtful discussion. Air cooled engines done right are better at passing the emissions test than water-cooled. Really they are, we and the EPA have the numbers. Making 150HP would not necessarily affect that. The new 1125R is really good at tailpipe emissions for a water-cooled, due to the DDFI3 system, but not quite as good as the XB motor. Noise without the water jacket, however, as was mentioned above, is definitely worse. It is not an issue now, but one we continue to work on for the future. And we will continue air-cooled development and improvements for many years to come. They are in no way near to the end of their lifecycle, and do have some very endearing qualties for quite a few types of motorcycles. | ||
| Firebolt020283 |
Hey that is cool to know that the aircooled bikes are not going to die out because of the new bike like it has been metioned here. I will be getting this bike but i still LOVE the xbs and tubers and would hate to see them totaly do away with the aircooled plant. | ||
| Roehrcycleguy |
In general, a liquid cooled engine will have lower emissions, they simply have more efficient combustion chambers. It is possible for an aircooled engine to have good or even better emissions than its liquid cooled counterpart but only at the cost of reduced engine performance. Since liquid is a more efficient cooling agent than air, an aircooled engine is almost always limited to two valves per cylinder in order to provide enough cooling fin area between and around the valves. To increase performance, the usual tuning methods are applied, larger valves equals larger included valve angles, equals less efficient combustion chambers and poor emissions. Longer duration cams increase overlap and dirty up the emissions as well. Liquid cooled 4 valve engines have very shallow valve angles allowing for an efficient combustion chamber design and don't need as much valve duration, while still outflowing their aircooled counterpart. The question really isn't, can an aircooled engine continue to pass ever tightening emission standards? but can it do so and still produce competitive power output? If we compare the Helicon engine with the Thunderstorm we can see that they both produce roughly the same emissions, however one has substantially more power. I don't think the aircooled engine is dead though, as long as ultimate engine performance is not a priority. | ||
| Djkaplan |
"If the piston expands more than the cylinder, I can see the point. It seems like aluminum cylinders would also run hotter too though, so wouldn't they also expand more due to the air cooling scheme?" I'll posit this: The aluminum piston runs through a steel (or iron?) liner on a stock aluminum cylinder. Wouldn't it make sense that the aluminum piston would expand more than the steel (or whatever iron alloy) sleeve and need more clearance at ambient temperatures? | ||
| Anonymous |
Sorry, Roehrcycleguy is wrong. Our air cooled engines are better for emissions than our water-cooled, and both are far better than the norm. He is making claims as to which he has no knowledge. I could tell you all the specifics of why, but it would take many pages, bore many to tears, and then I'd have ta kill y'all anyhow! | ||
| Roehrcycleguy |
I did say that it was possible for an air-cooled engine to have better emissions in certain cases, however, show me a 146HP emission legal air-cooled 1200cc twin. Lets say we did tune a 1200cc air-cooled twin for 146HP (which is possible), it would be nearly impossible to get it emission compliant. | ||
| Anonymous |
You have no idea what you are talking about. | ||
| Spatten1 |
Roehr is at least giving logical engineering/physics reasons, not calling names. Annony, maybe you could explain why Buell does not have a 146HP emission legal air-cooled 1200cc twin. Seriously, we have all been interested in that since speculation of an RR based streetbike began last year. (Message edited by spatten1 on July 15, 2007) | ||
| Djkaplan |
"I could tell you all the specifics of why, but it would take many pages, bore many to tears..." What... this crowd? Have you read some of the stuff we've argued about through the years? C'mon, man... spill it. | ||
| Aesquire |
Anony is right. The Air cooled engines pollute more myth began with the 1970's emission standards, & the death of the Beetle. The old VW engines ran very hot in the heads, producing excess oxides of nitrogen. It's a 1930's design, Updating it to meet standards would have been nearly as expensive as what they did, develop a whole new line. So they used the switch to watercooling for an excuse to go to an all new product line. Water cooling does let you build high output engines, but the real trick is the power density. My old GS1100E made about 100 ponies, stock. The Honda CBX made about the same, but briefly. After 1 or 2 hard 1/4 mile runs, or just a brief run at 100+, power dropped off a lot as heat built up. Modern 1000cc class machines are scary at 150+ hp, in a more compact package, because the radiator lets you shrink the powerplant, & remote the cooling. It's like fighter planes in the WW2 era. The U.S. Army Air Corps went to liquid cooled engines, not for power, but for improved streamlining. The narrower, longer Merlin ( 1000-1600+ hp ) & Allison packaged nicely in the noses. The Navy stuck with air cooled engines, in some cases with twice the power ( the R2800 @ 2000+hp ) and accepted the compromise in design, a wider body, to get more on board fuel/weapon capacity, and most important, more reliability with battle damage. A single bullet can bring down a P-51 ( Rolls Royce/Packard Merlin ) because the radiator is critical. A P-47 ( Pratt & Whitney R2800 ) would fly home with cylinders shot off, con rods flailing in the breeze and oil everywhere. | ||
| Roehrcycleguy |
I agree, an engine will not pollute more just because it's air-cooled. The point I'm trying to make is that a liquid-cooled engine allows the use of multi-valve technology to produce more power while still being emission compliant. | ||
| M_singer |
There are lots of air cooled 4 valve per cyl motorcycles. My Bandit 1200 for example. | ||
| Spatten1 |
Yes, I've owned a Suzuki with 4-valve air/oil cooled too. All of the late 1980's Suzuki sportbikes were. It does not change the fact that every manufacture that makes air cooled and liquid cooled bikes has higher horsepower engines that are liquid cooled and emissions compliant. I have a hard time believing that it is just a choice or a conspiracy, not that it is dictated by engineering realities. If that is not the case, why did we not get the air cooled Buell XBRR for the street with 145 horsepower? | ||
| Anonymous |
Sorry Spatten, but no name calling is involved, just facts. Roehr does not know what he is talking about here, as he has not been involved in certifying these bikes of different configurations for decades. That's not name calling, it's simply fact. And water cooling and four valves do not provide a magic solution. If they did the 120HP water cooled V-Rod would have met Californai emissions without a catalytic converter. But it didn't and the air cooled Buell XB 1203 did easily. And emissions is not the reason there isn't a 146HP air-cooled Buell engine, I can assure you. None of this means any of these engines are "bad" or "good", I'm just stating simple engineering facts. | ||
| Diablobrian |
I would be inclined to believe that the reason we haven't seen a high hp air cooled twin based on the RR has nothing at all to do with the top end of the motor. I suspect the pressed together single pin crank as being the weak link when you attempt to increase the intended service life. A race motor is built to run for minutes, or hours, not for years and thousands of miles. I could be way off base, but that would look to me like the weak link in the chain. I know the guys at Buell would be thrilled to be able to offer up everything we ask for (and more) but there are certain limitations that they have to deal with, like service life and EPA/DOT regulations. | ||
| Gregtonn |
Roehr is at least giving logical engineering/physics reasons, not calling names. Annony, maybe you could explain why Buell does not have a 146HP emission legal air-cooled 1200cc twin. Seriously, we have all been interested in that since speculation of an RR based streetbike began last year. I guess I missed the name calling. Why would air cooling NOT be more efficient with regard to emissions? Excess emissions are primarily due to combustion chamber hot spots, not cylinder wall/piston temperatures. With modern computer modeling technology there is no reason that air cooling could not eliminate these hot spots. However even with the parasitic forces inherent in a air/liquid cooled system, it easier to pump more liquid coolant to hot spots than to add or move cooling fins. There is also no logical reason the an air cooled engine could not use four valves per cylinder. By the way all motorcycles are air cooled. Some just use liquid and radiator fins to transfer heat into the air.(If you think you've heard that before it's because I've said it before.) G. | ||
| Aesquire |
The reasons a 150hp air cooled engine is difficult to make is that radiative surface is needed to dissipate the wasted energy. Big fins, good airflow. I suspect the reason Sportster derived engines have issues is piston speed, & valve train mass/distorsion. The answer for years has been cubic inches, & improved breathing. A 101hp stock S3, to a 150hp 84 cubic inch ported model is about the limit, without getting rid of the pushrods, & shortening the stroke. That's with rational street reliability. The XBRR is a race bike, and pushes the limits as you would not want to with a street machine. Liquid cooling improves the power you can get from, not cc's of displacement, but, cc's of engine outside size. Power density. Remote the cooling function from the engine compartment. Radiators can be put under the seat, in the tail section, or in pods, letting you more easily position the engine for best handling & make a smaller frame to hold it, than a huge finned beast. | ||
| Thespive |
I love when Anony comes in, says something, then comes back to argue his/her/its point. Too often Anony offers a gorilla warfare attack, states a point, then never comes back. Win, lose, or draw, this Anony has points in my book. --Sean | ||
| Gregtonn |
Aesquire, The reasons a 150hp air cooled engine is difficult to make is that radiative surface is needed to dissipate the wasted energy. I'm not sure what you're trying to say. 1. Wasted energy equals wasted horse power. 2. If by "Big fins, good airflow." you mean big fins are needed for efficient cooling, that idea also has some issues. Cooling fins with an aspect ratio of about 5:1 are just as efficient a fins with a larger aspect ratio. More small thin fins are more efficient than large thick fins. Take a look at your average liqid/air exchange radiator. Lots of very thin, very small fins surrounding the liquid tubes with a shroud to help direct air through them. Many small thin air fins correctly placed could be as efficient as an air/liquid radiator especially if shrouds were used to direct air flow. The biggest issue with such a design a would be machining or otherwise forming the fins. I thought we were talking a new design here so I'm not sure what the Sportster design has to do with the discussion. G. | ||
| Spatten1 |
Excess emissions are primarily due to combustion chamber hot spots, not cylinder wall/piston temperatures. I think that there are many other factors than hot spots. Valve overlap would be one. That (and lean misfire conditions)is what accounts for HC emissions. High horsepower motorcycle engines make the most power at high rpm. Emissions test primarly focus on low rpm. The high horsepower engines are running at their least efficient during these tests. Raw fuel pours out the exhaust because the overlap time is too long at low rpm, so the catalyst is employed. (Message edited by spatten1 on July 16, 2007) | ||
| Spatten1 |
I suspect the pressed together single pin crank as being the weak link when you attempt to increase the intended service life. Also the roller bearing journals. I don't know how many times Kevin Cameron has discussed the weaknesses of roller bearings at rpm and load. S&S has addressed both of those issues, as well as others like the rocker arm mass. | ||
| Paintballtommy |
i do not understand how hot spots in the compustion chamber would cause bad emissions? i do agree valve overlap or any condition within the system which prevents the air fuel mixture from fully burning causes bad emissions. have you ever seen a hopped up motor that idles all lumpy dumpy and sounds really cool. thats a product of incomplete or inneficient combustion. this is because of the overlap and duration that the valves experience because they need all that open time to fill the chambers when they are spinning the engines to kingdom come. if the new efi system is as good as they say it is emissions should be pretty low on the new bike even with that 10k rpm screamer. alot of |
