| Author | Message | ||
     Ar15ls1 |
I am wondering exactly why our air cooled engines tend to run out of power over 100mph. Yes, my buell still pulls hard over a 100mph, but compared to the inline fours it literally falls on its nose. I already basically know the answer, but want a more detailed explanation from all of you brainy people. Whenever I am in a race with inline fours,even dohc twins, I run real close until we get on the topend. This is when its all over for me. | ||
| Sportsman |
That is when it's all over for everybody. That is alot of the discontent whith Buells. Over 100 it's all HP and arodynamics till you hit redline. Once you get the areo, or HP, then you hit redline, gear higher, and start over. It has nothing to do with the cooling. | ||
| Rick_A |
If you have a stock Buell, look at a dyno printout and note the torque curve...usually drops right after 6200 rpm. Aerodynamics aside...the biggest top end impediment is the cylinder heads. Look in the KV dyno section. There are some dramatic improvements that can be made through some good head porting. | ||
| Ar15ls1 |
I was not implying that it ran out of power because it was air cooled. I did not mean for it to sound that way. I am talking flow characteristics. Is it because of the 2 valve design, bore, stroke, weight of the flywheels etc.Probably one of the main reasons is the low rpm redline that our motors have to run within. I believe that someone(probably Blake) proved how even a 600cc that only makes 40ft lbs of torque is actually making more than the heavy flywheel twins . It had to do with the rpms of the motor in relation to the back wheel rotations. Im not exactly sure how he explain it, but it made sense to me. This is why a buell with the same horsepower as a jap bike will still lose because of its rpm limits. | ||
| Roc |
2 bikes with the same weight, aerodynamics, gearing, traction, rider/rider input, and HP - did I forget anything - should run the same speed and accelerate at the same rate. The RPM limits you assign to the Buell are really HP limits. If a Buell makes 100 HP at 6,500 RPM and a CBR makes 100 HP at 11,000 RPM they both make 100 HP. Maybe you have a bike that makes 85 HP and 75 foot pounds of torque and you are comparing it to a bike that makes 100 HP and 40 foot pounds. Your bike will pick up faster when you roll it on, while cruising, because it makes more power at lower RPM. However, when it comes to top end you will find 85 HP to be less than 100 HP and the speed/acceleration will be less. "Is it because of the 2 valve design, bore, stroke, weight of the flywheels etc." - Yes I think so. Just think of an engine as an air pump, the more air it pumps through itself the more power it makes - as a rule of thumb. Is this even close to answering yoru question? | ||
| Ar15ls1 |
Thanks Roc. Yes this helps, but remember that this air pump also has fuel mixed into the equation. | ||
| Blake |
Simple... HP and aerodynamics. Why is our V-Twin down on HP? It cannot rev due to valvetrain and piston speed limitations. Even if it could rev, it mmight have trouble breathing in enough air/fuel to keep up. There is where the four valves come in. The easiest thing to do is send your engine to Cycle-Rama or Nallin Racing along with some money. You can then keep up with the 600's in the straight line contests. Or there's always a nitrous system.  | ||
| Imonabuss |
AR151, I'm probably being redundant here to Roc, but with the same horsepower and aerodynamics, an air-cooled two-valve will run the same top speed as any four-valve water-cooled bike. That is unless it is geared deeper, in which case it will out-accelerate the other bike. RPM does not buy speed, it is all equalized by gearing. The bottom line is available horsepower at a given vehicle speed...nothing else matters. | ||
| Mikej |
There is the little matter of leverage. What's easier, to lift a 1Lb weight 1 foot by cranking a lever twice in 1 second, or by cranking a lever 10 times in 1 second? The RPM's do factor in somehow. Take two bicycle riders, just to make this more understandable: Both are traveling at 20mph, Rider one has a pedal revolution speed (cadence) of 85rpm, Rider two has a cadence of 60rpm. Both are doing the same work, going 20mph, but if all cycling history is any indication rider one is being more efficient and should outlast rider two, all else being equal. The higher rpm's do factor in somehow, I just can't prove it with math. | ||
| Torqd |
Well I got the ponies but not the right gearing and aerodynamics...Raced an R1 and spanked him to 120 then he came up on me...(I think I scared him :-0 )man I need to get some bodywork and the right gearing... I am going to race him when I get a 29 tooth pully...130hp with a 27 front pully is stupid crazy! But fun:-) | ||
| Aaron |
Imonabuss is right ... hp is torque x rpm. Torque and rpm are weighted equally in the formula because they're interchangeable, by using gearing. For example, say you're turning 10,000 rpm and making 50 ft/lbs of torque. Gear that motor 2:1 and you're turning 5,000 rpm and making 100 ft/lbs of torque. Rpm and torque are totally interchangeable. Ultimately, horsepower describes the total combination of the two, without describing the individual torque & rpm makeup. You use gearing to turn the torque & rpm makeup produced by the engine into the torque & rpm makeup you want at the back wheel. | ||
| Ar15ls1 |
I knew that I would bring out the smart people! Aaron that is what I wanted to know. So does this still explain why a 600cc inline 4 actually makes more torque than our vtwins because it revs so much higher? | ||
| Aaron |
Yes ... say for example it makes 45 ft/lbs at 12,000 rpm. Gear it 20:1 and you get a 600 rpm rear wheel speed (about 44mph) and 900 ft/lbs of torque at the rear wheel. Now take a bike that makes 80 ft/lbs at 6,000 rpm. Gear it 10:1 to get that same 600 rpm rear wheel speed, and you'll only have 800 ft/lbs of torque at the rear wheel. The bike with the most HORSEPOWER is the one that'll put the most torque to the rear wheel for a given rear wheel rpm, even if the motor is making less torque. That's why horsepower is the performance metric. Engine torque by itself is not a performance metric, it's meaningless without considering rpm, and when you do that it's called horsepower. | ||
| Imonabuss |
Mikej, What you are talking about is torque. Yes, less torque applied more times equals the same power. But, given more torque at the same RPM you get more power. Basically, however, power is the way to measure work that can be done, so at a given vehicle speed the power available from the engine at that speed will tell you how much work can be done...ie. can I accelerate more. Now, an engine with more torque is kinda like Lance Armstrong vs. you or me. In short, Lance will kill us in a roll on, even if geared taller!!! Actually, I'll bet there are differences in cyclist bodies that require them to gear differently. In short, a body with lots of high endurance muscle would gear for more RPM, while a body with tremendous strenth would gear for torque. All analogies aside, horsepower is what gives top speed, wide powerbands give acceleration without shifting. So, in a pure drag race with sticky tires horsepower is king. But in roll ons in twisties, a wide powerband is the best. There are also some harder to measure issues at hand, like traction, which is a serious issue on a motorcycle, especially during racing. Traction is more easily maintained with farther apart power pulses and more flywheel weight, which is why a lower revving twin with equal power will wax a multi in cornering exit, especially in slippery conditions. Math exists for all of this, some of it is a little more complex than what we usually see. | ||
| Mikej |
Speaking of Lance, he almost always is referenced as having a higher cadence than most of his competitors. Next time he's in town maybe I'll race him and see how I fare, I will of course use the Buell instead of a bicycle.  | ||
| Hans |
Yeah, but the famous Eddy Merkx had always a tooth more on his front blade than his competitors: Even uphill while not being an lightweight. Torqui legs and much HP. Hans | ||
| Ar15ls1 |
Very well explained! Now I can go and tell this to all of my hot rod buddies and sound like I know what Im talking about! Thanks! | ||
| Ar15ls1 |
Now, does this mean my firebolt engine is actually making more torque than the older buell motors(stock for stock) because it has roughly 1000 more rpm to play with. Or,because the horsepower is slightly lower it does not make enough of a difference. I wonder this because my firebolt stock was slightly faster than most of the s1's and x1's that I have run. In some cases they were not completely stock. The riders were about the same in experience as I am. Maybe its because the firebolt has less rotating mass than the older buells. The wheels are a little bit lighter. I miss the bottom end grunt of my thunderstorm headed sportster, but my xb is deceivingly (I think thats how you spell it) quick. | ||
| Aesquire |
6 speed tranny, gearing to match engine, both bikes naked, same top speed. You need a Baker & body work off the LSR bike.  I on the other hand need Nailin racing heads, new pipe, , um maybee I'll put some miles on, & learn how to launch this M2 after break in, I HATE WINTER!!!! | ||
| Rd350 |
I thought it came down to the right gearing. If you can run a R6 bike up to 15,000 rpm with 6 spds and start out with a low gear it will pull faster and longer in each gear. Compared to Buell at 7,500 rpm with 5 spds. That is why the civic si or type R are so fast. 4.11 or 4.43 gearing and running up to 8,000 rpms and they don't hardly make any HP and little torque. Or am I looking at this wrong? | ||
| Rick_A |
Power to weight has some to do with that. | ||
| Blake |
Given a reasonable useful powerband, say 40% of the rev range of the engine, HP is ALL that matters. Yes a 6th gear helps better keep the engine within the optimum power band. If our Buells were built to do 150 mph, we could use another gear. Aerodynamics are significant when talking about triple digit acceleration and top speed. Weight is important when talking about a drag race or low speed roll-on. |
