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/cgi-bin/YaBB.pl General Category >> The Cafe >> Thinking aloud..... re: horsepower /cgi-bin/YaBB.pl?num=1363303331 Message started by raydawg on 03/14/13 at 16:22:11 |
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Title: Thinking aloud..... re: horsepower Post by raydawg on 03/14/13 at 16:22:11 I might not be able to phrase my question properly, for I'm not sure how to ask it :P But I'll try. I think HP (horsepower) is measured on the energy delivered to the drive train, yes? What I'm trying to understand is the relationship to motor size, or CC's, in our case and its relationship to HP. Can a smaller engine than ours deliver more HP than what we have? Does stroke (travel of piston) play into HP? Does HP not really equate to speed, that is gearing? I know my bike has a lot of power, it can utilize that power regardless of terrain (hills, etc) tho it does take more throttle, the power is available, where you might find a smaller bike, on flat ground can out run us, but not when it has to pull it load uphill, etc, why? Do my questions make any sense? |
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Title: Re: Thinking aloud..... Post by WD on 03/14/13 at 17:27:18 More horsepower per cc is no problem, pretty much any 2 stroke dirt bike over 150ccs puts out higher hp than a Savage. I've got a 4 stroke 248 cc (15 cubic inch) parallel twin (great grandfather of the 250 Rebel) OLD (1963) Honda Scrambler that makes 24hp. My 40 cubic inch 1998 Savage makes what, 28-32hp? Almost triple the displacement making 4-6 extra horse power... :-? Torque is what causes forward momentum. HP is simply torque divided by something else. No torque = no horsepower. Small high revving engines have less available useful torque, so they bog down in hilly terrain to a greater extent than the tractor engine in a Savage. Efficiency plays a big role in what you'll feel when riding. The Savage stone stock should top out around 85 mph. My 250 stone stock had a top speed of 79 mph (est). Stock Savage gets in the 50s-70s mpg, stock 250 80s or better. You also need to factor in gearing, terrain, bike weight, etc... Put bluntly, the Savage is a serious design compromise. Externally an English thumper circa 1964. Internally... early 60s Japanese valve train and very tame cam profile, with a 1930s wet clutch. It has the potential for considerably better performance numbers, but, power costs, money, time, fuel economy... Biggest "problem" with the Savage and its less than stellar power output... it was neutered to meet US EPA standards. The other middleweights switched to fuel injection, better intake and exhaust geometry, liquid cooling... fewer emissions, better power. Suzuki isn't going to make a loss leader match what higher end bikes achieve. |
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Title: Re: Thinking aloud..... Post by engineer on 03/14/13 at 18:09:50 You have the general principle right. HP is defined as the rate of doing work and work is defined as application of a force over a distance, think of lifting a big pail of water out of a mine shaft. One horse hitched up to a big bucket might take one minute to lift the water, put another horse in the harness and the two of them will hopefully do it twice as fast. So it is a measure of the rate of doing work. Keep in mind that torque is a measure of twisting force and not a measure of work or energy so sometimes the definitions of the words get in the way of understanding something. If two engines were identical in terms of efficiency the bigger one would put out more power because it is going to burn more fuel and make bigger bangs. If two engines are the same size but one has higher compression and burns more fuel per power stroke it will produce bigger bangs with each power stroke and will put out more power. If two engines of identical sizes have different bore and stroke the one with the shorter stroke will likely put out more RPM but the one with the longer stroke will have more torque. A longer stroke means a longer throw on the crank shaft which is the same as using a longer lever on something, it applies more force but has to move over a longer distance to do it. The shorter stroke engine turning at higher rpm is going to experience more "bangs" per minute and more energy. And since HP is the rate of doing work it will crank out more HP. That's why engines produce more power near the top of their RPM range, more bangs per minute. Engines today, on average have shorter strokes compared to the pre-WWII engines. HP has everything to do with speed. Wind resistance is a function of the square of the speed so to get moving fast you really need a decent amount of horse power. Gear ratios have a lot to do with it but if you don't have the power you won't have the speed. The Savage needs several more horses to be a solid 100 mph bike. And finally there is the matter of efficiency. Engines don't burn all their fuel or they produce a lot of friction and so they don't put out the ponies that they theoretically should. If all engines were equally efficient then the one that burns the most fuel would put out the most HP. It is called conservation of energy, and engines are simply devices to convert combustion gases into movement. Hope I didn't confuse matters too badly. |
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Title: Re: Thinking aloud..... Post by raydawg on 03/14/13 at 19:08:33 No, you guys are really helping....I'm beginning to see the relationships. Re: longer stroke, your explanation (engineer) brings to mind another questions then.... Often I do use a "longer lever", or we call it a "cheater bar". I have to torque castellated nuts to a very high setting, often, I have to put that longer lever on, to achieve it, where as if I stayed with the shorter one, I lacked the strength. So, I'm using less of my HP to achieve a higher what, output, torque? Would that not suggest it (the longer handle/stroke, is more efficient then? I know my arms aren't as tired, so I didn't burn as much energy ;D But of course if another person was able to use the smaller wrench, he could run more nuts up over the same time span, because he would not have to travel as far as me to achieve the same results....which would then make him more efficient....... :-[ Am I confused with apple and oranges? |
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Title: Re: Thinking aloud..... Post by rfw2003 on 03/14/13 at 19:52:18 You are kinda comparing Apples to Oranges there. TQ is a rotational force where as HP is the actual work done. I.C.E.'s of the piston type will have both TQ and HP plus they will be equal at approx 5252 rpm. The reason they have both TQ and HP is because you have to turn a linear motion into a circular motion to get any useful power of of the Piston type I.C.E. Now in I.C.E.'s TQ is what is gonna get you going but HP is what is going to keep you going and do the actual work. Here is a link that may help you understand it alittle more. http://www.epi-eng.com/piston_engine_technology/power_and_torque.htm Hopefully this helps you out some. R.F. |
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Title: Re: Thinking aloud..... Post by Pine on 03/15/13 at 07:08:58 42514954514757300 wrote:
I liked your example... but would add to your experience. Cheater bar versus standard rachet So the cheater bar let you acheive the torque you needed and without over taxing the muscles.. BUT look at the distance the end of the cheaterbar had to move. A big long arch.. versus the short arch of the standard rachet. In both cases you did the same work, but with the cheater bar you spread the work over a longer period/distance. So stroke on the engine is pretty much the same. By having a longer stroke, torque goes up. Wanna make it REAL fun... I read up on steam engines. Torque-wise they make ICE engines look like a joke. With a steam engine the load WILL move or something breaks. Thats why they worked well on trains. Today we dont use steam engines on trains... but we dont use ICE engines either!! We use electric motors to actually make the train move. Why??? torque! I love my torquey little Savage... I like that about it MUCH better than a high reving sport bike. Yes the sport bike will beat me everytime, but I'm not racing ... I am just scooting from home to work, with as little fuss and drama as possible. You can even tell, just by listening how the sport bike has to be revved up to get enough HP/torque just to get moving. While my bike gets the poor clutch let out while the revs drop to a putter. As for what all WD said.. I have to just agree... coulda shoulda woulda. The Savage is what it is.. it could be improved.. but why bother? Oh for an engine that makes near zero torque.. look up Sterling Engines (models). neat little things! PS: Many years ago ( 20) I read a Motor Tend when they built up a Mustang 302 and they achived 300HP. The article when on to state that getting 1 HP per cubic inch was pretty dern good. Current "muscle cars" like mustangs and vettes.. blow that way with 300CI engines making 570 HP!! So our little 40CI savage making 30HP is underwhelming by todays standards, but right in line with tech of 1980! Now to make that all wierd.. I was looking up Lycomming IO-390 airplane engine. The thing is 390 CI.. same as my 1965 Thunderbird V8. But it at best produces only 215HP, while the 1965 tbird made an easy 300HP. I really cant figure that one out! (And would love to hear why that is) |
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Title: Re: Thinking aloud..... Post by Cavi Mike on 03/15/13 at 08:27:44 063F3833223924560 wrote:
There are no American engines to this day that can get 570hp out of 5L without forced induction. I'm not sure there is a single production engine on the planet that can do that but it sure won't be an American car that does it first. The old 302 you're talking about was naturally aspirated making 300hp and its pathetic that it was so difficult to get 1hp per 1ci and it had to be BUILT. The rest of the world had no problem doing it on their production cars. The rest of the world is getting 100hp per L naturally aspirated - that would equate to a 500hp Mustang. The Big-3 has a LOT of catching up to do. |
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Title: Re: Thinking aloud..... Post by Pine on 03/15/13 at 08:41:25 426077684C686A64010 wrote:
There are no American engines to this day that can get 570hp out of 5L without forced induction. I'm not sure there is a single production engine on the planet that can do that but it sure won't be an American car that does it first. The old 302 you're talking about was naturally aspirated making 300hp and its pathetic that it was so difficult to get 1hp per 1ci and it had to be BUILT. The rest of the world had no problem doing it on their production cars. The rest of the world is getting 100hp per L naturally aspirated - that would equate to a 500hp Mustang. The Big-3 has a LOT of catching up to do.[/quote] I stand corrected: 5L normal asp 420 HP 5L Supercharged 662 HP Still... beats the heck out of 1980's and sub 200HP for the same CI. http://www.ford.com/cars/mustang/specifications/engine/ |
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Title: Re: Thinking aloud..... Post by Dave on 03/15/13 at 08:51:53 41787F74657E63110 wrote:
Now to make that all wierd.. I was looking up Lycomming IO-390 airplane engine. The thing is 390 CI.. same as my 1965 Thunderbird V8. But it at best produces only 215HP, while the 1965 tbird made an easy 300HP. I really cant figure that one out! (And would love to hear why that is)[/quote] The Lycoming is very much like the Savage....very understressed. The engine turns about 2,400 rpm and swings a big propeller....it needs torque......not horsepower. Most of these engines don't have a spark advance built into the magnetos, and they run fairly low compression for the octane they burn.. |
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Title: Re: Thinking aloud..... Post by Charon on 03/15/13 at 09:35:41 03383522333F242239313C23500 wrote:
Now to make that all wierd.. I was looking up Lycomming IO-390 airplane engine. The thing is 390 CI.. same as my 1965 Thunderbird V8. But it at best produces only 215HP, while the 1965 tbird made an easy 300HP. I really cant figure that one out! (And would love to hear why that is)[/quote] The Lycoming is very much like the Savage....very understressed. The engine turns about 2,400 rpm and swings a big propeller....it needs torque......not horsepower. Most of these engines don't have a spark advance built into the magnetos, and they run fairly low compression for the octane they burn..[/quote] Piston airplane engines are run at relatively low RPM because most of them are direct drive to the propeller. The propeller has to turn fairly slowly to keep the blade tips under about Mach .85. Those engines are actually pretty highly stressed because they operate at high power settings (typically about 75% power) for hours at a time. An added factor is that they are built to be as light in weight as possible, so parts are not built with huge reserve strength. Horsepower, ignoring some constants, is the product of torque and RPM. Torque is fairly constant per displacement, and isn't greatly affected with short-stroke/long-stroke differences. That is because, for a constant displacement, the area of the piston goes down as the stroke goes up. The force on the piston is the product of gas pressure and area, so as the area goes down with a smaller bore the force goes down. But the smaller force is working on a longer lever arm (the crank throw) so the overall torque remains about the same. The reason long stroke engines (by the way, the LS650 is not a long-stroke engine but a so-called "square" engine whose bore and stroke are equal) are usually credited with good torque is that the valve timing is usually optimized for lower engine speeds, which moves the torque lower in the power band. |
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Title: Re: Thinking aloud..... Post by Pine on 03/15/13 at 11:52:07 Interesting on the piston airplane motors. My first assumption would be that spinning a prop would be a low torque/high rpm deal... NOT the other way around. But if the engine has to create its power at a low rpm ... then I can see where numbers might look funny. To be sure - the old ford engine is not making 300hp at 2400 rpm! It also has 4 cylinders on the IO-390... so theres that. Just goes to show what thinking will get you. |
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Title: Re: Thinking aloud..... Post by Cavi Mike on 03/15/13 at 12:03:06 They even have gear reduction boxes to spin the prop slower than engine speed then use variable pitch blades to increase thrust. |
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Title: Re: Thinking aloud..... horsepower Post by Jiggyfly on 03/15/13 at 21:56:40 a/c engines are not built to be "lightweight", nor are they "stressed". They make incredibly low HP for their displacement, so "75% power for extended periods of time" doesn't mean it's stressed. 75% of 5500 rpm isn't exactly screaming. Aircraft engines are designed with one thing in mind, first & foremost: reliability. I single prop plane has an engine failure.....very bad. The Savage design is about as bad as it gets for making decent power. I road race a Ninja 250.....& one of the first things a ninja 250 rider will want to know is, "how can I make it fast?!".....either throw it off a cliff, or buy a different bike!!!! Same pretty much applies here. You can improve the power characteristics on the Savage.....but don't expect it to become a fire-breathing monster. ;) |
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Title: Re: Thinking aloud..... horsepower Post by Boofer on 03/15/13 at 23:48:20 Raydawg, To me, learning about any of my hobbies enhances them. I subscribe to magazines, and my Cycle World mag helps me get through the off months of winter. Kevin Cameron has written several articles dealing with your questions. In the March issue he touches on the subject of friction in larger engines and asks if it is worth the extra friction in a larger engine making enough power to keep up with traffic. Basically more weight takes more horsepower, but this takes more fuel. I believe the simplicity and effeciency of the Savage is its strong suit. It is a strong little dragster when put up against Vee Twins and it does so with low weight, good mileage, and a top end that is perfectly adequate for a thumper. Cycle world has a good website for newbs, also. Questions we answered long ago are still very important to those who still tense up when coming to a busy intersection or notice a huge dog getting ready to make a run at them. Reading is still a valid and enjoyable way to learn about the lifestyle we have chosen. :) |
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Title: Re: Thinking aloud..... horsepower Post by Serowbot on 03/16/13 at 00:17:18 Breaking it down into regular English... Size matters,.. bigger is more... ... but speed matters, too... It's all about burning energy... ... a bigger chamber will hold more fuel to burn (displacement)... ... faster refilling of the chamber, will burn more (fast moving mufti-chambers = RPM)... ... squeezing more fuel into the chamber (compression)... ... better flow, will move fuel faster (air, carb, valves, exhaust,will add flow)... ... and, you need enough spark to light it... Mufti-cylinder machines can make higher RPM's with less massive moving parts... and make more power... ... but,..the higher the the RPM goes, the narrower, and higher the power-band is located... So,.. gaining HP by using mufti-cylinders, and better flow, raise HP at the expense of torque-band width... ... bigger cylinders, increase power, but lower the potential peak RPM... ... and increased compression,.. packs more fuel, and thus more heat, in whatever size chamber you use... (and this affects reliability, and longevity)... So,.. you trade one, for the other... Peak HP... top speed... Torque-band,.. pulling power... Heat/longevity,... compression, chamber size, RPM, flow... You design the engine you want,.. for the job... ... or something like that... :-?... |
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Title: Re: Thinking aloud..... horsepower Post by jcstokes on 03/16/13 at 02:13:57 Well done Jiggyfly. |
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Title: Re: Thinking aloud..... horsepower Post by cowboy on 03/17/13 at 07:05:11 There needs to be a I S O for HP how can a 250hp gas engine say chevy 350 do the same work as a cummins 250hp or a honda 1100 engine? no transmission hook up to a honda is going to pull a load or move a load like the Cummins. and the cummins is not going to get there fast. I,ve been trying to understand this for 30+ yrs [slow learner] it should be torque that it's rated in. the chevy mite put out say 200 fp and the cummins put out 700 and the honda maybe 50. alittle bell helicopter engine put out 250 hp an weighs 168# were as the cummins weighs 2500# there are some wild a$$ clams out there that' s why you can't get bike manufacturers to tell you hp they did put it out in days past :-[ |
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Title: Re: Thinking aloud..... horsepower Post by Charon on 03/17/13 at 10:49:42 Measuring horsepower isn't as easy as it sounds, because it can't be measured directly. One has to measure torque and engine speed, then compute horsepower. It can also be difficult to attach a dynamometer to the engine, particularly on unit construction machinery like motorcycles. Another issue involves time. Is the power measured for a very brief time, as on a Dynajet dyno? Or is it measured for hours, as done in the Nebraska Tractor Test Lab wherein a tractor is expected to pull its rated load on a test track for ten hours? The first case puts essentially no heat into the cooling system, while the second requires the cooling system to dissipate waste heat for hours. Some airplane engines were rated with a five-minute rating for takeoff power and a lower rating for continuous use. Automotive engines are seldom used at full power for any significant time while engines used to drive irrigation wells may operate near maximum for several days. I personally doubt that any automotive engine (except for the sub-250cc class in small motorcycles and scooters) would survive an hour at full throttle without overheating. To a first approximation, the heat released when fuel burns in the internal combustion engine is divided into thirds. One third exits the engine as hot exhaust gasses. One third is lost into the engine cooling system. The remaining third is converted to mechanical energy, then part of that is wasted in internal friction and other mechanical losses. This means the cooling system has to dissipate more energy - heat - than makes it out as useful work. When the engine is run on a dynamometer the dyno has to dissipate a lot of heat, too. |
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Title: Re: Thinking aloud..... horsepower Post by raydawg on 03/17/13 at 11:41:51 Reading these replies really helps me to understand, uh, understand why I'm so confused with the subject ;D You guys are a wealth of knowledge, and its obvious well versed in the matter too! And Boofer, your recommendations I really appreciate. I haven't subscribed to a mag in years, but your reasoning sounds good to me. I will also check out that web site too, for I do have more questions than answers, and if its geared to accommodate newbies redundant questions without stanching the flow of the board, all the better, THANKS! |
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Title: Re: Thinking aloud..... horsepower Post by mpescatori on 03/18/13 at 05:05:13 Measuring hp is like measuring a rubber band, there are systems to measure hp and there are ways to express the individual items. Horsepower is the "strength" required to execute a certain amount of work, ok, but there are different ways to measure horsepower, especially when it comes to the ICE (Internal Combustion Engine). There are those who measure "net hp" such as the American Society of Automotive Engineers" (SAE), and they would unhook all ancillaries to the engine, no mufflers, no water pump, no dynamo/alternator, no gearbox, to the extent they would even use an electric oil pump to eliminate all possible sources of external power absorption (consumption) . This system would give a "SAE net" hp reading, and it is through this system that US manufacturers would claim a certain V8 engine could produce... 390hp. (1970's big blocks everywhere, from the 360 Hemi to the 442 to the 454...) This includes those UK and Italian sports cars productions up to the 1960s (Italy) all the way to the 1980s (UK) So a 2-liter 16-valve Triumph Dolomite Sprint was rated at 140hp (SAE net) vs. a 2-liter Alfa Romeo (150 SAE net) vs. a 2-liter Lancia (140 SAE net) Then there were the Europeans, who would use the German system "Detsche Industrie Norme" which required the engine to be tested with ALL expected ancillaries connected; not surprisingly the hp reading would be lower, yet often those cars equipped with the "less powerful" engines proved better performers that the "more powerful" SAE net competitors (130 hp DIN BMW 2002 Tii vs. 140 SAE net Triumph Dolomite Sprint) So, Horsepower may be defined as "the capability of an engine to PUSH a load", hence the capability of a more powerful engine to push a car to a faster top speed vs. the same car with a less powerful engijne - you have to push through wind resistance. TORQUE... hahaha, define that !!! Torque is the "twist momentum", i.e. the capability of a crank to operate a pulley, or... of an engine to gather speed (rpm) under a defined load. So, an engine with 100 hp and "X" torque will accellerate the 1/4 mile with a certain time and exit speed; BUT equip the same car with an engine which, with the same hp, delivers more torque, and that car will accellerate through the gears faster and exit the 1/4 mile quicker, because the engine with better torque will labor less and gather rpm faster. As an anecdote... did you know that the average saddle horse will only develop 1/2 hp? :-? That's because, when first asked to measure the "power" of a steam engine, physicists used the huge "draught" (draft) horse, the large (generally stallion) with thick, feathered legs and woolly hooves used for towing large loads. A normal "stock" horse is only half as powerful in mucle terms, hence is 1/2 hp. http://upload.wikimedia.org/wikipedia/commons/thumb/c/ce/Logging_in_the_Larch_wood.JPG/800px-Logging_in_the_Larch_wood.JPG http://upload.wikimedia.org/wikipedia/commons/thumb/4/46/MuttAndJeffHorses.jpg/720px-MuttAndJeffHorses.jpg Pictured, a logging horse and Mutt & Jeff ;) |
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Title: Re: Thinking aloud..... horsepower Post by justin_o_guy2 on 03/18/13 at 09:35:23 We did a test in Science class, holding the back of a chair, jumping & putting toes on the seat, over & over. Calculated weight & height X Jumps/minute & I came in 2nd overall at .8 HP. Not too shabby for a skinny kid, |
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Title: Re: Thinking aloud..... horsepower Post by Charon on 03/18/13 at 18:52:30 You might find the Wikipedia article - http://en.wikipedia.org/wiki/Horsepower - to be interesting. It describes some of the calculations about the amount of work a horse could produce, and the idea behind ratings in "horsepower." |
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Title: Re: Thinking aloud..... horsepower Post by Jiggyfly on 03/24/13 at 23:36:49 0C272E3D20214F0 wrote:
& these, too are older approximations. The thing about HP & torque is that their constantly changing constants. The theory's never change....it's physics. But things like "the 3rds" change, with advances in cooling, anti-friction coatings, electronics, etc. for comparisons sake, they must be done on the same day, on the same dyno, under the same circumstances, etc. My dyno run in South Carolina vs your dyno run I'm Iowa is like comparing is like saying "if my aunt had balls......she'd be my uncle!" so much of this is over-thought, & under used. I've seen 50hp motorcycles catch, pass, & leave 100hp+ motorcycles on a racetrack. The first question about horsepower is, "are we really using all we have?"......!? As a racer amongst racers, the first thing everyone wants to do is give it more HP! What percentage are using all that they have? Answer; few. I can post videos of me running away from 170hp motorcycles on my 30hp Ninja 250. The point being, a vast majority of us would be better suited to suspension upgrades, & true rider training than simply more HP. Don't get me wrong! I rode a 130hp Yamaha R6 while I instructed at CMP 3 weeks ago, & banging 4th gear @ 115mph & having the front end come up was exhilarating! 130hp I can handle......maybe not like an AMA factory guy, but I could qualify for an AMA national. Now a 1000? No thanks! :o Interestingly, I've always enjoyed lower HP bikes far more than excessively powered bikes. Besides.....everybody's got a 'Busa! :P |
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