[iowarider]

I am not a mechanic and can only perform the most basic of service on my bikes. However, the thing I can never figure out is the vast difference in Horsepower and Torque form engines of the same displacement or even larger. Examples.

1982 Honda CX500, it is the first shaft drive, water cooled, V-twin Honda made, or so I have read. Transverse V twin Guzzi style.
Rated Horsepower: 48
Rated Torque 37.

I know a good part of the horsepower was because it was an over square engine and wound to 10,000 rpm. cruised 70 at 7,500

Royal Enfield G5: Rated Horsepower 27 and Torque 37

My Shadow Spirit is a 750 and get this, rated horsepower is actually lower than  my cx500, Rated Horsepower; 44, Rated Torque 46. These are things that make me go hmmmm.

[Ice]

The Bullets 90mm stroke does make for some very nice usable torque.

 The old drag racers adage of "torque wins races, horse power sells cars" is IMHO true of motorcycles as well.

[prof_stack]

...
Royal Enfield G5: Rated Horsepower 27 and Torque 37

...

Those numbers are "ahem" very optimistic for the stock UCE.

[Chasfield]

Also, the 1980s were the low point for manufacturers telling fibs about their motorcycle engine outputs. They would always say they had 65 hp, or whatever, just to drive another nail in the coffin of the British motorcycle industry and its 50 hp big twins.

Nowadays, they are more likely to minimise quoted outputs as they are scared of getting stomped by the next batch of anti-motorcycle legislation.

[iowarider]

Those numbers are "ahem" very optimistic for the stock UCE.

Kinda thought that. But, it came from and add. Go figure, an add was optimistic in its horsepower rating.  never.

[barenekd]

Manufacturers ratings are with a bare engine with no accessories measured at the crankshaft. That means very little in the real world. Road tests in magazines usually get the bikes, and sometimes cars, are tested on local dynos with the power measured at the rear wheel. The results are much different. SportBikes advertise from about 180 to 200 hp. Most of them produce about 160 hp at the real wheel. The torque measurements have dropped accordingly. I had a Triumph Scrambler that was rated at 55hp by the factory. 44 on the dyno.
Just depends on how much you want to impress someone. Basically, if you don't know where or how it was tested, take it with a grain of salt.
 My G-5 has 18.75 hp at the rear wheel and 25 lb.ft. of torque, which seems about par with the other dyno readings I've seen on the forum with about the same exhaust and intake mods.
Bare

[single]

Before I moved 2 times and have thoroughly lost or misplaced everything,I had an old magazine test of the "super" bikes of my era.Funnily enough,the only one tested that produced the claimed horse shit rating was the RE Interceptor.

[Arizoni]

iowarider
The reason that two 500 cc engines can make two different amounts of horsepower is because of the design of the engine.

Horsepower is equal to Torque (in ft/lbs) times Speed (in RPMs) divided by 5252.

In your example for instance the torque is given as 37 foot pounds for both machines.  The higher horsepower of the CX500 is due to the higher speed that it can run but things are not always as simple as that in the real world so simply running the engine to a higher speed will not necessarily produce more horse power.

If one looks at the amount of torque produced by the UCE  Enfield at different speeds they will see it increase up to about 4000 rpm.  As the speed goes higher the torque will slowly start to decrease until the engine reaches 5250 rpm and then the torque will start to fall much faster.  That is why the Enfields maximum horsepower happens at a engine speed of 5250.

The torque falls off pretty fast above this speed so even though the engines speed keeps going up the reduced torque isn't enough to keep the horsepower rating up.  This results in the horsepower falling off and becoming less and less as the speed continues to increase.
That's why running the engine up to its red-line doesn't  improve the acceleration.

I don't have the data for the Honda CX500 but I'm sure it produces its maximum torque at a little higher speed than the Enfield.
More importantly because of its design it can maintain this torque while the engines speed keeps on increasing.
Using the 48 horsepower you mentioned and the horsepower formula along with the 37 ft/lbs of torque you mentioned,  that 37 ft/lbs of torque would have to be maintained (or reached) when the engine speed is 6813 rpm to produce the horsepower you mentioned.

Like the Enfield, above this 6800 rpm speed the torque will begin to rapidly fall off so the horsepower will begin to decrease as the engine continues to climb towards its red-line.

I hope this makes the torque and horsepower thing easier to understand.  

[olhogrider]

ANd the Honda requires a drive shaft and a radiator to do it. MyCX500 was so ugly... It was hot-wired with a toggle switch. Flip the switch and ride away. Some thief cut the strap on my helmet and stole that but left the Honda behind!

My random music player just put on Little Honda while I was typing this.

[Arizoni]

I also owned a CX500.
The thing was just about bullet proof but it didn't handle very well and was butt ugly.

After riding it to work for about 5 years, one day a guy who was about 4 labor grades below me rode in on a new Goldwing.  I says to myself, "What the H. are you doing riding this CX?  If he can afford a new bike, you sure as H. can too."
That said, I tried to trade the CX in on a new BMW-K75.  The dealer figured the cost of the new bike 4 times, with and without the CX trade in.  Each time it came out within a few dollars of being the same total due.  

I kept the CX and bought the K75.
Then I tried to sell the CX.  No one wanted to give me $500 for it even though it was in excellent shape.
I finally found one guy who seemed interested so when he said, "How much for the bike?" I said $300.  "Sold" said he.  

[iowarider]

 the Honda requires a drive shaft and a radiator to do it. MyCX500 was so ugly... It was hot-wired with a toggle switch. Flip the switch and ride away. Some thief cut the strap on my helmet and stole that but left the Honda behind!

My random music player just put on Little Honda while I was typing this.
[/quote]

LOL, OK, now your just making fun of my bike.  That wasn't a real story was it? I do know what you mean, a beauty queen they are not.

[cyrusb]

I'm having a  hard time with a 48 hp cx500. Really? Iv'e ridden them, and they are like cushmans. Fibbing about power is rampant with the manufacturers.

[iowarider]

Arizoni, Yea, handling was not a strong point for these bikes. It was my learner bike, manged to jump a median strip cause it didn't much like slow speed turning. Dropped the thing at a stop light in front of a Semi that was behind me, did I mention they are a bit top heavy? And the most embarrassing moment, was when I rode into my local Honda dealer, new motorcycle license in hand, got off the bike, heard a funny noise, It was laying on the ground!! uh, forgot to put the side stand down.    yep the best thing about that bike still is, it just doesn't care. Put it through most abuse and it just starts up and goes again.

Thanks all I appreciate the answers and the fun group.

[iowarider]

I'm having a  hard time with a 48 hp cx500. Really? Iv'e ridden them, and they are like cushmans. Fibbing about power is rampant with the manufacturers.

I know, I was surprised to, Google cx500 horsepower, that's the number that comes up most often, Even a couple dyno sheets posted. 

[olhogrider]

LOL, OK, now your just making fun of my bike.  That wasn't a real story was it? I do know what you mean, a beauty queen they are not.

True story. Parked at the short term parking at terminal 4 LAX. I was making fun of MY bike. I never make fun of other people's bikes unless I really know them well.