I have been sitting here thinking about all the posts on the topic of "Horsepower" and what it does for us on our bikes.

You have all sorts of "Horsepower" - depending on where it is measured, what method of calculation is used and how it is measured.

To avoid putting all sorts of misleading information out, I decided to go an take a look at Wikedpedia just to see what they say.

Here is some very interesting information for you to use.

Now, according to what I've just read, our bikes are rated at Brake Horsepower for insurance reasons. From this, it is assumed there is a loss of about 10 "Horsepower" when it is measured at the rear wheel, as in "Rear Wheel Horsepower" or what a chassis dyno gives us.

Seems as though all this is very confusing - at least to me - when it comes to what works and what doesn't work when it comes to making the throttle make us happier when we twist it.

I know that Nobrakes was kind of down in the mouth when he first took his Big Bore 331 KLX and put it on the chassis dyno and got back the results. It was kind of disheartening. I kind of felt this hurt the first time I strapped my ZRX on the chassis dyno at the dealership I was working at and did a baseline test. It was reading lower than I thought it should. Then I did some reading and found out that the calibration of the dyno, local weather and a whole host of other influences can affect the outcome of the testing.

One of the things that I do know is that my "Butt-Dyno" can feel when it is better, or at least when it feels better. I think all of us can rely on this. Man, I hope that doesn't make us a bunch of smart butts! But seriously, the fact that the bike accelerates better in one spot than it did before the modification is something that can be felt. In our cases, a half "Horsepower" increase can surely be felt.

Properly used, a dyno can help a tuner with the development of jetting kits, carb mods and other things that affect the way the bike runs. "Snappiness" is something that we can feel in our bikes.

Probably the only true measurement of how good a bike runs can be determined in a race. Which bike is faster, or actually quicker, is easy to see, just watch who crosses the finish line first.

So, if you're making "Horsepower" which kind are you really making and just how much "Horsepower" are you making?

 

Good ol' wikipedia

Since my dyno run I've learned there were a number of factors that limited my results, even aside from the normal variations that can affect things from machine to machine and run to run. Two things stand out, though, and that is my use of knobbies and that the mixture was too rich. The inertial dynos rely on contact friction of the rear wheel to turn the machine and knobbies slip which give a low reading. And the power output is just not very good when running rich - it is analogous to running with the choke on, but not quite to that extreme. The stock gearing can also affect the results on an inertial dyno which also contributed my pessimized results. And not only that, but my knobbie tire is a 120/100 size which is 2cm taller than the stock 100/100 and that is also like changing the gearing in the wrong direction for the dyno. There there were a number of factors that worked together to produce a low dyno result. But even so, my paltry 22.23 HP and 16.58 ft-lbs of torque are the highest posted so far. I'm sure if just set up my bike differently with a better dyno tire and upped the gearing a bit and with my now better tuned carburetor, I'd be higher. I won't guess as to how much because I'm sure I would be wrong.

But now I've got my carb adjusted pretty well and if I ever do another dyno run, I'll be sure to put on a much less aggressive tire so that I get better contact with the dyno. But regardless of the absolute measured HP or torque output of my bike, it is currently just about right. Where before the installation of the 331cc and Keihin FCR I was actively seeking better performance, now I am no longer doing that. It's running great now. At least for me. Not that I wouldn't accept more power if it was handed to me, but I'm no longer actively looking for it. I have enough.

 

Nobrakes,

I'm going out on a limb here, but I'm almost ready to say that if the ability existed to measure the crank horsepower, similar to what the manufacturers do when they advertise their horsepower, I would say you're in the area of 34 to 36. Now, considering that a KLR650 makes about 45 horses at the crank, I'm really impressed! Half the size, about 25% less power!

Good job!

 

from my experience, depending on the dyno manufactuer, outside temps (which can be factored into the dyno program), type of transmission used, chain or shaft driven, etc ... on average - you'll see a 8-15% loss in power from drivetrain.

 

Some more info.
http://www.rc51.org/dynotuning.htm

 

If the Michael Wheeler is the person that wrote the second part of that article is the same person that runs "Wheeler's" at Deal's Gap, then the man knows what he is talking about.

I've had the pleasure of having a chat with Mr. Wheeler at Deal's Gap and he is one savvy mechanic!

 

First off horsepower is nothing more than a word made up to sell cars/bike off the showroom floor. It is torque that you should be thinking about, that is what you feel. I also don't think that the pumper carb is to add horse power nor did marty or nobrakes put it on expecting it to make more horsepower it was for instant throttle response. Also if you factor in what nobrakes said about his dyno run he is probably down 2-4 horse's from his reading which would mean 10 to 20 percent more power than tony's bike. Dyno posts on this forum are just about useless to compare unless they were done on the same dyno at the same time. All dynos have error in them, if a 300 horsepower car gets a reading of 4 horsepower off its not a big deal but 4 horespower off on a 20 horsepower bike is a different story.

 

Iowaguy - If you don't have anything nice to say...don't say it at all. Your posts almost always rip on someone or something...

 

I agree with one of hte above posts that TORQUE is really what matters. Horsepower is just a function of torque at a given RPM. Speciafically HP = Torque (ft-lbs) X RPM / 5250. Torque is a measurement of the amount of rotational force produced. Torque factored in with the gear reduction of the transmission, sprocket and wheels gives you your net "motive force" at the rear wheel. This is what acclerates you and counters wind drag and rolling resistance (mostly tire flex).

SO here's what can really throw you off when comparing 2 vehicles. You need to consider the gearing of the bike. If bike A is a 600cc sportbike making 50 ft-lbs of torque @ 10,000RPM, and bike B is a 1000cc sportbike making 75 ft-lbs @ 10,000RPM Bike A with can match the accelration of B with a 3:1 gear reduction, compared to a 2:1 reduction.

So you need to compare vehicles by considering what gear ratio and RPM your typically using. One reason for example that I like BMW's is because they make lots of torque at lower RPM's. You have great acceleration where you use hte bike most without shifting.

The KLX accelerates very well in 1st, 2nd and 3rd gears where it can make best use of it's available torque with lots of gear reduction.

That's also why you comtimes need to use a taller gear on slippery surfaces, your effectively reducing the amount of force your bike puts out, but increaseing the speed range that it can travel at. So reducing the gear ratio will make the bike acclerate quicker comparatively in each gear, but may reduce your top speed and will increase your RPM's when crusing.

I hope this helps.