HERE is a interesting read i found on dyno numbers and how they are made

I will go ahead and tell everyone that I am NOT an expert tuner of drag ATVs. I do review a large number of dyno pulls.
So I do know a little about dyno's and their results. First that dyno's don't "read" horse power, that number is a figment of the operator and computers imagination. They only read torque which is twisting force on the drum only. Then you have to look at what size drum & how much weight of the drum & what is the calibration or lack of on the unit. If you have a dyno that is calibrated for 500 ft. lbs. with 1%. Then drop back to the atv range let's say 50 ft.lbs. just to make the math easy say 50 ft lbs. now we could be 10% off now.

Their is also the "weather station" & corrected h.p. when I see this on a dyno sheet it is highly suspect. The operator can move them where ever you want. That is where the amazing results of the mobile dyno guy comes from at bike shows. They pull your bike on their make a pull then screw with the carb correct the weather numbers & now you get 10% more horse power WOW! So in closing a dyno is just one tool for helping in racing & tuning

also Chassis dyno add too many variables that if not calculated correctly will reflect on output numbers.
Not to mention crank dynos that are designed for smaller engines are better than +/- 10% on accuracy.

CRANK DYNO's

The crank dynos are way more accurate than anything else, there is a huge difference in the way it samples the motor. There is no clutch, no gears, no chain, and no sprocket. The correction programs are alot easier to use as well. So by far its nothing like running on a drum. Drums dont even have an engine break either

Chasis dynos are a better comparison for real riding/driving as they read the torque through the entire drivetrain which can be helpful to see how all those components interact. I have more experience with cars strapped to the chasis dyno than atv's. When I had my car tuned while strapped on the dyno, we were able to see that the clutch was not sufficient enough in the upper rpms thus drivetrain loss can also be accounted for. I still feel that the numbers to me don't mean to me as much as to some people. I like to see the differences in between the changes, that's where dynos prove to be great tools and what they're meant for.

Then there are those who like to pull the dyno sheet from their consol and say, "ya but check this out." I say, "lets run and find out."

I own and operate a dynojet. it is a tool just like opening the tool box to grab a 10mm wrench or a screwdriver. it will though show you what you did with the 10mm wrench and a screwdriver (right or wrong). doesnt matter what kind of dyno it is. if you want to brag put it on the track IMO.

Part of this is true. Horsepower is a number derived from torque. On the second part of the calibration, that makes no sense for the most part unless you are tuning your ATV on an automotive dyno.



I have personally never seen more than a 1 HP/1 FtLb fluctuation in changing weather station outputs. I played with this some on my bike in the days when my dyno was new, and I was in an exploring mood. However, I dont see any reason to input manual numbers. The dyno is a tuning tool, and thats what its used for....whatever the weather station says the weather is, thats what its tuned on.



Regardless what the variable are, thats what is going to the ground. On a proper torque measuring dyno, the only variable needed to be calibrated is the engine RPM through the smart tach. If its correct, all is good and believe me, if its not right, you will know it.



Crank dynos are not as accurate as this cat is making them out to be. Its one thing to have two different types of chassis dynos that read differently, but its another thing to have dynojet, superflow, powerdyne, ect.. that all sample in the same method but put it out way different numbers.

The whole reason to use a chassis dyno is to see what kind of power in going to the wheels. You can tune an engine dead nuts on with an engine dyno and it will be off when it hits the fenders. Cant say that about MOST chassis dynos. His comment "Drums dont even have an engine brake either" does hold true to inertia type dynos. Any proper dyno uses a torque measuring meter and you will also find an eddy brake attached to the drum for loading purposes....same principle as the brake found on the engine dyno. Oh yeah, inform him its "brake" not "break".