I got thinking this from another thread. How do calibrate a chassis dyno? I know how to calibrate a flow bench, you get a standard flowing orafice. An engine dyno or break is hanging a set weight on the torque arm ( 100 lbs at 2 ft from the center is 2oo ft. lbs). But what do you use for a chassis dyno? I have little chassis dyno experiance, except to help a few friends tune, and the operator's could not tell me how they set a standard. It's set at the factory was the standard reply.
I know how often I check the engine dyno, because it is easy, maybe 20 min.

 

basically it (mine) is an enercia dyno. (spell check disabled) the drum is a set weight and the readings are based off of acceleration. ie: how long does it take car A to get through 3rd gear spinning an 1800lb drum. ect

 

Can you calibrate it? I hear lots of this reads high, this reads low etc. Is ther a standard, that can be set? Just curious.

 

as far as i know DON there is nothing that can get out of calibration its simply a roller that weighs a certain amount. now i am sure there are standards somewhere deep in the software that can be changed but i dont know how to do it .

 

Thanks, I know beraring wear, rod end and bushing wear make some differances on the engine dyno, so I just check calibrations.Water temp. going into the brake can also change numbers so we monitor that also. I would think rotationl friction on a heavey object could make a differance. Do not know though.

 

All my experience and training has been on a dynojet 248c, which was done right at dynojets head office in Las Vegas. From what I recall, the dynojet calculated power based on accelerating a known mass over time. That part didn't require calibration since it was two known variables that would not change. From experience with the dynojets, the main differences between readings from one to another were mostly due to the correction factors used to calculate total power output in the software. Things like ambient air temperature readings and humidity that were collected by the dyno sensors would vary. It's almost as if two dyno's sitting side by side wouldn't always read the same variables even though they "should". I doubt that this would be the sole reason for major discrepencies in power readings though. My personal feeling is that some people may tamper or incorrectly imput some data/variables into the dyno which causes incorrect readings. So generally speaking I think the key in accuracy is to keep everything on the dyno in good working order and if the owner/operator is dilligent in making sure the set-up is the same for everyone it should be pretty accurate. Because of the "people factor" dynos seem to vary...

 

Thanks. Would the bearings the rollers run in, change friction numbers at 30 degrees VS 95 degrees F? How do you set constants? I can ask Mfg. but I want some answers from people who actualy have used them.

 

That's a good question and I'd assume that temp would have an effect on friction numbers. From what the guys that trained me said in a nutshell, the dyno doesn't require any specific calibration, it's software is designed to correct for most variables. I realise that is a pretty broad definition and honestly only dynojet knows if they factored bearing temps etc into their software correction factors but I'd probably say they didn't..

 

Does the engine acceleration rate change the readings at all? Or can a constant RPM be checked?

 

constant can be checked

 

How? I do not know. I can load my dyno and hold an engine at any RPM for as long as I want. Not sure how this works on a chassis dyno.