PSI or the XXX ?
- Thread starter 117bigdog
- Start date
Fibersnake
Banjo Playing PsychoBilly
05Chop,
I will agree that the numbers do not look right, however a few corrections. You mention that the h/p and toque start to drop off at 4300 RPM, well the torque does but the HP continues to rise until they intersect at the standard 5252 RPM point. Also all dyno will show torque cause in order to get the HP you have to know the torque and RPM, this is due to HP is a measurment of the torque (work) and combined with the RPM (time) we get the power! Dyno can not directly measure HP and comes up such based on the calculation of the other 2.
Also DynoJets do have the capability of measuring the Engine RPM easily though many shops do not have such extras. It is done through knock sensor, induction p/u, or sometime direct to EHC.
The MPH that many shops post on their sheet does not really mean much since it is related to the speed of the wheel over a time, this is effected by size of tire, air pressure and many other factors and also since we are looking for HP, it has no direct realtionship since MPH is a speed and not power (Work/Time). That as well as not being related real world since we have factors that would be restricting us (air pressure, cross winds, etc). Or we can show that on a dyno that our speed of the wheel at a certain RPM would give us a certain speed, however to gain that same speed on the road would require more force to overcome the resistance and thus what is on dyno sheet for MPH measured in coorelation to HP would be different on the road.
All the above said, a typical DynoJet is able to calculate the power based on how fast a fixed calibrated rotational mass (the roller that is of a certain weight) can be spun up. This is through the use of interia forces (once again work/time or another way if I know that I have a a 1200 lb wheel with an outside diameter of 12 inch, I know the amount of force that it will take to rotate the wheel (torque) and measuring how quick gives me the time factor which can be quickly calculated to HP.
Now what this doesn't show is the a/r ratio, the SAE correction factor, ambient temps, barometric pressure, humidity, and the other factors so that any measurement can be corrected to another to come up with a common parameter.
What we do not know is does this particular Dyno run strictly conducted on an inertia dyno (typical quick HP/Torque Run of a few qucik seconds to WOT or desired RPM) or is there a brake being used (an option on DynoJet) such as an eddy current, water break, mechanical, etc..
So with the basic inertia dyno that is most common with DynoJet set up, the HP/Torque are showing what it took to move that calibrated wheel through the use of the rear tire. How accurate is it and how it compares to a similar bike is unknown without having proper calibration factors used to allow for an apple to apple run. I think that the best to run a dyno is to used the 1:1 to ratio (which I understand on the BDM is in 6th gear).
I also think that the basic information posted is not a great representation of what most of us would see with the same set up at the local Dyno Shop. It is suspect.
Just my 5 cents
I will agree that the numbers do not look right, however a few corrections. You mention that the h/p and toque start to drop off at 4300 RPM, well the torque does but the HP continues to rise until they intersect at the standard 5252 RPM point. Also all dyno will show torque cause in order to get the HP you have to know the torque and RPM, this is due to HP is a measurment of the torque (work) and combined with the RPM (time) we get the power! Dyno can not directly measure HP and comes up such based on the calculation of the other 2.
Also DynoJets do have the capability of measuring the Engine RPM easily though many shops do not have such extras. It is done through knock sensor, induction p/u, or sometime direct to EHC.
The MPH that many shops post on their sheet does not really mean much since it is related to the speed of the wheel over a time, this is effected by size of tire, air pressure and many other factors and also since we are looking for HP, it has no direct realtionship since MPH is a speed and not power (Work/Time). That as well as not being related real world since we have factors that would be restricting us (air pressure, cross winds, etc). Or we can show that on a dyno that our speed of the wheel at a certain RPM would give us a certain speed, however to gain that same speed on the road would require more force to overcome the resistance and thus what is on dyno sheet for MPH measured in coorelation to HP would be different on the road.
All the above said, a typical DynoJet is able to calculate the power based on how fast a fixed calibrated rotational mass (the roller that is of a certain weight) can be spun up. This is through the use of interia forces (once again work/time or another way if I know that I have a a 1200 lb wheel with an outside diameter of 12 inch, I know the amount of force that it will take to rotate the wheel (torque) and measuring how quick gives me the time factor which can be quickly calculated to HP.
Now what this doesn't show is the a/r ratio, the SAE correction factor, ambient temps, barometric pressure, humidity, and the other factors so that any measurement can be corrected to another to come up with a common parameter.
What we do not know is does this particular Dyno run strictly conducted on an inertia dyno (typical quick HP/Torque Run of a few qucik seconds to WOT or desired RPM) or is there a brake being used (an option on DynoJet) such as an eddy current, water break, mechanical, etc..
So with the basic inertia dyno that is most common with DynoJet set up, the HP/Torque are showing what it took to move that calibrated wheel through the use of the rear tire. How accurate is it and how it compares to a similar bike is unknown without having proper calibration factors used to allow for an apple to apple run. I think that the best to run a dyno is to used the 1:1 to ratio (which I understand on the BDM is in 6th gear).
I also think that the basic information posted is not a great representation of what most of us would see with the same set up at the local Dyno Shop. It is suspect.
Just my 5 cents
Last edited:
lee
Well-Known Member
that's what I was gonna say!
Fibersnake
Banjo Playing PsychoBilly
Lee
I hope not then you would be as wordy as me sometimes and though I try to get a full picture out, many times people will stop reading before they get all the information presented.
Bad habbit of mine but it goes back to part of my background.
Short I think we all agree the Dyno run does not look right or is leaving out something.
BTW Congrats on the good showing for England in the Six Nations, much better than I expected seeing the first games.
I hope not then you would be as wordy as me sometimes and though I try to get a full picture out, many times people will stop reading before they get all the information presented.
Bad habbit of mine but it goes back to part of my background.
Short I think we all agree the Dyno run does not look right or is leaving out something.
BTW Congrats on the good showing for England in the Six Nations, much better than I expected seeing the first games.
scubaman15
Well-Known Member
Did we ever see a video?