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Launch Em High
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Discussion Starter · #1 ·
I've recently got my bike dyno tuned..
Only one area I believe wasn't taken in consideration... I have a 28T pulley, and I haven't gotten the Harley's flash download for the recalibration or installed the eletronic component that recalibrates/corrects for the pulley..

My question is.. will this affect the true readings for the actual dyno tune results? ( I know the bike is on the roller and reading the rear wheel, but the computer the tech uses is hooked up to the power commander)
thanks

:helpme:
 

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Do It Movin...
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hvrod:
It seems like we have a close setup except I did the HD download when I went to the 28t pulley.

There are a lot of people here that know a lot more than me, but here's my slash...

When you say "true readings" you mean rwhp and lb/ft (torque) right? If so, and I may be wrong, but those reading are derived from a measurement of the resistance between the rear wheel and the roller.

To get maximum power within an RPM range, or to keep the bike from running too lean, adjustments are made to the fuel table on the PCIII or HD/RT.

I think the fuel mixture numbers, running too lean/rich, are derived from exhaust gas measurement.

If the purpose of the dyno tune was to bring air to fuel mixture back into specs after an exhaust mod; my guess is that without the download you maybe close the limits of adjustments from the PCIII...

Knowledgeable Ones Please Chime In Here
 

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NO! :kaz:
 

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Do It Movin...
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Sorry Kaz I wasn't thinking about you, I ment the TRULY Knowledgeable Ones... :sinister:
 

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It can affect if they used a stock final drive ratio. They should have calculated a final drive ratio using the 28 tooth in the equation.
 

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SNAFU
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Dynojet dynos don't use a calibration for the drum speed. All the dyno does is measure the torque applied to the drum by determining the rate of acceleration. The computer then takes the RPM reading from either sensing the spark pulse or reading it from the PCIII. Once they computer knows the RPM it can calculate HP.

Bottom line, the gear rations mean nothing to the final HP number.
 

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spit happens
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What about the torque #?Will that be different.since the 28t is a lower gear you feel more torque.wouldn't that show up?
 

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If your dyno chart has a mph scale, torque or hp @ x mph, with the 28t and without calibration, your reading would be slightly incorrect right?
 

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mjw930 said:
Dynojet dynos don't use a calibration for the drum speed. All the dyno does is measure the torque applied to the drum by determining the rate of acceleration. The computer then takes the RPM reading from either sensing the spark pulse or reading it from the PCIII. Once they computer knows the RPM it can calculate HP.

Bottom line, the gear rations mean nothing to the final HP number.
:stupid: what Mark said! :rolleyes:
 

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The dyno has to be calibrated to the bike. There are a few ways to do this, inductive, directly off the coil, using the bikes tach, and calculating the final drive ratio. One of the surest ways is final drive ratio, as there can be no interference of a faulty pickup to determine rpm. Torque is related to force, or in other words, the pulling force experience while accelerating, whereas the power output can be explained as the pulling force at a certain speed. Therefore, the harder a vehicle pulls at high speed, the more power it produces. It is actually quite simple. Torque should be the same, but the hp will differ if incorrect ratios are being used.
 

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SNAFU
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HP is nothing more than (Torque * RPM) / 5252. There's no calibration for drive ratio on a standard DynoJet that I am aware of, they use RPM read from either an inductive pickup on the spark plug, a tach feed or from the PCIII. HP @ MPH is a meaningless number, I don't know why that would even be calculated.

BTW, reading RPM directly is the only 100% accurate way to accomplish a HP calculation. There are some dynos that use the drum speed to derive RPM but that induces errors such as tire aspect ratio, tire inflation, tire growth and slippage. Admittedly the errors would be minor but they are there.

Bottom line, pulley diameter, gear ration or gear selected have no bearing on the HP calculation unless the dyno uses a factor to calculate RPM from the drum speed and that factor is not set correctly to match your bike.
 

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Launch Em High
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Discussion Starter · #13 ·
I will have to check with the dyno place to see if they allowed for the 28t pulley then..
thanks for all the input..
 

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Drum speed is essential!! . To calculate power you have the weight of the drum and diameter of the drum and a formula for calculating the energy to rotate the drum one revolution. Now as the speed of the drum increases it will require more energy = more power. We seem to agree regarding some of the methods used to calculate rpm howevere final drive ratio is also a secure method. That is why you would calibrate the dyno in a certain gear. Go ahead and do a dyno run in 4th then don't change a thing but do the run in 5th and you will see different results. Why ?? because the final ratio will be different.
 

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Launch Em High
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Discussion Starter · #15 ·
Just a note..
I had a dyno done already.. and thought the results should of been 5% higher. due to the 28t pulley..
 

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Why do you think you should have a 5% gain due to the pulley? Have you dynoed the bike on the same dyno before? ( before the change?) What were the results before and after? Each dyno is different and will rarely give the same numbers as another.
Were there any other changes done to your bike at the same time as the pulley install? There could be a number of reasons that would change the outcome.
 

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Launch Em High
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Discussion Starter · #17 ·
Its the first dyno..
and I was told there was a difference of about 5% , to speedometer.. (for 28T)
And again some dyno's don't adjust for the 28T.. and then some readouts of other bikes have very close similar setups with mine, ( post of output and torque are higher then what I obtained)..
so with all that tolerances.. I probably didn't get an accurate reading..
 

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SNAFU
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Derek said:
Drum speed is essential!! . To calculate power you have the weight of the drum and diameter of the drum and a formula for calculating the energy to rotate the drum one revolution. Now as the speed of the drum increases it will require more energy = more power. We seem to agree regarding some of the methods used to calculate rpm howevere final drive ratio is also a secure method. That is why you would calibrate the dyno in a certain gear. Go ahead and do a dyno run in 4th then don't change a thing but do the run in 5th and you will see different results. Why ?? because the final ratio will be different.
OK, I'll concede that different gear ratios can effect the results. If you were able to dig into real time data I'm sure you would see higher torque numbers in the lower gears (or in the same gear with the 28T vs. the 30T) but after the RPM data is factored in the background calibrations should move the "corrected" torque and HP closer to a standard and factor out the difference in gearing (up to a point)

As I understand the functioning of a DynoJet the software utilizes a number of factors in calculating the torque applied to the drum. One of these factors is the engine speed. Knowing the engine speed and the drum speed the system can calculate the effective gear ratio. By knowing the gear ratio the system can calculate the torque multiplier thus effectively taking the gearing OUT of the final, corrected calculation. Since the DynoJet takes readings every 200 rpm the reading are more accurate in the higher gears but I suspect the system can easily adjust for the 7% gearing difference with the 28T.
 

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Launch Em High
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Discussion Starter · #19 ·
Heres some setup info of my bike currently..
Topless,
K&N filter, even stack intakes, power commander PC111R, 28T pulley,
TT exhaust, stock rear tire.

attach is the Dyno result..
 

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Mark, I have seen some tuners use excisting data logs from previous similar bikes to determine the final ratio. My first response was to clarify that a different reading is possible if the particular bike was not "set up". I think we are on the same page regarding the workings of the dyno.
 
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