Scatter Plots for Beginners

[PoorUB]

For example you matter-of-factly mention the TTS calculator doesn't take into consideration pressure when calculating duty cycle.
Can you explain how duty cycle is affected by pressure?
Bet not,
Bob

[Coyote]

..
Simply put, duty cycle is the amount of time a fuel injector is energized or on during an engine cycle (intake, compression, combustion and exhaust).
Nothing more to it Andy.

Duty cycle is not a measurement of time.   5th grade math is right..

[Tsani]

Well the first two links appear to be useless on a Harley big twin using known information.
RB's, surprise, surprise. Matches info not only given by HD but also listed in the TTS calculator.
Fuel pump and pressures on the HD Big Twin are more than capable of the task.
Fuel pressures are held in a narrow range min. and  max. Deviate from that area and you are going to have issues.

Really want to complicate things, wrap your head around what is really going on with fueling in that shared intake tract.

Simple engine, simple design, KISS applies here.

[FLTRI]

Bob,  The time that a fuel injector is energized is Pulse Width

Duty Cycle is the percent of the 720 degrees of crank rotation that the fuel injector is energized. (assuming 4 stroke)

Here are a few of the calculators out there on the net.

http://fuelinjectorclinic.com/flow-calculator

http://www.rceng.com/technical.aspx?UserID=18803956&SessionID=yezGGk73j6w4ToNQiReC

https://www.rbracing-rsr.com/calcinjpulse.html

Andy,
Retread what I said. Not just the highlighted words.
Bob

[whittlebeast]

I was typing on the computer tonight and created a new field

EstimatedFuelFlowFront

And defined that field as

([RPM]*[MAP]*[VE New Front]/[Set Lambda]/1000000)

It tracks almost perfect with Duty Cycle Front (the entire test must be run at one altitude)


Also create a filter named

Transients HD

and define that as

[Acel Enr] >0 or [Decl Enl]>0 or [Acel Enr-1]>0 or [Decl Enl-1]>0 or [Acel Enr+1]>0 or [Decl Enl+1]>0

Have fun tuning

Andy

[whittlebeast]

This may be the best tuned Harley I have seen to date.  At least from bike that was not running Target Tune.  They tend to be even tighter than this.

http://www.nbs-stl.com/HarleyTuning/log0030.zip

I don't recall how he tuned it.  Possibly, he will chine in and share his methods.  He runs his Harley about as hard as anyone I have run across.  This is a little over an hour of data.

Well done.

Andy

[1FSTRK]

..
Simply put, duty cycle is the amount of time a fuel injector is energized or on during an engine cycle (intake, compression, combustion and exhaust).
Nothing more to it Andy.

Duty cycle is not a measurement of time.   5th grade math is right..

Could someone post the equation for figuring duty cycle?
What are the needed inputs and what is the math?
Thank you

[hrdtail78]

Duty cycle is the time the injector is open compared to how much time it has to be open.

If it has 100 seconds to be open and is only open for 40 of those seconds.  40/100 = .4 or 40% duty cycle.

Engine speed will tell you how long you have.  Figure how many milliseconds it takes for the engine to spin 720 degrees and how many milliseconds the injector was open.  you have 20ms available at 6000.  If the injector is open 16ms.  16/20=.8 = 80%

[Don D]

Jason
In your experience have you found that the motors run better pushing the high end of duty cycle or going up to the next injector size. I know different tuners have different thoughts on this topic. Lets assume not overkilling the size up to keep low speeds tunable and smooth. What about pushing the injectors with higher than standard pressure?

[whittlebeast]

Time for two rotations of the crankshaft is

[RPM]=0?1:120000/[RPM]

I define that as MsPerEngineCycle

Then to get Duty Cycle Front

[INJ PW F]/[MsPerEngineCycle]

This also works for TTS Logs but the name for Pulse Width Front changes

Andy

[whittlebeast]

Jason
In your experience have you found that the motors run better pushing the high end of duty cycle or going up to the next injector size. I know different tuners have different thoughts on this topic. Lets assume not overkilling the size up to keep low speeds tunable and smooth. What about pushing the injectors with higher than standard pressure?

Great question....

I have not experimented with changing injector sizes on Harleys and completely retuning the bike to get fair back to back testing but.......

Generally, the typical max allowable duty cycle is 85%.  That works fine in the engine speed that most Harleys spin so let's work with that number.  I have found that the max power WOT Duty Cycle of stock Harleys tends to be way less than 85%. I see more like 55% is common.  That implies that the injectors are on the large size of the normal range in the industry.  I am suspect it has something to do with the what calibration engineers are dealing with fighting a Y intake manifold.  If you think about it, if both injectors we running 100%, how would you do front to rear fuel balancing.  The closer you get to 100%, the larger this balance act gets.

Andy

[hrdtail78]

Jason
In your experience have you found that the motors run better pushing the high end of duty cycle or going up to the next injector size. I know different tuners have different thoughts on this topic. Lets assume not overkilling the size up to keep low speeds tunable and smooth. What about pushing the injectors with higher than standard pressure?

I believe in the benefits of lower duty cycle.  I see it more at lower throttle setting, idle, and cruise.  More fuel on a open valve.  I have been working with some 8.1's that have great low DC control.  Dead times are real close to the stock 4.3's.

Edited to add:  I have tuned a bike and during the last part of it realized I needed bigger injectors.  I retuned with bigger injectors and I liked how it ran after the swap better.  Got no way to prove it though.

[whittlebeast]

Could someone post the equation for figuring duty cycle?
What are the needed inputs and what is the math?
Thank you

In MLVHD, most of the time, you can just turn them on.

http://www.nbs-stl.com/MLVDemo/025%20Turn%20on%20MAPxRPM.PNG

Andy

[FLTRI]

..
Simply put, duty cycle is the amount of time a fuel injector is energized or on during an engine cycle (intake, compression, combustion and exhaust).
Nothing more to it Andy.

Duty cycle is not a measurement of time.   5th grade math is right..

Could someone post the equation for figuring duty cycle?
What are the needed inputs and what is the math?
Thank you

Here ya go:
IDC (in %) = [IPW (ms) * RPM]/1200

So, for example, if IPW = 16ms at 6000 RPM, then IDC would be (16*6000)/1200 = 96000/1200 = 80.0%. The injectors are properly sized for maximum RPM operation.
Bob

[q1svt]

So, for example, if IPW = 16ms at 6000 RPM, then IDC would be 80.0%. The injectors are properly sized for maximum RPM operation.

"At idle speed a 5ms fuel pulse will have duration of 18 degrees of crankshaft rotation, a 10ms pulse at 3000 RPM will last for 180 degrees and a 10ms pulse at 6000 RPM will last 360 degrees."  Motec
http://www.motec.com/forum/viewtopic.php?f=39&t=769

SO, if a IPW is 16ms at 6,000rpm then it will take 575* degrees of crankshaft rotation to provide the required fuel...   on a motorcycle than has a shared runner/manifold firing every 405-315-405-315-405-310*

There is a lot of sharing of fuel between them cylinders that no ECM, tuner, or god has any control over 

[FLTRI]

So, for example, if IPW = 16ms at 6000 RPM, then IDC would be 80.0%. The injectors are properly sized for maximum RPM operation.

"At idle speed a 5ms fuel pulse will have duration of 18 degrees of crankshaft rotation, a 10ms pulse at 3000 RPM will last for 180 degrees and a 10ms pulse at 6000 RPM will last 360 degrees."  Motec
http://www.motec.com/forum/viewtopic.php?f=39&t=769

SO, if a IPW is 16ms at 6,000rpm then it will take 575* degrees of crankshaft rotation to provide the required fuel...   on a motorcycle than has a shared runner/manifold firing every 405-315-405-315-405-310*

So what is the correct way to size injectors. I've been led to believe 80-85% max DC is best.
What formula do you use to determine best sizing?
Bob

[q1svt]

I'm finding it has to do with the motor in question, and it's intended use. normal, mild, high performance...

Then there are harley's with shared runners/manifolds 404-315*, where at first I through up my hands.

That with harley's we need to run larger injectors [lower duty cycles].  So going plus 1 or 2 may allow a longer rpm range where the IPW is still firing on an open valve AND still be tunable at idle...   I'm about to test one that is for 4 cylinder 1800/2000L turbo OEM or light performance turbo tweaked motors.  idle IPW controllable/stable to 1.1ms.

Todays injectors are far better than years ago, the spray patterns are better too, so larger no longer means 'fire hose' at low IPW's

I believe it will be the tuners that can/will figure out for HD style injectors which are controllable at idle but still can deliver high er volume.

 

[whittlebeast]

So what is the correct way to size injectors. I've been led to believe 80-85% max DC is best.
What formula do you use to determine best sizing?
Bob

________RPM____Max Allowable Duty Cycle
________6000_______85.0%
________6200_______84.5%
________6400_______84.0%
________6600_______83.5%
________6800_______83.0%
________7000_______82.5%
________7200_______82.0%
________7400_______81.5%
________7600_______81.0%
________7800_______80.5%
________8000_______80.0%
________8200_______79.5%
________8400_______79.0%
________8600_______78.5%
________8800_______78.0%
________9000_______77.5%
________9200_______77.0%
________9400_______76.5%
________9600_______76.0%
________9800_______75.5%
_______10000_______75.0%

In MLV I use the formula Max Allowable DC = 100*((120000/[RPM])-3)/(120000/[RPM])

[hrdtail78]

I also pay attention to DC at max tq and just not max RPM.   TTS has a nice way to show it as well.

[FLTRI]

So what is the correct way to size injectors. I've been led to believe 80-85% max DC is best.
What formula do you use to determine best sizing?
Bob

________RPM____Max Allowable Duty Cycle
________6000_______85.0%
________6200_______84.5%
________6400_______84.0%
________6600_______83.5%
________6800_______83.0%
________7000_______82.5%
________7200_______82.0%
________7400_______81.5%
________7600_______81.0%
________7800_______80.5%
________8000_______80.0%
________8200_______79.5%
________8400_______79.0%
________8600_______78.5%
________8800_______78.0%
________9000_______77.5%
________9200_______77.0%
________9400_______76.5%
________9600_______76.0%
________9800_______75.5%
_______10000_______75.0%

In MLV I use the formula Max Allowable DC = 100*((120000/[RPM])-3)/(120000/[RPM])

So you agree that max is 80-85% DC for Harleys and the rpms they run at?
Bob

[whittlebeast]

VRods can run into the issues around 74.5% DC.

[FLTRI]

VRods can run into the issues around 74.5% DC.

I've tuned a few over the years and haven't seen issues at 80%. That said these are not Destroyer race bikes. They are relatively stock bikes with various exhausts. Some Most don't work very well and all. Not enough volume. Rebaffled stock 2into1into2 works very well.
Bob

[whittlebeast]

Here is what it looks like in MLVHD when you are right on the edge.  The trace at the bottom.

http://www.nbs-stl.com/MLVDemo/975%20Duty%20Cycle%20Reserve.png

[rbabos]

VRods can run into the issues around 74.5% DC.

I've tuned a few over the years and haven't seen issues at 80%. That said these are not Destroyer race bikes. They are relatively stock bikes with various exhausts. Some Most don't work very well and all. Not enough volume. Rebaffled stock 2into1into2 works very well.
Bob

Pretty sure these bikes could benifit from an Exup valve also. Would make life a lot easier to have good sampling in the low end for nice stable closed loop. That seems to go to chit as soon as you slip on some better flowing mufflers.
Ron

[whittlebeast]

I got some data today from a guy that was concerned about fueling issues.  He supplied with a fairly large but mostly tame riding that was in the area he was concerned with.  A VRod is a TPS based VE cal.  We can still tune with what we see in the MAP vs RPM scatter plot. At the same time we can display the MAPxRPM vs Duty Cycle and the RPM vs TPS that controls the fueling. 

http://www.nbs-stl.com/HarleyTuning/VRodTpsBasedFuelingIssues.png

You can see in the center plot that the fueling is fairly well controlled.  I am a little concerned that the light blue areas are lean.  The light blue color is all scaled the same in all three plots.  I would advise the own to increase the fueling by about 10% in those blue areas and retest to see if the bike rides better.

I also advised him to add the O2 voltage to the log so that we can at least determine if the AFR is swinging leaner than 14.7 at this same place in the fueling.

Have fun tuning

Andy