so you're telling me that when someone maxes out their injectors at 100% then they are spraying fuel AGAINST A CLOSED VALVE FOR COMPRESSION, COMBUSTION, AND PART OF EXHAUST strokes???!?!?

I am NOT being sarcastic!

I think 100% 'duty cycle' means 100% of the intake duration, referencd from the time the valve is open or something like that.

I won't let this die until it makes sense, cause right now, it does not! (Then again, i am a certifiable nut according to some, so its no big deal.)

 

Ok, this has me all confused All I have to offer is one question. How does the ecu know how long the intake valve is open? When you swap cams with differing opening/closing/duration values, you don't change any parameters in the ecu. (Ok, some of you can with standalone can ) All the ecu knows is what position the crank is in (TDC, etc.) Plus, all the cams I have seen have more intake duration than 180 degrees (actual amount of time for intake stroke). What does this all mean...you tell me

 

falconGSR...your one of the people I thought was being sarcastic .

Anyhow, duty cycle is expressed as a percentage of the ratio of the on time/ total time as I had stated earlier.

Aside from injector talk, lets steer the discussion over to the world of electronics, specifically square waves. Lets say you have a square wave at 1Hz. This means that ONE cycle is completed in 1 second.

So the waveform looked something like this:
|-----| |
| | |
| |-----|

It had a rising edge, falling edge, and another rising edge. The time from rising edge to rising edge is 1 second (for my example). Note: The time between succesive rising edges (or falling edges) is called the period of the waveform. 1/period = frequency.

Now looking at the diagram, I've tried to make it so that its HIGH for as much time as its LOW, or stated another way, I've tried to make the ON TIME 1/2 as much as the TOTAL TIME.

Again:
|-| |
| | |
| |---------|

In the above diagram, the same cycle completed in 1 second, or 1Hz, however, you'll notice the time thats its HIGH (or ON) is smaller compared to the TOTAL TIME...thus, duty cycle has decreased. Using the dashes to try and get a number...I've set it to 10% duty cycle.

Typically Hondas like to idle with a PW of 2 - 3ms....however, this doesn't tell you anything about duty cycle, does it? In order to get that number, you need to know the TOTAL TIME of the injector waveform....which means its time to break out an O'scope or DMM that has that functionality.

 

Ahh mine says the same 2.2mph. I am hoping it is like some sort of grounding issue beause my greddy turbo timer is tapped into the VSS Wire. I'll have to ask on the hondata forum.

Dustin

 

I am definately telling you that. How do you think carburetion works?

In a GSR @ 8000rpm, the intake valve opens 62 times a second. If we the motor could only inject fuel during the intake stroke it wouldn't deliver enough fuel at full throttle.

 

Yes, that's what we're telling you.
You'd be wrong.

The injection start time is programmed into the ECU. There's a cylinders position sensor in the distributor that says that a new engine cycle has started. After that the ECU can use the TDC sensor or crank angle position sensor to figure out the start of the injection event. The injection event start time is just a number of degrees before TDC and that time is decided on when the ECU is originaly programmed. The ECU has no idea when the valve closes. At low rpm's it's easy to keep the injection events limited to just the intake stroke. At high rpms it's virtually impossible. This is all regarding sequential injection. Batch fire doesn't need a home signal and fires once a revolution. It doesn't care what cycle the engine is in.

If you know the pulse width and the rpm you can calculate the duty cycle, you don't need on oscope for that.

The left column would be for batch fire and right would be for sequential.

 

I just love what I started.. This is what I wanted to see when I posted this. I knew you guys would come through for me and I really thank you..

art

 

DirtyLude - How can you calculate Duty Cycle from PW and RPM alone?

The chart you posted makes no mention of Duty Cycle.

If the chart you posted is Maximum PW (and PW is the ON Time)...then there was a portion of the waveform that was OFF.

And once again, on time/ total time is duty cycle.

Perhaps I'm not seeing something that you are....could you share please.

 

and thats why i kept hammering. work sucks - i'll go back and read all this tonite.

 

At 7500 rpm you have 16ms max injection time before the two revolutions are over and you need to start again. If you have a 8ms pulse width at 7500rpm you are running 50% duty cycle. The injector is open half of the time. If you have a 16ms pulse width at 7500rpms there is 0 time between the end of the last injection event and the start of the next, so you have 100% duty cycle.

 

Ahh...I see your logic now.

But I think I see a flaw with it. Your using the Maximum amount of time that the injector can be open as the figure for Total Time.

Are you using this figure because of the way that the ECU uses the CYL, TDC & CKP sensors to time injection?

I'm pretty sure I see what your talking about....thanks for the enlightenment sir.

 

This has to be one of the best threads in a while... I think Joe(falcongsr) and I love it when people get real technical and use formulas to find a solution. Again, very good info everyone gave.

art

 

The amount of time the injector /can/ be open is total time.

You take one complete cycle (on/off). Total time = on time + off time.

Dustin