supra5677
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posted May 22, 2007 02:13 PM
To Y2K, Doug M, RR
Can you tell me the length in seconds for the intake stroke?
Also can you tell me the length of the injector pulse for the injector?
thanks,
Supra
   
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madmike
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posted May 22, 2007 02:36 PM
this may be a dumb question but doesent that all depend on the RPM of the said motor being a stocker or a stroker???
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dougmeyer
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posted May 22, 2007 03:09 PM
Stroke? At what rpm?
There is one intake stroke "event" for every 4 rod movements, right? So that means that the stroke length is covered AS AN INLET EVENT at a rate of 25% of the rpm.
If the RPM is 10,000 and the stroke is 2 inches, your making an inlet stroke 2500 times per minute- you're moving the piston 2 inches 2500 times in a minute, or 2 inches 41.6 times per second. So in this example one inlet stroke would take 1/42 of a second which is 2.5 % of or .025 sec.
Somebody can probably distill that into a formula for you but that's the way I'd think it through.....
The duration of the injector pulse is expressed in milliseconds (ms). Ridge probably knows..... I have the numbers for DTA and EFI but not stock stuff.
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rgeorge
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posted May 22, 2007 04:07 PM
11625RPM = 69750 deg/s = 0.014337 ms/deg
So the 180 deg intake stroke takes 2.58ms
Or, if you want cylinder fill time in ms, multiply .014337 by your intake cam duration. I cant remember exactly what it is.
The injectors turn on at a certain crank angle before the intake stroke. RR probably knows exactly when. The length of time they are on is determined by how much fuel called for by the ECU + Power Commander. If you need so much fuel that the injectors are at 100% duty cycle (not desirable), then you could say that their duration is 720 deg.
For 85% duty cycle, the injectors would be on 8.77ms
Why?
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ridgeracer
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posted May 22, 2007 04:30 PM
Actually a simple formula for the duration of a 180 degrees of rotation is
1 / (RPM / 30)
Of course the inlet valve is actually open for 300 degrees or 0.83 of a rotation which would be
1 / (RPM / 50)
As for the injectors it varies, a lot, depending on throttle, rpm, air temp & pressure, coolant temp, etc. Besides even if I could give you a typical internal value I haven't gone thru the ECU code enough to be able to convert the internal injector numbers in the maps into real world values of duration yet.
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supra5677
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posted May 22, 2007 06:12 PM
Just reading RR fuel map from the ECU.. I wanted to know why maxed fuel was made at 7422 rpm's .. So I wanted to figure out length of the intake stroke in milli seconds and the length the injector can be held open without fuel being wasted.. follow me?
supra
basically from 11,625 which is close to max rpm..
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supra5677
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posted May 22, 2007 06:14 PM
So if the intake stroke is 2.58 milliseconds I would assume that the max intake pulse without wasting fuel would be 2.58 milliseconds correct?
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rgeorge
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posted May 22, 2007 07:15 PM
no, the fuel is not wasted.
When the valve is closed (no airflow) the fuel injector covers the back of the valve and the intake runner walls with liquid fuel. When the valve opens, the rush of air causes the fuel to vaporize and mix with the air.
This process was anticipated when the engine was designed and it works well. In fact, the majority of the time, everything except high throttle high rpm situations (high duty cycle); the injector is done spraying fuel BEFORE the valve opens.
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supra5677
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posted May 22, 2007 07:57 PM
why then doesn't the ram air map, match the fuel map? the ram air map increases almost is a linear manner where the fuel map does not..
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ridgeracer
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posted May 23, 2007 06:27 AM
The simplest answer is that you are looking at fuel injected and not air/fuel actually delivered
The air flow dynamics of any engine are very complex. At different RPMs the air pulses flow at different velocities and create different types of reflected pressure waves that can interfere with the pulse or be in phase with it and increase it. Then there is the scavenging effect of the exhaust pulse. In a perfect world you would have all the elements of a size and shape that would resonate and valve timing to take advantage of it. But the valve timing is fixed and the rest of the engine is a real world compromise.
Each component will have different efficiencies at different RPMs. Put them all together and sometimes they work together and sometimes they fight each other. If you look at the air map you can see a sinusoidal variation of peaks and valleys. Around 7400 rpm is an air flow valley. For whatever reason, weird inlet turbulence, back wave interference with inlet popping open, etc the engine was getting more air than fuel. It was a dead spot and they probably adjusted the fuel map to compensate for what ever unique combination of elements created it.
This is the whole reason ECUs have maps. You can calculate air / fuel ratio with a pretty straight forward formula but you can't predict and therefore can't calculate all the real time fluid dynamic effects all the different components working together will have on the air fuel flow and mix. Not with a computer that will fit on a bike anyway. The map lets you tweak the fuel to compensate for unexpected design peculiarities under certain conditions.
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supra5677
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posted May 23, 2007 06:45 AM
"but the valve timing is fixed and the rest of the engine is a real world compromise"
the benefits of variable valve timing..
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supra5677
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posted May 23, 2007 06:54 AM
how do we determine how much fuel is actuallty delivered?
In the power commander this is shown in terms of plus or minus a number.. Is there a way we can cross reference the fuel injected map with a pc3 map and compre the difference?
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dougmeyer
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posted May 23, 2007 07:43 AM
Whoa, there. Supe.
As usual nothing is this simple.
The duration of the stroke is but a factor in the event. The instaneous piston speed effects the velocity of the charge, no? This, along with pressure above the injector, inlet valve duration, overlap reversal, and probably more, effects mass air flow into the cylinder.
All this can be lumped into what's commonly referred to as "volumetric efficiency".
Like Ridge says, this is why you need a "map" on a digital system.
On an "analog" system like a carburetor, the fuel demands are constantly satisfied (whithin limits defined by "jetting") by the air flow at hand. This is precisely what carbureted engines can be smoother than DFI engines.
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supra5677
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posted May 23, 2007 08:25 AM
Agreed Mr. Meyer..
I'm looking for the fuel map RR posted that looked similar to a PC map.... numbers, minus and pluses..
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