EFI duty cycle question
#1649467
07/22/14 12:09 AM
07/22/14 12:09 AM
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Joined: Dec 2003
Posts: 22,722 Bitopia
jcc
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I'm confused ( as normal ) So a 4 cycle motor has 720 crank rotation for each power event. Typical cam has intake open, say for arguments sake, 250 Degrees. Assume air intake pre valve is moving or turbulent for a slightly longer period then when valve is open. I don't think the exact amount is crucial to my question. Typical Seq port injection has injector approx 5" from backside of intake valve. If when designing an EFI system, target is never, under full load/WOT, to have injector open/flowing more then 90%? of the time, correct? So the question is, what is happening to all that fuel being sprayed in at 50?psi 5" from an intake valve in a relatively stagnant air intake tract? Seems like it would really want to puddle upon hitting any surface other then the hot? intake valve, and it's doing this for over 300 degrees of crank rotation while the intake valve is closed?
Reality check, that half the population is smarter then 50% of the people and it's a constantly contested fact.
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Re: EFI duty cycle question
[Re: jcc]
#1649468
07/22/14 01:07 AM
07/22/14 01:07 AM
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Joined: Jun 2003
Posts: 52,972 Romeo MI
MR_P_BODY
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It really doesnt puddle to easy but it only fires the injector just prior to the valve opening so you have very little time when there isnt any air flow.. for production we didnt like going past 85%.. I flowed a FEW THOUSAND injectors when I was working.. I'm setting my injection up at 55 psi.. I'm use to that pressure EDIT I'm drilling 2 manifolds tomorrow for my injectors
Last edited by MR_P_BODY; 07/22/14 01:11 AM.
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Re: EFI duty cycle question
[Re: jcc]
#1649471
07/22/14 12:15 PM
07/22/14 12:15 PM
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Joined: Dec 2003
Posts: 22,722 Bitopia
jcc
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So the consensus is the injector on seq, is only firing around when the time when the intake valve is moving?
Reality check, that half the population is smarter then 50% of the people and it's a constantly contested fact.
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Re: EFI duty cycle question
[Re: jcc]
#1649473
07/22/14 12:37 PM
07/22/14 12:37 PM
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Joined: Oct 2005
Posts: 1,305 Lakewood, Colorado
herkamer
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Information about wall wetting/puddling: http://www.megamanual.com/ms2/xtau.htmI would think the goal would be to fire the injector at the open valve, but at high speed and long PW times it may overlap with a closed valve.
Matt 69 Dart Swinger 340 83 W350, Megasquirted with 46RH Old news: 72 Demon street/race mobile Latest: 70 Duster backhalf car and even more
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Re: EFI duty cycle question
[Re: jcc]
#1649479
07/22/14 04:52 PM
07/22/14 04:52 PM
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Joined: Jun 2003
Posts: 52,972 Romeo MI
MR_P_BODY
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Quote:
Quote:
Information about wall wetting/puddling: http://www.megamanual.com/ms2/xtau.htm
I would think the goal would be to fire the injector at the open valve, but at high speed and long PW times it may overlap with a closed valve.
Yea, that's what I talking about, the link might take a few rereads to digest.
This leads into another related topic, seems like any intake tract coatings would have a downside regarding the wall wetting/evaporation issue, either by causing worse puddling with a slick coating, or slow down evaporation with an insulating style coating.
Thats why we spray the fuel in at higher pressures.. it will atomize much quicker.. the fuel particles are much smaller.. and the pattern of the spray makes a big difference also.. most all of the injectors now spray a cone shape with different amount of fuel in different areas of the cone.. I had to measure the amount of fuel in each section of the cone... vs the straight spray of fuel.. this type of injector would puddle and as said, was hard on emissions.. you dont just spray in a certain amount of fuel but how its sprayed in
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Re: EFI duty cycle question
[Re: go green]
#1649481
07/22/14 05:32 PM
07/22/14 05:32 PM
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Joined: Oct 2004
Posts: 8,165 Left Coast
BobR
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Quote:
What do you think a carbureted engine is doing during the closed intake intermission ?How about mechanical fuel injection ? If your injector is at 90%, its time to buy bigger injectors.
You have a thingy in EFI that is called a "injector phase angle " it is where you tell the injector to fire in relationship to the valve opening .Just think of it as example of the law of diminishing returns . When you are idling around ,the EFI has a measured fuel delivery at precise times and all is happy , but when you are a 8000 RPM its pretty much just blasting fuel in at precise times .
The reality is not the slow-motion lazy fuel hanging around the valve mental image that you are imagining .
If you could see the 9500 rpm event in slow motion the injector isn't closed much. Also, you really don't even need a cam position sensor on a race car.
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Re: EFI duty cycle question
[Re: BobR]
#1649482
07/22/14 05:41 PM
07/22/14 05:41 PM
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Joined: Jun 2003
Posts: 52,972 Romeo MI
MR_P_BODY
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Quote:
Quote:
What do you think a carbureted engine is doing during the closed intake intermission ?How about mechanical fuel injection ? If your injector is at 90%, its time to buy bigger injectors.
You have a thingy in EFI that is called a "injector phase angle " it is where you tell the injector to fire in relationship to the valve opening .Just think of it as example of the law of diminishing returns . When you are idling around ,the EFI has a measured fuel delivery at precise times and all is happy , but when you are a 8000 RPM its pretty much just blasting fuel in at precise times .
The reality is not the slow-motion lazy fuel hanging around the valve mental image that you are imagining .
If you could see the 9500 rpm event in slow motion the injector isn't closed much. Also, you really don't even need a cam position sensor on a race car.
Even at 85% duty cycle(WOT) you would swear its on all the time. I know it isnt but the sound sure sounds like it.. its just a buzz(I was testing this stuff on a test stand built just to test injectors without any engine in play) so I could flow the injectors at different duty cycles and we tested at different voltages.. you would be really surprised at how they act at low volts
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Re: EFI duty cycle question
[Re: 383man]
#1649484
07/22/14 10:24 PM
07/22/14 10:24 PM
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Joined: Jun 2003
Posts: 52,972 Romeo MI
MR_P_BODY
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Quote:
Heck back in 1989 I was trained on the Dodge Monaco which was not like the old Monaco's as this used a foreign V-6 and it sprayed all injectots all the time everytime an injector fired they all fired. Mopar also did this before they went to ported and sequential injection. The 3.0 v-6 would fire half the injesctors all the time. Which 3 depended on which cyl was fireing. And before that they used throttle body injection as most were 2 barrels and would spray both injectors on every dist signal. Course didn't need a cam sensor on that setup. They finally went to sequential in the early to mid 90's. Mopar also used the 02 just for the fine tuning as the addaptive memory had a larger control over fuel mixture and then once in the right addaptive cell the 02 would fine tune it. Ron
I use to flow the throttle body injector(note singular) back in the beginning of Chrysler injection.. I built the first flow stand at Chrysler years ago for testing injectors... I've flowed a FEW injectors over the years
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Re: EFI duty cycle question
[Re: MR_P_BODY]
#1649485
07/22/14 11:07 PM
07/22/14 11:07 PM
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Joined: Dec 2003
Posts: 22,722 Bitopia
jcc
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You mentioned different spray patterns, is there an injector that sprays at closer to a 90 degree angle,ie downstream, instead of the floor of the intake opposite of the injector?
Reality check, that half the population is smarter then 50% of the people and it's a constantly contested fact.
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