It is generally accepted that you are supposed to have the "right size" injector for your engine and all of that, and with as much information available with a simple google search, you can pretty much look up the size that you need, based on the rest of your build.

But I was wondering,
would it be better to have a smaller injector with a longer cycle
OR
the next size up injector, with a shorter cycle?


I'm talking in general terms

but if you need an engine/set up, I'm working on a 300zx, NA, VG30DE. Going to have a good stack of bolt ons and some decent tuning. Looking to make power, but also MPG since it is going to be daily driven.
It is going to need new injectors. Debating on if it is worth doing all of the work (and money) for the updated fuel rail and run either the stock size 270 injectors or step up to the 370 injectors.
It isn't going to "need" the extra fuel, but I'm wondering if a short burst of fuel would be better than a longer burst, equaling the same amount of fuel.

 

i'd say a short burst of fuel, would be better then a longer burst equaling the same amount. but i dont have any data to back that up.

 

Almost forgot I posted this thread.

Yeah, that's what I would assume too. Which would make the larger injectors a better choice.

But then again, I was reading over on a hypermiler forum and one guy got all kinds of crazy and set up a custom fuel rail that had two injectors for each cylinder. He used the smallest injectors he could find because he felt that the smaller injector atomized the fuel better, which makes for a more efficient burn.
he didn't have much scientific data to back that claim up, but it does make some sense.

 

argeed that the better the fuel is , atomized, the more effcient the burn, sounds like someone need to do some kinda of bench test, to see if you can still get the same atomization, from a larger injector with a short burst vs the smaller injector with a longer burst.


but i bet his mpg was amazing using that two injector setup!

 

Isn't atomization based on the % of the duty cycle of the injector and the pressure imparted on said injector. Think efficiency of the injector. Empire my friend this question is so you. You'll have tons of info to be searching for on this topic. Be honest, wasn't this a rehtorical question...you didn't really expect and answer did you? Hence, you forgot you had posted it. LoL.

 

Not sure how to effectively set up a bench test considering it wouldn't be something you could be able to see with the naked eye... or at least, you shouldn't be able to see it.

the main point between that injector set up was to be able to turn one set off when it wasn't needed. forcing it to run more lean than the ecu would want to go.
it was a really interesting concept. Run as lean as possible, but go slow. and then flip a switch, double the fuel, double the power, when it is needed.
He also ran a water mist injection system to keep temps under control.

lol
you know me too well.
i was actually hoping for some of the tuners/more experienced than myself to chime in.
But I know many of them don't frequent the forums much any more.

it has been interesting doing the research into this. Lots of conflicting info. Hoping some of the engineering students at FSU can produce some decent info.

 

It is a shame, isn't it. There is a chance some more experienced builder might wander through...but that chance is very slim. :\

 

IMO: The type of injector is more important than anything, besides having enough flow to support your power goals. All injectors are not created equal. Brand A will have different atomization quality than brand B. Duty cycle shouldn't change that. You may also want to look into injector deadtime. This is the only thing that will effect idle and duty cycle. If your using a slow injector, The duty cycle could be maxxed before the flow rate is. It also makes idling a big injector a real pita. There are lots of info on this on ID, RC, and moran performance websites. I also feel that the moran injectors are the greatest thing to hit the injector market since the dawn of electronic injectors. Fully billet design, patented atomization design, and sizes from 100lb/hr-500lb/hr(that's 5000+cc/min no typo)

 

Its not going to make a noticeable difference till you take it to the extremes.

The problem with giant injectors is that no matter how much you are injecting it still has to go in through the same spot, in the same time frame. So when you get up to ~1000cc/min you start to get more of a full-on water hose effect than a "mist" setting on a sprayer. The spray pattern itself tends to be more uniform when injecting through a lesser-flowing unit. This creates problems with idle quality as well. Say you need 1cc of fuel per rev per cyl to idle. Your factory 250cc injector would be open for .004 seconds, where your 1000cc is open for only .001 seconds. Any variance in voltage, or fuel pressure, whatever, is more likely to drastically affect the 1000cc injector for its entire .001 second duty cycle, rather than the 250cc injector having the extra .003 seconds to stay open and slowly and steadily inject...


You just need the right size, quality injectors and a good tune. Keep em below 80% duty cycle for safety and longevity..Ive had no problem tuning for a good idle on 750+cc injectors on a 2.0...

I used to run my 2.4L 9:1 turbo Eclipse @ 15.7:1 AFR w/ 40 degrees advance while cruising....could get like 36mpg outta that bitch on the highway.

 

Duty cycle is important when you are building a car that will use the injector to its upper limits. When you are talking about this kind of power 80-85% duty cycle is preferred as to not over work the injector. With that said I have increased the duty cycle to over 100% on my setup before, although it is not advised by anybody. With a NA VG I would say the 370cc injectors would be definitely all you need, as long as you are going to tune it. Unless you are going to spray the car you will never get to the upper threshold of 370cc injectors with an NA VG. Long cycle or short cycle will make zero difference where your build is concerned. Either injector with a tune will idle effectively and operate well within its designed capacity.