im still confused on what injectors i might need...right now i have accel 30#.... i was hoping to run around 15-18psi...what would be the ideal injectors for that...or if someone could give me the formula and guide me through it.... i have a 14b and warbro 255.... what will i max out at with the 30#....thanks in advance
doug

well 30lbers are too low in fuel flow pushing 15-18psi. here's an example:
est HP at 15psi=300-320crankhp, let's use 300hp.
300 x .525 x 10.5 / 4= 413.4375cc of fuel volume.
now duty cycle of 85% is 413.438/.85= 486.3976.

so now we're gonna see why 30lb or 315cc injectors are too low...

(486.3976/315)^2(43.5)+15= 118.717! way over 100psi.

so invest in bigger injectors. with 440cc injectors is a little safer running at that psi level. so don't risk using those injectors running that much boost.

would 370cc injectors be able to run 15 lbs? if not what is the max at 370cc, i see the formula but am not sure at what all the values represent.

im with him^^^ how do i use the formula?...what psi can i run with the 30#....what about 390's..... i thought the 440s were shitty idle situations though?..i have a sfmu if that helps...thanks for the input though....
doug

yo im looking into buying injectors too.. guys with a stage 2, what injectors you guys have? i'm running the stockers but i need bigger ones just to be on the safe side.

i think youd be good with my 30#.... i might be selling them soon if i find out what i actually need
doug

good post. i was about to post something like this too. what is that max for each size injector? 390, 415, 440...


New/More Mods Comming... New 1/4 Times In March/April

ok....now im thinking maybe ill just get some dsm 450cc and do the resistor pack thing...anyone help with that? how about maximum boost with those/idle? thanks
doug

Originally posted by lickscissors
ok....now im thinking maybe ill just get some dsm 450cc and do the resistor pack thing...anyone help with that? how about maximum boost with those/idle? thanks doug

I got all of the above... 450CC DSm injectors with a custom resistor pack.. currently running around 19psi...
They idle pretty nice... kinda meaty sounding... stock ECU does a fine job of idling them. Stays in open loop at idle no prob.

well 370cc will give you 90psi of max pressure using a 4:1 disk(since it's the lowest). another thing you can do is lower the fuel pressure 10psi and it'll give you a less amount of max pressure. then tune from there. atleast it's more safer to push 15psi, but i would still buy 440cc just to be safe.

i too, was about to buy RC eng. 440cc injectors when some1 pointed out that hahn sells accel 415cc injectors for 60 bucks a piece, when the RC's were like 85 a piece so im just gonna go with the 415's. will 415's be good for 15lbs???????


Mods:
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accel 415 for only 60 bucks a piece? Looks like I need to make a call.

It's not about how much boost an injector can support. It's how much horsepower it can support. That's the end game. You'll need just as much fuel per cylinder if you can make 300hp on 6 psi as you could 300 hp on 15psi (of course there are other factors but assuming everything else is constant).

EDIT: YES I KNOW I'M OVER SIMPLIFYING! I'm just trying to get a point across.

ok mr. slick...your way seems like what i want to do...cheap and runs good.... i might be able to get a hold of a set of 2gt injectors for free...can you give me some insight, maybe a mini write-up on the resistor pack?....so i should be able to run at least 18psi with those injectors? youre running 19psi with a 16g, so i would think 18 with a 14b would be fine...do you think i can run any more}( .... thanks
doug

here are a few links i have collected along the way in my pursuit of grasping injector knowledge... PS-anyone know the cc/hr on the accel 40lbs? is it about 420cc/hr?

http://www.autospeed.com/cms/article.html?&A=0102&P=1
http://www.2gnt.com/www/corbin/chooseinj.html
http://www.2gnt.com/www/corbin/example.html
http://www.rceng.com/technical.htm#WORKSHEET

:sigh:

To convert lb/hr to cc/min : lb/hr * 10.5 = cc/min

If you need cc/hr (why the hell would you?) : cc/min * 60min/hr = cc/hr

hmm.....im getting confused....i used the equations with an approximate hp of 300...and im getting 555 injector sizes??? i dont think thats right...anyways... im leading towards the 450 dsm injectors..... can i get away with about 18-20 psi with that?...mr. slick, can you guide me through the injector resistor pack? is there a write up....thanks
doug

Originally posted by lickscissors
hmm.....im getting confused....i used the equations with an approximate hp of 300...and im getting 555 injector sizes??? i dont think thats right...anyways...

Ok, I'm going to try this again to set everyone straight. The flow rate of the injector has NOTHING to do with the amount of boost you can run. The more air you have, the more fuel you need to combust it safely. The more air you have the more power you can generate. See I could run NA but as long as I draw enough air into the combustion chamber I would need the proper amount of fuel injected to be able to combust the mixture safely. So boost has NOTHING to do with it. More air, more fuel, bigger boom.

Anyway, back to the question at hand. I honestly don't know which equations you used but I think I have an idea. The flaw with your assumed is after completing those calculation it's assuming that to support 300 hp you need 555cc/min (I actually got 595cc/min when I did the calc but we probably used different BSFC and/or max duty cycles) at 43.5PSI. That's the kicker ... it's all assuming 43.5psi of fuel pressure. You won't be using just 43.5 psi of fuel pressure (hell stock we run 52psi of fuel pressure).

Ok now that we know what the problem was lets take it a step further. Say we are using 440cc/min injectors. I'm going to use the numbers from my calculations just for this example but you can do whatever. When we are trying to produce 300hp we need 595cc/min injectors at 43.5psi. We can make smaller injectors act like bigger injectors by increasing the FP behind them (once you get to a FP that is just too insanely high the injector efficiency will go down plus other crap). So using all the equations (look at RC engineering's site) for figuring out injector flow rates we can make the 440cc/min injectors flow the same amount of fuel as teh 595cc/min injectors @43.5 psi if the 440cc/min injectors have 78.5psi of fuel pressure. From there figure out what boost pressure you want to achieve that power at and figure your rise rate accordingly.

Remember that most injectors are rated at 43.5psi to get their specified flow rates. If it was the only amount they an injector could flow our 235cc/min injectors could never see above 120hp in a turbocharge application. This is alot of information to digest but you guys need to understand that there is no DIRECT relationship between injector size and max boost pressure. There are a lot more factors in between.

ok, thats making some sense now....i figured out there was no relation to boost and fuel....thats why i was estimating around 300hp.... now the 43.5 fuel pressure that they are always using, and your 73 fuel pressure you said i should run with 440s, is that min/max pressure?? im not completly clear on how to set up the fuel system..i have a sfmu with what ive been told has the disk for 30# injectors....i would think id need to change the disk....now how do i set the limits on the fuel pressure (min..max).... everything else is going pretty well, except the fuel... again, does anyone know how to make the resistor pack for the 450s? what years do these injectors come off of? thanks again avenger!
doug

bump

Hi guys,

I've been real busy the last couple of days with some serious personal shit going on with the family... so I don't have much time right now. I'll see if I ca come on later tonight and snwer your questions...

Originally posted by lickscissors
ok, thats making some sense now....i figured out there was no relation to boost and fuel....thats why i was estimating around 300hp.... now the 43.5 fuel pressure that they are always using, and your 73 fuel pressure you said i should run with 440s, is that min/max pressure??

The 73 psi is most likely a max pressure at 15-20 psi of boost. But really, it's hard to say. All anyone can do is approximate. EVERYONE needs to tune their own cars, with their own set of very individual attributes. The bottom line is plug in your HP approximations, find out how much fuel is needed at a given boost level and choose your own injector. But yes, it's fairly well accepted that 440's can do the job up to about about 300HP with an adjustable FMU. Once anyone has their injectors pushing more than 85-90 psi of FP, it's time to go with a bigger fuel injector.

Originally posted by lickscissors
im not completly clear on how to set up the fuel system..i have a sfmu with what ive been told has the disk for 30# injectors....i would think id need to change the disk....now how do i set the limits on the fuel pressure (min..max).... everything else is going pretty well, except the fuel... again, does anyone know how to make the resistor pack for the 450s?

Every stock turbo 4g63 DSM has a resistor pack. I don't think anyone has precisely set out the instructions on how to apply it to our 2GNT's yet.

Originally posted by lickscissorswhat years do these injectors come off of?

90-99 turbo DSM's, except a/t 90-94 turbo DSM's.

ok...i guess when it comes to that point ill ask for some specific help.... what disk will i need in the sfmu for 450's....thanks
doug

Originally posted by lickscissors
.... now the 43.5 fuel pressure that they are always using, and your 73 fuel pressure you said i should run with 440s, is that min/max pressure?? im not completly clear on how to set up the fuel system..

The trick is to set the idle(with vac) or static(without vac) fuel pressure in such a way so the engine has the same(or about the same) amount of fuel as it currently does with the stock fuel pressure and injectors. You can compare the overall HP rating of the injector/f-pressure setup to get a good idea of what it new idle fuel pressure should be. In this case, lets say that our stock static pressure is 50. I'm also assuming a BSFC of 52.5%. At that pressure the stock injectors flow 24 lbs/hr. Since the pressure is higher that what they are rated for it flows more that what its rated for. There is an equation, but I don't want to get caught up in that right here. So if our stock injectors flow 24 lbs/hr, we'd have to use a idle pressure of 15 or so to mimic that flow rate with the big 440s. The pressure is much lower than what they are rated for, so they will flow much less. Again, the math involved is buried in the links that people have already provided.

Once you establish a static or idle fuel pressure you can figure out what your fuel pressure should be at maximum boost. For boost, I'm going to assume a BSFC of 60%. You have to know how much HP you think you'll be making - In this case we'll say 300. You also have to know how much boost you'll be using - In this case we'll say 18 psig. With that setup a 4:1 rise rate would put you right at 300hp worth of fuel at 85% duty cycle on the injectors when you hit max boost. Your fuel pressure will be 87.

You don't have to be exactly at 15psig idle and 87psig max boost. Its an estimate based on a ton of formulas. I use spreadsheets sometimes and sometimes I use a half finished java app that I built to help figure this stuff out. Corbins articles about MFI and choosing injectors are real good. There are plenty of articles on how fuel pressure effects fuel flow, but his stuff on how boost pressure affects injector output is very important for a high(greater than 1) rising rate system like this. Sorry I can't tell you what disk that is or what spring to use, but it shouldn't be too far off - theoretically.


95 Eclipse RS : 5 speed
15.7 @ 87.9mph
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thanks, that helped alot.... so i should roughly start around with 450s at 15 psi at idle and around 87 at max boost?...then i can tune from there correct?... i have a warbro 255, this should be able to handle this correct?... now all i need to know is if i have to change my sfmu disk, and how to install 450s...thanks again
doug