Cobaltpunk

I bought LS2 edit, and have a question about injectors. Currently I have stock l61 injectors. #24 or #26, I cant remember. Anyways, I bought some #32's. I need to figure out the new Injector flow rating. Here is what the LS2 edit user guide says.

"4.3.2 Injector Flow Rate
This table defines the size of the fuel injector. It should be modified only if you replace the Fuel injectors, or change the fuel pressure.

If you change the fuel pressure, you can calculate the new injector constant use this formula:
RatingNew = (sqrt (PressureNew/ PressureOld)) * RatingOld

The table shows the Fuel Flow rate in Grams per second, as a function of the intake manifold MAP in Kpa"

But that formula is for changing fuel pressure, not Injector size. So im rather confused. Right now the Injector constant is 3.41, Help is appreciated. Thanks!

SCcobaltSS

iTrader: (2)

This is how I am understanding. The injectors are in Grams per second instead of lbs/hr so do the conversion 1 g/s = approx. 7.93 lbs/hr.

So you have 32 lbs/hr divide that by 7.93 and you get 4.035 g/s. That should be your constant, 4.035.

Your current rating is 3.41 g/s multiply that by 7.93 and that is 27.04 lbs/hr..

I guess someone else can chime in and see if they get the same thing before you go and change anything but it seems that is the way to do it.

Dirty25RS

I did a simple linearity model

3 examples. since you weren't sure about your current injector size

24Lb 24/3.41=32/x x=4.547
25Lb 25/3.41=32/x x=4.365
26Lb 26/3.41=32/x x=4.197

32lbm/hr=4.032g/s
3.41g/s=27lbm/hr

SCcobaltSS

iTrader: (2)

So your answer is this. 32lbm/hr=4.032g/s and the constant should be 4.032.

Just trying to make it easy for this person to read it, since he seems new to tuning.

Dirty25RS

I'm not giving an answer, just some math.

Its up to him to judge which scenario is correct. Each scenario has assumptions.

I dont know what his stock injector size is.
I dont know what this injector scaling factor represents in the injector pulsewidth equation.

When tuning new fuel injectors scaling is a tweak variable anyways. you tweak it untill everything operates the way it should.

I just got done going from 1200cc/min to 2200cc/min injectors on my Evo and went through this BS....and more.

SCcobaltSS

iTrader: (2)

Ok I see what you mean.

Yah my buddy has a high HP Evo and he tunes. He was saying how he tuned his injectors and it is totally different than how I do for my cobalt.

Dirty25RS

Its different in how the ECU handles the scaling value, but the same in tuning procedure. I have HP Tuners and know how different cobalt tuning is than mitsu/subaru/everyone else.

Cobaltpunk

Sweet, You guys are great. While were on the topic of tuning my car.. hehe. Can you guys give me any tips with spark advance? Or with Power Enrichment, or if there is anything I need to change since I went from stock airbox to Injen CAI. there are so many parameters and tables the the guide doesnt explain.

Dirty25RS

more spark advance, more torque, up to a point. a point you usually can't reach because of knock.

so you put the spark advance at KLSA, knock limited spark advance. Its the value at which you as the tuner make a judgement that the amount of knock is acceptable. sometimes this means no knock.

power, or acceleration enrichment, is the amount of extra fuel to add when a rapid positive change in throttle position is detected. This is to make sure that during tip-in you dont momentarily run lean. I have it set between 1-1.62% of base fuel table enrichment on my evo depending on rpm.

Cobaltpunk

So, I have been turning the advance up more in the higher rpm's and more in the higher loads. Is that a good idea? Also, I did 110% on a section then 115% on another section(inside the first) and It seems pretty good. But I dont really know what to expect with Engine knock. Does it literally sound like knocking?

Dirty25RS

you wont necessarily hear it, its what our knock sensor is for.

timing advance is nothing to **** around with

That "ideal" spark advance changes with rpm and engine load. basically the idea advance that makes the flame from hit the piston at when the piston is at top dead center. If you think of everything in extreme slow motion...you have the piston going upward. the spark plug spars and creates a flame front & pressure wave that radiates outward with a given speed.

you want that flame front to hit the piston when its at top dead center. otherwise you would spin the engine backwards. so at higher rpms you have higher piston speeds, so you need to spark the spark plug earlier than at low engine speeds, but the amount of "charge" in the cylinder also plays a role in how fast the flame speed moves which makes it more complicated than just "more rpm more spark advance"

spark advance is one of those things that makes a tuner a tuner. OEMs spend millions of dollars and hours building fractal models of combustion events to understand things like perfect spark advance, because along with power comes efficiency and fuel economy in this respect. Its not something you can calculate on the back of a napkin. Tuners are experienced individuals who have developed a "feel" for dialing in spark advance.

I suggest reading this book if you want to learn more. Amazon.com: Building & Tuning High-Performance Electronic Fuel Injection (9781884089794): Ben Strader: Books

Cobaltpunk

Thanks for the advice. And btw, If the knock sensor goes off it knocks down to a lower advance table (which I have not touched). But you probably knew that

Dirty25RS

yeah, but all it takes is one bad knock to blow a hole in a piston or cylinder wall. you want to avoid it.

Bika

iTrader: (3)

L61 injectors are 24 lb/hr.

Timing does not always advance with rpm, atleast not in boosted cobalts. if you look at a stock main timing map, you will see the timing actually decreases as rpm and cylinder airmass increases.

Dirty25RS

looking at this hptuner map, across any given cylinder load line it does.

If it doesn't, thats bad. KLSA increases with rpm due to kinematics. If the actual desired timing doesn't increase with it, your getting less and less power and efficiency and more incomplete combustion as rpms rise.

Bika

iTrader: (3)

well yeah, given a constant airload the desired timing will increase...