Anyone know or have a link to the actual Injector Constant formula? Im not talking about the simplified version where you take the current size divided by new size.
I wanna get ahold of the actual formula. I know the formula includes injector flow rate based on the engine size per sec.
----------------------------------------------------------------
www.bradsairsoft.com
Its right at the bottom of the box
Injector Constant: The injector constant in Liters per Gram per Second.
Which means---- the displacement of 1 cylinder in liters divided by injector flow rate in grams/sec.
or for a 2.4 in approx. #s -------- .598 /2.95=
where .598= displacement of one cylinder
and 2.95 = flow rate of injector in g/s which is approx. 23-24 lb/hr
sig not found
No. I know its liters per gram per second. I mean how to find the actual number.
But iv searched and failed. Im working on making a spread sheet to figure it out.
IF PEOPLE CAN POST THEIR STOCK CONSTANT and there STOCK INJECTOR SIZE please do so. I think iv stumbled onto how this number is figured.
----------------------------------------------------------------
www.bradsairsoft.com
19 lb/hr 198cc inj. constant= .2406 i believe
DRIVE HARD OR DONT DRIVE AT ALL!!!
2200 has 19 lb injectors? I thought it had 17 lb injectors.
----------------------------------------------------------------
www.bradsairsoft.com
I dunno, based on the math the constant would be 0.22971 for a 2200 engine with 19 lb injectors. which is close. So maybe im headed to the right path.
----------------------------------------------------------------
www.bradsairsoft.com
CheesyPackerFan wrote:No. I know its liters per gram per second. I mean how to find the actual number.
But iv searched and failed. Im working on making a spread sheet to figure it out.
IF PEOPLE CAN POST THEIR STOCK CONSTANT and there STOCK INJECTOR SIZE please do so. I think iv stumbled onto how this number is figured.
No, I told you exactly how its figured out.
When you are an amateur, "shade tree" "tuner", you refer to injectors in terms of cc/min or lbs/hr.
These refer to the weight or volume of the fuel, which changes with temperature and pressure, which change, compared to time, which does not change. (but in the scope of things weight is a horrible way to measure fuel flow but volume isn't really bad)
When you are an automotive calibration engineer, you refer to injector sizing in grams per second, which exactly defines the mass of the fuel being delivered.
Why is it different? Lets say theoretically you took your car to the moon and it has 24lb/hr injectors on earth. On the moon the weight of 1 hour of fuel flow would be much lower because the lack of gravity means 24lbs is now <1 lb, but the actual mass remains the same either place.
So grams per second is a much more accurate rating. Now the issue is that no one in the aftermarket world seems to use it. Yet if you went to delphi and asked for flow info about your stock injectors, they would give you a grams/sec response.
There is no exact conversion factor that I know of to convert lb/hr or cc/min to g/s.
But to get you in the ballpark,
1 lb/hr is approximately 0.1265 g/s
I haven't ever tried to come up with a conversion factor for cc/min.
sig not found
To the OP, I would take Todd's advice.. He is da' man....
P&P Tuning
420.5whp / 359.8wtq
You figured out complete injector flow rate but im trying to figure out the Injector Constant which includes the engine size inside of the equation.
I have a 98 cavalier with a 2.2L in it. I have 550cc injectors. What is my precise injector constant without knowing the original constant value?
^thats the equation i want to know. You gotta convert lb per hour into grams a second, but i wanted the rest of the formula. I think i figured it out but it seems to be totally differnt from vehicle to vehicle
----------------------------------------------------------------
www.bradsairsoft.com
ok, what iv come up with is this. example... a 2.2L with 19lb injectors.
19lb * 16oz = 304 oz\h * 28.35 = 8618.4 g\h divided by 3600 = 2.394 g\s A= 2.394 g\s
2.2L \ 4 = .55 L per cylinder. B= .55L
so B (.55L) divided by A (2.394 g\s) = injector constant of .229741
I really dont like math... am I doing this right? I made a spreadsheet in excel after hard thinking that does it.
----------------------------------------------------------------
www.bradsairsoft.com
But here is the problem. My car's stock injector constant is 0.25026. If I do all the math for it, it is showing 14lb injectors which cant be right.
----------------------------------------------------------------
www.bradsairsoft.com
The figured injector constant is really a base line for tuning.....as is the flow rate of your injectors....there is % error in both, you have to calculate a number, and go from there. I honestly think you are overthinking the problem.
But protomec is right as far as calculating injector constant.
Ignoring differences in gravity, and differences in fluid temperature your calculation is correct, however it does not take into account the pressure behind the injectors. Making the injectors seem smaller to the ECU makes the ECU hold them open longer, running richer. Welcome to GM ECU's, the S/C flash with the 310cc injectors actually has a smaller injector constant than the 252's that come stock. You also need to take into account the mileage on your injectors (edit: theoretically and ideally, this would be measured in duty cycle vs hours, but most people don't keep that kind of info logged), how clogged they are, opening/closing times, etc. The theoretical flow rate of your injectors certainly is 19lb/hr, but they really don't flow that, especially over their lifetime.
Edited 1 time(s). Last edited Wednesday, June 04, 2008 12:09 PM
4cyltuner.com - Information Source For 4 Cylinder Tuners
Buy stuff from CarCustoms Ebay! Won't be disappointed!
right... I am over thinking the problem. People recomend doing current injector constant * (old flow/new flow). I was trying to think up a new way to do it. Although, after figuring the rest of the math up... the recommend way of doing it gets almost the same answer as the whole equation does, just slight differences.
i dont know. i was just trying to figure it out, but like you said even GM uses the constant to hold injectors open longer durring the reflash. It seems that its lost hope. Too many variables to consider to get a dead on answer.
Sadly, I bought 550 cc injectors from someone on Jbody, but they are comming up way short of that. Based on the math i should ahve to use constant around .080800 or so. But when my car was non turbo and running on gas i used near .10200 to get it to run right.
ON turbo and E85 i am using a constant of .14251. That comes up to be .11012 on regular gas which would be serious overfuel at an idle. If fuel pressure is at 42, Does that mean that i probally got jipped and got a 350cc-450cc injector instead of 550cc? Not that it matters in the end, either is plenty for what i am doing.
----------------------------------------------------------------
www.bradsairsoft.com
I think you are throwing to much stuff here at once....
#1, did you have the 550cc injectors on NA and tune for them on pump gas??
#2, what are you basing "running right" off of? A/F ratio??
#3, what does the rest of your tune look like?? There is more than injector constant that deals with fuel...
#4, what brand injectors....can you cross reference a part #??
#5, what all are you doing to run E-85?
I am running 500cc on pump gas, with little-no problems from them....50cc should not make that much of a difference, but my injector constant is majorly different than yours is...
When I first started tuning my car I was thinking the same thing you are, but figured out that was not my problem.
SHHHH!!!!
dont tell them my secrets...lol
Well, the rest of the VE tables are near stock (except near boost values)and have been tweaked slightly based on A\F ratio. I Am running a Ratio of about 12.3 to 1 full throttle with a commanded ratio of 11.5 to 1 after the RPM multiplier.
Fuel pressure is regulated by vac\boost. It idles at around 40 - 42 psi and reaches 58 - 60 psi under boost. Brand of injectors are RC. No part number availible that i can.. might have to pull one off to double check but i never remember a part number.
My injector constant has been changed to allow approximately 30 percent more fuel. But like I said it used to be around 0.11012 with the turbo on pump gas, and around 0.10200 when it was NA on pump gas.
----------------------------------------------------------------
www.bradsairsoft.com
CheesyPackerFan wrote:You figured out complete injector flow rate but im trying to figure out the Injector Constant which includes the engine size inside of the equation.
Yeah, it does take into account engine size, you are correct.
But do you understand that the word displacement is a term for "engine size"?
And from that "displacement of one cylinder in liters" would mean the exact measurment of 1/4 "engine size" for a 4 cylinder engine!
CheesyPackerFan wrote:^thats the equation i want to know. You gotta convert lb per hour into grams a second, but i wanted the rest of the formula. I think i figured it out but it seems to be totally differnt from vehicle to vehicle
-displacement of 1 cylinder in liters / injector flow rate in grams/sec-
Since I don't know the bore and stroke of a 2200, I will simplify the example by using 2.2 liters as its displacement (it isn't exactly 2.2 liters at all in reality).
2.2 / 4 = .55 liter ----- aka 1 cylinder of displacement in liters
and
550cc = about 52.38lb/hr or 6.6 g/s
so....
.55 / 6.6 = .0833333
for comparison
just for S&Gs 19lb/hr is about 2.34 g/s, pretty much the # you got in your calculation.
.55 / 2.34 = .2350473
How close is that to your stock #? Remember that we did not use exact #s, only general guesses (2.2 and 2.34), so it won't be the exact #.
Shifted wrote: Ignoring differences in gravity, and differences in fluid temperature your calculation is correct, however it does not take into account the pressure behind the injectors.
Yes it does, if you are using the correct # for g/s it will already include the use of the correct pressure to flow that #.
If you plan on changing pressure, then you will need to get the correct g/s measurment for the injector at the new pressure.
Shifted wrote: Making the injectors seem smaller to the ECU makes the ECU hold them open longer, running richer. Welcome to GM ECU's,
Yes, of course it works that way. If you cut the injector size in half you need to open them twice as long to get the same amount of fuel. Welcome to ALL OEM ECU's.
Shifted wrote:the S/C flash with the 310cc injectors actually has a smaller injector constant than the 252's that come stock.
In normal instances the 310s would always have a smaller constant than 252s in the same engine, just as you stated.
But the 2.4 sc flash has a larger constant than the stock 2.4 with smaller injectors.
This is because the engineers that calibrated the engine used a virtual displacement that is based on 2.4 airflow under boost equated to the displacement of an NA engine that would swallow the same amount of air.
My suggestion is that you talk to someone who works for the company who calibrated the 2.4sc package for GM to get some accurate info how and why things were done for it.
Shifted wrote: You also need to take into account the mileage on your injectors (edit: theoretically and ideally, this would be measured in duty cycle vs hours, but most people don't keep that kind of info logged),
No you don't! No one does. The OEMs definitely don't do that.
Edited 3 time(s). Last edited Wednesday, June 04, 2008 2:48 PM
sig not found
protomec wrote:
2.2 / 4 = .55 liter ----- aka 1 cylinder of displacement in liters
and
550cc = about 52.38lb/hr or 6.6 g/s
so....
.55 / 6.6 = .0833333
for comparison
just for S&Gs 19lb/hr is about 2.34 g/s, pretty much the # you got in your calculation.
.55 / 2.34 = .2350473
How close is that to your stock #? Remember that we did not use exact #s, only general guesses (2.2 and 2.34), so it won't be the exact #.
Yes, I figured all that into the above equation by me. Thats not really that close to stock injector constant. Stock is 0.25026. If i used the figured number as a replacement for the stock number, the car would run lean. But the numbers are close enough that the car would still run. I just dont understand why the math doesnt add up to their number. Obviously they tinkered with it to get the injectors to flow what they wanted. Thats my theory.
----------------------------------------------------------------
www.bradsairsoft.com
this is why the first modification should be a stand alone...
we did not get a very flexible ecu from GM.
DaFlyinSkwir(LS61) /PJ/ OEM+ wrote:this is why the first modification should be a stand alone...
we did not get a very flexible ecu from GM.
Imagine how much easier this could be if there was a "skin" on HPT that only showed you what we care about. Say you want to change the timing at 5500rpm at WOT, make one change and HPT makes changes to all the tables that are required. New injectors, punch in the new size and it changes the constant, and scales the VE tables where neccesary.
HPT opened up a whole new world for GM FWD performance, but it is still very limited in what you can do (boost tuning via MAP), and how easy it is to do it.
15.3 @ 89.97mph - '01 SFGT
'98 Acura 1.6EL Sport 5M Y7/Y8 mini me
Its not really meant for FWD J-bodys in the start of it. It was just ment for the V8 LT and LS series stuff (i dont knw much about V8's
)
----------------------------------------------------------------
www.bradsairsoft.com
