Finally I get the true result for the injector flow test: My stock Cobalt SS/SC injector filled a 95 cc graduated cylinder in 30 seconds flat, BUT THE DUTY CYCLE OF THE TEST WAS 50% (it was a dynamic test). So it means that stock injector flow is 380 cc/min @ 43,5 PSI ! (380 cc/min divided by 10.5 = 36 lb/hr @ 43,5 PSI).

Don't forget that the stock LSJ fuel pressure runs somewhere between 50 and 62 PSI (highest numbers at WOT). For those who want to make some calculations, since this car is a forced induction one, you MUST use the differential pressure (I mean if there is 62 PSI in the fuel rail at WOT with the stock supercharger pulley running at 12 PSI, the differential pressure through the injectors (bone stock) to be used for calculation is 62-12 = 50 PSI).

Some notice that the fuel rail pressure can increase up to 70 PSI when running a 2.9" pulley, giving a differential pressure of 55 PSI.

I have myself done a lot of calculation, the Brake Specific Fuel Consumption (BSFC) of the car seems to be 0,585. Stock maximum injector duty cycle seems to be around 90 %.

Remember that the SS averages 210 WHP stock (4th gear dynojet); plus the 14-15 % drivetrain loss, that gives roughly a 240 SAE BHP number to be used in the formula.

As an example, here is the injector flow calculation for the stock SS.

240BHP x 0,585 (BSFC) / (4 (number of injector) * 0,9 (90% duty cycle)) = 410 cc/min (at a 50 PSI differential pressure).

To know how they flows at the standard rate of 3 BAR (43,5 PSI), you must multilply 410 cc/min by the square root of (43,5 / 50). The results gives 380 cc / min (36,2 lb/hr) @ 43,5 PSI, as I saw on the flow bench.

Now I am in the process of choosing the right injectors for my car, since the 38 lb/hr I had purchased are too small.

Hope this help.

Have a nice day !

 

i though or stockers were 35 lb injectors. or am i way off.
edit: and arent 195 cc kinda small?

 

Deleted the post : There is something that doesn't match.

 

Deleted the post : There is something that doesn't match.

 

You guys must have been really good in school. I feel really stupid when I read this thread.

 

It's good info, something I'd like to learn, but I'm pretty much duhhhhhhhhh on the whole thing right now too.

 

Obvious;y no one knows but I wonder how much bigger are the injectors in the Stage Upgrades as opposed to the stockers

 

Yeah thats like only enough to handle 130 HP max. Something is up.

 

Deleted the post : There is something that doesn't match.

 

yeah I used .50 for my calculation

 

Get the right answer from them yet Jmc007???

 

i have a friend that works at 1 of the plants that makes the s/c injectors , and they are 35-36lb injectors

i just put a set on my s/c cav , and took off my 32lb and the car now finially runs rich , lol

 

isn't the stage 1 upgrade 36lb injectors???

 

No answer yet unfortunately about the stockers. About the stage 1 injectors, they are 42,4 lb/hr, but they didn't mention at which pressure. It should be the run pressure of 55 PSI or so, but it can't be too ...

 

Any idea of the true specs ? 35 OR 36 lb / hr ? At 43,5 or 55 or 58 PSI ? ... ???

 

the pressure they are rated at is the working pressure for your motors , im not sure what it is

they way they do the injectors as he explaned it to me , the 35-36 takes into consideration of the +- factors

i think CC rated is 360 or 370

the fuel pressure on my 32lb i was running about 60psi , and with the 2.0 s/c's i had to drop to 30psi , to keep from running to rich , i saw it dip into the 9 range on my wide band o2

but that extra room will allow me to put alot smaller pulley than im currently running

 

I wonder if the Saab 2.0 Fuel Injectors will work??? The one that made the 210hp they had 2 different 2.0's in the 9-3 one made like 186hp the other made 210. I think the turbo's were different andyways maybe there injectors are bigger?

 

Why not strap on a fuel pressure guage and go for a drive? I'm pretty sure you can get one at Advance.

 

yeah

 

So I was reading Super Chevy tonight, and found a pretty good article on fuel pumps/injectors and such. Heres some formula they gave on how to determine the size injectors that you need.

HP * BSFC = pounds of gas
pounds of gas/number injectors = pounds per hour @ 100% duty cycle

SO.....

205 * .75 (given BSFC for supercharged motor) = 153.75 lbs fuel
153.75/4 = 38 pounds/hr @ 100% duty cycle, or, 47.5 lbs/hr @ 80% duty cycle

250 * .75 = 187.5 lbs fuel
187.5/4 = 46 lbs/hr @ 100%, or, 58 lbs/hr @ 80% duty cycle

300 * .75 = 225 lbs fuel
225/4 = 56 lbs/hr @ 100%, or, 70 lbs/hr @ 80% duty cycle

WOW! Surely I'm missing something here. Assuming you do have 205 hp stock, this means you need 38 lb injectors. And at 300hp you will need 56 lb injectors. Not even considering the duty cycle.

 

The BSFC you used is too high !

 

Oh really? Thats what they had listed for supercharged applications. What sounds more reasonable to you?

They didn't really explain how they got that number, so I dunno to much about that.

 

BSFC for a supercharged application is 0.55 to 0.65. Some uses 0.57.

 

I finally had the answer, see the corrected statements in the post #1.

 

the 2.0 s/c uses the same injectors as the saab 2.0T(high boost turbo)