39# injectors good to what rating?

[fromadig91]

Tossing a pulley (2.76 with idlers) on the 04 Cobra next week (hopefully, if all goes well) and was wondering when exactly are the stock 39# injectors not ample for my fuel needs? When I do upgrade them is it best to go sraight for the 60#?

Only mods I currently have is a magnaflow cat back and soon to be JLT Cold air intake (just ordered )

 

[Mikie]

I think its right around 500 rwhp that they are done.
Im curious as to what the factory GT pump and your Cobra pumps are good to?
I went ahead and got the 60s at a good deal, now I need the pump upgraded to go well beyond the 500 mark. ( Heads and cams )

 

[fromadig91]

I thought 500 HP was the mark for upgrade but I wasn't positive, and Yeah i'm figuring about 450 ish outta the pulley and tune

 

[Stan Weiss]

There is no one answer fits all. Based on how efficient your engine is the more HP per pound of fuel it will make. 8 - 39# injectors at 90% Duty Cycle.

Equation       (39 * 8 * .9) / bsfc
                   bsfc         Flywheel HP
                   0.4000     702
                   0.4200     668.57
                   0.4400     638.18
                   0.4600     610.43
                   0.4800     585
                   0.5000     561.6
                   0.5200     540
                   0.5400     520
                   0.5600     501.43
                   0.5800     484.14
                   0.6000     468
                   0.6200     452.9
                   0.6400     438.75
                   0.6600     425.45
                   0.6800     412.94

 

[fromadig91]

I wish I could make sense of that chart ....could you gimmie a break down?

I also appreciate the responses I have gotten so far, thanks guys

 

[Stan Weiss]

An N/A engine may have a BSFC of around .4. That means it will make 1 HP from each .4 pound of fuel per hour. While a boosted engine is not as effcient and may be around .5 pound of fuel per hour. 8 - 39# injectors at 90% Duty Cycle is 280.8 lbs /hr of fuel.

The more efficient your supercharge is the less HP it will take to compress the air and the more HP that will show at the flywheel.

 

[billfisher]

(fuel pressure)

 

[Stan Weiss]

fuel pressure - boost pressure = pressure differential. Are you running a boost referenced fuel pressure regulator?