foru2nv4

is 30lbs injectors enough for the supercharger or do I go bigger? The car doesnt hesitated or anything. Im figurin car around 500 HP engine. FYI, I have a series IV saleen supercharger with a smaller pulley upgraded to 75mm accufab TB put in 4.10 gears JLT true cold air gatorback belt supercharger came with 30lbs injectors and saleen programmed at the saleen facility.

school boy

if your car is putting down 500fwhp, then you need 42lb or 60lb injectors

zero2005

13lbs of boost i'd recommend 60's, and a better fuel system. i'm assuming your running a GT? you dont have a vehicle listed or anything in your sig. also, with that high of a boost, your lookin at a very limited time span on that block if your running stock internals on a GT, expect to throw a rod, or take off alot of "wear time" before something else breaks if you drive it hard at all. not saying its not possible, just saying that 13lbs is alot of boost to throw at a stock block...

dunno how good saleen tunes are, but with 30lb injectors, i'd find it REAL hard to believe if your making any higher than 380 at the wheel... my guess is with 30lb injectors, they're pulling ALOT of timing... which in turn means less hp...

dwtjr3

i would say 60's. And are you still stock block? Thats a good amount of boost, hope its not your dd?

mrtstang

60's would be a better choice IMO. You say you're at 500 at the engine?? If that's right that puts you at maybe 420-430 rwhp. 42's would be enough, but at 500 rwhp with a blower it might be too much

cliffyk

42 lb/h injectors (at 40 psi fuel differential) would be at 95% duty cycle at 530 fwHP or so, far too close to going static and up into the danger zone.

As mrtstang said at 500 rwHP they will not cut it (at 40 psi fuel pressure)...

scottybaccus

Cliffy beat me to the tech part, but a good rule of thumb that's based in physics is 1/2 lb/hr per HP. It takes a half pound of fuel (similar to gasoline), per hour, for each HP, so that can literally translate into 8 x 30 lb = 240 lb/hr, divided by .5 lb = 480 HP. Now that is with zero margin, so if you want to avoid lean conditions up high with variations in fuel pressure or added air, etc., you need some safety margin.
At 8 x 42 lb, you have fuel for 672 HP at the max rating of the injectors. Aim for about 75% duty cycle and you get 672 x .75 = 504 HP. A little room for error, depending on how safe you feel. You might have more capacity at higher fuel pressures, as Cliffy was eluding to, but 30 lb is small. 60 lb injectors should support something like 700 real HP safely.
Somebody with a book of specs is sure to come in and tweak my numbers, but this is a safe rule of thumb.

cliffyk

Here are a couple formulas for making "starting point" sort of design decisions:

Basic formula for flywheel HP:



where:
HPmax = flywheel horsepower;
lb/h = actual injector capacity at the design pressure differential;
Dutycycle = maximum desired duty cycle as a decimal number;
Cyls = number of cylinders/injectors;
BSFC = Brake Specific Fuel Consumption--rule of thumb values = 0.5 lb/h for n/a and 0.6 lb/h for f/i;


Calculate injector capacity for altered fuel pressure differentials:



where it is spelled out pretty clearly.

FRPP injectors are rated at 39.15 psi, so the rating in their specs should be used with an unmodified returnless fuel system.

If you increase the fuel pressure then use 39.15 as the "oldPSI".

With return type systems things get a bit more complex because the differential fuel pressure across the injector becomes the rail pressure minus the manifold pressure.

So while not in boost it is the rail pressure minus the negative pressure (vacuum) in the manifold--E.g. with 20 inHg vaccum (-9.8 psi) and 30 psi rail pressure the differential across the injector is 30 - (-9.8) = 39.8 psi.

In boost at 10 psi manifold pressure and 30 psi at the fuel rail the drop across the injector is only 30 - 10, or 20 psi. Without boosting the rail pressure your 42 lb/h injector just became a 30 lb/h injector;

(20/39.15)^0.5 * 42 = 30.0

This is why vacuum/boost controlled AFPRs are common on return type systems.

uberstang1

Don't feed the troll.

Sash

my car made 463 with 42 and they have plenty more to support,eater 42 or 60,Ill say go for 60 so you have more room to grow.
good luck.