If Im Running 13PSI Of Boost.....
09-02-2011, 06:20 PM
#14
6th Gear Member
Join Date: Jan 2007
Location: MI
Posts: 5,884
Sash i'm really surprised you had a lot of room left in those 42's with your power. Did Lidio say at what percent duty they were working at?
09-02-2011, 07:40 PM
#16
2nd Gear Member
Join Date: Nov 2004
Location: MI
Posts: 355
rod, that dude Chris is making 500+ with 39....
09-02-2011, 08:36 PM
#17
6th Gear Member
Join Date: Jan 2007
Location: MI
Posts: 5,884
Yeah now that you mention Chris's ride it kind of all makes sense when i think about it. I forgot for a moment that you have a 5.0 stroker motor, and not the regular 4.6. That right there helps to explain your scenario as well.
09-02-2011, 09:02 PM
#18
Underboss
Join Date: Jan 2006
Location: Helaware
Posts: 20,273
09-03-2011, 12:34 PM
#19
6th Gear Member
Join Date: Feb 2007
Location: South FL
Posts: 8,540
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.
09-04-2011, 10:42 PM
#20
4th Gear Member
Join Date: May 2005
Location: New York
Posts: 1,648
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.
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.