Blown353
03-05-2005, 11:30 PM
OK guys, here's my dilemma and I'm hoping someone can offer advice. My car as of now is maxing out my 52 lb/hr fuel injectors at 5600 rpm with the throttle 90% open. Base fuel pressure is 42 psi, and the regulator is boost referenced; at 5600 rpm my supercharger is making about 12 psi of boost and fuel system pressure is at 54 psi. I haven't been able to run the engine up to my typical 6600-6750 rpm yet because it was going lean as the injectors went static, but I'm expecting to see about 15-16 psi of boost.
Before I go to the effort to swap injectors, I flow tested my SX fuel pump this afternoon. Looks like I'm nearly out of fuel pump as well as injector. To be on the conservative side, I tested the pump at 60 psi fuel pressure. My pump is putting out just under 500 lbs/hr at 60 psi, and just under 600 lbs/hr at 50 psi.
Now, 8 each 52 lb/hr injectors at 60 psi can flow 488 lbs/hr when static. So bigger injectors alone may not cure my problem, as I'm nearly at the limit of the fuel pump given the current configuration of the system. If I simply go to larger injectors I will run out of fuel pump before I run out of injector and I'll likely still go lean.
However, knowing that fuel flow will increase if I drop the pressure, I'm thinking of going with 75 or 83 lb/hr injectors but dropping the static fuel pressure down to about 35 psi; the lower pressure willl increase the flow out of the pump and it will no longer be a limitation. The lower pressure should also keep the injector pulsewidth at idle and cruise a bit higher, which may make things even smoother at cruise and idle since the computer will have more control over the injectors with the longer pulsewidth. If I lower static pressure to say 35 psi (so the system will only see ~50 psi under full boost) the fuel pump picks up an additional 100 lb/hr additional flow, and based on the math the 75 lb/hr injectors at 50 psi should still flow more than enough to support the power I'm making without going static.
Finally, here's the question: I just don't know how low I can safely drop the pressure without having negative effects on the spray pattern. Any advice here?
Worst case, I guess I can go to a larger pump, dual pumps, or get a "volt booster box" to run the fuel pump at 16 volts, but IMO the best/simplest way is to go a bit bigger on the injectors and drop the fuel pressure-- I just need to know how low I can go without negatively affecting the spray pattern.
Troy
Before I go to the effort to swap injectors, I flow tested my SX fuel pump this afternoon. Looks like I'm nearly out of fuel pump as well as injector. To be on the conservative side, I tested the pump at 60 psi fuel pressure. My pump is putting out just under 500 lbs/hr at 60 psi, and just under 600 lbs/hr at 50 psi.
Now, 8 each 52 lb/hr injectors at 60 psi can flow 488 lbs/hr when static. So bigger injectors alone may not cure my problem, as I'm nearly at the limit of the fuel pump given the current configuration of the system. If I simply go to larger injectors I will run out of fuel pump before I run out of injector and I'll likely still go lean.
However, knowing that fuel flow will increase if I drop the pressure, I'm thinking of going with 75 or 83 lb/hr injectors but dropping the static fuel pressure down to about 35 psi; the lower pressure willl increase the flow out of the pump and it will no longer be a limitation. The lower pressure should also keep the injector pulsewidth at idle and cruise a bit higher, which may make things even smoother at cruise and idle since the computer will have more control over the injectors with the longer pulsewidth. If I lower static pressure to say 35 psi (so the system will only see ~50 psi under full boost) the fuel pump picks up an additional 100 lb/hr additional flow, and based on the math the 75 lb/hr injectors at 50 psi should still flow more than enough to support the power I'm making without going static.
Finally, here's the question: I just don't know how low I can safely drop the pressure without having negative effects on the spray pattern. Any advice here?
Worst case, I guess I can go to a larger pump, dual pumps, or get a "volt booster box" to run the fuel pump at 16 volts, but IMO the best/simplest way is to go a bit bigger on the injectors and drop the fuel pressure-- I just need to know how low I can go without negatively affecting the spray pattern.
Troy