Injector question?
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From: Humble, Texas
Injector question?
Once I get the testing done with the ASP pulley I should be right at 250hp. I'm ordering JBA headers within the month and that should put me up to 260hp. well that comes out to 21.58lb. injector size. Is this ok to run with stock 19lb. injectors? I should pick up another 50hp with my intakes/heads/cam. With 310hp N/A I would need 25.8lb. injectors... SO, if I were to buy 24lb. injectors would that be too much to run 21.58lb and would 24lb. be enough to feed 25.8lb flow?
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Joined: Mar 1998
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From: Virginia
Hi Talleywhacker,
First, and this will probably help you the most, you do not have to *exactly* match injector size, you can go a little bit larger, you generally do not want to go any smaller, though when *very* close, you can sometimes make do.
Assuming you will be at a power level of 310 horsepower in a 6 cylinder engine, your figure of 25.8 is right there, 25.83 is the exact number. Glad to see you remembered the formula!
You need a bit more with these newer returnless fuel systems, but the basic formula is, you need 1/2 lb./hr of injector capacity fior each horsepower you make, and that will work regardless of how many cylinders, etc. This assumes an 80% duty cycle on return systems, so that can be pushed a bit at a nominal fuel pressure of say, 37-40 PSI. I'm not a fan of cranking up fuel pressure to push the stock injectors.
So given all that, and that you have a returnless system, your 19 lb. injectors would not really be considered "sufficient" for the 260 horsepower level by the numbers; normally you'd say that 6 19# injectors would be good for 228 hp @ 80% duty cycle, but you can usually get about 250 hp or so out of them at 100%, and perhaps a tad more for brief spurts, but you wouldn't do a top speed run like that.
You could make do if you don't drive it at full throttle all the way up to the redline in the top 2 gears. So for example, if you wanted to not have to buy 2 different sets of larger injectors, because you're doing your engine modifications in stages, sure, you could use the 19 lb. units for awhile longer. Then when you get the heads & camshaft done, just install the correct final injector size and a matching MAF at the same time.
In your other example, 24 lb. injectors could probably do the job when 25.83 is needed in that formula, but a little bit larger is the smart way to go.
The thing to do would be to use 30# injectors (well, if 26# or 28# units could be had....), the injectors don't have to *exactly* match, you want the injectors to be a bit larger than what you need. You don't want to be TOO big, as then you're drowning in fuel and have to do a lot of work on load, injector pulse width, etc. At 310 real horsepower, SAE Net at the flywheel, a 30 lb. injector (well, 28# would be nice) is probably going to be the ticket.
Give us a call if you want to go over any of this!
First, and this will probably help you the most, you do not have to *exactly* match injector size, you can go a little bit larger, you generally do not want to go any smaller, though when *very* close, you can sometimes make do.
Assuming you will be at a power level of 310 horsepower in a 6 cylinder engine, your figure of 25.8 is right there, 25.83 is the exact number. Glad to see you remembered the formula!
You need a bit more with these newer returnless fuel systems, but the basic formula is, you need 1/2 lb./hr of injector capacity fior each horsepower you make, and that will work regardless of how many cylinders, etc. This assumes an 80% duty cycle on return systems, so that can be pushed a bit at a nominal fuel pressure of say, 37-40 PSI. I'm not a fan of cranking up fuel pressure to push the stock injectors.
So given all that, and that you have a returnless system, your 19 lb. injectors would not really be considered "sufficient" for the 260 horsepower level by the numbers; normally you'd say that 6 19# injectors would be good for 228 hp @ 80% duty cycle, but you can usually get about 250 hp or so out of them at 100%, and perhaps a tad more for brief spurts, but you wouldn't do a top speed run like that.
You could make do if you don't drive it at full throttle all the way up to the redline in the top 2 gears. So for example, if you wanted to not have to buy 2 different sets of larger injectors, because you're doing your engine modifications in stages, sure, you could use the 19 lb. units for awhile longer. Then when you get the heads & camshaft done, just install the correct final injector size and a matching MAF at the same time.
In your other example, 24 lb. injectors could probably do the job when 25.83 is needed in that formula, but a little bit larger is the smart way to go.
The thing to do would be to use 30# injectors (well, if 26# or 28# units could be had....), the injectors don't have to *exactly* match, you want the injectors to be a bit larger than what you need. You don't want to be TOO big, as then you're drowning in fuel and have to do a lot of work on load, injector pulse width, etc. At 310 real horsepower, SAE Net at the flywheel, a 30 lb. injector (well, 28# would be nice) is probably going to be the ticket.
Give us a call if you want to go over any of this!
Thread Starter
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Suspended For Violation of Vendor Rules
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From: Humble, Texas
well, after i get the heads and intake... I will go ahead and get the 70mm throttle body and 80mm mass air to match the injectors. real crank hp should be around 320. I will be done with all my engine modifications after that except for the supercharger. I do not mind doing injectors twice but not 3 times. once i get the headers and pulley on i'll be at 260bhp. this means the 19lbs. will definately not be enough for my top speed runs. I'll give you a call monday Mike to discuss this. My only other question is Fuel Pump. I have no idea if the stock pump will be enough for the 320BHP.
