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Old 01-23-2008, 05:21 PM   #1
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Default injector and pump sizing?

Would someone please describe how to determine proper injector sizing, then how to determine what size fuel pump would be needed. I think i am looking for a universal formula based of engine size, lbs boost, fuel type( 93 vs E85).
Thanks in advance,
Aaron
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Old 01-23-2008, 11:28 PM   #2
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Originally Posted by Screamin_K View Post
Would someone please describe how to determine proper injector sizing, then how to determine what size fuel pump would be needed. I think i am looking for a universal formula based of engine size, lbs boost, fuel type( 93 vs E85).
Thanks in advance,
Aaron
I'll try to put a complicated answer into laymens terms for you. The first thing to know is it takes .5 lbs of fuel per hour to make one horsepower. Once you know that the formulas I'll give you will make sense. First to determine fuel pump size: Let's say you want to make 500 horsepower (at the flywheel) multiply 500 x .5 = 250 so it takes 250 lbs of fuel per hour to make 500 horsepower ( this is naturally aspirated, I'll explain power adders in a minute) so you'll need a fuel pump that flows 250 lbs per hour plus a 20% cushion to be safe which would be 300 lbs per hour . Understand fuel flow rating for a fuel pump is greatly affected by voltage at the pump and pressure the pump will be run at. Less voltage or higher pressure will reduce the pump flow rating. Most fuel pump manufacturers have flow charts for each pump if you request them. If you are using a power adder it is best to use .6 instead of .5 as a multiplier to compensate for parasitic loss by the blower or turbocharger. (it takes horsepower to turn a blower and pumping loss to turn a turbo which cost horsepower to the flywheel) so 500 HP using a blower would be 500 x .6= 300 plus a 20% cushion which would be 360 lbs per hour of course. Notice it requires more fuel to run a power adder application than n/a for the same horsepower. Adding voltage at the pump will increase it's flow capacity, this is what's being done when you add a KB Boost a Pump to a fuel system. It's also why it's a good idea to run your power supply directly from the battery through a relay to your fuel pump, you'll get less voltage drop in the wiring and connections so the pump will flow more . Now for injector size. This is really simple. Once you know your lbs. per hour just divide by the number of injectors you are using. So 500 HP using a blower will require 360 lbs per hour of fuel. Divide by 8 and you get 45 lb. injector. Remeber, this is flywheel horsepower. To get rear wheel horsepower you will lose about 15% with a manual trans and about 20% with an automatic trans. So lets say you want to make 500 rwhp with a stick: 500 x 1.15= 575 (this would be your aproximate fwhp) then take 575 x .6=345 plus your 20% cushion = 414 / 8 injectors= 51.75 lb injector. I would round up to a 60 lb injector and you're all set. I hope this makes sense and helps everybody understand this better. If you need more help or have more questions shoot me a pm or an email to [email protected]
Jerry
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Old 01-28-2008, 04:56 PM   #3
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Originally Posted by [email protected] hp View Post
I'll try to put a complicated answer into laymens terms for you. The first thing to know is it takes .5 lbs of fuel per hour to make one horsepower. Once you know that the formulas I'll give you will make sense. First to determine fuel pump size: Let's say you want to make 500 horsepower (at the flywheel) multiply 500 x .5 = 250 so it takes 250 lbs of fuel per hour to make 500 horsepower ( this is naturally aspirated, I'll explain power adders in a minute) so you'll need a fuel pump that flows 250 lbs per hour plus a 20% cushion to be safe which would be 300 lbs per hour . Understand fuel flow rating for a fuel pump is greatly affected by voltage at the pump and pressure the pump will be run at. Less voltage or higher pressure will reduce the pump flow rating. Most fuel pump manufacturers have flow charts for each pump if you request them. If you are using a power adder it is best to use .6 instead of .5 as a multiplier to compensate for parasitic loss by the blower or turbocharger. (it takes horsepower to turn a blower and pumping loss to turn a turbo which cost horsepower to the flywheel) so 500 HP using a blower would be 500 x .6= 300 plus a 20% cushion which would be 360 lbs per hour of course. Notice it requires more fuel to run a power adder application than n/a for the same horsepower. Adding voltage at the pump will increase it's flow capacity, this is what's being done when you add a KB Boost a Pump to a fuel system. It's also why it's a good idea to run your power supply directly from the battery through a relay to your fuel pump, you'll get less voltage drop in the wiring and connections so the pump will flow more . Now for injector size. This is really simple. Once you know your lbs. per hour just divide by the number of injectors you are using. So 500 HP using a blower will require 360 lbs per hour of fuel. Divide by 8 and you get 45 lb. injector. Remeber, this is flywheel horsepower. To get rear wheel horsepower you will lose about 15% with a manual trans and about 20% with an automatic trans. So lets say you want to make 500 rwhp with a stick: 500 x 1.15= 575 (this would be your aproximate fwhp) then take 575 x .6=345 plus your 20% cushion = 414 / 8 injectors= 51.75 lb injector. I would round up to a 60 lb injector and you're all set. I hope this makes sense and helps everybody understand this better. If you need more help or have more questions shoot me a pm or an email to [email protected]
Jerry
You're right.

I use this 'Fuel Injector Worksheet' from RC Injectors to quickly figure out what size injectors are needed for a specific application. For E85 the bsfc is typically around .77. If the OP has any questions about tuning for E85 feel free to ask away, we've done quite a few E85 on forced induction setups.

http://www.rceng.com/technical.aspx
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