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Discussion Starter · #1 ·
I have a mild build 357c in my '73 Montego, here is the info:

30 over 9.5:1 Keith Black pistons
273/282 duration 458/486 lift flat tappet cam
studded mains and heads
Custom one-off EFI setup
70mm throttle body
76mm mass air
ultra 40 plug wires
indexed MotorCraft Platinum plugs
Jacobs FC1000
Jacobs UltraCoil
roller rockers
screw-in studs
guide plates
mild intake porting & polishing
smoothed out exhaust ports
A9L computer
adjustable FPR
1 piece Ferrea stainless valves
4bbl springs

I now have 19lb injectors and would like to supply more fuel to the engine. What size injector should I go with? I heard something about keeping the duty cycle 80% or lower to prevent premature injector failure. Should I go with 24lb'ers or 30lb'ers. I guess I have around 300hp as a guess, I could be wrong though. I want to prevent a overly lean condition and long injector duty cycle.

Thanks in advance, Chris
 

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At least 36lb. I might go to 42's, you can find them all over, they arent that much more $$$ and it allows for increased power for the future.
 

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Discussion Starter · #3 ·
Really? That high? I didn't think I needed that high lb/hr injectors. Even for a mildly modified motor?
Chris
 

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19lbs = ~250 - 300
24lbs = ~300 - 350
30lbs = ~350 - 400
42lbs = ~500 - 550

1st number is recommended
2nd number is if you play around with fuel pressure.
* you can fudge these numbers by pushing the duration, but it is not recommend, especially for sustained use.

be sure you have enough fuel pump and/ or larger fuel lines to supply the injectors.

There are many sites on the web that will give you pretty accurate injector sizing guideline. Do a web search. "injector sizing".

http://www.iroczone.com/calcs/injectorsize.htm

http://www.injector.com/injectorselection.php
http://www.rceng.com/technical.htm
http://www.race-technology.com/WebPage2/Other/Utilities/InjectorSizing/InjectorSizing.html
http://www.compsystems.com.au/TechTalk/TN010504.htm

You could also search old posts, lots of good information there.

On 2004-12-02 13:58, Beoweolf wrote:
I ran the numbers, just to check. Making a couple of assumptions as to the probable horsepower of the un-NO2 boosted engine.

These are approximate and could also require adjustments to fuel pressure, timing or other adjustments.

At 350 hp...you need 24 lb injectors, 175 pump lb/hr
At 400 hp...you need 27 lb injectors, 200 pump lb/hr
At 450 hp...you need 31 lb intectors, 225 pump lb/hr


<font size=-1>[ This Message was edited by: Beoweolf on 12/3/04 2:04am ]</font>
<font size=-1>[ This Message was edited by: Beoweolf on 9/28/06 1:04pm ]</font>
 

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Discussion Starter · #5 ·
What does 160gph equate to? Should this pump be enough?
Thanks, Chris
 

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That should be enough fuel pump. As a rule of thumb if you divide your expected rear wheel HP by 10 you will come up with a good injector size to run a an exceptable duty cycle.
 

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On 2006-09-28 16:07, MontegoMan351 wrote:
What does 160gph equate to? Should this pump be enough?
Thanks, Chris
Weight of One Gallon (U.S.) of Water, Gasoline, and Ethanol

1 gallon of water equals 8.33 lbs.
1 gallon of gasoline equals 5.8 to 6.5 lbs.
1 gallon of ethanol equals 6.59 lbs.
 

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Discussion Starter · #8 ·
I finally got around to buying injectors, I got 24lb/hr with a C&Lcal. tube for the C&L housing, fuel pressure set to 50 without vacuum. It runs good, now the rear gear and wide ratio AOD, and I will be set.
Thanks for the help and suggestions, Chris.
 
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