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Old 09-22-2013, 12:22 PM   #1
Levi05
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Bigger fuel injectors. When?

When are bigger fuel injectors needed on a 2.3l NA build?


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Old 09-22-2013, 12:58 PM   #2
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I would suspect never. If you end up with a really high injector duty cycle it's probably smart to upgrade.
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Old 09-22-2013, 09:39 PM   #3
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I would suspect never. If you end up with a really high injector duty cycle it's probably smart to upgrade.
This^^^^^^^^ But that'll never happen. All you'll do is wash your rings out.
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Old 09-23-2013, 09:21 AM   #4
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I would suspect never. If you end up with a really high injector duty cycle it's probably smart to upgrade.
Probably once you start exceeding 180whp you might want to look at your duty cycles. I'm using 39# injectors for my N/A build.
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Old 09-23-2013, 12:34 PM   #5
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I had noticed other people used bigger injectors on their builds so i didn't know when the stock ones maxed out.

I was actually thinking id like to aim for around 180whp. I need it to be reliable for my DD ...and not rediculously expensive...
Egz, what setup are you going with on your build and where do you think you'll be hp-wise?
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Old 09-23-2013, 02:02 PM   #6
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Quote:
Originally Posted by Levi05 View Post
Egz, what setup are you going with on your build and where do you think you'll be hp-wise?
2003 Ford Focus ZX3 2.3l N/A = 221 HP, 162 ft-lbs, 13.967@100.88MPH

http://www.focusfanatics.com/forum/showthread.php?t=206700
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Old 09-24-2013, 08:36 AM   #7
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I had noticed other people used bigger injectors on their builds so i didn't know when the stock ones maxed out.

I was actually thinking id like to aim for around 180whp. I need it to be reliable for my DD ...and not rediculously expensive...
The equation for fuel injector sizing is:

(Crank HP * BSFC) / (# injectors * duty cycle)

BSFC and duty cycle gives some wiggle room, but I try to aim for a 0.8 duty cycle, and use a 0.5 for the BSFC for a N/A engine. For crank HP, I estimate it by dividing wheel hp by 0.15. So 180 at the wheels would be roughly 210 at the crank.

(210 * 0.5) / (4 * 0.8) = 32# injectors

Which is in the middle of 2 common sizes, 24 and 36. I would try to find some 30# injectors, but worse case scenario, go up to 36#. 24# would be at 100% duty cycle (unless you want to get into the mess of playing with fuel pressure to compensate)
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Old 09-24-2013, 12:54 PM   #8
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Ahh, you were referring to the build you already completed. The way you worded it, i thought you were working on a new one. Haha. Nice numbers!

Thanks for the math Egz. Building a motor can get way too complicated... Good thing other people have already done the hard work.
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