How much RWHP are 30# injectors good for??? - Ford Mustang Forums : Corral.net Mustang Forum
 
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post #1 of 6 Old 04-22-2002, 04:41 PM Thread Starter
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Question How much RWHP are 30# injectors good for???

Well, I have an issue of 5.0 mag that states what injectors are good up till but they don't say engine hp or RWHP.


If I am not mistaken, 30# injectors are good until about 360 RWHP? Am I right. I know you don't want to run the injectors at 100% duty, but, I am just wondering because I am running 30's now and plan on making around 330 RWHP in the future.

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post #2 of 6 Old 04-22-2002, 05:20 PM
 
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I am still using 30lb injectors and I am putting down 390rwhp / 377rwtq. My A/F ratio is from 11.1 to 11.9 See sig for my setup.

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post #3 of 6 Old 04-22-2002, 05:35 PM Thread Starter
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Well that is music to my ears. With my 10# pulley I will be looking at 300rwhp and then this summer with the addition of heads and longtubes, I should see 330-350 rwhp. Good thing I won't have to change injectors!
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post #4 of 6 Old 04-22-2002, 10:25 PM
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I found a number of interesting calculators including fuel injector sizing, here.

The X factor is the brake specific fuel consumption (BSFC) which is as near as I can tell a measure of efficiency for the engine. Since a supercharged engine is not as efficient as a naturally aspirated engine it can actually take more fuel to achieve the same HP level thus potentially requiring higher flow injectors.

Since I'm basically heading down the same path you are, I've been looking into this one recently too. Without really knowing what the BSFC for our engine is, I put a worst case 0.55 into the equation and it came up with 380 crank HP with 30lb injectors at a 90% duty cycle. So it looks like 330RWHP could be pushing the 30lb injectors to their limit depending on what the real engine efficiency is.

Disclaimer: I only know enough about this to be dangerous. I would love to get an accurate estimate of what the BSFC is for the 2V 4.6l engine with and without the SVO blower.

Atlantic Blue '98 GT Convertible with stuff
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post #5 of 6 Old 04-22-2002, 11:03 PM
 
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Quote:
The X factor is the brake specific fuel consumption (BSFC) which is as near as I can tell a measure of efficiency for the engine
BSFC fuel consumption per brake horsepower hour. Basically it is the amount of fuel burned per unit of power produced. It is indeed a measure of engine efficiency. Car makers used to give you that data upon request; they probably still do. I don't know who you would write to get it though.

Typically supercharged cars are anywhere between .55-.65 though most are on the high side of that. Naturally aspirated sports cars, not having to expend power to turn a compressor, are a bit more efficient having a BSFC of .45-.55

By my calculations, if our supercharged 4.6 had a conservative BSFC of .6, the upper limit of a 30lb/hr injector at 85% duty cycle would be about 350bhp

.6*350/(8*.85) = 30.8

At 100% duty cycle you get 400bhp
.6*400/8 = 30.0

If you don't know the exact bsfc of your engne typically you can just err on the conservative side and be ok. Just don't take it to the edge, knowing that you estimated a value in there. That is to say, don't run 400hp just because I calculated it here. Since I guessed on the BSFC there is a +/- error of 10% or so in the calculation.
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post #6 of 6 Old 04-22-2002, 11:07 PM Thread Starter
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GARRETT.....your numbers are making me see blurry.


you got PM by the way!

later!
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