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In light of numerous injector and fuel pm's I have received, I feel this post would be great FYI and should entertain most of the Q's I receive...

HP / Number of Injectors x Brake Specific Fuel Consumption (BSFC) / Duty Cycle

(For a naturally aspirated engine, BSFC is typically. 50. Competition engines with high volumetric efficiency should use a BSFC of .45, while forced induction engines should use a figure of .65.)


Let's say we have a 200 WHP Civic/ 4 injectors x .65 (FI engine) / .85 duty cycle

200 / 4 = 50 ---> 50 * .65 BSFC = 32.75 ---> 32.75 / .85 duty cycle = 38.53

This means you need a 39 lb/hr injector to support that type of power.

38.53 * 10.2 (to convert to CC's) 393 CC injectors

To convert lbs/hr to cc's, multiply by 10.2. To convert cc's to lbs/hr, divide by 10.2.


Feel free to ask Q's and/or comment. Also, if you learned from this and leave some rep points. undefined

 
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i did learn from that, but now it just makes me wonder what happens to engines with to large of injectors compared too it's potential horsepower.

 
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too large of injectors create unstable idles, possibly too rich fuel conditions based upon duty cycle and fuel pressure.....

 
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ah, and too small of injectors i guess would just run really lean (especially in a forced induction situation)? whats the effects of running too rich/too lean? trying to suck up your knowledge while i can heh.

 
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too rich, the car swims in fuel....poor fuel economy, can lead to fouled plugs, carb/soot deposits in exhaust components, drives a little sluggish, can have higher EGT's too.


too lean, the car starves for fuel.....better fuel economy, more power, less reliability, higher EGT's which can lead to warps, cracks, burns in engine internals due to intense heat.


Must be a good balance....Stoich in Vac, Rich under boost (12.5:1 is the most common ratio)

 
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nice info dezod, so where do the rxs injectors fall into this?

 
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They run circa 330 CC

 
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14.7:1 is the perfect ratio for air to fuel.

 
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If u work the other way around, can u use injector CC to determine the approx. whp the injectors will support?

Stock injectors flow 240 CC, and use 80% duty cycle right?

whp = #injectors * 1/bsfc * duty cycle * 1/10.2 * injector CC

NA engine whp = 4 injectors * 1/.5 * .8 * 1/10.2 * 240 = 150.588

FI engine whp = 4 injectors * 1/.65 * .8 * 1/10.2 * 240 = 115.837

So u have to increase fuel pressure to make more hp on FI engine.

 
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Well, you have to increase fuel pressure on FI, in order to keep the injector working correctly, as they work off of pressure differential. Say you run 43.5psi base fuel pressure, and are running 20psi of boost. Now, you have 20psi on the manifold side of the injector, and 43.5psi on the fuel rail side, so only 23.5psi of "pressure." You should to increase fuel pressure 1:1 generally with boost, to keep the injectors consistant.

 
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for N/A yes, but for FI 12.5:1 is the best....

 
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FI requires far more fuel in the ratio because of the increased air flow.

 
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I agree........ better safe than sorry.......

 
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ok dezod, lil off the thread topic, but why you are spilling some knowledge, i'm curious about this torque converter i hear of. i guess autos have them and in fourth gear when i'm cruising on the highway it locks up. i know when it locks up i cant accelerate as quickly, but what is it even doing? and why do people talk about getting a torque converter when installing turbos, are their higher grade ones that offer more benefits for a a/t?

 
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TC are a questionable subject when it comes to turbos.....some people feel it is a worthy investment....others not.

Read this:

http://www.howstuffworks.com/torque-converter.htm


After further insight into it, make the decision on your own.

 
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up!!!!!!!

 
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Unless you are running a stock block. 11.5-10.5 is an excellent conservative tune. There is a lot less of a chance to fry your ring lands with these numbers rather than 12.5....

But - you're right, 12.5 is almost spot on. The only problem is - the ECU is a bitch to tune because it will attempt to compensate for changes....That's why its better to tune a little more conservative if you can (unless you want a pure track car and don't care about the reliability of the motor).

 
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Bump For Some Good Info!