fuel injectors - Team Camaro Tech
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post #1 of 5 (permalink) Old Sep 14th, 04, 06:18 PM Thread Starter
 
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I'm looking at about 475 hp out of a lt-1. I used this formula to figure out size. But is this rerally necessary?

470 x .5 = 237.5
8 x .8 = 6.4
237.5 / 6.4 = 37.10

According to this formula I would need 38#ers. Is this right it seems a little extreme. From what I've read on boards 30s are fine. Possibly 36.
Any input?
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post #2 of 5 (permalink) Old Sep 15th, 04, 04:23 AM
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Jim
 
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Try this site. They're a little more into this sort of thing. http://web.camaross.com/forums/index...095b18765c23e7
Jim
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post #3 of 5 (permalink) Old Sep 15th, 04, 05:33 AM
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I made 458 HP and 465 ft lbs on my 93 Vette LT1 with the stock 24 pound injectors. 30's are fine for that power range.

Jody


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post #4 of 5 (permalink) Old Sep 15th, 04, 03:25 PM
a67
 
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The biggest problem with figuring out injector size is what BSFC to use. The modern day heads, cams, and intakes (mostly head chamber design) are getting todays engines in the .36 to .42 BSFC range.

You can also run the injectors up to 85% to 90% duty cycle (DC). I prefer to size them at 85% DC.

The other side of the coin is at what RPM is the HP peak going to be at. The higher the RPM the larger the required injector. This is due to the time available to inject the fuel getting less and less. For a DC less then static there is a finite amount of time to open the injector. This eats into the actual time the injector is flowing fuel.

With all that said, at 475 HP, negating RPM limitations, at 85% DC, and .40 BSFC:

475 (HP) * .40 (BSFC) = 190
190 / 8 (injectors) = 23.75#/hr
23.75 / .85 (DC) = 28 #/hr

If willing to go to 90% DC:

23.75 / .90 (DC) = 26 #/hr

Running them static with 24 #/hr is enough fuel too. Can also run the numbers with a BSFC of .36. Don't need much injector at all then. Of course using a BSFC of .45 would be a more conservative approach.

And, this is for an N/A engine, boosted apps use BSFC in he .55 to .60 range.

Bob.
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post #5 of 5 (permalink) Old Sep 15th, 04, 04:59 PM
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Plus, one of the biggest noob errors ppl make with injectors is going bigger is better.... not true with EFI... since it is the pulse width, duty cylcle that is important. Are you using a MAF or MAP for you airflow sensing?

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