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Originally Posted by GTmustang04
Does anyone know what size injectors a stock 04 GT has. Also, would it be worth it to put larger injectors in my stock motor? im planning on running the 70mm throttle body and plenum combo.
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I believe the 04's may have 21# injectors (can't remember where I read this - most late models run 19#, as does my 02 GT vert).
To compute injector size, I got this info from Summit:
"Calculating Fuel Injector Size
Here is the formula for calculating injector size in pounds per hour:
Injector lbs./hr. = horsepower x BFSC/number of cylinders
BFSC is short for Brake Specific Fuel Consumption, which is the amount of fuel required to produce one horsepower. According to Accel, a BFSC of .45 is a good general figure for normally aspirated engines, and .55 is good for supercharged engines.
Let’s do a calculation for a 400 horsepower, unblown V8 engine:
Injector lbs./hr. = 400 x .45/8
Injector lbs./hr. = 400 x .05625
Injector lbs./hr. = 22.5#" - summit racing"
Hence the stock 19# injectors, which give some headroom in a 260hp stocker, will fall short somewhere above 330hp:
Injector lbs./hr = 330 x .45/8, or 330 x .05625 = 18.6#
Personally, I've always felt these numbers were a bit optimistic, since 100% efficiency/consumption of fuel is rarely achieved. (quote from one of my other posts).
I find this info very valuable when evaluating injector sizing. It is something of a backward way of doing it, but it really does work.
In the case of simply bolting on a plenum/tb combo, I doubt this will need any upgrade to larger injectors. You'll be lucky to get 15hp or so from this upgrade (I've got the 75mm combo, and I netted about that much). Unless you're going to go through the complete engine (ported heads, big cams, long tube headers, performance tune, etc, etc), leave the injectors alone for now.
Hope this helps.
tripleblack