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Injector sizing info 

 

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 Post subject: Injector sizing info
Posted: Sat Nov 01, 2008 4:51 pm 
Getting Side Ways
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Quote:
One area that seems to cause more than a little confusion is fuel-injector sizing for a given engine application. While it may sound difficult, it's actually pretty easy. All electronic fuel injectors are sized based on the maximum amount of fuel they can inject, generally expressed in terms of pounds per hour of fuel (lb/hr). This also depends on the fuel pressure at the injector. Most injectors used in the performance industry are rated at 3-bar (43.5 psi). As an example, let's look at a performance injector rated at 40 lb/hr. Multiply that capacity times eight injectors to get 320 lb/hr of fuel. If we assume a generic brake-specific fuel consumption (BSFC) number of 0.50, this means that to make 1 hp for 1 hour at WOT demands 0.50 pounds of fuel. Given this, to find out how much horsepower this size injector can feed, we multiply 40 (lb/hr) x 8 injectors x 2 (to give us 1 pound of fuel to make the math work out), which equals 640 hp. This isn't quite accurate because it would demand 100 percent open time on the injector-called a 100 percent duty cycle. This is very hard on injectors and burns them out, so the typical industry safety margin is 15 percent. So if we multiply 640 x 0.85, we get 544 hp. This is what you could expect a 40-lb/hr injector to safely deliver.


this interests me because using thier calcs our stock 6 cyl 19lb/hr injectors are good for 193 horsepower (19 x 6 X 2= 228. 228 x .85 = 193), when operating at a safe duty cycle (.85 being the safe duty cycle). and converting 157kw (for the later sohc engines) is about 210 horsepower. Ive heard others say the stock injectors are fine for a warm 4/0l build, but this math argues differently?

using this math, the 24 lb/hr injectors seem to be a better choice even for a tuned setup? (24 x 6 x 2= 288 hp. 288 x .85= 244.8 hp)

245 hp being roughly 185 kw....

thoughts?

 

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Posted: Sun Nov 02, 2008 6:38 am 
Getting Side Ways
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then how is it that xr6t owners are making 300ish rwkw on stock injectors I wonder.

 

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Posted: Sun Nov 02, 2008 2:06 pm 
Getting Side Ways
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hence the reason why i posted this, i wanna know how and why. If they are pushing near 100% duty cycle to do it, then they will run into injector failures...

found this at the end of the article which may explain a bit more ( i posted before the end of the article lol)

Injector size = engine hp x BSFC /
number of injectors x 0.85

700 hp x 0.5 = 51.5 or a 50 lb/hr injector
8 x 0.85

therefore
standard (210 hp x .5) / (6x .85) = 105 / 5.1= 20.58 lb injector.

xr6 (219hp x .5) / (6 x .85) = 109.5 / 5.1 = 21.47 lb

as for xr turbos this is taken from aps website:

Quote:
Unlike a*** methods of increasing fuel flow through the standard injectors by increasing fuel rail pressure and/or utilizing inferior pintle style injectors, the APS High Capacity Directional Quad Orifice injectors deliver a precise spray pattern designed for the XR6T's multi-valve head - particularly at high flow rates required to produce in excess of 300 kW of power.

Fuel injectors in general are designed to deliver fuel within a certain range of fuel pressure, duty cycle and volumetric flow rate parameters. When any of these parameters are exceeded, the spray pattern and atomization properties of the fuel being injected degrade rapidly - which is particularly evident with the standard XR6 Turbo injectors.


so anyone getting 300 at the wheels with stock injectors could be doing them harm.

 

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