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Speedy Squirrel Speedy Squirrel is offline
Rocket Scientist
 
Join Date: Jun 2008
Location: Detroit
Posts: 824
Injectors

Type: Siemans DEKA VI
Flow: 4.8 to 5.0 gm/s static flow at 300 kPa
Tip: Extra Extended Tip (17.5mm)
Spray: Pencil type, no bend

For a comparison, the stock k-jectronic injectors are flowing around 3.9 gm/s at 300hp(flywheel)@5500 RPM.

The formula I use for sizing injectors is:

Flow (gm/s) = (target flywheel HP)*0.0790/(number of cylinders)

I was shooting for around 400HP at the flywheel, so that comes out to 5.2 gm/s, which is how I arrived at my injector size.

For 650HP at the flywheel, you get 8.55 gm/s (67.7 lb/hr), so the injector size depends on how much power you want.

Be realistic! Bigger is not better. The reason is that a large flowing injector performs very poorly at idle. The pulsewidth becomes so small that the injector can't handle it. Rather than spraying in a small amount of fuel, it just shuts off.

65 lb/hr is probably the biggest that most people on this board will need. 85 is ay too big, unless you're making over 800HP at the flywheel.

Nothing wrong with designing to run at 100% duty cycle at max power. That's when the injector is running the best! Flow is not interrupted, just one big garden hose of fuel spraying in.

Pay attention to the spray pattern. All injectors are NOT the same. Most multi-intake valve engines actually have two narrow sprays coming out of one injector. Put those in our motor and you have two narrow sprays onto the port walls. Not Good!
Old 07-06-2008, 05:19 AM
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