Jet Sizing for WRX

[wrxdaddy]

What is the recommended WI jet size (cc/min) when tuning a 300whp 2.0L motor? Currently running on 785cc fuel injectors @ 65% IDC.

[Richard L]

4x 785 x 65% = 2041cc/minute of fuel.

Based on 10-15% of water to fuel, the jet size should be between 0.5mm (225cc/m) - 0.8mm (300cc/m).

[wrxdaddy]

Thanks for the formula. At 150psi pump pressure, how much does a 0.5mm jet flow (cc/min)?

[PuntoRex]

I'm a little confused.
When we're talking about w/f ratio, it's mass or volume?

[hotrod]

Most of your technical references like the NACA reports specified by mass, usually lb water / lb fuel.

Injectors are rated on a volume/min basis if their flow is specified in cc they are rated in cc/min. American cars sometimes specify injector flow in lbs/hr. The assumed density of gasoline is usually about 6.5 lbs/gal.

A U.S. gallon is defined as 231 cubic inches volume, or 3785.4118 cc.
A gallon of water weighs 8.337 lb at normal temps, or 3785.4118 grams (454 grams /lb AND 454 cc/lb)

Water is the standard for density, ie 1 cc = 1 gm so for practical purposes you can measure the WI flow either as mass or volume.

1 gal/hr is approximately 63 cc/min

Methanol = 0.793 g/cm3
gasoline = 2950 g/gallon = .7795 gm/cc (approximately depending on the blend)

Larry

[wrxdaddy]

Originally Posted by Richard L

4x 785 x 65% = 2041cc/minute of fuel.

Based on 10-15% of water to fuel, the jet size should be between 0.5mm (225cc/m) - 0.8mm (300cc/m).

I am using a 0.5mm jet. What is the pump pressure (psi) to flow 225cc/m mentioned above?

I would like to continue using this jet size and increase pump pressure to arrive at a higher flow. Is there a simple formula to compute this?

[hotrod]

As I understand it, the aquamist flow chart does not use a fixed pressure, but the pressure their pump will deliver in service at the flow rate of an individual jet.

On the chart the 0.5 mm at 225 cc/min is operating at about 10 bar pressure, and the 0.8 mm jet at 300 cc/min is operating at a pressure of about 7 bar.

You can correct either one to another pressure very easily.

The flow rate through a nozzle or orfice changes at the square root of the pressure. For example if you increase the pressure by 4 times, you will only increase the flow by 2 times.

New flow = rated flow x ( sqrt ( new pressure/rated pressure))

The 0.8 jet running at 7 bar (100 psi) and 300 cc/min would flow 1.22 times the rate 100 psi flow at 150 psi, or about 367 cc/min.

Larry

[wrxdaddy]

Larry, thanks for your detailed info. I am using the 0.5mm Aquamist jet and a 200psi Shurflo adjustable pump. Even now, I do not know if I am really flowing 225cc at my current 140psi pump pressure setting. Oh well, I guess I need to make sure by running my pump for a minute and measure the water going to a graduated flask.

[honki24]

Originally Posted by Richard L

4x 785 x 65% = 2041cc/minute of fuel.

Based on 10-15% of water to fuel, the jet size should be between 0.5mm (225cc/m) - 0.8mm (300cc/m).

how does this work in gal/min? I did the conversion online... but I'm just not sure.... My lancer runs 550's and I'm pretty sure I'm running around 90% on the injectors so by that math 4*550*.9=1980cc/min therefore 15%=297cc/min which is .8mm for your setup, but the injectors I work with are rated in gpm and the online conversion tells me that 297cc/min = .08gal/min ....but the jets are rated at numbers like 4.9. That must be gallons/hour right? b/c .08*60=4.8. Sound abour right?? :roll: