# calculating flow based on pressure and nozzle size?

#

**1****calculating flow based on pressure and nozzle size?**

Is there a mathematical way... or an online calculator to figure out what kind of flow to expect from a particular nozzle size based on pressure?

I'm running a mechanical preturbo AI system that is used by pressurizing a tank. It's used with boost pressures between 15 - 20 psi. The nozzle is rated at around 380 cc @ 20 psi. I was planning on increasing the nozzle size to somewhere around 0.03125" - 0.4" (1/32" -1/25") to get more flow. I was reading the nozzle size sticky and read that the .9 MM (.0354") equates to the M5 and flows 316 CC/Min at 100 psi. I also found an old post by rotary racing that said he modifies his nozzle tips to about a 1mm opening to give around 700cc of flow @ under 20 psi.

I don't know the exact size of my nozzle but I'm pretty certain its not bigger then 1mm. So something isn't quite adding up. If my nozzle flows 380 cc at 20 psi, and rice racing's is 1mm (.04") (the M7 is .045") flowing 700 cc 20 psi, then why does that chart in the sticky show the same size nozzle (M7) flowing only 442 cc at 100 psi? That's a HUGE difference in flow for the same size orifice, especially considering the nozzles rated at flowing much less, are at a much higher pressure. 20 psi vs 100 psi

What gives

References:

post #23 (size/chart sticky) https://www.rx7club.com/auxiliary-injection-173/ai-nozzle-jet-delivery-sizing-587197/

Post #5 RR modified nozzle https://www.rx7club.com/showthread.p...ghlight=sue18a

I'm running a mechanical preturbo AI system that is used by pressurizing a tank. It's used with boost pressures between 15 - 20 psi. The nozzle is rated at around 380 cc @ 20 psi. I was planning on increasing the nozzle size to somewhere around 0.03125" - 0.4" (1/32" -1/25") to get more flow. I was reading the nozzle size sticky and read that the .9 MM (.0354") equates to the M5 and flows 316 CC/Min at 100 psi. I also found an old post by rotary racing that said he modifies his nozzle tips to about a 1mm opening to give around 700cc of flow @ under 20 psi.

I don't know the exact size of my nozzle but I'm pretty certain its not bigger then 1mm. So something isn't quite adding up. If my nozzle flows 380 cc at 20 psi, and rice racing's is 1mm (.04") (the M7 is .045") flowing 700 cc 20 psi, then why does that chart in the sticky show the same size nozzle (M7) flowing only 442 cc at 100 psi? That's a HUGE difference in flow for the same size orifice, especially considering the nozzles rated at flowing much less, are at a much higher pressure. 20 psi vs 100 psi

What gives

References:

post #23 (size/chart sticky) https://www.rx7club.com/auxiliary-injection-173/ai-nozzle-jet-delivery-sizing-587197/

Post #5 RR modified nozzle https://www.rx7club.com/showthread.p...ghlight=sue18a

#

**2**100% Rotary Since 1983

**RX7Club Vendor**

iTrader: (6)

Join Date: Oct 2001

Location: Wisconsin

Posts: 5,215

i agree w your thinking that something is amiss.

the increased flow from going from 20 psi to 100 psi is the square root of 500. so flow at 100 psi should be 22.3% more than at 20.

i suggest you use an air pressure source, a reliable gauge and a pressure regulator and pressurize your tank. measure the amount flowed for a minute and let's see what is really going on.

perhaps due to the suction of the compressor you are getting more flow????

howard

the increased flow from going from 20 psi to 100 psi is the square root of 500. so flow at 100 psi should be 22.3% more than at 20.

i suggest you use an air pressure source, a reliable gauge and a pressure regulator and pressurize your tank. measure the amount flowed for a minute and let's see what is really going on.

perhaps due to the suction of the compressor you are getting more flow????

howard

*Last edited by Howard Coleman CPR; 04-13-09 at 07:24 AM.*

#

**3**
#

**6**There is about 50million to chose from. You should be able to find something for your application.

#

**7**
#

**8**I stuck a couple in the nozzle tip to check the size and my nozzle is right between a .65mm -.7 mm (0.026" - 0.028") which would be between an M4 and M5 according to post #23 in the size sticky.

My flow at 20 psi is supposed to be 378cc, an M5 is supposed to flow 379cc at 150 psi.(much much higher pressure)

Within the next couple days I will check the actual flow of my nozzle with a regulator and measuring container.

Howard how do you calculate the flow increase from a pressure increase? Earlier you mentioned the square root of 500 and came up with 22% increase from 20 to 100 psi. Could you show me the formula that allowed you to come to that number? I know the square root of 500 is 22.3 but how did you get the number 500 from 20 and 100? thanks

#

**9**"When you increase or decrease fuel pressure at the injector from its rated flow you change the amount of fuel that is actually forced from the injector (the injectors volume flow).

New Flow = SQRT(New Pressure / Old Pressure) X Old Flow Rate

Here is an example:

New Flow = Square Root of (55psi / 43.5psi) X 30 lbs/hr flow rate

New Flow = 1.124 X 30 lbs/hr

New Flow = 33.73 lb/hr"

Using this formula going from 20 psi to 100 psi with a starting flow rate of 380cc would increase flow to 850cc(much more then a 23% increase.) Here's the math using the formula above: SQRT(100psi/20psi) X 380cc = 849.7cc

I checked the math against the chart in the sticky (post #23) by using the 100 and 150 psi numbers and it checked out to be quite accurate. The smaller nozzles were within 5cc or so of the math's calculations. The largest difference was with the M11 of 17cc. Using the math formula it showed a flow of 850cc vs the charts 833cc. Still very accurate

For easier reference here is the chart below.

M1 - (.011") - 1.0 GPH @ 100 PSI, 1.2 GPH @ 150 PSI, 63 CC/min @ 100 PSI, 76 CC/min @ 150 PSI

M2 - (.015") - 2.0 GPH @ 100 PSI, 2.4 GPH @ 150 PSI, 126 CC/min @ 100 PSI, 151 CC/min @ 150 PSI

M3 - (.020") - 3.0 GPH @ 100 PSI, 3.6 GPH @ 150 PSI, 189 CC/min @ 100 PSI, 227 CC/min @ 150 PSI

M4 - (.024") - 4.0 GPH @ 100 PSI, 4.8 GPH @ 150 PSI, 252 CC/min @ 100 PSI, 303 CC/min @ 150 PSI

M5 - (.035") - 5.0 GPH @ 100 PSI, 6.0 GPH @ 150 PSI, 316 CC/min @ 100 PSI, 379 CC/min @ 150 PSI

M7 - (.045") - 7.0 GPH @ 100 PSI, 8.4 GPH @ 150 PSI, 442 CC/min @ 100 PSI, 530 CC/min @ 150 PSI

M11 - (.073") - 11 GPH @ 100 PSI, 13.2 GPH @ 150 PSI, 694 CC/min @ 100 PSI, 833 CC/min @ 150 PSI

Since my nozzle is right between an M4 and an M5 in size ill interpolate the flow according to the chart at 280cc (right between 252 & 316cc) @100 psi. Using the new formula and going off that chart would mean that my nozzle is only flowing 125cc @20 psi. I know for a fact its flowing way more then that given how quickly my container empties. Plus my nozzle is rated @ 20 psi to flow 378cc from a quite large and professional company. (though I do plan to check its flow anyway)

My guess is the nozzles either flow a lot more then what they are rated at in that chart.. or the actual size of the nozzles is much smaller. I think this is a very good explanation. The flow numbers in the chart comparing 100 psi and 150 psi seem to add up with the math so I think the sizes are wrong. In any case something isn't adding up and I don't think it's with my nozzle.

#

**11**Thread

Thread Starter

Forum

Replies

Last Post

Jose A.

3rd Generation RX-7 (1993-2002) Parts

32

09-29-15 01:20 PM

Frisky Arab

2nd Generation Specific (1986-1992)

13

08-18-15 05:30 PM

KAL797

Test Area 51

0

08-11-15 03:47 PM