Pressure

[Razor]

Ok..a little discussion.. the subject is alky pressure and boost levels. On another post Steve from SMC made a valid point that if the boost level increases so has to the alcohol pressure level to keep things in line. Same thing as our fuel pressure regulator having to increase pressure with boost to keep the A/F happy.

So .. if your at 12 PSI and spraying 60 psi from your alcohol pump, thats a net 48 PSI. Once your boost goes to 25 PSI thats a net 35. Seems backwards to spray less alcohol as the boost increases..

Does it matter that the net pressure amount is less when the boost increases? I have seen the pattern out of nozzles with the pump spraying at atmosphere..pretty intense at 60 PSI..but never seen what effects occurs when the spray is directed into a pressurized space.

So if I set my pump to 25 PSI and run 25 PSI boost..that would be zero alky.. Am I off or what?

Julio

 

[GN ERGY]

Just a thought, you are talking pounds per square inch, right.
So you are spraying 60 PSI thru a small hole in the nozzle, not much area for the PSI of Boost pressure to press against, correct?

So we are talking 60 lbs pushing out of a .030 hole and 29 lbs trying to stop it.

Does that make sense?? or am I just spinning my wheels.
Tarey D.

 

[Razor]

Steve .. great point on the airflow going past it..

But still, boost pressure is fighting the alcohol going in. Never thought of this this way.

Tarey, yup..thats why I used the hypothetical 25 PSI alky pressure and 25 PSI boost = zero alky..

Anyone guess the siphoning action?

 

[Red Regal T]

Originally posted by Razor


So if I set my pump to 25 PSI and run 25 PSI boost..that would be zero alky.. Am I off or what?

Julio

You're still going to have 25 psi of alky spraying out the nozzle into the up pipe. If it was 100 and 100, you'd still have 100 psi coming out the nozzle. The boost pressure is never going to overpower the pressure coming out of the nozzle.

 

[Razor]

Re: Re: Pressure

Originally posted by Red Regal T
You're still going to have 25 psi of alky spraying out the nozzle into the up pipe. If it was 100 and 100, you'd still have 100 psi coming out the nozzle. The boost pressure is never going to overpower the pressure coming out of the nozzle.

Thats what I thought at first..but then why would you increase fuel pressure with boost? To overcome the pressure inside the intake manifold. Your injectors work the same way as your nozzle..no different..

Now you know why I brought this up

And using NOS nozzles, when the car isnt running a boost level high enough to trigger the pump, isnt the air in the up-pipe pushing the alky back torwards the pump draining the lines? Or are the lines drained due to siphoning?

 

[Razor]

thinking

Maybe an easy test to perform, set a shureflow to put out 25 PSI of pressure,then get a piece of transparent tube and apply 25 PSI of air pressure, turn on the pump on and see what happens?

Wont be able to replicate air going past it for dribble effect..

dunno..what ya think?

 

[Razor]

Maybe a different story with other pumps...

Thats rite..i've read other posts where using selenoids for multistage systems pressure remained.

Thumbs up for the Shureflow.

Shooting from the hip..know what ya mean..

 

[1badTTA]

Re: Re: Re: Pressure

Originally posted by Razor
Thats what I thought at first..but then why would you increase fuel pressure with boost? To overcome the pressure inside the intake manifold. Your injectors work the same way as your nozzle..no different..

Now you know why I brought this up

OK, an even better example is the guys running blowthrough carbs, they have to boost reference the fuel pressure to be able to keep the float bowl filled. Otherwise 15psi of boost will blow the lines full of air when you only have 7psi of fuel presure.

The best way to overcome this is a boost referenced regulator, but an easier way will be to simply run higher pressures so there will be less of a pressure differential between low and high boost. If you run 100psi of alky, how much of a flow difference will there be between 12psi and 25psi of boost (88psi and 75psi of alky). I would guess that the nozzle will flow nearly identicle amounts at those 2 pressures much like increasing your fuel pressure to make up for undersized injectors. Law of diminishing returns works in your favor in this situation.

 

[Razor]

How bout 150 PSI

Great posts

 

[R-R]

I could be way off on this but isn't the nozzle converting a set pressure/ volume into a much greater pressure with less volume? Wouldn't the discharge pressure be considerably higher than the nozzle inlet pressure?

 

[1badTTA]

It isn't increasing the pressure, it is increasing the velocity. The pressure remains the same (actually drops a little from the restriction), it just makes the fluid move faster. HTH

 

[granitestategn]

Cool! A post I can answer!

This is a rarity! A post I can actually shed some light on.

To reference your example of a Shurflo pump regulated to 25 PSI and a TR running 25 PSI boost in the up-pipe: You were correct, you would get ZERO flow. Nozzle size has nothing to do with it. It is strictly PSI to PSI. No differential......no flow. It's that simple. You may have a slight siphoning effect as the air flows over the end of the nozzle if it crosses it at a 90 deg angle. Try blowing across the end of a soda straw at a 90 deg angle with one end in a glass of water. The water should climb up the straw a little. The reason our fuel regulators are boost compensated is to negate the boost pressure in the manifold so that the flow rate for the nozzle is relatively constant. This is also one of the reasons that more alky pressure is generally better. There is less differential change across the nozzle port and therefore less flow drop as boost rises. If you want to see how a nozzle flows under boost pressure you can just reduce the pump output pressure by the amount of max boost you want to run.

Another fluid fact. As a fluid increases its velocity, its pressure decreases. That's why the top of the airplane wing is curved and the bottom is kinda flat. Air moving over a longer path along the top of the wing has to speed up because its path is longer than the air following the bottom of the wing. Since it has to go faster, its pressure drops and, voila, you produce lift. Lift is what make the darn thing stay in the air. Water and alky mix is a fluid and follows the same rules. As it speeds up, it loses pressure. We won't get into compressability, that's another subject.

Sad to say, but that's about all I got out of two semesters of Fluids classes in college.

And I thought it was totally useless knowledge!

Screw that stuff, I'm a "solids" guy anyhow.

Oh yeh, and electricity doesn't exist because you can't see it. Let's keep that one between us. I don't want the guys on the board that work for the power company to feel like they've been wasting their time.

 

[DMan]

Re: Re: Pressure

Originally posted by GraniteStateGN
To reference your example of a Shurflo pump regulated to 25 PSI and a TR running 25 PSI boost in the up-pipe: You were correct, you would get ZERO flow.

Ahhh.. another rocket scientist!

Hey Razor, think of an analogous electrical circuit. You got a battery followed by a resistor to ground. Vin, on one end of the resistor, is Vbat. Vout on the other end of the resistor is -0- or ground. Now suppose you connect a battery on that grounded side of the resistor. Potential across the resistor is now Vbat-Vbat or zero, and we all know that zero potential means zero current (aside from siphoning).

 

[Red Regal T]

My notebook is getting full. All of this good stuff will definitely get me into the 11s, I guess . More pressure and flow could be better if I need it in my typical application. I'm still at the original 60 psi of my Shurflo pump, same diy alky kit I started with, and I'm at mid 12s on street tires. One might guess I would have lower times on slicks. So I guess what I'm saying, mainly to those who wish to install alky for the first time, this rocket science is fine, but don't worry about it. This thread will not help you. You'll be able to go 11s even if you're just a dope like me.

 

[87natl]

Since we a ptossing around some abstract theories here:

If you were in a vehicle traveling at the speed of light, and you turned your headlights on, would they do anything?

 

[Red Regal T]

THAT'S EASY........YOU'RE BACKUP LIGHTS WOULD GO ON.

 

[Razor]

I wrote this post for two reasons, one was to play with pressure ideas..hence why I make a progressive controller, and the other was to throw some numbers/ideas around.

With that being said, it is clearly better to run a smaller nozzle with higher pressure than a larger nozzle with lower pressure.

May/more than likely... be a better scenario to run a jet size two steps smaller and crank the pressure up on the shureflow. So instead of 60 run 90-100 on a smaller jet..same alcohol volume, but less pressure balance loss.

 

[RKturbo6]

Ummmmm yeah what you guys said. Great thread, Now I can talk with the big boys down at the water cooler. Oook maybe not.

 

[Razor]

Russ, come down to BMP sat nite.. i'll be there at the tampa racing event. Weather permitting off course

info at www.tamparacing.com

Good to have another aspiring Buick in the area.

See ya,

Julio

 

[RKturbo6]

You know what I actually will be in town this weekend. So I think I can make this one. The funny thing is I have been buying DIY kit parts and could always use tips from one of the Alky gods.


Russ