Port flow and velocity questions
04-28-2006, 12:53 PM
#41
No velocity isin't dependant on the pressure differential. The mass flow of the FI application is higher due to it's higher density.
For example a 700hp NA motor and a 700hp FI motor at the point where they both make peak power. (1000rpm different) The FI motor can have a pressure difference between the port and cylinder by about 4psi, where the NA motor is about 1psi. The velocity in the FI motor is slightly higher there, but over the entire lift curve it's about equal since at valve opening the NA motor has a large pressure difference due to the scavenging and at closeing due to the wave pressure effect. The big difference is the amount of CFM going into the motors. The FI motor can have 40% more CFM flowing thru the carb/TB, but it's usually at a much higher temp, maybe 200° F more.
It's a pretty complex situation, but if you have the same size venturi and valve and 700hp, reguardless of FI or NA, cubes or RPM the motors are moving that air/fuel around the valve in the same velocity range. Which makes sense because if it was all about velocity the sonice choke point would be reached much to quickly in the NA motor. There are so many things in play here that you need to look at the whole situation at hand, temp, pressure, mass flow ect all play into this.
Seriously do a little reading on sonic choke in intake ports, you can't rape mother nature, and you can't get much over .6 MACH in the intake port.
Bret
For example a 700hp NA motor and a 700hp FI motor at the point where they both make peak power. (1000rpm different) The FI motor can have a pressure difference between the port and cylinder by about 4psi, where the NA motor is about 1psi. The velocity in the FI motor is slightly higher there, but over the entire lift curve it's about equal since at valve opening the NA motor has a large pressure difference due to the scavenging and at closeing due to the wave pressure effect. The big difference is the amount of CFM going into the motors. The FI motor can have 40% more CFM flowing thru the carb/TB, but it's usually at a much higher temp, maybe 200° F more.
It's a pretty complex situation, but if you have the same size venturi and valve and 700hp, reguardless of FI or NA, cubes or RPM the motors are moving that air/fuel around the valve in the same velocity range. Which makes sense because if it was all about velocity the sonice choke point would be reached much to quickly in the NA motor. There are so many things in play here that you need to look at the whole situation at hand, temp, pressure, mass flow ect all play into this.
Seriously do a little reading on sonic choke in intake ports, you can't rape mother nature, and you can't get much over .6 MACH in the intake port.
Bret
04-28-2006, 02:02 PM
#43
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Originally Posted by SStrokerAce
No they both work on the same concept... the difference is the amount of CFM flowing into a motor at the same RPM, you increase DENSITY of the air charge in a FI motor. The velocity stays the same, the issue with a FI motor is that the difference between the cylinder pressure and port pressure stays at a more constant difference. You can have higher pressure differences in a NA port relative to the cylinder pressure than you can in a FI motor, but this is only at certain times of the intake valve lift curve.
There is also virtually no help from pressure wave tuning in a FI motor, The boost pressure is a much higher pressure at work in the motor.
The FI port might want to be larger due to the high volume flowing thru it, but that's when you start sizing the port due to the HP level you are working with rather than the RPM and cubes below it.
Bret
There is also virtually no help from pressure wave tuning in a FI motor, The boost pressure is a much higher pressure at work in the motor.
The FI port might want to be larger due to the high volume flowing thru it, but that's when you start sizing the port due to the HP level you are working with rather than the RPM and cubes below it.
Bret
Does the port for FI start acting almost like a chamber vs a runner on an FI'd app?
Hope that makes sense.
04-28-2006, 02:03 PM
#44
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Okay then maybe you can explain it to me so I can understand?
When you go from 15psi in the intake port up to 20psi (5 lbs of boost), then what exactly happens to the velocity of the air moving past the intake valve?
For that matter, what exactly happens to velocity in the port when you turn up the pressure drop on a flow bench?
If I'm not understanding the mechanism that imparts force into the mass of air to cause it to move and accelerate, then what exactly is the force that does it?
When you go from 15psi in the intake port up to 20psi (5 lbs of boost), then what exactly happens to the velocity of the air moving past the intake valve?
For that matter, what exactly happens to velocity in the port when you turn up the pressure drop on a flow bench?
If I'm not understanding the mechanism that imparts force into the mass of air to cause it to move and accelerate, then what exactly is the force that does it?
Last edited by white2001s10; 04-28-2006 at 02:40 PM.
04-28-2006, 02:34 PM
#46
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Originally Posted by SStrokerAce
When you increase the pressure the density gets higher the motor doesn't move the air faster, it just moves more of it.
Bret
Bret
^^These are terribly simplified, and assume laminar flow (ignore the right side equation), but volumetric flow rate depends on the pressure differential. I don't remember how velocity changes due to pressure differential right now, though. I could probably try and look something up. I like this thread
04-28-2006, 02:35 PM
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Bret,
You are correct, sir.. This is probably one of the hardest things for people to understand, and very difficult to explain to someone who has not played with air. You have done one heck of a job explaining it, and next time the question pops up...I will be giving them your phone number! J/K.
You are correct, sir.. This is probably one of the hardest things for people to understand, and very difficult to explain to someone who has not played with air. You have done one heck of a job explaining it, and next time the question pops up...I will be giving them your phone number! J/K.
04-28-2006, 02:42 PM
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Well I don't understand yet.
Let me clarify one important part of my question.
I'm not talking about velocity increasing in the main part of the intake port, but only around the valve.
Let me clarify one important part of my question.
I'm not talking about velocity increasing in the main part of the intake port, but only around the valve.
04-28-2006, 02:54 PM
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In that case, you are going to need to know the flow at each and every lift as well as the frustrum area. Then you can begin to figure out the velocity at the valve. It changes with lift and flow. Plus, its not equal on all sides of the valve. The top, long turn, will have more velocity than the short turn side.
This is getting into some pretty deep turbulant fluid dynamics!!!!!
This is getting into some pretty deep turbulant fluid dynamics!!!!!
04-28-2006, 02:58 PM
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I understand...but all fluids and gas have a theoretical maximum. .55 mach is about it for atmo air at normal conditions.
it is ...what it is.
take a garden hose with 50psi of pressure (well over 1k" of water). poke a .010 hole in it. observe the speed the water is moving, Now, based on your theory, if we put a .100" hole in the hose, the water would slow down considerably...I sure hope you are wearing a rain suit for this experiment.
Dennis
it is ...what it is.
take a garden hose with 50psi of pressure (well over 1k" of water). poke a .010 hole in it. observe the speed the water is moving, Now, based on your theory, if we put a .100" hole in the hose, the water would slow down considerably...I sure hope you are wearing a rain suit for this experiment.
Dennis
04-28-2006, 03:11 PM
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Originally Posted by airflowdevelop
take a garden hose with 50psi of pressure (well over 1k" of water). poke a .010 hole in it. observe the speed the water is moving, Now, based on your theory, if we put a .100" hole in the hose, the water would slow down considerably
04-28-2006, 03:43 PM
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Originally Posted by airflowdevelop
I understand...but all fluids and gas have a theoretical maximum. .55 mach is about it for atmo air at normal conditions.
it is ...what it is.
take a garden hose with 50psi of pressure (well over 1k" of water). poke a .010 hole in it. observe the speed the water is moving, Now, based on your theory, if we put a .100" hole in the hose, the water would slow down considerably...I sure hope you are wearing a rain suit for this experiment.
Dennis
it is ...what it is.
take a garden hose with 50psi of pressure (well over 1k" of water). poke a .010 hole in it. observe the speed the water is moving, Now, based on your theory, if we put a .100" hole in the hose, the water would slow down considerably...I sure hope you are wearing a rain suit for this experiment.
Dennis
You guys need to be more consistant with your analogies. You're talking about two totally different fluids. One is compressable, the other isn't.
I think its part of the reason people are confused.
04-28-2006, 03:53 PM
#53
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Originally Posted by sscam68
Old SSTroker and Dennis
You guys need to be more consistant with your analogies. You're talking about two totally different fluids. One is compressable, the other isn't.
I think its part of the reason people are confused.
You guys need to be more consistant with your analogies. You're talking about two totally different fluids. One is compressable, the other isn't.
I think its part of the reason people are confused.
The reason people are confused, is due to the fact that they want things to work by the manor that they think, not the manor that it really is.
their is no single formula that can prove what is occuring in an intake port, and assuming something works the way you believe due to the fact that it "makes sense" is absolutely wrong.
04-28-2006, 03:55 PM
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Originally Posted by white2001s10
I don't see how making a bigger hole is the same as increasing the pressure by 25%.
04-28-2006, 04:42 PM
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Originally Posted by airflowdevelop
what does this have to do with sonic choke....nothing.
The reason people are confused, is due to the fact that they want things to work by the manor that they think, not the manor that it really is.
their is no single formula that can prove what is occuring in an intake port, and assuming something works the way you believe due to the fact that it "makes sense" is absolutely wrong.
The reason people are confused, is due to the fact that they want things to work by the manor that they think, not the manor that it really is.
their is no single formula that can prove what is occuring in an intake port, and assuming something works the way you believe due to the fact that it "makes sense" is absolutely wrong.
But to be talking about water and air in the same context does cause some confusion. And I wasn't referring to your point about sonic choke.
04-28-2006, 04:42 PM
#56
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Originally Posted by sscam68
Old SSTroker and Dennis
You guys need to be more consistant with your analogies. You're talking about two totally different fluids. One is compressable, the other isn't.
I think its part of the reason people are confused.
You guys need to be more consistant with your analogies. You're talking about two totally different fluids. One is compressable, the other isn't.
I think its part of the reason people are confused.
It's exactly because air is a compressible fluid that a makes it possible to supercharge an engine. The 'charger packs more of the molecules into a given volume. Liquid pumps don't do that.
FWIW, a lot of supercharger technology came from piston aircraft engines during wartime. As you climb above sea level air pressure (air density) decreases, as almost everyone knows. Well, the few that don't probably don't frequent these forums anyway.
At 18,000 ft. the air density is about 50% of sea level, so NA engines are down about 50% on power. By adding a "density increaser" we are able to get back some of that sea level power. Unfortunately when superchargers were invented, the marketing guys didn't like "density increaser" for the generic name. They thought "supercharger" sounded great, and would allow them to sell some to the gullible horseless carriage folks (Mustang drivers) after the war was over. At least they didn't call it a "supervelocity pump". The Germans call it a kompressor, because it "compresses" the molecules of air closer together; in other words, it increases the density.
OK, another analogy: how do you evacuate the most people from a building with only revolving doors?
1) one person per segment and spin the hell out of the door?
2) maximum occupants per segment and normal revolving speed?
Assuming there is a pressing (pun intended) need to evacuate, it's my contention that humans will intuitively behave much like air molecules in a supercharger; they will pack together and move at a normal or slightly higher velocity. Well, a couple of posters in this thread might not.
04-28-2006, 04:44 PM
#57
Originally Posted by airflowdevelop
what does this have to do with sonic choke....nothing.
The reason people are confused, is due to the fact that they want things to work by the manor that they think, not the manor that it really is.
their is no single formula that can prove what is occuring in an intake port, and assuming something works the way you believe due to the fact that it "makes sense" is absolutely wrong.
The reason people are confused, is due to the fact that they want things to work by the manor that they think, not the manor that it really is.
their is no single formula that can prove what is occuring in an intake port, and assuming something works the way you believe due to the fact that it "makes sense" is absolutely wrong.
04-28-2006, 08:06 PM
#58
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Ed,
I don't think I can feel my forehead anymore.
Do you have any practicing engineers teaching you how to tune?
Oldsstroka-mabob..
I wish I had your english...you should be a speaker.
Dennis
I don't think I can feel my forehead anymore.
Do you have any practicing engineers teaching you how to tune?
Oldsstroka-mabob..
I wish I had your english...you should be a speaker.
Dennis
04-28-2006, 08:26 PM
#59
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Originally Posted by airflowdevelop
Ed,
I don't think I can feel my forehead anymore.
Do you have any practicing engineers teaching you how to tune?
Oldsstroka-mabob..
I wish I had your english...you should be a speaker.
Dennis
I don't think I can feel my forehead anymore.
Do you have any practicing engineers teaching you how to tune?
Oldsstroka-mabob..
I wish I had your english...you should be a speaker.
Dennis
You done inflating your ego?
Last edited by sscam68; 04-28-2006 at 08:42 PM.
04-28-2006, 09:29 PM
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Originally Posted by sscam68
You done inflating your ego?
I often wonder why comments like yours are necessary when someone is trying to stop people from getting a$$-raped by marketing gimmicks and BS...especially when I am doing it on my own dime..for no profit to my self...
at no point did I indicate that I was the best, smartest, capable...won this, does that... Not a word.
Just trying to help a couple guys understand how things really work...simple as that. If I stepped on your toes..I am sorry for that.
I will stop trying to help now...as it must be inflating to my ego.
Dennis