Port flow and velocity questions
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
Oldstroker is too old to be a speaker. He would fall over his walker on the way to the podium. Wait, I think he is younger than me. Crap!
11 Second Club
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From: Albuquerque NM - The Land of 8000ft DA
Originally Posted by airflowdevelop
Hmm.. I was not aware that I was inflating anything...I kinda thought it was humorous. You where the one who insisted that you are a practicing engineer...
I often wonder why comments like yours are necessary when someone is trying to stop people from getting a$$-raped by marketing gimmicks and BS...especially when I am doing it on my own dime..for no profit to my self...
at no point did I indicate that I was the best, smartest, capable...won this, does that... Not a word.
Just trying to help a couple guys understand how things really work...simple as that. If I stepped on your toes..I am sorry for that.
I will stop trying to help now...as it must be inflating to my ego.
Dennis
I often wonder why comments like yours are necessary when someone is trying to stop people from getting a$$-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
Basically what I was trying to say by stating "practicing engineer" is I am well aware that what we think should happen isn't what is happening.
3 years working in an engines lab taught me that. We did have a flow bench and an engine and chassis dyno but we were concentrating on emissions and fuel economy more than power. We were studying fuel atomization using image capturing equipement in a dynamic cylinder. No equations, a couple of mother natures rules and empirical information.
again, sorry
TECH Resident
Joined: Dec 2004
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From: K-W, Ontario
Here's my angle on Density vs. Velocity:
The air can only move past the valve as fast as the depression is created
in the cylinder.
Since the piston isn't moving any faster at 10 PSI boost than it would be at 20 PSI
boost @ 3000 RPM,
the density is higher but the air speed into the cylinder is relatively the same.
The air can only move past the valve as fast as the depression is created
in the cylinder.
Since the piston isn't moving any faster at 10 PSI boost than it would be at 20 PSI
boost @ 3000 RPM,
the density is higher but the air speed into the cylinder is relatively the same.
On The Tree
Joined: Oct 2003
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From: harrisburg PA
Originally Posted by sscam68
Sorry, I misinterpreted your post.
Basically what I was trying to say by stating "practicing engineer" is I am well aware that what we think should happen isn't what is happening.
3 years working in an engines lab taught me that. We did have a flow bench and an engine and chassis dyno but we were concentrating on emissions and fuel economy more than power. We were studying fuel atomization using image capturing equipement in a dynamic cylinder. No equations, a couple of mother natures rules and empirical information.
again, sorry
Basically what I was trying to say by stating "practicing engineer" is I am well aware that what we think should happen isn't what is happening.
3 years working in an engines lab taught me that. We did have a flow bench and an engine and chassis dyno but we were concentrating on emissions and fuel economy more than power. We were studying fuel atomization using image capturing equipement in a dynamic cylinder. No equations, a couple of mother natures rules and empirical information.
again, sorry
Have you played with a pitot before? What kind of depression have you worked with? What style of head?
Dennis
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From: Albuquerque NM - The Land of 8000ft DA
Originally Posted by airflowdevelop
good deal..I don't like ***** waiving...and am glad none occured.
Have you played with a pitot before? What kind of depression have you worked with? What style of head?
Dennis
Have you played with a pitot before? What kind of depression have you worked with? What style of head?
Dennis
We weren't into head development, or modifications for that matter. This was experimentation at a university engines lab. We were using lasers and cameras to study air fuel droplets as they entered the combustion chamber with a moving piston. The block and the heads were separated approx. 2ft apart and mated with a single crystal cylinder. Custom piston was made and a direct fuel injection setup was fabbed to study "dry" air as it entered the cylinder. This was on a GM Ecotec.
Funding got cut, we cracked a cylinder and I got married. Now I work for the "nuclear complex". God I wish I could get back into this stuff again.
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Hey Tony I have no beef with you. I know your company makes great products and I waited 6 months for your 225 heads for my 403 but could not wait any longer and put another head on the engine. I closely follow your projects and think you have some great ideas. I just happen to be an old guy who grew up keeping and engine in the power band and consider that part of being a competent driver. As you intimate one size does not fit all and our understanding about how things work has to change as we develop new methods. I did not start this thread to **** anyone off but to learn from others much more knowledgeable than myself concerning the trend to larger ports that I have witnessed since the 60's. Your ideas about velocity and port size are not wrong but they are also not the whole story. I applaude GM for pushing forward in this area and I hope AFR comes out with a head like this with their own style and craftsmanship. Thanks for all the thoughts on this...this forum is a great educational device for me. Chuck
Originally Posted by airflowdevelop
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.
Our job as engine builders and head porters is to understand what is going on and try to make sense of it. Reguardless of what you want it to be doing, theories need to hold up to every situation and work with it, if it's wrong in one situation then the theory needs to be fixed. BTDT before on the forums.... I guess that applies the most to this thread in terms of mover velocity = better cylinder head port.... first off that's just plain wrong, and secondly it's WAY OFF in terms of being a theory that is right even 50% of the time.
Bret
With all these old air-flow experts posting in here, it's unfortunate that an explanation beyond something like "it's too complicated for you to understand" has come out yet... at least not one that has convinced me.
Cut to the chase. Is someone going to step up and make the statement that the air around the valve is at the sonic limit already for the entire intake opening event on a naturally aspirated engine?
That is certainly what you guys seem to be suggesting here.
The only other alternative to this would be the suggestion that adding 5psi of boost to the intake port automatically increases the pressure in the chamber also by 5psi at equal points during the intake cycle. This would in effect keep the pressure differential at the valve a constant and explain the mechanism that also keeps velocity past the valve a constant as you say.
I'm listening if someone wants to explain the mechanism that drives this "magic".
Cut to the chase. Is someone going to step up and make the statement that the air around the valve is at the sonic limit already for the entire intake opening event on a naturally aspirated engine?
That is certainly what you guys seem to be suggesting here.
The only other alternative to this would be the suggestion that adding 5psi of boost to the intake port automatically increases the pressure in the chamber also by 5psi at equal points during the intake cycle. This would in effect keep the pressure differential at the valve a constant and explain the mechanism that also keeps velocity past the valve a constant as you say.
I'm listening if someone wants to explain the mechanism that drives this "magic".
Why don't you give us something that proves your theory that the velocity increases as pressure increases....
We have the way the world works on our side.
Seriously do some googling on the sonic choke speed of a cylinder head port.
"Mean Mach" would be a good thing to look up.
Bret
We have the way the world works on our side.
Seriously do some googling on the sonic choke speed of a cylinder head port.
"Mean Mach" would be a good thing to look up.
Bret
Last edited by SStrokerAce; Apr 29, 2006 at 12:57 PM.
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Joined: Jun 2002
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From: Upstate NY
Originally Posted by H8 LUZN
yeah.. you even have my father beat... lol
Its always good to have the "old wise one" around... and i think we all know who carries that title!
Its always good to have the "old wise one" around... and i think we all know who carries that title!
"With Age comes Wisdom, but sometimes Age shows up alone."---Anon.
On The Tree
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From: Houston/ Austin, TX
So... out of curiosity, why is mach number in the port limited to .55? I can understad if it were much closer to 1 because of shock losses when you have local sonic air.
Maybe due to the turning angles in the head, there could be local sonic air with an average mach number of .55.... maybe someone can clear this up for me.
(FWIW... I find it kinda funny that aircraft diffusers are designed to have an inlet mach number around .55)
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On topic of velocity vs cfm vs port size... I think most people dont fully understand fluid flow and how velocity changes and entropy generation can effect "quality" of intake air. "Quality" of air really boils down to how efficiently the port can move the air without generating entropy. In a purely isentropic flow (no entropy generation) there would be no increase in stagnation temp or pressure, but this is all ideal.
A better port will keep temperatures down.
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On FI... one thing you didnt mention was that mach number increases as the square of the temperature, so if you increase the absolute temp by 20% then you can increase the mach number by ~9-10%, which is directly related to RPM, which is why blown cars tend to run higher RPM with a given head than NA cars.
Maybe due to the turning angles in the head, there could be local sonic air with an average mach number of .55.... maybe someone can clear this up for me.
(FWIW... I find it kinda funny that aircraft diffusers are designed to have an inlet mach number around .55)
-----
On topic of velocity vs cfm vs port size... I think most people dont fully understand fluid flow and how velocity changes and entropy generation can effect "quality" of intake air. "Quality" of air really boils down to how efficiently the port can move the air without generating entropy. In a purely isentropic flow (no entropy generation) there would be no increase in stagnation temp or pressure, but this is all ideal.
A better port will keep temperatures down.
---------
On FI... one thing you didnt mention was that mach number increases as the square of the temperature, so if you increase the absolute temp by 20% then you can increase the mach number by ~9-10%, which is directly related to RPM, which is why blown cars tend to run higher RPM with a given head than NA cars.
