MUSTANGEATER

iTrader: (10)

Dennis,

You are the man, has Bret told you about Malarks yet?


Floyd

airflowdevelop

malarks? must not have..not familiar.

MUSTANGEATER

iTrader: (10)

you need to ask lol.

Ed Wright

iTrader: (1)

Hell, I barely stumbled through an Oklahoma high school.

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!

SScam68

iTrader: (20)

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

Adrenaline_Z

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.

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

SScam68

iTrader: (20)

Pitot tube, yes plenty of times for a lot of different experiments.

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.

ChucksZ06

iTrader: (9)

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

SStrokerAce

iTrader: (2)

If you think what I said was right on... this is even better.

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

Old SStroker

Vintage 1943.

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!

white2001s10

iTrader: (4)

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".

SStrokerAce

iTrader: (2)

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

Old SStroker

"With Age comes Wisdom, but sometimes Age shows up alone."---Anon.

Ed Wright

iTrader: (1)

Nov 7, 1943 here.

DavidNJ

I'm not telling. However, my brother-in-law was born during the Hoover administration.

disco192

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.