velocity and tubulance

[bob664spd]

Hi I didnt know what area to ask about this so here we go. I finally put the velocity probe on and also put a string to my intake port . at 500 lift it was at 380 and 390 on the floor just in front of the short side radius and half way up it goes down to the low 200s. With the string it is straight as a arrow on the floor and the string goes crazy as you go up. What I am asking is if any one thinks I should go after this roof area and try and get the velocity evened out? I know that this huge guide needs to be taken down. Also I know it is going to be trial and error. Any Ideas?
Thanks from another new guy.
Bob

[jfholm]

It would help if you give us what type of head it is - valve sizes - what is the flow cfm and at what lifts. Does the flow go backwards at the convergent lift? That is where the window area that the lift has created equals the square inches of intake vale area. That is usually about 1/4 if the diameter. i.e. if you have a 2.00" lift the convergent lift would be .500" whcih is equal to 1/4 of the diameter of the valve.

John

[200cfm]

What cylinder head? Any photos of the port? Making a mold helped me a lot. Do you have a mold yet? That is a high speed for laminar flow on the floor. I don't see that number until the floor starts to roll over the "event horizon" of the SSR. (tom)

[bob664spd]

It Is a buick nailhead. The intake is a 1.87, very small . small runner also. It is seeing about 215 at the 500 lift. but it is hitting a wall at 400. It does not go backwards, it onlly gains1 ccfm or stays still after 500. I have not touched the thing with a tool yet. This runner has a slight curve to it. I am told there is very good swirl with this head.Thanks
Bob

[bob664spd]

trying to post a picture

[bruce]

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[86rocco1]

[bob664spd]

Edited By bruce on 1238960102

[jfholm]

You know, it seems to me that for 1.87 inch valve 215 cfm is not too shabby for an untouched port. A stock small block Chevy with 1.94 intake valves is around 202 cfm stock.

John

[bob664spd]

John and everyone, I was mistaken. I had to go out and look at my notes. I went out and redone the intake . This intake has some bowl work done and ssr. I also went from a 1.87 to a 1.90 11/32 valve. I have a old head I am starting to work on and am comparing the two runners. I was surprised that at 500 I heard the sound change and the cfm went down. I am going to work on the roof and guide. The velocity that I am posting is the best # I could find on the floor just in front of the ssr area and the other # is up top in the roof area. I think I will play with this and see what happens.
lift cfm ssr area roof area
100 76 227 180
200 138 286 204
300 185 373 261
400 202 406 343
500 195 411 324
600 192 401 324
The runner was not ported, just clean the rust off
Thanks
Bob

[jfholm]

Looking at the flow numbers I would say that the SSR needs to be worked on. Lay the SSR back some but don't necessarily lower it. Here is a rough drawing, the red lines are the NEW port profile and you can see what I suggest for the SSR
John

[larrycavan]

I'd see if I could get some area on the tight side of the guide. Then use the string to figure out where the flow is becoming detached from the walls....

Actually wait a sec. Let's start at the start.

Get your port data first.

Throat % in relation to the valve size.
CC the port, get the centerline measurement and calculate your current Avg CSA.
Measure up your bowl and see how it relates in & to valve size.

This is just me...but I always like to have all that data aquired before I go grinding away at anything.

Once you get that sorted, then go hunting for CFM.

JMO