air flow entry

[bob664spd]

Ok so I clean up the rust and flashing off the bowl and runner and make it nice and shinney with my 60 grit roll. I take down the guide and just smooth up everything. I only opened up the bowl and smoothed the short side, just what it needed to look like a normal head. This is a old rusty practice head. Also a 1.90 valve and a valve job awhile back. When I get to .500 I start to hear the sound go back and forth and cfm up and down. I started to do somthing around the intake and noticed the sound change and I gained 10 cfm. So I went on to .600 and it was completly turbulant and I put my hand across the clay flat and gained 10 more cfm. Is there somthing I am missing or does that just change the entry of the air into the runner and changes everything To the valve? Any thought on this? This air really flows on the floor and here is what I am getting.
lift cfm fps
100 77
200 138 250
300 180 325
400 211 391
500 225 415
600 237 410

From what I have been reading the speed is really high?
I was just wanting some thoughts on if this is common to pick up cfm with messing around with the clay?
Thanks

[jfholm]

[color=#000000]First of all are you Bob?

Somethings I have found on some of the stock ports that have problems you can gain by playing like you have done. On a 2000cc Pinto head I gained a lot of flow by sticking my thumb up about 1/2" above the floor at the entrance. It happens.

What kind of head are you doing? I would make a radius adaptor to bolt on at the port opening so it would be the same each time. If you search this forum you should be able to find some. If not let me know and I will post a picture of mine.

The speed is pretty high if it is a 2 valve domestic style head. For a drag racing head you would probably want around 260 fps. A good street head could probably go to 300 fps to 325 fps.

The flow characteristics you are talking about could be SSR or even the valve shape. Varies from head to head and is a trial basis thing. On my Dart 180cc Iron Eagles I was using some 2.05" Milodon Megaflow valves and at .450" lift the port went to heck as far as smooth flow. All I did was back cut the valve 35

[bob664spd]

Thanks for the reply John, Yes my name is Bob. I dont recall what the back cut is on this valve job, its been a long time since I was going to start on these heads.I guess I do need to look into a plate. To answer your quistions this is a Buick nailhead head. Last made in 1966. They dont flow real good stock they were more of a low rpm torque engine. Anyway the little bit I have done really kinda woke it up a little. Here is what I had stock
100 60
200 112
300 156
400 176
500 188
That is a stock 3/8 1.87 valve. I now have a necked down 11/32 valve in it at 1.90.
I think I am happy with these numbers fo now. I am going to put them on my car soon so I can drive it this summer. I have another old set I am going to try and max out this summer and see what I come up with. I will make a mold and all the stuff I am learning from this site on them.I have been reading a lot but I will be asking quistions. Thanks for any advice

Bob

[Flash]

Bob, with your new found air flow, you my need a custom made cam to work with your new found air flow.

In other works, if you put the heads on, and find the you lost a lot of bottom end............ then a properly timed cam may make you smile again.

Just somthing i wish some one would have told me before i ported my first heads, that i left behind, becouse i thoght I had made them to big!!!!!!! :O

[coulterracn]

I have a question about using a radiused entry plate at the intake port opening. I understand the purpose for using the plate, however the question I have is how much difference in port flow CFM when using the plate? will there be an increase in CFM?

I'm asking this question prior to doing my on test. The reason I ask is I'm flowing a pair of Trick Flow Twisted Wedge heads for a SBF. My friend and I are porting this set for his son.

I'm not getting the same flow numbers Trick Flow advertises. I'm still 29 cfm lower than Trick Flows advertised numbers and I've spent several hours on this intake port. I flowed an 'AS CAST' intake port and my readings were 40 cfm lower than Trick Flow numbers.

At this time I'm not using a radius entry plate nor shaped clay at the port opening. I have made an entry plate and going to get some modeling clay and flow the 'AS CAST' and ported ports again for my own learning experience.

Ray

[GordonE]

Hi Ray!

If you use a radiused entry ther will be a big differens, I wouldnt be surprised if you gained at least 30CFM.
On smaller ports this makes eaven bigger differance, because the higher air speed.
The area that the air must go trough is only a percentage of the total port inlet area if i understands it right. In the lower pictures you can see different values, that i belive can be translated to the area of the restriction.

There is a big differance between 0.98 and 0.80 as your case should have!



Heres a picture of different Coefficients of Discharge



Hope you found some more CFMs!

/Gordon

[coulterracn]

Thank you Gordon

This is the type of information that makes sence to me. The old saying 'A picture is worth a thousand words' is alive and well. You have explained alot in what to me is simple terms and easy for me to understand.

I used the string in the port method earlier in my test to see where the air was moving the best and hugging the wall. I noticed the string fluttered in the turbulance in the center of the port. I the first picture I see how the entry plate will correct this and give the air more direction in the center of the port.

Ray

[bob664spd]

Hi John, as for the velocity I am seeing would opening the port some slow down the velocity some? I know this is going to take trial and error. I know the biggest valve I can use is a 1.94. Also is there a minumuim distance I should stay with for unshrouding a valve?
Thanks
Bob

[coulterracn]

[jfholm]

[stevenford]

Never test without a radius entry

search Vena contracta

[johno]

I realise that flow-testing with-out a radius entry will usually give lower readings due to contraction at the port mouth at higher flows, but would'nt it be better to test with the actual manifolds that will be run on the engine? I try to do most of my flow-testing with manifolds fitted as i have found readings can vary dramatically between manifolds! Case in point; my 202ci 6 cyl drag head , after much time and money, was flowing 105.7cfm bare. I returned several days later with same head and my four barrel manifold and carby fitted, flow dropped to 103.6cfm @ 10". Not happy with that manifold/carb system, i decided to borrow a triple-webber manifold and carb set-up to try. There i found a HUGE (for a holden 6!!) improvement and flow hit 115.5cfm @10" ! Now i realise there is huge difference between the two 'systems', and maybe i was seeing a boost from 2nd harmonic wave reflection, but using the radiused guide in bare flow-testing gave me incorrect readings!! ???

[jfholm]

One reason you at first test without an intake manifold is to give you access with a velocity probe (pitot tube). The radiused adaptor kepts things constant and repeatable and to me makes the port act more like it will with an intake manifold attached. I notice a big improvement in the smoothness of the port once I install my intake on my small block Chevy.

You will not get any effects from wave action like you mentioned unless you are on a running engine. When you are on a flow bench the intake may direct the air better and thus the gain in air flow. I would be willing to bet if you put a radius adaptor on the head and flow it you will see that gain in air flow over with 4 barrell intake. The weber manifold is going straight in with no bends so will flow much better than 4 barrel manifold with turns in it.

John

[johno]

Sorry mate, i was-nt thinking at the time i wrote it, i meant to say a 'Ram effect' caused by the 'branch' style manifold as, of course, there would'nt be any induction pulses/pressure waves when testing on a flow bench. You have convinced me that i should pull my finger out and make some flow entries!! Do you have any diagrams/plans for any? :;):

[jfholm]

Here is what I use. Keep in mind it is the finished port size and I have it mounted on a port that I have not ported yet in this picture.
John