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Old 12-01-2022, 11:18 AM
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Default Head flow revisited by vizard

I found this insightful (if ya got a Chevy..) but seems our factory iron Heads do not have this problem. Surely though, awareness and bowl cleanup is well-guided with these thoughts by Vizard.

https://www.youtube.com/watch?v=eLJU1h-raUg

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Old 12-01-2022, 12:51 PM
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On our Pontiac heads or any head that has a push rod pinch point area reduction, that area does not become a restriction until the port area after it ( down stream from the pinch point) is saturated with air flow, unlike other parts of the Intake port.
This is because the push rod pinch is a mostly straight lenght of runner .
This ties in with the other cut in stone rule about high speed air, that being with anything sharper then a 15 degree change in flow path a large high speed air mass will just sheer way staying on the path of least restriction.

Also you just can't A/B our Pontiac heads in regards to the push rod pinch area with a SBC because our post 67 heads have a 14 degree valve inclination angle and the SBC has a 23 degree.
This factor greatly changes how much of a restriction the push rod pinch is from the bottom to top of the runner.

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Old 12-01-2022, 08:24 PM
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Agree-able. does sbc have a pushrod bulge pinch?
How about that sbc bowl far-wall vs PMS, and corresponding flow, for PMD design advantage.

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Old 12-01-2022, 10:52 PM
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Quote:
Originally Posted by 25stevem View Post
On our Pontiac heads or any head that has a push rod pinch point area reduction, that area does not become a restriction until the port area after it ( down stream from the pinch point) is saturated with air flow, unlike other parts of the Intake port.
This is because the push rod pinch is a mostly straight lenght of runner .
This ties in with the other cut in stone rule about high speed air, that being with anything sharper then a 15 degree change in flow path a large high speed air mass will just sheer way staying on the path of least restriction.

Also you just can't A/B our Pontiac heads in regards to the push rod pinch area with a SBC because our post 67 heads have a 14 degree valve inclination angle and the SBC has a 23 degree.
This factor greatly changes how much of a restriction the push rod pinch is from the bottom to top of the runner.
Steve,
Have you ever cut a Pontiac head apart like David did the SBC and flowed the pieces? If so what was your findings.

Thanks,
Stan

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Old 12-02-2022, 01:43 PM
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No I never have Stan, but now you have given me something interesting to try and accomplish on Sunday.

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Old 12-02-2022, 11:40 PM
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Surely our 2.11" valve flow way more than the chevy 2.2" valve (140@25" 151@28") at Half-Inch Lift.

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Old 12-03-2022, 06:57 AM
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Actually you would be wrong about that if your talking about peak flow numbers.

In terms of a SBC 1972 era head like a 487x casting with its 1.94” intake valve the peak flow @.600” can be 205 cfm, which is a dead match for the average Pontiac head with a 2.11” valve from the factory.

This is because the Throat in the SBC heads like the 487x is a hair bigger then our D port Pontiacs.

Even a hood SBC 462 casting with a 1.94” intake will break the 215 cfm@28” mark at .600” lift..

The SBC Vortec 906 casting with its 1.94” valve will top 225 cfm.

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Old 12-03-2022, 12:09 PM
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Quote:
Originally Posted by Half-Inch Stud View Post
Surely our 2.11" valve flow way more than the chevy 2.2" valve (140@25" 151@28") at Half-Inch Lift.
Mark,
I think you are missing the point of the video. The point is to take the head you want to work on and find the point of least flow. Many people are time / money limited. This will show where to get the best results for less amount of time / money. Also the point of least flow will not always be in the same place in the port this depends on the head design.

Stan

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Old 12-03-2022, 03:49 PM
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I was surprised that in-the- video, the modern sbc chevy 2.2" valve section flow poorly due to the far wall.

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Old 12-03-2022, 06:12 PM
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Quote:
Originally Posted by 25stevem View Post
No I never have Stan, but now you have given me something interesting to try and accomplish on Sunday.
Steve,
I just talked with David (I had some other thing I needed to talk to him about) and ask him if he used a radius entry on each piece when he flow tested them and he said yes.

Stan

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Old 12-03-2022, 06:45 PM
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Thanks Stan.
Yes, I would think that he would would have rigged up a way to do such..

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Old 12-04-2022, 11:26 AM
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Yea, ya have to use something to rid the 0.6 coeff of entry "the discharge coeff", yet at some length the form becomes a nozzle or venturi that really helps the velocity rise for flow.

I use an intake port form ground from 3/4" aircraft plywood. I've seen some folks go to 2" longk clay forms, to get the good numbers. Pedestrian Disclaimer is i go for lowest noise, not numbers.

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Old 12-05-2022, 09:27 AM
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Quote:
Originally Posted by 25stevem View Post
No I never have Stan, but now you have given me something interesting to try and accomplish on Sunday.
Steve,
Were you able to work on this?

Stan

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Old 12-05-2022, 09:47 AM
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I have a good start on it Stan.
I do not have any heads that are poor enough to just cut up like David did, so I made a mold of the port and will today order some casting resin to then make a mold of that to cut up and flow test.

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Old 12-05-2022, 10:11 AM
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Hmmmm, so Vizard has a video about raising the floor about a Half-Inch, for nearly 25% CSA drop yet gets record CFM, HP, TQ, discharge efficiency, and BMEP.

Then he shows how to reliably epoxy (Goodman epoxy, or JB-Weld was deemed okaay) the floor, and grind to new shape. Also makes the pushrod bulge blind straight view to the bowl.

If you could mold around a good cfm silicone Intake form, then raise the floor & straighten the bulge to bowl ( toss uniform CSA a first) then see what the CFM (and noise) yields.

That would be great.

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Old 12-05-2022, 10:13 AM
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Steve,
That sounds great. Which head casting did you use to make you mold?

Stan

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Old 12-05-2022, 10:17 AM
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Quote:
Originally Posted by Half-Inch Stud View Post
Hmmmm, so Vizard has a video about raising the floor about a Half-Inch, for nearly 25% CSA drop yet gets record CFM, HP, TQ, discharge efficiency, and BMEP.

Then he shows how to reliably epoxy (Goodman epoxy, or JB-Weld was deemed okaay) the floor, and grind to new shape. Also makes the pushrod bulge blind straight view to the bowl.

If you could mold around a good cfm silicone Intake form, then raise the floor & straighten the bulge to bowl ( toss uniform CSA a first) then see what the CFM (and noise) yields.

That would be great.
Mark,
Do you have any high end CFD software at work where this type of thing could be done?

Stan

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Old 12-05-2022, 10:26 AM
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I have a Siemens CFD package at work but I would need to have the port in Solidworks or similar CAD software.

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Old 12-05-2022, 10:47 AM
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Quote:
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Mark,
Do you have any high end CFD software at work where this type of thing could be done Stan
No. But have evaluated CAD abilities for "in-pipe" flow (including thermals in the fluid-air) vs propeller environments. Solid Works, et al is fantastic for "in-pipe" flow of intakes and exhausts.

Toughest part was getting the intake runner shape into CAD: hand-held scantools exist now to scan a runner mold into CAD, clean any warts, and go.

Yet, FWIW, a PSA:
However, propeller/wing evals are bogus on 100% of the CAD-Sims out there, SW being just okayreason is all propeller (car drag coeficient too) SW environments put the air volume in motion (air has momentum, this has the energy!!) and keep the propeller (vehicle, wing etc) in a fixed position, like a wing tunnel. So 100% of the Reference models are "standing on their head" yet the professional go by the results for mediocre aircraft. NASA Ames had a chance to turn that around over a decade ago, but propriety has kept it to "ya cannot CAD that until ya spend the money to develop the CAD equations from models: empirical data required to make models.

Very clever propeller code does exists by/with a tiny few applied to competition use (thrust, noise, smooth), but doesn't see daylight nor the internet due to propriety, and awaiting funding to pay for their sweat equity. Proposals into our Mil have gone uninterested despite the begging need to keep our Mil propeller plane crew from nausea from props drumming the fuselage. A big deal.

Such open-air flow-code would be in the same boat as Vizards camshaft synthesis tool. Adopt when funded the work to develop the code for physical models-in-motion. Who wants to run models in motion THRu STILL AIR, to record the forces in X, Y, Z? Decades...

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Old 12-05-2022, 05:32 PM
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Stan I used a 6X-4 casting.

This will likely flow little more then pre 74 heads since the runner is more rectangular then the other heads.

If all this casting work does not turn out to be a big project then I may do the same to a 1968 casting.

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