Porting the VW/Audi 8v head with port energy discussion

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Re: Porting the VW/Audi 8v head with port energy discussion

Post by jarmoyp »

Maybe not 30 cfm back but most..
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Re: Porting the VW/Audi 8v head with port energy discussion

Post by Smoke ring »

Carnut1 wrote: Thu Nov 30, 2017 6:06 am Smoke, is that a bolt on for VW RB head?
Doesn't appear it is. Here's the link to where I found it with some talk of using Toyota stuff in the mix. https://www.vwclub.co.za/forum/viewtopi ... 94&t=86891
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Re: Porting the VW/Audi 8v head with port energy discussion

Post by Smoke ring »

jarmoyp wrote: Thu Nov 30, 2017 6:11 am Maybe not 30 cfm back but most..
I have no doubt if the carnut got a hold of it he'd work it over until it flowed proper, and then some 👍
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Re: Porting the VW/Audi 8v head with port energy discussion

Post by Carnut1 »

Smoke, if it followed the rest of the weeks work it would lose 40 cfm!
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Re: Porting the VW/Audi 8v head with port energy discussion

Post by Erland Cox »

Carnut1 wrote: Sat Nov 25, 2017 5:52 pm 2017112495150412.jpgAngled ssr experiment string held top right roof intake .35" lift. Notice all three string pics show very steady high speed airflow. Strings did not change position at higher lifts. The angled ssr may not show higher cfm but I believe the smoother the string the more laminar the flow and I feel that is worth power. Input welcome. Thanks, Charlie
The flow is never laminar, it is always fully turbulent.
What you mean is that the flow is following the port walls without separation.

https://www.grc.nasa.gov/www/k-12/airpl ... ndlay.html

https://en.wikipedia.org/wiki/Stall_(fluid_mechanics)

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Re: Porting the VW/Audi 8v head with port energy discussion

Post by Carnut1 »

You are right Erland, there must be a way to clarify that with some bench time you can hear the difference between a more organized port vs. a port that sounds different and usually flows less with similar csa.
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Re: Porting the VW/Audi 8v head with port energy discussion

Post by mag2555 »

It's been my finding that shallow Exh ports like these ( long side ) coupled with a average amount of production Head short turn height like these Heads gulp down the biggest mass of Exh flow down into the bowl and roof on the cylinder wall side once the valve is open a given amount.

Anything you can do porting wise to give this natural flow bias / tendency less restriction helps to calm down turbulence especially at the lift point where the mass of flow changes from following its way around the seat angles and valve head ( path of least restriction) to where the increased air mass must now follow the shapes and contours of the port at increasing velocities.

Most ports like these are always dealing with two different air speeds trying to merge from different areas of the bowl and that takes some time to think about getting that down to a minimum!

Many times you have to give up some high lift flow for a noiseless port that flows more average air across a lower lift range, and if you are not flow testing with atleast a 45 degree bent tube on the port your just plain full on foolish!

My rule of Thumb is the unless a Exh port has a very gentle overall bent to it, or its atleast 1 1/2 to 1 3/4" deep from the bottom of the 45 seat I never hog out the valve guide area on the Intake valve side of the bowl transition from the rear wall to the roof.
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Re: Porting the VW/Audi 8v head with port energy discussion

Post by Erland Cox »

Never raise the roof on this type of exhaust port.
This will only worsen the separation over the short turn.

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Re: Porting the VW/Audi 8v head with port energy discussion

Post by mag2555 »

Yes true!
I widen the roof as much as possible after pitot tube checks as to which side of the port after the crown of the short turn that the mass wants to favor.
As always let the air go the way it wants to first before trying to guide it else where!
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Re: Porting the VW/Audi 8v head with port energy discussion

Post by Carnut1 »

vw1.jpg
The way this port is developing is interesting. Looking at this string pic the center of the cylinder is on the left side of the port. The ssr likes to be angled lower towards the center of the cylinder and the upper right hand side of the picture is the cylinder wall roof likes some enlargement, not too much. The bowl likes to be relatively tight and the throat percentages kept low. The exhaust is actually developing very similar. My highest flowing intake port was 188 cfm @ .5" lift, I decided to just cut it deep to water and see what happens. Widened bowl, throat ratio, raised roof and widened the faster parts of the intake. I was rewarded with a port that delivered 175 cfm with much slower velocity with water hole plugged. The swirl also dropped from 1777 rpm to 910 rpm. On this application of hot street design and a small cube motor, swirl will be important. Remember that my swirl meter is below my usual bore adapter and a 2" VW block slice so that swirl number is how fast the impeller is spinning inside the large bore. Thanks, Charlie
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Re: Porting the VW/Audi 8v head with port energy discussion

Post by Erland Cox »

When angling the floor that way the flow will move towards the bore wall and spiral down.
I have also found it to be beneficial.

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Re: Porting the VW/Audi 8v head with port energy discussion

Post by mag2555 »

Your findings with the height of the floor left to right are what I have seen also!

Efforts in Expanding and lowering the floor on the cylinder wall side makes for a situation where added flow over the short turn on that side just can't get out and around the tight fit of the chamber wall at a certain rate of flow.
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Re: Porting the VW/Audi 8v head with port energy discussion

Post by peejay »

I don't know what "RB" is, but I do have a twin DCOE manifold for the non-crossflow heads that I'd bought for my GTI.

The ports look STRANGE. They have to go from maybe 50mm to the port opening in only a couple inches (the firewall needs modified regardless) and the ports also have to clear the mounting bolts, so the port gets a kind of strange corkscrew funnel kind of shape. I had only been planning on running 40mm DCOEs, so the idea I had was to do some massive epoxy-filling in the ports.
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Re: Porting the VW/Audi 8v head with port energy discussion

Post by Carnut1 »

RB is the engine designation, would you be able to post a few pics of that manifold? Modifications to the firewall are out on this project but cutting and welding on stock manifold are a good possibility. Thanks, Charlie
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Re: Porting the VW/Audi 8v head with port energy discussion

Post by Smoke ring »

Charlie, if I had to do this here's the approach I would take. Cut the flange to head off, cut the plenum where the throttle body connects off, figure out how much plenum volume you need and runner length, how much taper in the runners it should have if any, get a half inch plate for runner plenum entrance and dress it as needed to flow and make your new plenum box and runners and rebuild the thing. Burr finish all the internal areas and have a local welding shop tig the thing together. If time is money and hp is the ultimate goal this makes the most sense to me. It's gonna take cutting and welding to make anything out of it anyway, just as well make it what will work the best. Just my opinion.
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