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DIY Z6 Manifold Porting

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tools used:



1,2,3 took off themajority of the aluminum. 4,5,6 did the touch ups. then followed by a sanding drum and finally flapping wheel.









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better shot of the runners


runner 1


runner 2


runner 3


runner 4





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end results.








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top section that was cut off. first try with sanding flapper


wasnt satisfied so i went back for more and higher grit





im still not finished. i have to order the snake attachment for the dremel so i can get all the way down the runners. i want to smooth out the 90* bend below the plenum.


will most likely have it brazed back together. and mated to a 60mm throttle body



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so... you are essentially doing this for nothing then?


You are not doing one of the most productive parts of a P&P job and you have no clue if you improved it or just made it worse. very smart.

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ive enlarged the runners, increased volume in the plenum, removed most of the casting marks thus increasing air flow.


anything helps. now if i were to remove an amount of metal that would cost me the midrange power that the z6 manifold attributes to then yes i made it worse. but i havent. i actually have yet to touch the majority of the runners. and the only thing i have done is enlarged the ends and removed the casting marks.

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That's just it, widening does not equal increase airflow. Removing casting defects will help, but smoothing out the metal surface doesn't directly improve airflow either. Smooth metal does not mean faster air flow.


To hit upon a few of these topics with more than just flaming:


smooth surfaces usually cause air to flow with more turbulence and the total flow becomes less as the velocity of turbulent air is reduced. The reasoning for this is that with a smooth surface the air brushes against it and is slowed down and the air behind it swirls around the slower particles and disrupts the entire flow. The textured surface is faster because the uneven surface of the metal catches and holds air molecules in the crevasses and the air moves more smoothly and with less friction across an air to air border then an air to metal border. Ever wonder why a golf ball has dimples?


Wider is not always more volume into the chambers. Depending on your air filter, intake tubing and throttle body the volume of air entering the intake manifold is a fixed quantity depending on the rpms the motor is running at. The intake runners are specifically shaped to funnel the air into the tubes proportionally and they narrow down as they approach the combustion chambers. During this process the air volume has not changed and the air is being compressed which makes it flow into the chambers at a much higher velocity. If you widen the runners too much the air will not properly compress and you will end up with a net negative in the quantity of air into the chamber.


This is why you need a flow bench to get your before and after cfm rating.

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thats all find and dandy but i have absolutely no access to a flow bench. and ive heard time and time again that i should not worry about flow benching or port matching if its a daily driven car. if it were a track car that would be a different story


and if doing this will hurt, then why does the performer x and edelbrock manifolds have such large plenums? and very large runners?



in the runners i am merely going to remove the casting flaws. at the ends of the runners is where i enlarged them, but very very slightly.

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You can make your own flow bench with a shop-vac, a workshop bench and an airflow meter. Google it, son. The readings you get do not need to be industry precise. Even if your readings are not perfect your margin of error will be the same on both before and after. you just need to get before and after readings on your manifold to see if you improved it or made it worse.


There is a possibility you will stumble across a combo that works great and flows better. Larger runners and plenums does not mean it is bad, it just does not guarantee improved performance simply because it is larger. The aftermarket intakes would have all been tested for improved flow across the board. The entire package works together to improve airflow.

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yeah thats true. i am trying to get the computer fixed first before i get started on anythign else. but ill look into the flow bench.


the runners i didnt actually enlarge, just removed the casting marks. and i havent even gotten all the way down the runner.


ill check things out and see what i can come up with

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