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............by someone that knows what they are doing. For any particular cyl. head would one type of porting be better than the other?

More detail can be provided if necessary.

Tony
 

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............by someone that knows what they are doing. For any particular cyl. head would one type of porting be better than the other?

More detail can be provided if necessary.

Tony

A Computer Numerically Controlled Head if done with a good program
is better than a hand ported head! All ports that are cut with that program will be exactly the same it don't matter how good a hand porter is he can not reproduce the same port every time! If a CNC ported head is done properly The person that is doing the job first sonic testes the head finding the thin spots then using this data the program is printed to maximise the port for that head!

This is not to say all CNC heads are better than a good hand ported head!
 

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Ok that sound about right, anyone else with something to add about this topic?
Only that CNC-ported heads are digitized for a computer controller from a hand-ported head. ;) This has a few benefits and at least one possible negative.

First benefit is that only one nearly perfect hand-ported port must be done. If we *assume* it was done really well, then (benefit #2) all of them will be equally good. Also, CNC port programs can then be modified to cut test ports much faster and more accurately than hand ports, with very specific changes for additional testing and improvements.

The first negative is that all the ports are identical - generally thought a pure benefit. The issue is that flows are not the same between the end and center ports, nor front to rear, and where experience and skill come into play. However, the ability to make the same port, but with changes just for a specific location is nearly impossible in the real world for most.

If given a choice for hobby and semi-pro level engines, it seems that starting with all ports the same (identical with CNC) is most productive, if they are then modified for individual flow as-required. I know there area high-end heads out there that are fully CNC, but each port is not the same, adn the pro teams pay big for them. ;) Hope that makes sense.

David
 

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Discussion Starter #6
Thanks for that info, quite informative. I had never thought about flow being different at different ports in a cyl. head even if all the ports are identical.

So it sounds like a CNC fully ported head just "might" not be the cat's meow as compared to a hand ported head (ALA you know the person doing the porting knows what he's doing).

Now the reason why I'm asking this question, I will start wrenching on my 09 Z06 next week removing the cyl. heads and having them fixed (due to the valve guide issue LS7 heads have). While the heads are off I will be doing a cam swap also and will get the heads ported too.

I don't trust any local shops to do this job so I'm doing the labour AFA the re & re and the heads are going to a highly recommended shop on the west coast of the US. They will be hand porting my heads since they don't use a CNC program.

LS7 heads are already CNC ported from GM but apparently there are still areas in the ports that can benefit from porting so that's what I'm doing.

Tony
 

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Get this book, David Vizard's How To Port and Flow Test Cylinder Heads,
ISBN 978-1-934709-64-1. Great stuff!
 

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Good, bad and ugly of CNC work

Some shops that CNC heads don't even have flow benches. They as well as some that make the aftermarket heads Just increase the port by 5, 10, 15% give or take its length. This doesn't work that great often as this or that wall want more or less this or that.

The port is cut from the valve side in ward then from the intake face inward.
Were they meet in the middle for best results needs to be hand blended. Many shops just make the walls wider instead of doing the hand blending which gives a better air flow, air speed and port volume balance.

Shops to increase production will use larger steps for the cutter path.

To begin CNC work often its best to go after some areas were the cutter could catch or become deflected possibly causing damage to the equipment head or the intended port shape in areas

After the CNC work is done and hand blending is need it can be taken a bit further by hand than CNC but it can be the difference between 600.00 of port work and 1500 dollars. I am not necessary adding in part costs.
At the 600.00 point say a stock set of DOOE heads might flow 235 CFM @.500, going to the 1500.00 point flow might go as high as 250 260 @ .500 lift

The 1500.00 ones are for some really competitive classes for the most part and not needed really for street strip.
 
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