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Old 08-11-2008, 12:35 PM   #1
methaddict
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Default Valve job questions, need answers from experienced head porters

I have my heads at Portflow in Harbor City, CA. I gave Tom a call today and he says after removing the valves on the intake side he says there's a lip on the "long side", he called it "core shift" and that any shape on the valve seat whether they do a 3 angle or 45 with a radius won't matter because the air flow will just hit that lip and disrupt the flow. He says it just needs to be ported. That's just the way it comes the factory. He said he'll lap them so I could see what he's talking about and that I needed to come down so he could show me.
Any experienced porters know about this "core shift"?
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Old 08-11-2008, 02:36 PM   #2
methaddict
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I googled "valve job core shift" and found an explanation on an archived Endyne tech question/answer section:

Sand casting is the dominant form in the automotive industry...some using pressure as well. In order to cast a hollow and complex component you must have a core box that you insert the compressed sand and resin "female" ports and water jackets in. There is frequently some misalignment, howecer most takes place during the process of pouring the aluminum into the completed core box = mold. After cooling the box is opened and the process of vibrating the sand from the water jackets and ports begins. When there is a slight shift, you'll see a casting (mold mark) in a port, even after the head is ported. Any material removal in an area where the shift went the wrong way might make the port pretty, but it'll cost in flow. There are many heads that people feel cheated on because the porter didn't remove any material here or there, but fact is the head probably needed material added in those areas.............=$$$$.
The Asian heads are certainly better than domestic pieces, as far as being "out of the box" good, but with the exception of some Toyoda pieses we were involved with back in 1987 (they were investment cast), I've yet to see a "perfect" head casting that had al the shift in a favorable direction.
You'll be seeing some new and innovative casting technologies in the OE soon, and the heads will be so uniform that I really don't thing anything other than a valve job which will allow one to taylor low lift flow vs. mid and high will be necessary.

So it sounds like, during the process were sand is seperated by vibration there may have been a shift in the cast itself. I'll be headed down to Portflow to see what he's talking about. I'll try to take some pictures and post them up.

Last edited by methaddict; 08-11-2008 at 02:47 PM.
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Old 08-11-2008, 03:14 PM   #3
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Interesting......
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Old 08-11-2008, 03:14 PM   #4
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I think I may have run into the same problem. I took my heads to a motorcycle guy to do the seats, motorcycle guys use a post style machine which rotates around the seat to get it uniform. But he said if these were motorcyle heads he would throw them out because the material in the seat was so shifted. My heads are ver. 8 JDM.
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Old 08-11-2008, 04:09 PM   #5
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If you have oversized valves installed and open up the throat a bit more, it could help get rid of that edge you're talking about. Otherwise, you could just ask the guy at portflow to just lightly break that edge with a die grinder so that the air isn't hitting a 'wall', so to speak. I wouldn't worry about it so much since the bulk of the air flow follows the floor and short turn of the port anyway... so a little edge on the long turn might not make a big difference. I wouldn't be real concerned about it imo..

By far the worse import cyl head core shift I have ever experienced is the modern mitsubishi 4G63.. Honda heads are the best, Subies are middle of the road.
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Old 08-11-2008, 04:53 PM   #6
methaddict
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Just got back with some pics:

Sorry text is to small. It says this is a pic from under the valve seat that shows the lip where the seat overhangs over the casted port and would disrupt airflow as air flows up between the valve and the seat.

See the shadow on the right side under the seat. Well that's how much it overhangs over the port.

The mark in the middle of the valve edge is where the valve seals against the seat right now. They're going to move the 45 angle more to the edge then transition into a radius. So by doing this there was no need for larger valves.


So Tom said what they have to do is bore out the throat on the valve seat then hand port the bowl. So there really was no need for larger valves. Plus he told me larger valves usually brings the edge of the valve too close to the edge of the combustion chamber which would then require opening up the combustion chamber.

Last edited by methaddict; 08-12-2008 at 11:56 AM.
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Old 08-11-2008, 05:32 PM   #7
charliew
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The core shift happens when the forms are set in the mold. They aren't exactly straight and then when the cnc cuts the insert for the valves in the casting, it is offset. That void seems to be on most of the subie heads I have. Moving the seat "ring" out isn't as good as bigger valves and that might completely clean up the void area. If you cut the stock seat insert thinner it might clean up yours but not some of the heads I have. When the seat is moved out the valve has more of a possibility of burning if the seat is too close to the edge of the valve also a lot of head guys put in larger valves on the stock seats and cut the seats inserts thinner to fit the larger valves which is what they are doing to your heads but staying with the stock size. I would ask for the difference in cost to go with larger valves on the stock inserts cut out larger you will wish you did after it's back together. Flow test have shown a improvement with bigger valves. And over 6500 you will see the difference. I would imagine the improvement would be more on a 2.5 than a 2.0 though.

Check out all the head stuff already posted on larger valves.

Last edited by charliew; 08-11-2008 at 05:38 PM.
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Old 08-22-2008, 05:45 PM   #8
methaddict
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Picked up my heads yesterday. Tom from Portflow says these heads will flow almost as good as full ported heads due to having to bore out the throat of the seats and porting in the intake bowl area. Here are some pics showing the portwork to the core shift under the seats:





Brian Crower 272 cams installed:

Supertech black nitrided intake, inconel exhaust valves and resurfaced.
Supertech 70lb dual springs, ti retainers, and alloy seats, new oem retainers and keepers installed
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