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Port and Polish by Comiittee thread (Cool pics throughout)

 
Old 03-15-2008, 10:28 AM
  #61  
John Speake
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Your right to leave it to a clean up of manufacturing steps and irregularlities.

Bil Blydenstein, who was a very successful head tuner here, told me that he spent 40 years finding out where NOT to remove metal.

Hammer is right about not removing metal from the bottom of the port. The idea is to encourage the inlet charge to flow down into the cylinder. To achieve this some people work on the upper wall of the inlet to try and encourage this effect, and don't flatten out the lower wall.
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Old 03-15-2008, 12:08 PM
  #62  
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Originally Posted by Vilhuer View Post
Were these S3 or later head design?
the heads I have are Euro 16V heads, from a M28/11 or 12, if I remember correctly.

I'd have to go back and check the casting numbers.....

while I realize there are plenty of 32V heads out there (in the later cars) not much has been done with the 16V engines. there was some effort (and publications) to upgrade the US spec heads to flow like the Euro's, but I am not aware of much other than that.....

As Nickens Bros told me, these will now out-flow a standard 32V head (the one that I took in for comparison). And they should know.....they've experimented with 4 valve heads for their Hemi Pro Stock engines, but in the end they had better HP #s with the current canted 2 valve head they are using. Similar gains were realized with Dave Koffel's B1 big block Mopar heads (canted 2 valve).

back to my putting together some re-engineering for the cam towers......

--Russ
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Old 03-15-2008, 03:04 PM
  #63  
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The go-to guy for 16V heads and flow issues may be Lucky Ekman, the "EK" in the original (pre Marc and Susan) DEVEK operation. IIRC, he's headquartered in Florida someplace. Lucky has a wealth of 16V performance knowledge.

The slightly rough "finish" on an intake port may contribute some to laminar flow, at least in theory. Right around the valve area the flow is anything but laminar so no worries there. Exhaust the same way, especially on a long-duration cam profile.


In my deep dark past, I used to send heads for cleanup to a couple people, depending on the type of engine. Customers with Euro were treated to work by a guy who was working for Racing Services. He had a flow bench, and some very sophisticated (for the time) measuring tools and techniques. The port and chamber work was exquisite, with costs to match. Intake ports were never mirror-polished, for the reasons stated previously for carbureted engines. Exhaust ports were --always-- mirror polished, both to help avoid soot buildup and to limit heat transfer to the metal head.

Folks with American engines were traeted to another guy, and independant who had a huge following the in the road-race ranks. I built a primitive flow bench for him, and watched his work get refined and more consistent when he saw the actual results. He --always-- mirror polished both ports even though there was no measurable benefit shown. He said that customers came to him for a 'port and polish', so that's what he gave them.
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Old 03-15-2008, 03:50 PM
  #64  
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Originally Posted by largecar379 View Post
the heads I have are Euro 16V heads, from a M28/11 or 12, if I remember correctly.
I meant 4V head used in comparison.

I also asked them to do a volume comparison with a junk 4 valve head I had, and they said the 16V Euro's would easily out flow the 32V (read: cfm's)
Since '85-86 MY S3 head is totally different compared to '87-95 versions, result might not apply to later style if head used in comparison was from S3.
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Old 03-15-2008, 03:54 PM
  #65  
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I know the limitations of where I am in this. I do not have the experienced to change port shape, but as people have suggested, I don't think there is a problem in at least radiusing the face margin on the exhaust valve, and making sure there are smooth transitions, except for where steps are needed, like where the headers start - usually a step is required at the bottom of the port for anti-reversion and some sort of "tumble" that I read about.
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Old 03-15-2008, 04:01 PM
  #66  
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Originally Posted by Warren928 View Post
I have done porting and polishing on an engine, woke it up quite nicely, and looking at your last three pics, you could get in there and take out 2 mm of there all the way around, but not near the valve stem or seats, taper it down to nil near those points. You gotta change valve sizes if you are going to port all the way to the seat. Then make sure you match port the intake manifold side and gasket to match in terms of material removed.
.
When you say "take out 2mm" are you talking about taking out that casting transition on the intake port near the seat? Because you mention not taking it out near the seats - I guess I am confused - maybe smooth the transition but don't throat it totally into the seat?
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Old 03-15-2008, 04:25 PM
  #67  
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Brendan,
Travers Tool sells what you want. I can't make a link but if you go to their website & search page 945 you want the Cratex rubberized abrasives they sell. If you want to take off more material (I don't think you do) you'll need 6" carbide burrs. The Cratexes are what you need to blend the bowls & polish areas. They work fine with a dremel tool.

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Old 03-15-2008, 04:34 PM
  #68  
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If you are just looking for simple clean-up, have you considered extrudehone?

http://www.extrudehone.com/
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Old 03-15-2008, 04:49 PM
  #69  
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Originally Posted by 6.0-928S View Post
Brendan,
Travers Tool sells what you want. I can't make a link but if you go to their website & search page 945 you want the Cratex rubberized abrasives they sell. If you want to take off more material (I don't think you do) you'll need 6" carbide burrs. The Cratexes are what you need to blend the bowls & polish areas. They work fine with a dremel tool.

Hammer
Thanks Hammer. What do you think about that transition just above the intake seat? And that hard edge above the exhaust port?
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Old 03-15-2008, 04:50 PM
  #70  
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Originally Posted by bcdavis View Post
If you are just looking for simple clean-up, have you considered extrudehone?

http://www.extrudehone.com/
I have. Infact, I considered it all the way back when I was 13 and read a hot rod mag about the process - but the heads are already essentially rebuilt, and I am concerned about what would happen to the valve guides and the seat cuts.
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Old 03-15-2008, 05:03 PM
  #71  
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Originally Posted by BrendanC View Post
Thanks Hammer. What do you think about that transition just above the intake seat? And that hard edge above the exhaust port?
Blend in the valve bowls. (the area under the valve seats) Remove all sharp edges. Just imagine water being drawn through the ports & remove any edges that you sense would disrupt the flow. Then smooth & blend in all of the changes you make.

Hammer
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Old 03-15-2008, 06:04 PM
  #72  
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Originally Posted by RyanPerrella View Post
I was thinking about what it would cost to have the ports CNC machined.

CNC porting is becoming pretty common on aftermarket heads for US iron. What would it cost to do that for 928's? Its got to be the optimum way for getting more power and an equal flow in all 8 intake ports and exhaust. I imagine you would need to make a 3D model of the heads which maybe difficult but probably not impossible but once you have a single model then you could run the software and see via CFD where the problem areas are and if there is enough material to remove then write a program for all the ports. The initial pair of heads would be where all the work would come in but then once you have the program for the 5 axis machine you can have the ports duplicated and i dont know how a guy with a grinder would do better then using a modern CFD program along with a CNC machine to get the best results.

Not sure what it costs to do a pair of heads on a 5 axis CNC machine, maybe someone could chime in on what that would possibly cost. I think there are allot of people that would spend $1000 for a pair of CNC ported heads on a 15-20K stroker for sure. I think if the results were good on standard 5.0L cars then anyone doing a headgasket would probably have the heads ported as well. I know i would if it got another 30HP, but who knows, it could produce more. I guess you would want to optimize the intake setup then but i think the ultimate in port work would be done with computers using real tech with the Computational Fluid dynamics stuff thats common place in racing now along with the repeatability of the CNC machining doing the actual cutting.

Anyone else looked into this?
Ryan I think to right the program to have them machine would cost a fortune but it would be the way to go every port would be done evenly.
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Old 03-16-2008, 02:02 AM
  #73  
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Its weird that no one from other forums is even interested in discussing this.
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Old 03-16-2008, 02:18 AM
  #74  
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Originally Posted by BrendanC View Post
Its weird that no one from other forums is even interested in discussing this.


as I said earlier.....the number of shops that do this sort of head work is probably very few.

Especially when the Porsche name comes into the equation......and that drives the price through the roof. Flowbench time can be very, very expensive.

I was fortunate that Nickens Bros looked at my heads as just another small block Chevy build (wedge head), with overhead cams.

32V is another story---twice as many valves, twice as many ports (even though they blend into 8 intake/8 exhaust ports).

These mods are sort of along what a banned person said some time ago:

the number of people (read:market place) that are able and willing to spend large amounts of money for certain performance products (stroker, supercharger, turbo's, etc) is probably less than 200 folks worldwide.


I'll bet it's half that.......and that's what we're up against.

--Russ
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Old 03-16-2008, 02:25 AM
  #75  
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Originally Posted by RyanPerrella View Post

Anyone else ever heard of a dimpled combustion chamber design before?

Can you say Chrysler HEMI (the late version, in 4 door Chargers, 300's, trucks, and coming soon Challenger)

the block is essentially an early HEMI copy (315, 331, 354, 392), and the heads have a dimple in the chamber.....

--Russ
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