I'm just about ready to cc the new heads I have - and assuming they will have varibility in the chamber size - from one to another, I will have to match them.
I understand the procedure/methods for obtaining the correct cc for each chamber - but I don't get as to where I can remove head metal from the chamber. I keep hearing about unshrouding the valves - and read as much as I could get off the internet about this - but very little BASIC details were found.
What is this unshrouding? Where does this prodecure on the head take place? I'm guessing and hoping the valves do not have to come out for this
Pictures or diagrams would be very helpful - but probably not existant on the internet
I'm trying to get this engine back together and running by the end of this month.
The valves must come out to unshroud, the area of the port behind the valve is the restriction to be removed, to allow smooth transition to and from the head.
Thanks volksrod, It is a little surprising; remove the valves, remove a little metal from the area put the valves back, measure cc again probably wrong, ....take the valves out remove a little more metal, put the valves back in, measure cc - still not enough metal removed?..... take the valves out...
I'm not an expert either, but I understand unshrouding the valves is not related to cc'ing the chambers... Material removed between the valve head and the port will not make any change in the volume of the combustion chamber. Others need to chime in here... Volksrod's answer was to the question, "What is unshrouding?" As usual, if ya want the right answer ya hafta ask the question carefully! -BaH
Unshrouding means making more room for fuel mixture to flow OUT of the port, PAST the valve. INTO the combustion chamber. The biggest obstacle is the combustion chamber wall right next to the valve, on 3 sides. (The tub shaped chamber). You remove material from all 3 sides where there's room for it, to allow the mixture to flow in smoothly. The most challenging obstacle is the one where the combustion chamber vertical wall is closest to the cylinder wall. You can't remove much material there, but you should at least remove AS MUCH as you can, all the way to the cylinder wall distance, to remove the "step" you'd otherwise have there. This step is especially harmful on the exhaust valve side, because it obstructs exhaust gas flow TOWARD the exhaust port.
This is all done on the combustion chamber side, and it does indeed lower the compression ratio. To bring the CR back up, you need to have the heads flycut to suitable height. The "tub" then gets smaller in volume.
I have a ton of pictures I could share, even been planning to put together a whole how to-article regarding headwork. Maybe later.
The blue marker lines show where to remove material from. First, you place the bare cylinder into the head, and then you scribe a mark all around the cylinder edge on the inside, where it meets the head. Use a sharp object or a pen to draw the outline of teh cylinder onto teh head. That's how you know how deep you need to cut, what the safe distance is. I extended the "unshrouding" to the sides of the valve too (both valves) because there was not much room for improvement immediately by the cylinder wall, the distance is so short from the valve to the cylinder wall. But there was more flow to be found on the sides still.
Headwork in general does include the port work you mentioned. The most critical areas behind the valve face are the valve seating surface angles. The backside of the valve (facing the port) often has room for improvement, only a narrow band on the seating surface actually contrinutes to valve sealing and heat transfer. The rest needs to be shaped to allow better flow: remove ridges and steps that are on the way of the mixture flow. Some grind a smooth radius, but most prefer a "3-angle valve job" where the radius and smooth transition is achieved in steps, but much more moderate steps than if there was just one big step. Same angles must be machined on the seat side too, not just the valve.
Ok, now let's go in a few mm deeper, this was JUST at the opening. The next step, haha, is the STEP where the steel valve seat ends, and the aluminum head material begins. Due to manufacturing tolerances, there usually is a distinct step where these two meet. You should blend this area of two metals so that there's no step. "Seat blending".
the rest of the ports may need work too, depending on the engine. Sometimes a light cleaning is enough, but sometimes you need to do more. The idea is to try to straighten the path for the mixture flow, and to eliminate unwanted turbulence and obstacles. You don't always make the port bigger in diameter.
I'll just leave it at that. The rest is arguable and depends entirely on the rest of teh engine and the nature of it.
Jan wrote: "I have a ton of pictures I could share, even been planning to put together a whole how to-article regarding headwork. Maybe later"
Dang, now I'm going to have to add to my 'to do list" - that is to harrass Jan on a weekly basis to get those pictures up - : )
Jan, those pictures would be incredibly helpful. I have to keep rereading this stuff to get a good feel on what to do. I wish there were classes or something on how to do this - or a short video production ( hint, hint).
Without pictures, it still is hard to know when you've overstepped your actions and caused damage to the head ( i have a spare head or two and cylinders to work with, but still )- and the test is putting it all back together ( which is work), and coming across a problem, tearing remove and tear the engine down again and forking over more $$ for another head for another try. Going down that path, I'd like to have a very good chance of doing it right the first time!
Why was it said in the first post that you have to remove the valves to do this work - was that incorrect? Looks like I could dremel some of the upper area out within the blue lines that you marked - and stay far away from the valves -. How in the world do people learn to do this stuff?!
With as much thanks as I can express without monetary input;!! Matt S
Glad I was able to goober it up enough so the right info came out! Thanks Jan. I was not thinking very clearly was I? It all makes perfect sense now. -BaH
You remove the valves so you don't damage them while working on the combustion chamber. On the other hand, that leaves the very vulnerable seats unprotected.. one very good solution is to use some old junk valves to cover the holes while you dremel away. You need to go VERY close to the valve and seat with the rotating file, in fact with the bits I have (some are pretty slim) I still have to remove the valve to get good access to the area right next to the seat. Be very careful, one slip and you ruin the sealing surface, and the seat has to be re-ground and valve lapped in again.
A simple way of increasing flow and "unshrouding" teh valve would be to just cut off a wedge shaped area, starting from the blue line I showed in teh picture, and going straight towards the edge of the valve. But this isn't enough. You need to have a deep dish shape to the wall, almost a straight drop down from the blue line, and then as you get closer to the bottom, it radiuses towards the valve head. This is proper unshrouding, because the flow from the intake port is directed to the SIDES of the valve, it's trying to spread out in all directions like a flower. What it likes is a smooth, gradually changing path with no steps or sudden turns.
For efficient combustion, you want the "tub" walls to be as steep as possible, directing the gas expansion towards the piston. Any power from the combustion that spreads sideways, is power lost. You want gas expansion towards the pistons in a contained small space. If the edges of the "tub" were heavily slanted towards the cylinder wall, the flame front has to travel further sideways and the gas expansion would also travel sideways. Same thing with "squich" or "quench" area.. the flat portion of teh combustion chamber around the "tub". You should aim for the smallest safe deck height possible, to reduce the volume in that inefficient area, forcing the fuel mixture to concentrate in the tub area instead, where the spark is closer. The difference may sound marginal but it shouldn't be overlooked when building a high performance engine. I probably didn't explain this too well. A drawing could be nice... let's see if I can come up with one :)
Oh about removing valves: You also need to remove them if you do any port work at all (you should, while you are at it) because the shavings need to be washed out. Besides you don't even get to the critical parts of the ports without removing the valves.
ask, if it's unclear. When looking at the picture, remember that you are comparing the combustion event in two different shaped chambers, with all else being equal: Amount of fuel, air/fuel ratio, compression ratio, etc.
So the issue here is "how to get most piston-pushing power from a given amount of mixture"
BTW on high performance engines, HEADS are the most critical part.... the ultimate bottleneck, and the parts that offers most reward for modification.
Good heads are kind of pricey, but so is modifying "cheap" heads to perfection... Even the best high perf "ready to install" heads could use some cleaning up.
I bought a pair of cheap EMPI big valve 044 heads, long reach plug and more metal around the combustion chamber etc.
Price with valves and single race springs and other hardware: $750 Open up for 90.5 and flycut 1-1.5mm: roughly @100 Professional porting and flow bench testing: @250 Seat and valve modification: $100
Plus I have done a lot of combustion chamber work myself, unshrouding and radiusing and polishing.. several hours of work
That's way over a grand in cheap heads alone. :D
How much were those level 5 heads again at aircooled.net... ? hmm.. checking.... around $850 with similar mods. Darnit. (Shipping cost would hurt me)
How much was the rest of the engine again? LOL nevermind. Thank God I can do most of the work myself...
ahh, that explains a lot Jan, especially with the diagram. I am going to practice on some old heads I have, and probably will pick up one or two old heads real cheap to practice more. The only tool I have right now is a dremel tool to eat away at the metal I guess that should work I'm new at this as you can tell, but wanting to learn. I'm wondering what tool you use to compress the valve spring - I'll have to check some catalogs. Thanks so much for your help!!! & gtreat idea about using old valves to protect the new ones................. though will be still waiting for more pictures : )
How to Hotrod Volkswagen Engines by Bill Fisher published by H. P. Books, Tucson, AZ, 1970 ISBN 0-912656-03-4 (excellent book, well written and researched)
Once you work your way thru this, Berg has a good writeup on heads which is more modern, but you should get the book first, if only because it has lots of other good stuff in it, as well as photos of head work.
BTW, I think you'll find that a Dremel is too light duty for this. You need what is called a die grinder, I recommend an electric variable speed one. The air powered ones will remove metal faster, but that can be a problem.
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----------------------------------------------- Jim Adney snipped-for-privacy@vwtype3.org Madison, WI 53711 USA
Jim, Thanks so much for taking the time to write. I do have Fisher's book, - a very old copy- and the pictures are not quite clear in some areas. Also the booklacks in defining some terms. Maybe I have to study it more in depth. But the pictures inthat book vs what Jan showed me -Jans was so much more clear. I would love for somone to make a video about head cc'ing as well as other aspects of balancing parts, and other attention to getting the most out of your engine - as well aspects relating to making high performace engines - as well as the appropriate tools to be used. I think that owuld be great and betting there would be ample market for the effort.
I think the Fisher book is a terrific start for anyone interested in learning and understanding what they should know to get good reliability and power out of their VWs, but it's true that it isn't perfect and almost nothing it. I'm glad Jan's photos helped more.
My copy was new in about 1977. I probably first saw this book in about '71 or '72, but didn't buy one 'til later.
Berg's white papers on heads and porting are also useful. They have no photos at all, but you will be able to understand most of them once you have understood the Fisher book and Jan's photos.
I'm ASSUMING that Berg still sells those "white papers."
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----------------------------------------------- Jim Adney snipped-for-privacy@vwtype3.org Madison, WI 53711 USA
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