street
Posted a lot
6.2 ft/lbs of talk
Posts: 4,662
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So i've got my new cylinder head for the CVH sitting on my bench. Its already been skimmed a little and I set about looking at how to improve the flow of it, as i've heard the CVH is quite a poor performer in this area. I've never done this sort of thing before, but I got a few sanding type attatchments for the drill of various sizes and some 40 and 80 grit sandpaper anyway and began working to the old adage "The quicker you get the gasses in and out of the head, the more efficient it will be" by very carefully smoothing out any ridges, bumps, steps and generally improving the flow, whilst not altering the shape of the chamber much. Eventually I will polish up the exhaust chambers and leave the intake ports in an 80 grit roughness to keep the fuel air mixing nicely. Now, questions for you retro riders are: 1. What are "3 angle or 4 angle valves"? Is it something I can do/can be done to my valves or valve seats? Or is it something you buy? 2. Inside the ports, the short steel tube sticking out of the top where the valve goes through- is that called the valve guide? Or is it the valve guide boss? Or is it neither?!? Are these the things that need changing for this head to run unleaded? (as its a leaded fuel head) Is this the part the people reccomend 'streamlining' to make it less obstructive? How is it done? Bit techy, and I know someones going to say the magical words "Dave Vizard" while pointing towards the library (which is something i will get hold of and read) but i'm just fishing for any info on the subject from any of you seasoned DIY head modifiers  Thanks for reading  |
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3 angle cuts 3 different angles on the valve seat in help flow. Its a machine shop job.
yes, they are valve guides
No thats not what is replaced for unleaded. For unleaded the valve seats are replaced with harder ones.
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oh, and the bit that people recomend 'streamlining' might be the usual bulge where the valve guide exits the head (inside the port) if that makes sense.
don't start grinding the valve guides ;D
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i would also like to add ive never seen a head of any description other than vw beetle and mk1 scirocco. Ive also never ported anything, or seen a ported head, but I'm confident what ive said is right. Others will confirm/deny though |
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street
Posted a lot
6.2 ft/lbs of talk
Posts: 4,662
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oh, and the bit that people recomend 'streamlining' might be the usual bulge where the valve guide exits the head (inside the port) if that makes sense. don't start grinding the valve guides ;D Cheers VW ;D Yeah I think thats the bit I mean, tried to take a pic but its too dark to show up  So where the valve guides exit inside the port, that can be re-shaped? Some of it removed maybe? |
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i don't know, i just know what the bits are. Someone will tell you though.
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Sounds like you've got it sorted! Doesn't sound like you're doing it, but you can make the throats in the cylinder head too big mind - and loose velocity. I know that lower velocity causes the fuel to drop out of suspension in the inlet manifold but I'm not sure it's much of an issue in the head itself? And avoid a shiny finish ;D Just to satisfy your request - Dave Vizard A series book has some good general head work stuff, as does Four stroke Performance tuning by Graham Bell (I haven't tried it myself yet but it all seems very logical and well thought out/proven!)  IIRC if the valve guides protrude into the flow, you can usually buy 'bullet' ones that have smoother ends, or race profile ones that sit flush with the head. Not sure if they do them for yours but I'm sure someone could help. |
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Last Edit: Oct 5, 2006 14:57:32 GMT by Lewis
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Seth
South East
MorrisOxford TriumphMirald HillmanMinx BorgwardIsabellaCombi
Posts: 15,538
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Valve guides (the steel tubes) can be modified where they sit in the port by shortening and/or "bulleting" the ends but I would want to check with someone that knows the particular engine type before going ahead with that kind of thing.
Three angle valve jobs can help improve the flow and it is sometimes also possible to "waist" the valves themselves by removing material new the valve head but again I would consult an expert first or you might find the valve heads fall off....
My suggestion is that you simply remove any rough casting marks and smooth it all out a bit as it is possible to do more harm than good if you don't know what you are doing and go too far. You could also check to make sure you don't have an awkward step between inlet/exhast manifold and the head itself and that the gaskets don't cause any obstruction either.
There is a huge science to head work and I don't profess to know much of it but by keeping it simple you can't really go wrong or scrwew it up should you get a pro to do it in the future.
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Follow your dreams or you might as well be a vegetable. |
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B-8-D
Posted a lot
down to one car!!
Posts: 4,038
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one more tip.
spray wd40 or such like into the water jacket around the port u are grinding.
that way if that area is getting thin it will heat up and the wd40 will "smoke" thus indecating that u are about to break through! and u can stop before all nastynesses happen!!
si
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That's a great tip! Cheers ;D
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If you do break through, JB weld works ;D
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B-8-D
Posted a lot
down to one car!!
Posts: 4,038
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If you do break through, JB weld works ;D your right it does.... ive used it for ramping in ports before to great effect!! si |
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street
Posted a lot
6.2 ft/lbs of talk
Posts: 4,662
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Thanks all for your help, all taken on board It is quite a science isn't it, ive been reading little snippets elsewhere on the net and its incredibly complex if your really getting into it! Think i'll take you lots' advise and just stick to a little cleaning up and matching the ports to the manifolds for now. |
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slater
Club Retro Rides Member
Posts: 6,390
Club RR Member Number: 78
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When you match the ports make sure the hole in the inlet mainfold is slightly smaller than the hole in the head and vise-versa for the exhaust. don't try and match them exactly. A. its harder tog et them exactly the same B. Its works better with a lip to prevent gas trying to go backwards down the port.
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Normal carbide burrs wont cut it (no pun intended  ) they will clog very quickly and go blunt as the heat rises. You can get ally cut burrs, but they are real expensive, the alternative is to use sanding rolls and get some lanolin or wax. if you touch the roll surface in the lanolin etc it will stop it getting clogged with ally quite so fast and improve the cut. J |
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bstardchild
Club Retro Rides Member
Posts: 14,958
Club RR Member Number: 71
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When you match the ports make sure the hole in the inlet mainfold is slightly smaller than the hole in the head and vise-versa for the exhaust. don't try and match them exactly. A. its harder tog et them exactly the same B. Its works better with a lip to prevent gas trying to go backwards down the port. Now not many people know that |
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street
Posted a lot
6.2 ft/lbs of talk
Posts: 4,662
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More excellent advise, cheers Slater and Blownimp! |
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) they will clog very quickly and go blunt as the heat rises. You can get ally cut burrs, but they are real expensive, the alternative is to use sanding rolls and get some lanolin or wax. if you touch the roll surface in the lanolin etc it will stop it getting clogged with ally quite so fast and improve the cut.