Valve Shape.

[John W. Kelly]

As I was reading a piece (in a Chevy book) on valve shapes I got to thinking about VW's and thier valves. The topic was flatback and tulip shapes and how they affect flow. Basicly what was said was the tulip is a good way to guide the air from a fairly straight port (like the intake) into the cylinder and the flatbacked valve improved flow when the port has a steep turn (like the VW exhaust port). Seems to me that all the ( at least stock) VW valves I've seen are the other way around. Granted, this was used by the factory with a very tame cam profile. My question is what would be a good valve shape as cams have more lift and duration? Say a Web-Cam 86b or an Engle 120?

[John W. Kelly]

Bump

[Stephan Schmidt]

go to:

www.cal-look.com

and read the tech section under \"head porting\".  I just finished reading it.  very informative.  

I just don't have the time to type out 4 pages..

hope this helps

Stephan
 

[jim martin]

i think the most important factor that many will overlook is balance between
intake and exhaust.yes its true exhaust has the help of being pushed out as well as a suction effect due too exhaust desighn.but too keep a balance between the 2 ports has too be the most important.if you can get it in but cant get it out or vise versa that will equal poor performance in all rpm ranges.as far as that valve shape i would have too say they should be used at time of porting as too work them into the numbers during porting.

[Stephan Schmidt]

i think the most important factor that many will overlook is balance between
intake and exhaust.yes its true exhaust has the help of being pushed out as well as a suction effect due too exhaust desighn.but too keep a balance between the 2 ports has too be the most important.if you can get it in but cant get it out or vise versa that will equal poor performance in all rpm ranges.as far as that valve shape i would have too say they should be used at time of porting as too work them into the numbers during porting.

Over porting is a huge loss in some cases.  some people will Hog out the intake and do a bit of the exhaust, but the air/fuel mixture that is being sucked in will be too much for the exhaust system to push out, thus causing major back pressure and a loss in performance.  I've seen some performance aircooled VW heads with the exahaust actually facing at a 45 degree angle towards the outside of the car instead of the exhaust outlets facing straight back or forwards.  you must also take air speed into consideration.  air speeds up around corners; Therefore porting is great because you are taking out all the corners and making everything smooth for the air or fuel to flow around, also making it important for the valve to be grinded and smoothed so that they are round and can \"cut\" through gases entering or exiting the heads.

Stephan

 

[John W. Kelly]

What I see is the valve shape having a greater affect on the intake side on a NA engine.  The thing that's confusing me is that it \"seems\" the factory has it backwards. The intake valve is flat on the backside and the exhaust is tulip shaped.  Now I'm sure that those VW engineers are a hell of a lot smarter than the dumbass
behind this keyboard so there is a good reason they did the way they did. So I guess the question is what would happen if we changed valve shapes? Has anyone tried this?