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Could any of you guys explain me how are the radial valves working comparing to normal valves? I was asked this question the other day and I was like eeeeeh, not sure...

thanks
 

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I believe it has to do with the angle of the valves in the combustion chamber. They are not "straight", the valve stems don't ride flat on the cam lobes. The lobes of the cam are actually ground to compensate for the angle the valve stem sits at.

That is a non engineer explanation. Someone will come along and post a picture that will make it clear.
 

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Yupp, Carl is right, no complicated engineering explanation needed.

Now as far as why they do it, that would take the much more boring "engineering" explanation involving hydraulics, thermodynamics, and other dull words that you shouldn't use at a party:)
 

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I found a photo of a radial valve head showing you the angle of the valves.


xr600radial2.jpg
 

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XR-600 Honda, not a real good example.....the motor has rocker arms

single intake and dual exhausts......kind of lame
 

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Yes I know Noel,I was in a hurry finding a picture.Its only to give a general idea of the set-up.
 

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Yupp, Carl is right, no complicated engineering explanation needed.

Now as far as why they do it, that would take the much more boring "engineering" explanation involving hydraulics, thermodynamics, and other dull words that you shouldn't use at a party:)
With conventional multivalve heads each set of valves are have their stems parallel. For the radial, they aren't parallel. This means that the combustion chamber is more "hemispherical" in shape than the triangular prism shape you get with conventional multivalve heads. I believe that a hemispherical combustion chamber is more efficient.
 

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With conventional multivalve heads each set of valves are have their stems parallel. For the radial, they aren't parallel. This means that the combustion chamber is more "hemispherical" in shape than the triangular prism shape you get with conventional multivalve heads. I believe that a hemispherical combustion chamber is more efficient.
And for you Dodge fans out there, this is where the generic term "That thing got a Hemi?" came from. :laughing:
 

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And for you Dodge fans out there, this is where the generic term "That thing got a Hemi?" came from. :laughing:
But to be fair those hemis were in the days of 2 valve heads, so nothing radial required. I remember reading something about the twin overhead cam engine in my Alfetta GT. It was saying that even though they only had 2 valves, the hemispherical chamber design had a higher brake mean effective pressure than the modern Japanese 16 valve engines. I think this meant that the engine was more efficient.

Sent from Motorcycle.com Free App
 

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Here's a pic of a real hemi combustion chamber and you can see that it would be very difficult to fit 4 valves into that shape without using radial placement along with modifying the original chamber shape as well.

 

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In layman's terms, radial valves create a more desirable flow characteristic in the combustion chamber. Flow characteristics are a big part of my job, albeit, I usually deal with water or wastewater on a much larger and slower scale, but the applications are transferable. But again, believe me when I say that it's pretty boring stuff:)
 

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Discussion Starter #14
To understand what you guys said (I appreciate the effort) I need to know what is the stem of the valves...sorry. Let me google that now...
 

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Discussion Starter #15
Ok, by the photo Eric (thanks) posted, and with your explanations about hemipherical chamber, I got it!! Yeah! Thanks a lot, now I can explain how it works when I´m asked. :)
 

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Discussion Starter #16
So the advantage is probably to fit the valves in a tinier space than the regular ones...right?
 

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Someone here has taken apart one of these machines...but no one has a picture?
 

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The radial displacement angles of the valves is minimal on the MV....the purpose is improved flow. The MV radial valves are a result of Ferrari's F1 engine program.
The radial valves require camshaft lobes ground at an angle to match the lifters. The heads, with the 4 different angles for valve guides and seats relative to the center line (spark plug hole), is also more costly to machine and assemble.

As to the "It's got a Hemi".....The reality (sorry Dodge) is that a very flat combustion chamber yields better flame front propagation and therefore power. Look at virtually any modern high performance engine and you will find very flat combustion chambers.
The old hemispherical domed heads require big bulges in the piston crown to get decent compression, and have horrid flow characteristics within the chamber. Modern engines have flat piston crowns and flat combustion chambers.
 
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