Rfvc?

[07250ex]

Ok this Radial four valve combustion chamber really stumps me because a HEMI is a radial combustion chamber which im assuming because hemishperical is round as well as radial but HEMI's cannont have 4 valves they must be 2 valved can someone explain please?

[JOEX]

Originally posted by 07250ex
Ok this Radial four valve combustion chamber really stumps me because a HEMI is a radial combustion chamber which im assuming because hemishperical is round as well as radial but HEMI's cannont have 4 valves they must be 2 valved can someone explain please?
Why can't a 'HEMI' have four valves?

[07250ex]

The valve angles can't be designed to backmyself up on that source its also on the website howstuffworks.com

[JOEX]

I belive virtually all modern cars have 'hemi' heads and most have at least 4 valves.

Here's a picture from howstuffworks.com in the 'hemi' section...

Imagine there is another intake and exhaust valve right behind the ones pictured. They can't be seen because this is a profile picture.

[JOEX]

This may help...?

[JOEX]

Or maybe this:p

[07250ex]

i've seen the last picture but thanks JOEX i'm guessing this means the 400ex has a hemi =p i just dont get why howstuffworks said hemi's cant be 4 valved

[07250ex]

i also noticed in the picture on an angle it has white diamond and black diamond valves =p

[GPracer2500]

Here's an image showing Honda's Radial Four Valve Combustion (RVFC) design. The key thing to notice here is the angles of the valve stems. They splay out radially--there's not only an angle between the intake and exhaust valves but there's ALSO an angle between the each intake valve and each exhuast valve. This is just like if you placed the valves on the surface of an orange or softball.

http://www.motorcycle.com/mo/mcdirt/mcphotos/xr11.gif


Here's another drawing that illustrates these angles more clearly (similar to JOEX's third picture):

http://communities.zeelandnet.nl/data/xbr/upload/images/kleppen.jpg


About the "How Stuff Works" article: Boy, I'm really growing to dislike those articles. They're so dumbed down that at times they're flat out wrong. So tread carefully if you're getting information from that website. Just because someone took the time to publish something on "How Stuff Works" doesn't make it true or right. ;)

Here's what they said: "...One thing that a hemispherical head will never have is four valves per cylinder. The valve angles would be so crazy that the head would be nearly impossible to design..."

Uhh? :ermm: I don't think so. Almost every Honda XR engine above 250cc (including the TRX400EX) since the early 80's has had such a combustion chamber. The XR400/400EX combustion chamber is almost a perfect section of a sphere. And I doubt Honda's RFVC engines are the only ones.

Most modern, high effeciency gasoline engines use some variation of the pentroof combustion chamber design. This is easily adapted to more than 2 valves. And a pentroof design is often clumped in with "hemi" type chambers because they are sooo similar. In today's low combustion chamber volume, high compression engines there really isn't much difference between a truely hemispherically shaped chamber and a pentroof chamber. They're so close to being the same thing they're easy to categorize together. Actually, in that "How Stuff Works" article they label the pentroof design as "Pentroof hemi engine design".

http://static.howstuffworks.com/gif/hemi-pent-roof.gif

In my opinion, that article would have been structured better had they seperated Dodge's HEMI engines from hemispherical combustion chambers in general. Although Dodge made "HEMI" a household name many decades ago (and again today) there's a lot more to hemispherical combustion chambers than just what Dodge has done.