4-valve hemi
Moderator: scottm
4-valve hemi
was there ever a 4-valve hemi engine?
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dodgedifferent2
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Re: "Four valve hemis?"
No..there are no actual 4 valve "hemis". There are engines though, with 4 valves per cylinders and "pentroof" chambers...lots of them.
A "hemi" has a hemispherical shaped combustion chamber - ie- it's literally 'half a sphere'. Due to the round, half-sphere shape of the chamber, a four valve layout would require the inclined valves to be placed evenly around the chamber. The valve placement would make it virtually impossible to design valve gear capable of operating all four valves in such a layout. Also, the port layout would be an impossible nightmare, with four ports exiting evenly around the chamber. Where would you put the water jackets, the head bolts and valve gear? Where would the ports exit the head?? Imagine designing manifolds for such a set up!
But a pentroof is different.
A pentroof roof chamber is often confused with a hemi, because both use centrally located spark plugs at the top of the chamber and inclined valves. But a "pentroof"is not a "hemi" A pentroof chamber is shaped somewhat like the peaked roof on a house. It has two opposed, angled flat sides and it is not round or rounded as with a hemi. It's a simple matter to place one, two, (or more!) valves in each of the two inclined opposing sides of the chamber. Valve gear and port layout can be more or less conventional. All true "hemi" engines, regardless of make, use two valve per cylinder. All four (or more) valve per cylinder engines, regardless of make, use either a pentroof style chamber with inclined valves or like a lot of heavy duty diesel engines, a completely flat chamber with vertical valves.
mart
A "hemi" has a hemispherical shaped combustion chamber - ie- it's literally 'half a sphere'. Due to the round, half-sphere shape of the chamber, a four valve layout would require the inclined valves to be placed evenly around the chamber. The valve placement would make it virtually impossible to design valve gear capable of operating all four valves in such a layout. Also, the port layout would be an impossible nightmare, with four ports exiting evenly around the chamber. Where would you put the water jackets, the head bolts and valve gear? Where would the ports exit the head?? Imagine designing manifolds for such a set up!
But a pentroof is different.
A pentroof roof chamber is often confused with a hemi, because both use centrally located spark plugs at the top of the chamber and inclined valves. But a "pentroof"is not a "hemi" A pentroof chamber is shaped somewhat like the peaked roof on a house. It has two opposed, angled flat sides and it is not round or rounded as with a hemi. It's a simple matter to place one, two, (or more!) valves in each of the two inclined opposing sides of the chamber. Valve gear and port layout can be more or less conventional. All true "hemi" engines, regardless of make, use two valve per cylinder. All four (or more) valve per cylinder engines, regardless of make, use either a pentroof style chamber with inclined valves or like a lot of heavy duty diesel engines, a completely flat chamber with vertical valves.
mart
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dodgedifferent2
- Posts: 172
- Joined: Wed Jan 15, 2003 8:07 pm
- Location: Windsor, Ontario, Canada
- Contact:
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dodgedifferent2
- Posts: 172
- Joined: Wed Jan 15, 2003 8:07 pm
- Location: Windsor, Ontario, Canada
- Contact: