On 1/26/06, Levi Smith <[EMAIL PROTECTED]> wrote: > Aren't almost all engine's techinically "hemi's"? Or are there a lot of > engines out there with really odd shaped combustion chambers? > > Levi
The short answer to your question is "No." The long answer to your question I will not go into ... however, I will go into the medium answer. The first recorded use of a Hemispherical combustion chamber was a four cylinder affair that powered a car named the "Welch." In a HEMI engine, the top of the combustion chamber is hemispherical. The combustion area in the head is shaped like half of a sphere. An engine like this is said to have "hemispherical heads." In a HEMI head, the spark plug is normally located at the top of the combustion chamber, and the valves open on opposite sides of the combustion chamber. Most cars prior to the 1950s used what was known as a flat head, and many lawn mower engines still use the flathead design today because it is less expensive to manufacture. In a flathead engine, the valves are in the block, rather than in the head, and they open in a chamber beside the piston. If HEMI engines have all these advantages, why aren't all engines using hemispherical heads? It's because there are even better configurations available today. 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. Having only two valves per cylinder is not an issue in drag racing or NASCAR because racing engines are limited to two valves per cylinder in these categories. But on the street, four slightly smaller valves let an engine breathe easier than two large valves. Modern engines use a pentroof design to accommodate four valves. [Thanks to How Stuff Works for the bulk of this information] -- Knowledge is power... Power Corrupts. Study hard... Be Evil.
