Cool video about the origin of the 426 HEMI engine. 426 HEMI - How One Engine Revolutionized American Muscle (youtube.com)
Beautiful, and ready for the Dyno. So spark plugs were installed in the valve cover opening like on modern engines?
One difference being that you'll find an additional one for each cylinder (which many are unaware of at time of car purchase).
So if I pull the coil pack, I would see 2 plugs? Gotta dig deep in your pocket for 16 spark plugs I guess. And we still have ignition wires that cross over. Quite the design.
Many question the unconventional reason for two spark plugs per cylinder on modern HEMI engines. The answer lies in the design and shape of the combustion chamber and valves. Take a look at the picture of the heads of a 5.7 Hemi below. The valves on the 5.7 Hemi take up so much space, that there’s hardly any room in the center, let alone enough space to fit a spark plug. Keep in mind that the center is the most optimal place for a spark plug. Obviously, the only logical way to go around that is by placing a spark plug in a corner, but that creates another problem. If Dodge put a single spark plug in a corner, then the engine would have two problems- the mixture wouldn’t fully combust, and the flame would have to travel from one side to the other side. This would be incredibly inefficient. To fix that, Dodge simply decided to put another spark plug on the opposite side. While this is not ideal, it does minimize the potential issues caused by the shape of the combustion chamber and the size of the two valves. The benefits of this shortened flame-travel configuration are slightly more power, better fuel economy, and significantly fewer NOx emissions.
