epj3 said:
By the way, BMW has been using hemispherical heads for a very long time, if not forever. Nothing special other than its a much better head than GM's which is basically a block of steel with holes drilled in it for valves and spark plugs.
The Hemi head design was actually designed by Peugeot and Deusenberg way back when.
The fact that the Hemi head is "better" is debatable. Yeah, it has the potential to produce immense power if it's done right. Mainly because it was such a large combustion chamber that you could dump an incredible amount of air/fuel mixture into it and the compress the crap out of it with a huge, high-compression domed piston. However, the hemispherical head design is also the WORST design as far as emissions and fuel economy is concerned. One of the main reasons it died back in the gas crunch.
BMW has been using hemispherical heads forever? Ummmm, no. The spark plug has to be in the center of the combustion chamber and the combustion chamber has to be half of a sphere for it to be a true hemispherical head. That means that the combustion chamber looks like a perfectly round, smooth circular dome. The only BMWs that I am aware of having their sparkplug in the center are the newer DOHC heads, and the combustion chambers in those heads aren't hemispherical either. Just because the spark plug is in the center doesn't mean it's a hemi head. In that sense, the new Chrysler/Dodge "Hemi" engines AREN'T true Hemis, either. The labeling of these new engines as "Hemi's" is nothing more than marketing - the combustion chambers in the new "Hemi's" aren't hemispherical at all.
Plus, the new Hemi uses a speed density system instead of a mass air system for metering the intake air - that's crap. That's an even more primitive air-metering system than my '87 BMW has.