DOHC vs. OHC

And the Chrysler Hemi, the daddy of them all.

Fewer moving parts (no rocker shaft), less wear, less slop. One minor disadvantage is that, with the spark plugs in the middle, you need a long extension bar to get them out.

Even the Nissan Micra K10 had a hemispherical head, and that was a low compression, 8V SOHC.

Hemi heads are less popular these days because they don't work with 16 valves - a "pent roof" head is used instead.

Why 16 valves? Well, it's easier to fit two small valves side by side in the available space than one big one.

Quite right, it was called something like Compund Valve Hemispheric. It was a novel construction in an attempt to save one cam. The valve stems was angled in a special and unusual way, this gave the engine a characteristic noise, some said it sounded like a lawnmower.

The message from Johannes contains these words:

Nice to know there are still charitable people around!

the whole point of going twin cam is to have less leverage effect on the valves and have less moving bits in the top end to go wrong the second advantage of having multi valves is that you get more valve area than you can with just a single BIG valve and hence you get low down economy and top end power

I thought the Chrysler Hemi was a pushrod.....

More to the point you can get greater valve area for the same piston area.

I think it was. TC and a pushrod...hmmm