<blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:<hr /><font size="1" face="Verdana, Helvetica, sans-serif">Originally posted by mave:
<strong>Ah, but how many horses is 16V worth?
</strong><hr /></blockquote><font size="1" face="Verdana, Helvetica, sans-serif">It's well known that the bigger the valves, the easier it'll be to get the fuel/air/exhaust in and out of a cylinder and that's more important at high revs, where the valves are open for a shorter time. As there's a limit to how wide the valves can be on a 2 valve head, 4 valves are used to increase the valve area and improve breathing.
So, at low revs, where breathing isn't a problem, there may not be much difference in the relative output of a 2V v's 4V head. At higher revs, there will and you'll generally find that 4v head engines are able to rev much higher. More revs = more fuel burnt per second = more power.
This is only half the story. There are some who say that 16v engines produce more power because the design of the combustion chamber means that the spark plug must be situated in the middle of the combustion chamber roof (it might be off to the side if two big valves are used). With the plug in the middle, the flame burns symmetrically and more evenly. Of course the way to introduce that symmetry on a 2v head is to have two offset plugs. Now where have I heard of that idea before?
You asleep yet? Short answer: I don't know. But Alfa's 2v twin spark technolgy was pretty good anyway, so putting a 4v head on an EARLY* Alfa twin spark (if you can still find room for the second plug) won't get as big an increase as the same mod on some other types of engine.
* read my earlier posting for the differences between the 8v & 16v TS engines.