I'ma relative newbie to the Porsche scene and I have been able to learn some great things from you guys - now my wishes go far further than my money will stretch (now where have I heard that before??)
The one modofication I haven't came accross yet are multi valve heads. From the desigh of the heads there seems to be enough space in the combustion chambers and the rocker arem design could lend itself to split rockers or dual rockers - hell there could even be space for two camshafts per bank.
Has anyone tackled this on race cars or do the later model cars use 4V heads that could be modified to fit a 3.2 carera?

I'm pretty sure that this has already been done to death but I would appreciate being pointed in the right direction

Thanks in advance for all the great learning going on

 

I've been told that the reason that you don't see 4 valve heads is that our air cooled engines won't pass smog requirements. Apparently, the're quite dirty. This was the supposed reason that Porsche went to water cooled engines. Others--more knowledgeable than myself--are sure to have a more accurate assesment.

Cheers,
Chris

 

Bruce Anderson talks about this in his book. If I remember correctly, the reason Porsche never used 4 valve heads on a street car is inadequate mass for cooling. The extra material in the head is better for getting rid of heat.

They use a 4 valve head in the 935/78 "Moby Dick" but it had water cooled heads, welded to the jugs.

Tom

 

The 959 also had 4 valve, water cooled, heads.

 

Actually, if I remember correctly, a few years back I read an article on someone who was making billet 4-valve heads for the air cooled 911. The supposedly worked. By I don't think they are still around. I don't know if emissions are really an issue. Having a bunch of cars in our family some brand new, some not so new like my sc, it is the sc that always comes back from emissions with the lowest numbers. The issue is probably heat related. And another factor in Porsche not chasing the 4 valve head in a 911 is the fact that their high hp models were always turbocharged. With a turbocharged motor, a multi-valve head does not have the same importance as in a normally-aspirated motor. Neither does displacement for that matter if you look at Paul Rosche's 1.5 liter, 320i block motor that put out more than 1,300hp. But I think the heat related problems could be solved. And I think when I read that article about the 4-valve 911, the guy pretty much had it solved with a motor that put out significantly more hp for it's displacement. He probably ran into some money problems since this is a very serious engineering undertaking. Not only that, the aftermarket, performance market for the air-cooled motors is as firmly established as that of the pushrod v8 and air-cooled vw flat-4. With that in mind, I don't think the usual pushrod v8 gurus will be rushing over to try some 4 valve conversion for their motors. They are happy with what they have. Of course, we 911 guys are traditionalists, but also somewhat adventurous and would not mind trying such a part. I would love to see someone try. I think that with the latest developments in metalurgy, heat management and things of the sort, something could be done. I have always wondered if CMW, who makes billet 911 heads, could do it. Nonetheless, they already make some mean looking heads.