Aircooled 4valve heads

[slingshot-930]

Hello Porsche friends,

As I just posted a thread about a German racecar with watercooled heads and aircooled cylinders,
I would like to grab the chance to start another exchange of ideas.

The presentation of the Singer-Williams Mezger aircooled 4v engine led to some speculations around the Porsche forums. Are the Williams heads air-, water- or perhaps even oilcooled? The factory never used aircooled 4 valve heads. The Moby Dick and the 959 had watercooled heads.

Over the past decades, some trials have been made, to develop different heads for the
aircooled flat six and there have been also some boxer VW multivalve head projects, which
could have perhaps been – to a certain extent - „translated“ to a Porsche application.

In the seventies, my Italian friend and engine wizzard, Gabriele Gottifredi, developped
3 valve heads for the Mezger engine (see: Neat Post of the day: Porsche 911 3-Valve Engine!). Those heads were part of a race engine project, but it was frozen, due to a change of the rules. Unfortunately, my chap passed away in 2016 and the parts were sold. Perhaps the buyer will put everything together and make it run. Who knows...

More than 20 years ago, Canadian Kelso Technologies and German Cartronic offered a 4v
head for the 964/993 engine. I don't know, how many of these heads were installed
and tested under real conditions, but from a theoretical point of view - with reference to their brochure – the project offered some advantages. The heads were sandcasted from a more heatresitant alloy, in order to be able to manage the high temperatures, which was/is for sure one of the biggest problems to resolve. The valvetrain was supposed to be safe up to 9K rpm. They used 928 S4 valves, to make it more service-friendly The 4v solution was also supposed to have a much higher port velocity - especially when compared to big port /valve 2 v heads – with a better scavaging.

Here are some comparisons between the the stock 2v head and the Kelso 4v head.

Intake valve : 48,50 mm x 1 vs 37,05 mm x 2
Exhaust valve: 41,15 mm x 1 vs 34,80 mm x 2
Intake valve area: 1.851 mm2 vs 2.155 mm2 + 16 %
Exhaust valve area : 1.329 mm vs 1.900 mm + 43 %
Intake-/Exhaust port diameter : 41/38,5 mm vs 42-46/42 mm + 10 %

Now we have the Singer/Williamas solution.

And finally there is another project in the engineering pipeline. Robert Linton, US Porsche maniac,
is pushing the development of a 4l Mezger 4v engine, with aircooled heads. Some top notch parties are involved and perhaps we will even see a pneumatic valvetrain. Let's wait and see..

For sure, a functioning aircooled 4v head must be a very challanging task, if even Porsche didn't built it.

Needless to say that from a certain point on, these builds become tremendously expensive
and in certain cases I doubt if the juice is worth the squeeze. Nontheless, it is fascinating what is achievable with an unlimited budget and modern engineering.

I hope that some knowledgeable experts will chime in and share their ideas.

G

[rwest]

Very cool post, I have a question or two: how are the valves opened? Would it end up needing an extra cam on each side, ala 4 cam Carrera?