Half-finned Turbo cylinders - What was the reasoning?

[juicersr]

Can someone explain what the factory's thinking was on the half-finned stock Turbo cylinders? With the massive increase in heat from the Turbo'd engine, it seems counterintuitive (at least to me) to do something which would limit heat dispersal. Which years did they put them on? Has time proven, like the thermal reactors, for them to be flawed, with everyone ditching them in favor of later fully-finned/ aftermarket cylinders? Thanks

[NathanUK]

You are spot on. They had a theory, but it didn't really work.
They thought that if they only finned one side then there wouldn't be less expansion compared to the other side as air can only blow on the top and then the sides, never the bottom.
Air blew on to the flat surface (top).

The 964t has fully finned. RUF also had theirs made fully finned.

[juicersr]

So are the 'half-fins' pretty much junk? Anyone here use them in a rebuild? Am putting together a 'budget' turbo engine based on a 3.0 engine and was toying with the idea of using them.

[equality72521]

I don't know that I'd call them junk seeing as every 930 through 1989 used them and have been pretty darned reliable engines.

[juicersr]

Through '89 huh? That's what i wanted to know. Thought they were just for the early years (3.0) or something. Thanks Mark.

[NathanUK]

As I stated the 964t and RUF were the first cars to have fully finned.

I don't intend to change mine unless they break...

[fredmeister]

Porsche tried to control thermal expansion evenly by biasing the fins as stated above.

Whether this had an effect or not appears no as they later made them fully finned.

I would not sya there junk unless they are worn.

[NathanUK]

The FF might offer a little less chance of detonation but unlike twin plugging costs a fortune if you go with RUF 3.4 Mahles.