cylinder design question
 

I've been looking through pics of various engine parts just out of curiousity (you may have seen my thread on conversation pieces for desk) and I've noticed that the fins on some porsche cylinders are radically different. The fins on an early motor like 2.2 are quite different than on the 2.7 jug that I have, but I assume that's due to the different bore requiring creativity to get the same cooling, but what really surprised me are the 3.3L turbo jugs that are FS with nearly no fins

http://forums.pelicanparts.com/uploa...1161645177.jpg

I assume that the sides closest to the other cylinders don't have room because of the larger bore, but what about opposite the side that does have fins? Also, since I can't look at an engine, does the side with the big fins go up or down? I assume up towards the source of the air, but we all know what ASSuME will do for you.

This is pretty much like my 2.7L cyl looks like.
http://forums.pelicanparts.com/uploa...1161722165.jpg

thanks.

Even pics of a 3.2L cyl look the same, but I assume that the case was changed to allow for a longer space between bore centers.

If my memory is correct, the fins on the top of the cylinders are somewhat reduntant. This is because air flows from the top to the bottom, and so directly above the cylinders will be a high-pressure area with very little air flow. If there is no airflow, then there is relatively little transfer of heat from the cylinder to the air. The sides and the bottoms of the cylinder all have airflow over their surfaces, so in those areas the fins do convect heat out to the air.

That's my memory of the situation.

Ah, interesting, thx

As for the 3.3L cylinders, the cooling fins are situated at the bottom of the engine. By the way, this design - not fully finned - was far from optimal. I think Porsche thought that the cooling air provided by the fan would/could be distributed more evenly without the fins on top. On the 965 (964 Turbo) in 1991, this problem was rectified and the engines came with 3.3L fully finned cylinders.

Ah, ok, that sounds more intuitive.

During a rebuild of an original 930 engine, this is one of the first things that eats up the budget: those cursed half-finned cylinders!!! Some opt for the updated 965 version, others go for a bored out 3.2L cylinder that has been replated, or better yet, one of the 3.4L (98MM) versions. Anything to get those cooling fins!

hey thats my picture. anyhow the reason for the partial fin was really to allow for even cooling after the engine shut off to stop any potential oil leaks. This came straight from YODA's (henry@supertec) mouth. This was a big concern for ne wporsche owners and this was meant to apease them from the start.. Same with the disimilar head studs found on the SC and carreras

Yeah, I stole the pics from the classifieds.

PS thanks for all of the info.