newbie flat six owner questions.

I've been an owner for 8 days, as detail here: https://rennlist.com/forums/996-foru...-now-what.html Now that I've had the chance to look at the engine up close, I have a few questions about the flat 6 engine: - what are the major differences between a flat six and a traditional engine. is it just a V6 that is 180 degrees apart? - the pistons are resting on the cylinders in a flat engine, will that cause the uneven wear - flat engines have lower centre of gravity, but why do that put the intermediate shaft below the crank instead of above? seems like that raises the cg. - how do you count the cylinders? cyl1 is the rearmost or frontmost cylinder? Left side or right side? is the cylinder opposite cyl6, or cyl4? - does it rotate clockwise of anticlockwise (viewed from behind the car)? - something not related. what is the advantage of using an oil filter cartridge instead of a normal can like a typical car? thanks

- symmetry offers inherent balance and less vibration. Even firing angle (every 120 degree). https://en.m.wikipedia.org/wiki/Flat_engine - the wear will be more due to the thrust from the crank. The road side of the driver's side cylnders and the sky side of the paseengers cylinder are the two thrust surfaces - my believe is since it's a wet sump engine, it needs a sump with certain height to store the engine oil. The ims fits nicely under the crank drivng the oil pump. Cylinder numbering see diagram below. - clockwise, hence the thrust surfaces above. - more environmental friendly. Less stuff to recylce and lighter to transport. Also easier to recycle the residual oil. image.gif

Just to expand a bit technically the pistons are resting on a film of oil. The engine has cylinder oil jets, one per cylinder, that squirt a considerable amount of oil at the underside of the piston. This works to cool the piston -- drops its temp by 50C is what I recall reading in some Porsche literature -- and helps lube the piston pin and small end rod bearing and supplies oil to the cylinder/ring/piston interface. Also, when the engine is running the piston is centered in the cylinder from gas pressure which surrounds the piston and centers it in the cylinder. Thus really only the rings "touch" the cyliinder walls and then of coures not even metal to metal contact but ride on a film of oil. Given reasonable servicing and the use of proper oil the piston/ring/cylinder interface can last hundreds of thousands of miles with negligible wear, regardless of the flat engine with its horizontal piston position.

And don't forget that the flat "boxer" style engines are easier to air-cool. While not an issue since 1999, all of the predecessors needed it, and we tend to honor the pedigree. And, since no one answered yet, I prefer the cartridge because it's easier to inspect at each oil change without having to cut-open the can.

As you pointed out, the "flat" orientation of the cylinders allows a shorter vertical dimension - for low-profile cars and/or applications where the lowest c/g is desired, the boxer design makes sense. The direction of rotation varies on the application - for example, the M96 is oriented front-to-back in the Boxster, but back-to-front on the 996. The cartridge is manufacturer preference, although some would argue that it's (theoretically) cheaper to replace the cartridge. I think for the most part, using a cartridge, like placing the key on the left of the wheel, using lug bolts instead of lug nuts, and even the use of the boxer engine instead of a conventional V- or inline arrangement - while there might have been a manufacturing or financial reason to do so at some point - is now just an affectation/differentiator.

Thank you guys for the explanation. So the thrust on the cylinder wall during combustion are much higher than the static weight of the pistons at rest, and the oil film prevents wear. May be at engine start without oil it makes a little wear, but any oil on the wall should cling on a horizontal surface so the wall shouldn't be dry. I think the open element oil filter is a good idea, but one should check that the bypass mechanism work properly since it now has to last the life of the engine instead of being replaced at oil change time.