Long unanswered questions

These 2 questions are for the mechanics on the forum. (Might be a little stupid so don't laugh to loud) 1. I have always wondered why Porsche has their gearing set to run at or above 3,000 rpm when cruising at 70 to 75 mph in top gear. Both my previous Boxster and my current 911 cruise at 3000 rpm at 75 mph. This is much higher than most cars. My Buick (V8) cruises at 2,000 rpm and my Fusion (4 cyl) cruises at 2,200 rpm. So the question is, would this not wear out an engine 1/3 faster than a lower rpm engine. The crank, valves, bearings, water pump etc. are all working 1/3 more than a lower rpm engine. Would this be true? 2. If our engines are flat sixes, thus cylinders function at 90 degrees opposed to each other, do they wear more at the bottom of the cylinders sleeve. It seems like basic physics that the weight of the piston would wear the rings more on the bottom with the friction of miles of driving as apposed to an in line 6 cylinder running straight up and down. Is there any proof of this. Told you it is kind of stupid, but I bet others have contemplated the same questions. Plus it is Saturday night and I was bored.

I Don't know about the 2 questions, but IF it's SATURDAY NITE where you are, you've got me a lil' Confused! Lol! OR, should i say WHAT part of the World are you in cause it's FRIDAY where i Am!

Sorry, meant Friday night. Been a difficult week and was thinking about tomorrow.

1. Porsche never had dedicated overdrive gears until 991 with 7 speed manual, so your 5th gear in tip, or 6th in manual is the gear you reach your top speed in at or close to redline. Other manufacturers have dedicated OD gear or focus on fuel economy. And Porsche needs you to spend that money on their overpriced junk parts. 2. Great question.

My experience is both my Boxster 5-speed manual and my Turbo 6-speed manual get real good gas mileage when cruising at the 75mph range. I've driven slower sometimes for extended periods and gas mileage is always less. Not sure why. Maybe that resonance flap plays a role? Maybe the VarioCam Plus variable intake valve timing plays a role? But for both cars the engine appears to be a in a sweet spot RPMs wise running around 3K. So I believe you are seeing some kind of a problem with Porsche engiens operating at approx. 3K RPMs vs. some other car engine operating at 2K RPMs being a problem when there really no problem. Operating the Porsche engine at too low an RPM may cause the bearings to get pounded more, so there's that to consider. You have to consider that Porsche could have geared the cars just about anyway it wanted to and it did it the way it did for a good reason. As long as the oil is good there is no measurable wear at 2K RPMs or 3K RPMs. Both of my cars have spent considerable time operating at 3K (or higher) and neither engine shows any signs of any wear. This means that the piston/cylinder should not experience any real wear anywhere, although there are reports some engines have been found to have oval shaped cylinders. This has to be some kind of oiling problem -- probably the oil was left in service too long. BTW, good ol' 'merican V8's can develop oval/tapered cylinder bores too. It is not an engine layout thing it is a lubrication thing. The rings/piston ride on a film of oil. For the Porsche engines there is an oil jet for each cylinder that sprays a copious amount of oil at the bottom/underside of each piston to help cool the piston but to supply more oil to this area than would get there from the oil slung off from the crank/rod bearings. Besides the oil there is gas pressure which works to help center/support the piston in the bore. Really you are seeing problem where there really is no problem. When there have been cylinder/piston problems, real problems, in other engines the problems make themselves known in really no time at all. It doesn't take a decade of time to pass and huge miles for any shortcomings to make themselves known. The problems can show up, the symptoms that is, can show up in just a few tens of thousands of miles (or less) of engine operation. Remember the Vega engine? The BMW engine that reacted badly to sulphur in the gasoline? The first and short-lived GM diesel engine? (Even a Porsche "air craft engine" that reacted badly to lead in aviation fuel.) Owners were experiencing problems in practically no time after buying the vehicle/engine.

Porsche's newer cars have much taller overdrives as noted above, and in particular the seven speed manual and PDK. I think Porsche was not really too concerned with fuel economy until the greenies started putting pressure on car companies to reduce greenhouse gasses. I too have wondered how much more wear there was on the engines when they ran 1/3 faster or so. I don't think the answer is 1/3 more wear across the whole powertrain, but certain parts maybe. Regarding a flat six with it's 180 degree opposing pistons; There are significant other pressures on a piston moving up and down in it's bore thousands of times per minute that would supercede pressure due to gravity. Really the side of the piston is not meant to contact the side of the cylinder bore. There should be a layer of oil that prevents the contact. The piston rings do come much closer to touching, but again there should be a microscopic layer of oil preventing contact and wear. The bore scoring and general piston/ring wear are more related to excessive heat and dirty (debris laden) oil.