Mark993TT

siitech

This tread brings me to a somewhat unrelated question: when the auto start/stop is activated, and when engine stops for instance at a traffic light, does it also stop the circulation of oil? And if yes, wouldn't this be harmful especially for turbo charged engines?

Gonzalo38

Great question..... don't know the answer but the fear of a shorter life of the turbos because of a sudden lack of lubrication and cooling is the reason why I always turn off auto start/stop.

Valvefloat991

To achieve full torque at 1700 rpm requires full boost, which means holding full throttle for several seconds. If that were harmful to the engine, presumably the engine management system would not allow that condition (which it could easily limit since boost is electronically controlled). In which case, Porsche would not claim full torque at 1700.

Am I missing something, or have the parameters of lugging changing since the days of the Fuhrmann engine?

Mark993TT

Valvefloat991

I'm sorry but this is the blind leading the blind. The notion that using full throttle at low rpm is somehow "Inefficient" is the exact opposite of reality. Low rpm has less friction and full throttle reduces pumping losses, both effects making the engine more efficient. That's why modern cars have multispeed transmissions to keep their engines at low rpm on the highway. And they have turbos to produce sufficient torque at low rpm to avoid the need for frequent downshifts. If you think running at high rpm and light load is more efficient, try driving across the country in fourth gear and see what your mileage looks like.

The same for this obsession with pre-ignition. Modern engines that are not worn out aren't full of oily blow-by and glowing particles of carbon. They are simply not subject to pre-ignition. Turbocharged engines are, of course, always susceptible to detonation, which is something completely different and definitely potentially harmful. That's why modern engines have knock sensors that detect the earliest signs of detention and retard spark timing, reduce boost, and/or richen the mixture in order to stop it quickly.

In this litany of nonsense, nobody discussed the only genuine potential problem with the combination of high load and low rpm. That's damage to the main and rod bearings that could occur when the combustion loads on these components exceed the hydrodynamic pressure of the oil film, which is weakest at low rpm. This would cause the bearing shells to physically contact the crank journals and that would cause undesirable wear, or worse. However, I would expect that Porsche engineers thought about this when designing their engines and made sure this wasn't a problem.

In any case, there's no doubt that for maximum acceleration, one needs high rpm and low gear. But for moderate acceleration, full throttle in an upper gear is often sufficient. I have no doubt that a 991.2 engine can't possible be adversely affected t by full throttle at 2000 rpm. I'm pretty confident about 1500 rpm as well. 1000 rpm might be a different matter--but then the engine can't make much boost at that rotational speed so perhaps that's also OK.

SpinDoctorMario

Thanks for all the tips. Recently moved from a 2017 Cayman 718 Base to a same year 911 Carrera S. Literally the day before my planned trade-in pick up I took the 718 for a spirited drive (although it was still in suburbia, so didn't see much harder than I've pushed any other car over the years, including Audi, BMW, etc.), and on my return trip home it started blowing gray/white smoke like I had lit a smoke grenade while taking enemy fire. After making it home, having cleared out some two lanes of traffic behind me along the way, I noted oil dripping from the tailpipes. Thankfully, as the 718 was still under warranty, the dealer took it in trade anyway without any hassles. Turns out the turbo had started sucking oil into the engine. However, this gave me a bit of PTSD, and I've since been nervous to drive the 911 aggressively at all (it still has a few months of warranty left, and I plan to buy the extended Porsche warranty unless someone here suggests something else that makes more sense). It's only been a couple of weeks, but trying to make sure that nothing I did in my last 718 drive contributed to or caused this, so I don't end up with a costly repair on the 911.

Norge911

For turbo charged engines, lugging is bad. Lugging the engine will depend on the gear but as key takeaway, don’t drive near or below 1000rpm. In 2nd and 3rd, don’t go below 1300 rpm, in higher gears stay north of 1500-1800 rpm. Personally since I have a manual, I prefer to stay north of 2500 rpm, engine noise is not too loud for cruising and still have good up and go.

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