Even with meticulous maintenance, is it inevitable for engine performance to degrade over time? If so, what sort of degradation are we talking about? Are NA engines or Turbocharged engines affected more?

I'm sure there are many variables, but is it possible to quantify e.g. a 10 year old engine initially rated at 500hp, now with 50,000 miles might suffer a 2-5% decrease in hp?

 

May I suggest you also ask.. "As an engine loosens up over time, can HP numbers increase?" Interesting post OP....JB

 

Wish I had the pics from my 993 rebuild at 120K. It went to 161K no issues when I sold it.

Things I noted that could rob HP:

Intake valve was clean as a whistle, so no loss there. Use of Techron and Chevron gas explains that, said the tech.

Exhaust valve, cylinder head and piston head coated with carbon deposit, so HP loss there I guess. Due to less volume for air/fuel mixture, and more weight of moving parts.

Cylinder wall clean as a whistle, could even see factory applied scoring marks. No loss.

Seat of pants, I could not tell any difference before/after, that on a 282 HP engine.

480 HP at 91K miles today, still feels like 480.

 

Meticulous maintenance can only provide the engine with fresh vital fluids that help combat the ravages of use.

But in most cases the engine will not suffer significant drop off in performance even after thousands and thousands of miles provided the engine is treated with some empathy.

An engine that is thrashed every chance the driver gets could -- almost certainly will -- experience degradation in performance over time.

(As an aside, generally engines that are broken in "aggressively" while they develop max power sooner will also suffer a more rapid decline from this peak compared to an engine that is broken in properly.)

Regarding engine output drop off over time/miles, for specfic numbers one can dyno his engine at various mileage points and chart the drop off if any. Be aware that different dynos even the "same" dyno can deliver variable measurements so you have to take that into account.

Before one notices a drop off in performance -- unless the drop off was severe enough -- he would probably note other things. Perhaps emission numbers creep up. Oil consumption might go up too. And more work to chart but oil contamination rates might go up even if oil consumption stayed fairly level.

An owner of a 996 Turbo accumulated over 400K miles on his car's engine and never commented about any drop off in power. Upon engine tear down -- prompted to address some leaks but to also address suspected wear -- a thorough check of the engine turned up no measureable wear.

I can tell you first hand my 2003 Turbo engine feels as strong as ever with over 142K miles and even my 2002 Boxster engine with just a few miles to go before reaching 300K miles still feels as good as it ever felt.

Give your Porsche proper servcing. Enjoy the car every chance you get.

Put any concerns about any drop off in engine performance out of your mind.

In the event in the future and you are in the market for a used car you have to fully check out the vehicle, including a thorough road test, to ensure its performance/behavior are up to acceptable levels. The odds are before you would encounter a worn out engine with seat of the pants detectable power level issues you would notice other issues that would be sufficient to reject the car.