The race version, the legendary Carrera engine with.
However, if you feel & hear the engine actually revving up sporadically as the tach is indicating, then perhaps the clutch is slipping. Dieter Landenberger: The early Porsche 356 from the 1950s and 60s are characterized by the very typical sound of the four cylinder boxer engine. It is not likely to be a reflection on the health of the motor. If it doesn't happen again I wouldn't be too concerned about it, but I would make sure to get an oil change with an approved oil, and have them check & clean the magnet on the drain plug just to make sure there are no metal shavings in there.The tach jump is probably an intermittent wiring connection or ground somewhere due to the effects of time & weather. This is more likely if it was a hot day, and we know the oil cooling is not ideal for high rpms at low road speeds, as you would have been doing, the car's cooling systems work best at higher road speeds with more air moving through the systems.
This guarantees high traction and lateral force potential. Tyre sizes: 255/35 ZR 20 at the front and 315/30 ZR 20 at the rear. The wheels have a titanium-coloured two-tone finish and the wheel centres feature a Porsche Crest. In fact, every year at the Museum, Porsche hosts a 'Sound Night'. The 911 Turbo is fitted with 20/21-inch 911 Turbo forged alloy wheels. Its no wonder that Porsche spends so much time, money and effort on ensuring that each model sounds just so and as close to perfection as possible. It is possible that the oil got stressed and didn't hold up 100% under the increased load, you could say it might have "thinned out". The sound of a Porsches exhaust note is as synonymous with the brand as the iconic look of the 911 itself.