With boats, we always do speed tests 2-way; with the currrent and into the current and then average the two to get an accurate number. I wonder if the test in question had a headwind, and what the effect of that would have been on top speed?

 

They did exactly that. Several times. All recorded with GPS.

 

I’m not sure this argument makes sense. GT3 achieves roughly the same revs in 7th - but the speed is higher due to taller gearing in top gear. The GT3 certainly does not come close to redline in top gear.

I haven’t seen any definitive evidence that the engine is electronically limited, rather than the Vmax being limited by aero drag and engine power (without artificial rev limitation).

 

From this vid the GT3 revs 300+ rpm higher, 8600, than the GT4RS, 8300. At 304 km/h the GT3 is about 8k rpm which accounts for the taller gearing of the PDK compared to 8.3k with the GT4RS. That can't just be drag induced. Something else is going on here.

 

So are you saying the GT3 has an electronic rev limit at 8,600 rpm in top gear? Because it does not - that is as fast as the car can go given the power and drag at those conditions.

I agree that it is surprising that the GT4 revs 300 rpm less, although it has lower gearing and nearly the same power (at 0 mph).

So there are a few possible explanations for this:

1. Porsche has placed an electronic governor to hamper top speed (I need to see some better evidence of this before I’m prepared to believe it).

2. The aerodynamic drag of the GT4 is higher than advertised (potentially exacerbated by the extra frontal area and Cd of the WP intake ears).

3. Maybe the GT4 RS was in high downforce mode, while the GT3 was not.

4. Maybe the placement of the GT4 intakes are located in a low pressure zone at very high speeds. This would decrease the volume of air that the 4RS can ingest at high speed, and maybe the power at 300kph is less than at 0 kph. Meanwhile maybe the GT3’s intakes are placed at an area of high pressure, so it achieves a gentle supercharging effect at high speeds.

5. Maybe the WP intake ears of the 4RS create air turbulence at high speed and makes the power at high speeds suffer further than the non-WP, despite the obvious marketing implications that the ears would enhance a ram-air effect.

6. Maybe the road conditions (wind speed and direction, temperature, incline, etc) favored the 3 more than 4RS.

 

What is being debated is that GT3 can achieve published Vmax and the GT4RS can't. So far every Porsche GT has met and/or exceeded published Vmax; until now.
But as stated earlier; little brother can't challenge big brother or the fanboys would be too upset.

 

That argument could explain why the published Vmax of the 4RS is lower than that of GT3, but it does not explain why the car can’t achieve its lower published Vmax in practice (while GT3 achieves or exceeds its own).

 

Would it be possible if one of the lovely GT4RS owners here could conduct such an experiment with their spoiler removed?

 

Ask @groundhog when he gets his. After all he is on the same continent as you.

 

Its not electronically limited - it could simply be there was a decent headwind and it tapped out - it could be there was a slight rise in the road - it could be a fuel issue or a heat issue in that particular car e.g it electronically self limited (which is normal). Its very hard to get Vmax out of these cars unless you have a perfectly flat military runway and perfect conditions in terms of temperature and wind. Yes you could get there on an autobahn again with perfect conditions.

Also at those speed its ~ 5 BHP (at crank) to overcome the air to advance by 1KPH

 

Don't you think its strange that 2 independent viewers posted a vid and arrived at virtually the same speed within 1km/h. Then there is a private individual on a German forum trying it and getting the same Vmax. 3 different people on 3 different roads at 3 different times all being within 1 km/h of each other. Wonder what the odds for that are?

 

All seems pretty futile, I won't go near that speed on my local race track (Philip Island) and unless you are on an autobahn no one else will get there either. And even if you can what does a few kph matter.

 

Red dashed line - theoretical Vmax 4RS (195mph ~ 315kmh, 20 inch x 295 x 30)
Blue dashed line - track max 991.2 GT3 RS (193mph ~ 310kmh, 21 inch x 325 x 30)

Once again, there is no special 7th gear cut out unique to the 718 GT4 RS - if a car is struggling to get to Vmax its due to other factors that could range from, going up slope, head wind, incorrect tire pressure, temperature, poor fuel, excess heat etc. The difference in rpm relative to speed between GT3, GT3 RS and GT4 RS are primarily due to the size of tires and wheels which impact on gearing.

 

Porsche maybe built in a lower safer 300rpm redline to compensate for many of us who will over rev the car with the shorter ratios?

 

Over rev with a PDK? Not sure how is that possible....