Marketing department rules. Its all in the timing.
I have a PAG internal product slide which shows PDK becomes available to the 718 GT4 generation from Q3 2020. Why wait till Q3 2020? Because if they install a PDK in the 718 GT4 today it would be quicker around a typical european 3 mile circuit than the "current" 991.2 GT3 (manual certainly but PDK also).
The 981 GT4 punched way above its weight. The balance of the platform is part of the equation. My 385 bhp GT4 with manual transmission was roughly 1 second per 1 minute lap slower than my 991.1 GT3 PDK. Same driver (I do alot of track days) same track. Thats with a smaller tyre patch (GT4). My 991.1 GT3 had 100 bhp more but the torque to weight ratio was almost identical.
My 981 GT4 is roughly 0.5s per lap slower than my 991.2 GT3 Manual. Same track same driver. Thats with 120 bhp advantage to the GT3. The GT3 now also has a little more torque N1 Cup2 tyres and slightly improved chassis.
The new 718 GT3 is now 80 bhp less than my 991.2 GT3. However it has the newer N1 tyres and an improved chassis. I ahve obviously not driven one at the track yet but I suspect the PAG marketing team have ensured that it is 1 second per lap slower than the 991.2 GT3 PDK! That makes it as fast as my manual 991.2 GT3 around the crcuit.
Now if Porsche launched a 718 GT4 in PDK today it would likely be as quick as their "current" 991.2 GT3 PDK. That cant be done - it would ruin the PAG marketing formula!!!
So the 992.1 GT3 with come out in PDK and put the 1 second per 1 minute lap back into teh equatuons so when the PDK GT4 is annonced it will fit again nicely within Porsches performance heriachy.....and so life goes on....
P.S. The real challenge is the GT4RS if and when it breaks cover. This cannot be done until the 992.1 GT3RS is announced for all the above reasons (and it will possibly be at the same time at Geneva in 2021 - similar to how they did it in 32015 with the 991.1 GT3RS and 981 GT4 at the same venue).
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2017 991.2 GT3 Manual, 2017 Alfa Romeo Giulia QV, 2017 Macan S (Petrol)