I think a couple years ago I said that the fact that the fact that Porsche have so much aero on their recent GT cars already, there wouldn't be much left for Manthey to do. Case in point here, the GT3 with the Manthey kit is only 0.8s faster, and that could be just part of the variance of noise. The car doesn't have any more power, it's not significantly lighter, has a little bit more aero, but the cost of the performance kit is some $60+k, which puts the car above the price of the GT3RS.
I can't imagine what's left for Manthey to do for the GT3RS since it's already so much more crazy and advanced than anything Manthey has done.

Car & Driver - Lightning Lap 2024



