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    • Dundon Motorsports building a 4.5 liter naturally aspirated flat-6 for a 981 Cayman GT4

      The 981 Cayman GT4 as you know featured a 3.8 liter flat-6 essentially borrowed from the Porsche 991.1 Carrera S. This is not a GT powerplant but Dundon is doing their best to take this naturally aspirated flat-6 to the maximum level with a 4.5 liter build.


      Yes, 4.5 liters which is the largest build you will likely see for a Porsche flat-6.

      Dundon is well known for their Porsche naturally aspirated flat-6 expertise so if anyone is going to pull this off it is them.

      PorscheBoost would like to know the bore x stroke specs here. The factory GT4 is at 3.8 liters with a 102mm bore by 77.5mm stroke. Adding another 700cc is not going to be easy and will likely require an aggressive stroke to accomplish.

      Dundon states 4.1 liters can be easily done with just increase bore:

      Quote Originally Posted by Dundon Motorsports
      GT4.5 going together.... Bored and Stroked from 3.8L to 4.5L. All parts designed by our team. Should make for a fun 981 GT4. 4.1L is also easily done with just bore no stroke
      To hit 4.1 liters at factory stroke they would have to go to a 106mm bore.

      To then hit 4.5 liters with a 106mm bore a stroke of 85mm is necessary. The bore spacing at 106mm will not make for a motor that can take a ton of boost but it sure will make for a naturally aspirated beast.

      This article was originally published in forum thread: Dundon Motorsports building a 4.5 liter naturally aspirated flat-6 for a 981 Cayman GT4 started by Sticky View original post