A Cheap Air Die Grinder & Carbide Bit and a Porting/Polishing kit is all you really need. On some Rotax's there are different Size Carb Intakes. You also want to Match your Carb Intake to the Cylinder External Intake Port on the Cylinder. Were Not building a Race Engine, so I'm not getting into all the Port Timing changes you could do if Racing. Could the Standard 335 be Ported to TNT Spec's, Yes, and you have your Port Timing changed doing that. With the different Port Heights 26.5mm vs 29mm, they will have different Port Timing! But can they both be Improved upon, Yes, using the General Rule of Thumb Formula, they can be Widened from 47mm to 51mm. I'm going to show you my Single Skidoo/Rotax 335(78mm x 70mm) vs my Skidoo/Rotax 340 TNT(78mm x 70mm) Intake Ports for comparison. Some 2 Stroke Porting enhancements you can make to make AirFlow better in your Engine with simple tools. Your Bore is a Circle or let's call it a Radius and once you Cut Ports in that radius, there is a General Rule of Thumb Formula on How Wide you can make that Port before the Ring might get stuck in that Port. The Rotax 618UL was rated at 6750rpms! Using 6750rpms vs 6500rpms equals 250rpms is like 3hp difference. Every 2 Stroke Engine is different in what can be done to make more HP, since this thread is about Porting will try to focus on just that aspect! For our purpose's here, 2 Strokes for Ultralights & Kitplanes were not after every last bit of HP we can get, as were not turning them any more Higher then Industry Standard for Planes today which is 6500rpms.
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