The problem with removing too much material is that this increases the volume within the crankcases which in turn reduces the primary compression. Whilst it makes sense that smoothing out all the rough edges within the block may help with flow and reduced turbulence there is only so much you can do without removing too much material. The higher revving the moped engine the more the difference you will see, but really we are only talking about it being critical on very high revving high-end race scooter engines. On the Stage6 MKII cylinder kit used in the blog we can see the before and after difference on a dyno fixed gear run but it is minimal and it certainly wouldn't be worth taking the engine apart to do if it wasn't already done, but if you are in the process of rebuilding the engine then it's good practise. You simply aren't going to notice any difference on a cast iron sports 70cc kit, nor will the ports be significantly different enough to mismatch badly. Not until you get to the very top end level of tuning. On some cylinders the porting is so enlarged that it's necessary to build up the outside material of the engine block before porting otherwise there would be no material left after the block 'ports' have been enlarged enough to match the enlarged cylinder ports. The more highly tuned your scooter is the more this matters and the more likely it is that the cylinder ports will significantly mismatch those of the engine block (casings). Flowing gases do not like to change direction and these mismatches can cause turbulence which interferes with mixture flow and therefore performance. In contrast the standard Piaggio engine casings are coarsely cast with sharp obstructions and the channels (ports) do not match up particularly well even with the standard cylinder ports. Quality manufacturers will spend time designing smoothly curved and enlarged ports on their cylinders with precise directional mixture flow. Once you go above the level of tune of the basic cast iron sports cylinder kits, cylinder design starts to become much more important to the performance of the cylinder. or any other 2-stroke scooter or moped engine.
Two stroke porting kit pro#
This article uses a Piaggio Zip engine and a Stage6 Sport Pro MKII cylinder kit but applies equally to Minarelli/ Aerox etc. This short blog is a basic guide to matching the cylinder ports to the engine casings when tuning or fitting a new cylinder kit. Basic Moped Engine Cylinder Port Matching
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