In reality to flow things perfectly you need to both build up areas of the crankcases (either by aluminium welding or sometimes epoxy) to add material in combination with removing material. This isn't entirely the whole story but it should be bourne in mind.
The smaller the volume in the crankcase the higher this compression ratio - this is partly why you bought a full-circle crank so as it would take up more space within the crankcases! This mixture is compressed against the reed valves until the piston travels down the bore far enough to uncover the cylinder inlet ports at which point it then rushes into the combustion area. On a 2-stroke, as the piston travels downwards it compresses the air/fuel mixture beneath it which has already been sucked in.
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.
Basic 2 stroke tuning 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. I do business that way too: honest, upfront and no-nonsense.Basic Moped Engine Cylinder Port Matching My wife and I founded our business on our love for each other and our commitment to Jesus Christ. I WILL answer any question I know the answer to or point you to someone I think might have the answer. If you don’t please don’t hesitate to ask. It is my hope that you find what you’re looking for here. Still a specialty engine performance shop specializing in the Yamaha RZ500, WP has gone on to build top engines for local racers in flat track and hill climb events and multiple engines and parts for enthusiasts worldwide. In the winter of 2001 WP opened for business and has been growing ever since. After three years of study and in- depth discussions with those willing and most importantly capable of explaining and teaching, WP was formed. Wilson Performance (WP) was formed out of the frustration of many two-stroke tuners’ unwillingness to provide answers to most basic questions about two-stroke performance tuning. Welcome to Wilson Performance, Your Two-Stroke Performance Authority.