Sure I can tell you all about them, but some people get butt hurt when I speak the truth.
I know the Terra Alps 870 kits being the most powerful engines made are a fully ported and welded cylinder to change the shapes of ports. Helps flow characteristics, gains airflow and hp. Also helps strength in areas and ring support for reliability. Spent weeks on the dyno doing little angle and shape changes in porting to maximize the hp gains. The piston is designed best for making hp and is lighter then stock so adds to hard acceleration and puts less stress on rods, since the 870 kit already makes great power gains. The head designed and built for proper coolant flow and turbulence and to get flow going thru cylinder properly. Domes that make power, help scavenging and work with balancing the engine package. Exhaust valves are fully machined.
Terra Alps also builds there own exhaust from Y pipes to Pipes to mufflers and is built to the big bore package to build the most power. Also designing the ecm tuning to makes great hp gains but also making the engine more reliable then stock. Why did Terra Alps only build a 870 kit ? not a larger displacement big bore. Cause the cylinder wont gain anymore power. Over boring the cylinders changes the shapes of the ports and start losing power. Power comes from proper port design and shapes. Which helps in scavenging fresh fuel and air and getting rid of the exhaust gases from the cylinder. 25 years of engine building and all the work that goes into these kits puts the Terra Alps 870 at top of the list by a long shot. Gained 22% from 143 stock to 174.6 on pump gas.
For other kits that I have seen people spend good money on. Big bore cylinders bored out with no porting at a plating shop. a little clean up porting by someone who does not know what there doing, exhaust valves not machined, poor head design and domes made by a machine shop not a 2 stroke specialists. Heavier pistons not designed by the engine builder but by a piston manufacture not knowing what the build is about. Then packaged with a pipe kit with wrong pressure and temp design or from someone else who does not build engines.
I have dynoed some making little to no gains, alot of people that spend money on there kits or get a deal on them claims there great though.
