Comparison between old and new SPI method?

According to my information, the "bypass booster port" porting style on the later slit exhaust cylinders had proved to be better than the original single groove dual bypass cylinders.

The original dual bypass cylinders had one big groove in each side. In an attempt to find more power on Non SPI (muffled or throttled) engines with slit exhaust ports, the slit exhaust cylinders added a single boost port to each bypass, which because of the way it extends slightly above the main bypass helps create a swirling effect of the atomised fuel into the cylinder during the intake stroke as well as providing a larger intake port.

This was discovered by Larry Renger and he attempted to enhance and improve this even further when he built this feature into the Venom cylinder. I believe some of these cylinders were also used in late model ie post 1997 Tee Dees. This would have also been a bonus in manufacturing time and cost as it removed a couple of steps in the milling process of the cylinders as the Tee Dee previously had two bypass boosters in each bypass and they discovered one was actually more efficient than two!

So it doesnt surprise me that by lightening the piston even further and adding sub piston induction would increase performance even further. After all, all high performance cox engines had sub piston induction in the past, so it must have been there for a reason. ie it worked!