Pipe testing is relatively easy. And we will test about every pipe that has a likelihood of working, or someone thinks will work, in most cases. And I am still willing to test on this motor.
But pipe development is not easy. Each pipe configuration will work better with certain setup than others. So the variables are nearly limitless. That is why some pipes won't work for some people/setups, and will for others.
Remember most Blaster pipes are designed to work at least "OK" on a stock motor. Those pipes are at an inherent disadvantage to a pipe designed to work on a drastically improved cylinder/setup.
I know 47hp sounds like a lot, but as far as we are concerned there is still much testing that has potential for gains. If not in peak power, there is usable power gains to be had still, imho.
As to specifics, I have to preface my comments by saying that can not give away what I use to feed my family. I will say that the porting is extensive. There is material added to both sides of the cylinder (intake/exhaust), and a lot taken out too.
The head has no welding, but it is significantly reconfigured. The head gasket is eliminated, and replaced by a viton o-ring. Not for performance reasons, in that we can get the same head configuration with a gasket. But the o-ring is reusable, and that has it's advantages on a test motor.
The jetting range on the pipes tested was 145-170 main, and the 39pwk liked a large pilot (68) and rich needle (custom). Ignition timing was advanced a couple degrees on the dyno runs posted, but some of the pipes would have liked less timing for sure.
What we hope to test soon: A Blaster intake, and V-force reed, and another pipe along with some ignition alterations. All these things might be worse, but need tested nonetheless.