He's not trying to do the "block off" mod to prevent the decel popping. Tenn is attempting to gain some Hp by creating a vacuum in the crankcase which in "theory" will allow the pistons to decend quicker on the power and intake strokes and therefore increase power.
I've heard the theory before and I think it's BS. The problem is that when 1 piston is coming down, another is going up. So really the air displaced in 1 cylinder as the piston comes down is actually pushed into the cylinder with the piston going up. If you create a reduced pressure in the case then it's going to hold back the ascending pistons so any gains you might see in Hp by "sucking down" the decending pistons is gone. This is all based on the fact that you could actually create enough vacuum in the case to make a difference.
I'd like to see some hard numbers on this to back up the statement that "the engine is more efficient with the pressure drop"
I thought and argued the same thing for a long time several years back. I said the same exact thing when a friend and I started brainstorming this
idea for our ZX12's back in 01 I think. The best thing to do if you are curious is do a search on "crankcase vacuum pumps". There is a reason the make and sell these pumps.
The question (for me) is how much vacuum does my bike have? I have a vacuum gauge, but decided not to hook it up. Hg doesn't matter to me. I would like to see the cfm.
I beat my 12 to death on the dyno along with other board members. There are gains to be had. Just put this out there for those who might be interested.