I know the primary induction tube is 3

 

It tapers from 4" to 3", its not the drastic step they lead you to believe.

 

I have not seen any in person only pictures.

The pictures are miss leading then it looks like it is a very abrupt set up in diameter.

So the majority of the piping is 4 inches with the last little bit tapering down to 3" at the TB; with a section of the pipe before the taper starts to be a tube in tube setup.


Anyone know the approx internal length the 3 inch section extends into the 4

 

I have no idea how long the taper is, I just gave one a quick visual inspection last summer while it was off a member's car.