yes they change the turbine housing to the hx-40 style.

 

They must have adjusted the turbine blade tip to housing clearace. I just tried mine and its to tight without machining it out some. Are they using the same turbine wheel as well. Interesting stuff. Anybody have pictures?

 

I resurrected this thread just to answer the EH housing question... real world results in... the primary lites so fast-- even before the wastegate opens-- that the larger EH is not necessary unless you are throwing a ton of fuel that makes it necessary for the sake of lowering drive pressure.

To put it in relative terms, comparing to my old 35/3b set up (wastegate on the hx35 set at 24psi), the bottom BB turbo lites twice as fast (no exaggeration here-- real deal) as the BHT3B to 25psi and this happens before the top wastegate (set at 40psi) opens. This is with the "smaller" EH on top. What I have found is in the new setup the bottom turbo participates a lot sooner and shares more of the load throughout the psi range than my old setup.

 

I posted this back in the "twin turbo" thread as well so this is a duplicate... but for future "searchers" the answer to the question above is that the bottom turbo goes from 2 psi to 27-30psi in the time it takes me to say "one-thousand-one"... or about one second.