I couldn't remember what the decision was on these splitters, so I did some research, and pasted the quotes I found below.  Unfortunately, I still don't know the answer. Lynn, Leon, what say you?

Rusty (shopping for sandbags)

 

The following quote is from Tracy's squawk_muffler page, and would tend to suggest that there isn't much HP to be gained with the turbo housings, though he isn't making a definitive statement to that effect.  

March 3, 2001  Mufflers.. the Saga Continues

... Now the question  is,  If all other things are equal, is there any significant power difference between the turbo and non turbo rotor housings? Ever done an A/B comparison on this?  I did have a small increase in power when I changed to turbo housings but  that was comparing an old junkyard dog engine with lower compression rotors to a freshly blue printed engine with high compression rotors.   If it turns out that there is no significant difference in power,  we've been going down the wrong path with the turbo housings.  And here I am with a brand new 20B with turbo housings..........

The following quote is from the archives, about 6 weeks later.  This would suggest (second hand) that Bruce thinks there is significant HP to be gained by using the turbo housings.   


Date Wed, 18 Apr 2001 103007 -0700
From "Mike Wills" <willsm@spawar.navy.mil>
Subject Re Engine Selection for 13B

Bob,

  I discussed this with Bruce Turrentine who is currently assembling an NA
engine for me. It just so happened that Tracy mentioned his conclusions
about using the splitter equipped housings when Bruce was buying the parts
to build my engine.
  Bruce told me the NA housings would likely cost as much as 15-20HP. After
discussing the options with him I decided to go ahead with the turbo
housings.

(the rest snipped)