I did read that some one tested the flow of the Cat housing with the one smaller passage and even though it was smaller flowed fine

Since then 440Source now has a housing with their name on it, changed, not sure if it has the small passage, if it matters anyway.

Then again I read another post about opening up the small passage with a die grinder , an easy job.

All in All I have the small cat housing on my stoker motor with NO overheating problem