And re the step in a Honda exhaust duct.
When using a T port or a properly designed tripple port exhaust, the area just outside the port is way too big during the blowdown phase,and alot of velocity is lost.
I have found that a good rule of thumb is to gradually reduce the duct exit at the flange, to around 75% of the total chordal area.
This will often equal the area of just the main port in a tripple setup.
If you make the duct exit the width of the header, and then reduce the height, forming an oval to give the correct area, a heap of power is created, in part due to the much better flow from the outer parts of the port width of a T or the
aux ports in a tripple..
Steps work OK, but a CNC formed oval to round transition in the flange works best.
Note well, this technique DOES NOT work in a single Ex port engine, no matter how big it is.
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