Still need to do that manifold flow test but before that I have run some numbers on the bench for BMW K throttle bodies - these are lovely dinky little things 34mm bore.
yoeddynz and biturbo228 tagged here
K1000 ITB's
One removed and a pair of typical pliers for scale !
Cobbled together a mount.
Good enough to get a measurement
So running the tests
And then I had a play
The ID of the trumpet is around 32mm - slightly smaller than the bore of the ITB and I expect this is all about torque. On the K series these ITBs are direct to head so very short distance to the valve - the trumpets in the airbox would pretty well double the inlet tract length - the trumpets are 175mm and overall the length from ITB/head interface to the trumpet intake is 260mm
So there you go - oh and for the double length trumpet with strange expansion section - 158CFM @28"
If you go back and have a look at the flow number on a 1.5" Stromberg and a 40mm IDF with 32mm venturi - you will see the numbers for those little ITB's is pretty impressive. They flow so well that you can sacrifice ultimate flow for some extra port length and flow velocity / mass flow.