Hi, today I use the flow testing equipment and software from Torqsoft to measure the Flow Flow Area of my exhaust port/duct.
https://www.torqsoft.xyz/index.html - see further below for links to the equipment list for the venturi and manometers.
Also I have been watching David Vizard - hi YouTube channel is here: https://www.youtube.com/user/marvingvx1/videos
Jan Thiel's book details are here: legacyjanthiel@gmail.com
and: https://www.facebook.com/groups/671081149638729/permalink/6915535795193202/?ref=share
TorqSoft equipment list:
Venturi 20 mm is most suitable for cylinders with port diameters of less than 33 mm: https://www.shapeways.com/product/FTPHNUF3X/flow-venturi-20mm?li=shop-results&optionId=59345290
Venturi 27 mm is suitable for cylinders with exhaust port diameters between 30 and 44 mm, and is shown below.: https://www.shapeways.com/product/ZFQJ7UAL2/flow-venturi-27mm?li=shop-results&optionId=59381039
Manomenter: https://www.amazon.co.uk/dp/B07K87NQMD?ref=ppx_pop_mob_ap_share
Brass nipple - 3mm: https://www.ebay.co.uk/itm/390948209350