A Twin Cam 110" Screaming Eagle head on the flow bench, always flow test the head with the complete intake and exhaust in place, this is known as a full system test and is the only way I flow test.
Companies that test open (no carb or pipe attached ) usually do so to give exaggerated flow numbers as the ports will flow more in most cases without the full system attached, also its quicker to do.
When you test the full system you can accurately set the flow ratio, this is the relationship between the intake flow rate and the exhausts. We set the flow ratio depending on the application, ie a street head flow ratio is different to a road & track set.
Also by testing the exhaust system the two pipe flow volumes front & rear can be balanced out, this is important as they will flow differently due to the bends being different, also you can test for back pressure because this is not desirable in a performance exhaust system.
A34 head on a extremely accurate modified Vernier toolmakers fixture.
This jig sets the heads up on any angle or position to bore the valve guide holes in the castings, machine the spring seat pads, the spark plug bores, decompressor bores and for the external drains
We also use this kit to set up factory heads with damaged guide bores and re-machine them for oversize guides, twin plugging, spring pad machining for larger OD heavy duty spring kits, piston pocketing manifold facing + a few other little tricks