The flow won't be restricted by that diameter but with the set up you describe you may have a problem measuring the flow out of the jet whilst at the same time keeping the height of water at 36 inches . Do a search on this forum eg
http://www.fordbarn.com/forum/showth...w+testing+jets and you should get some ideas. I made a rig from copper tubing off cuts and some plumbing left overs I simply connect it to the water tap rather than having a pump recirculating the water as some of the rigs are. If you get stuck email or let me know and I'll send you some pictures. Give my love to Denmark. John B