Hi there, I have made a few suction venturi nozzles over the years, as I couldn't find or couldn't afford store bought. The last one was four inch and I used a 3/4 inch jet with a flare out to the 1 1/2 inch supply. My pump is a 5 hp Honda driving an Onga pump - a factory built pump/motor unit available here in NZ. The old shop bought venturi had worn totally out and was very hard to get jammed rocks out of. Mostly because my hand wouldn't fit up past the nozzle restriction.
I lined up the new 3/4 inch jet to be slightly pointing downward but up the center of the pipe - so the water jet would hit the bottom of the pipe about 3 or 4 feet up. I used alloy for weight reasons, but also because it was what I had on hand.
I will try to load 2 photos showing what I came up with.
The result was great, power increase was such that the water and gravel came up the hose with such velocity at high rpm, that it shot right over the sluice box and landed back in the creek 2 feet beyond it! I had to slow it right down to be able to wash the gravel. The water was only 2 feet deep where I was working, but the old venturi did not have had that sort of power.
I made a removable restriction nozzle so I could get my hand in to clear blockages, and for easy replacement as it wears out.
