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: Hello. : I made a venturi from a section of pcv pipe that is 3" in diameter and I made the smaller venturi section 2". I have placed it in a flow of pipe like so: : http://www.mlbuie.com/transam/Black_LS1_TA/venturi_black_ls1_ta.jpg : The compressor is a Supercharger (SC) on a performance vehicle that maxes at 10 PSI of boost. I was hoping to run the size pulley I have driving the SC for when I want this level of boost, but need to decrease the boost to, say, ~ 6 or 7 Max PSI when I am driving around on pump gas. I can only run 10 PSI at Wide Open Throttle (WOT) if I have fuel additives or race gas (100 Octane or better) without risking damage to the engine from detonation. I'd like to be able to WOT it on the street on 93 octane and need to limit it to about 7 PSI max. : The little restriction I designed yielded the following observed results: : http://www.mlbuie.com/transam/Black_LS1_TA/venturi_phenomenon.jpg : So, with the size of the stricture, I DO reduce boost pressure over the overall range of rising boost, but the peak boost is still about the same. Is this because of the increased velocity of the air on the outlet side of the venturi? : I know I could reduce the boost by simply reducing the size of the inlet tubing with some restrictor, but my desire by using the venturi was to also reduce the inlet temperature of the intake air because of the vacuum induced. : Can anyone tell me if I am totally barking up the wrong tree, and why? : And can someone tell me how I might calculate the size of the venturi's smallest point, starting from a 3" opening, to obtain a drop in boost output of about 30%, from the compressor? : Thanks! : michael@mlbuie.com

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