Just a Quick Venturi Question.

Thats what your PCV system is for.

The gasses that build up inside your engine are very flammable so the last thing you want to do is give it a direct line from the exhaust system (that produces flames inside it at times) to the inside of your engine. Unless you want to be replacing engine seals every few weeks.

Thanks for the response. I realize what the PCV system is for. Under normal conditions gases under the valve cover get sent back through the intake to be combusted, instead of being just dumped into the atmosphere. This application is for a turbocharged vehicle. It is good to have a bit of a vaccuum at all times but when the car goes into boost the PCV system vents into the intake of the turbo to burn it off. Effectively, the extra oil and vapour cause build up and also lower effective octane of the fuel, causes problems such as knock, ect.

Although it is not meant for on-road use, it is not illegal where I live to vent these gases to the atmosphere or whatever. I am trying to find a way to make MORE suction from the exhaust to make a vac condition on the motor under boost.

Venting gases directly to the exhaust is not unheard of, I am just curious on a scientific level (that I'm not - lol) if you make the venturi opening larger, does vac increase through that line. I hope this make sense.

The under-pressure (I prefer this to vacuum) is given by the gas velocity in the exhaust tube. If you make a bigger opening you ONLY allow more flow from the volume you want to suck from.

As far as I know the presence of oil in the air-gasoline mixture will increase the equivalent octane number and not decrease but as usually I may be wrong.

Why the check valve, and what are you trying to do?

That's not a simple question, and the answer can vary. But, in the general case, no, that doesn't give more vacuum.

Now, to get a really accurate answer, either build a few and test them, or model it in a CFD package.

Also important to draw/vacuum is where the end of the tube is in the flow stream.

Highest velocity will be in the center of the tube. Tubing bends will create turbulence, which also affects the draw. Or you might take advantage of the increased pressure/velocity at the bend. Who knows?

I'm with TVP 45. Get some tubing and experiment.

All right, thanks for all the responses guys!