Question on boost.

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434 nova
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Question on boost.

Post by 434 nova » Sun Jan 14, 2018 6:00 pm

When running a turbo say at 40#s does that boost make it to the cylinders or is boost just a reading in the intake manifold? Or does the lb per min rating of what a turbo flows gets into the cylinders? So what I’m asking is does boost #s or lb per min on turbo rating get in the cylinders.

F-BIRD'88
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Re: Question on boost.

Post by F-BIRD'88 » Sun Jan 14, 2018 6:27 pm

boost is back pressure. #/ minute is a MASS flow rating..
If what gets into the cylinders matches exactly the output (mass flow) of the turbo there would be no back pressure.

There would be no boost. There is boost because the engine consumes less air than the turbo is outputing.

With any turbo on it, make that engine pump more air thru and power goes up and boost goes down.

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MadBill
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Re: Question on boost.

Post by MadBill » Sun Jan 14, 2018 8:57 pm

Another way to look at it is that because of air friction there will always be a net pressure drop through an intake system if any flow is to occur, boost or no. The amount of drop will be proportional to the mass flow and to the system restriction, so for example if a supercharged engine was developing a peak of 20# boost and then the heads and cam were changed for bigger ports and more lift, the mass flow and resulting cylinder pressure would increase but the boost pressure might drop to 15# or less due to the reduced restriction. The important point here is that in the second case, despite the lower manifold pressure, more air equals more power potential.
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