F150 turbo question on boost

[Ozark]

I keep seeing people mention boost values of 17-20 psi on turbo charged gas and diesel engines. My question comes from an engineering background not a truck mechanic background so I probably just don't understand the system. If the turbos are in the exhaust downstream from the intake how can the boost exceed 1 atmosphere or 14.7 psi? I drive a 3.5 ecoboost and am just curious.

 

[eggman918]

OK I'll give it a shot,but this is just the way I understand it and I'm neither an engineer om a mechanic................however I do play both from time to time
there are a couple of things that multiply the mechanical advantage of the turbo first is the size difference between the turbine wheel and the compressor wheel approximately 2-1 with the turbine being smaller second the volume of exhaust gas generated is greater add to that greater volume the energy of the waste heat in that greater volume of gas there is your gain.The newer generation of wheels on both the hot and cold sides also have much better designed blade geometry thanks to the increase in computer power it's a lot easier to model what is going on inside the housings...........so boost pressures well above drive pressures are the norm in a properly matched turbo/engine combo giving us the performance and fuel efficiency that we all love.
This is just my two cents as I've come to understand things.........so If I'm not grasping it all I'm all ears for input from those that grasp this better than I do.

 

[five0merc]

From what it looks like you are asking how the turbo creates boost in the engine?? The turbo is spooled by the exhaust and the piping for the turbo goes to the intake and that is how the system gets pressurized.

 

[Ozark]

Ok I see the answer in your diagram. The drive turbine is in the exhaust but the output turbine is in the intake. Thanks, now I will have to go back to wondering who invented barbed wire while driving down the road.