Congrats...you just stumped a retard ******* and a Canuck.
You and your parents should be proud.
LOL...seriously though, I don't understand all the ins and outs of turbocharging gas engines.
I do know that by design, a gas engine has vacuum to draw air into the cylinders...have to have vacuum before the turbo spools up and then forces air in... that's the transition from vacuum to boost.
By design, diesels (turbo'd or not) have no vacuum. That's why these types of gauges really aren't designed for diesels. It's way more complicated than this I'm sure, and I'm by no means a great source.
Well, I'm no "ricer" but I did stay at a Holiday Inn Express.
Gassers are spark ignition, so they rely on a stoichometric fuel/air charge supplied to the cylinder (where we oil burners just get air on the intake, compress it and then shoot fuel into the compressed air near TDC). To "prepare" the fuel/air charge for the gasser engine they used to rely on carburetors - the vacuum drawn in the intake and across the throttle plate sucked atomized fuel out of the carb through jets. Next came a throttle body - computer controlled fuel inlet, but still "sucking" the injected fuel across a throttle plate. Latest technology is fuel injectors in the manifold runners but the throttle plate is still there to control the air and the engine is still producing vacuum in the manifold to pull the fuel/air into the cylinders. Even a turbo-charged gasser will have manifold vacuum at idle and low rpms, or it couldn't get any fuel. As rpm rises and the turbo begins to boost, manifold pressure goes positive (boosted) which is "pushing" the air charge and fuel from the injectors into the cylinders.
Because you can? Since the manifold pressure "swings both ways" why have a gauge that pegs out and doesn't monitor full-range full-time? Manifold pressure is being monitored continuously on an FI engine for the computer to control injection- so that could feed an electronic gauge. Because of the throttle body, manifold pressure can plummet on a throttle chop to deep vacuum (great for compression braking) and that's why racers and ricers have blow-off valves to dump the turbo output when the throttle plate slams closed and the turbo is still spun-up.
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