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Jimm44

Please Explain How Turbos Function

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I understand that turbos force air into the engine and the reason for them. My question has to do with when are turbos working. Do they work all the time or just when accelerating hard? For example, if I do 0-60 in 30 seconds is the turbo just idling in the background ready to go if you put your foot into the pedal or is the turbo constantly operating? I would imagine on a max run to 60 the turbo is running for the full 7, 8 or 9 seconds. True? Thanks.

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The exhaust goes through the turbo so they are always turning.  The faster the RPM the faster the turbo spins but it's always spinning.  There is a blowoff valve that releases to prevent over pressurizing.

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Yep, they are always turning but not always applying boost to the engine.   If you accelerate gently or even what most would call normally, they are not pressurizing the combustion chamber and adding boost.   In some engine applications, the boost comes on more readily than others.    I installed boost gauges in my turbo vehicles.    On my 3.5 ecoboost MKS, it took fairly quick acceleration before boost was required.   On my 3.0 Continental, I get boost with less throttle input than I did with the MKS.   Of course, either one would generate boost at heavy throttle applications. 

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So then from the above 2 posts, I presume that better economy is obtained when normally accelerating and power is achieved 

during heavy acceleration. Correct?

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Like any other engine, turbo engines deliver best fuel economy with lighter throttle input and max power is achieved with heavy throttle.    I sort of look at turbo engines like having 2 engines in one.   Let's say you have a 3.0 liter V6 engine.   Drive it reasonably, staying out of the boost and it delivers top fuel economy like a 3.0 V6 should.    Drive it harder and it delivers power like a much larger engine...... but also uses more fuel like a much larger engine.     

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The way to understand forced induction (turbos and superchargers) is to first understand that an internal combustion engine is just an air pump.  It uses oxygen in the air to generate combustion and it adds enough fuel to match the incoming oxygen.   Air is the limiting factor - you can always add enough fuel to maintain the proper ratio.  When you open the throttle on a car you allow in more air and the computer adds fuel accordingly.

Forced induction allows more air and therefore more oxygen to enter the combustion chamber producing more power.  The faster the turbo or supercharger spins the more air gets packed in and the more power.  Nitrous works the same way because it contains a lot of oxygen.

A smaller turbocharged engine uses less fuel at light throttle but when you increase throttle it produces power like a larger engine.   That’s why you get better fuel economy when driving normally but still have excellent power when you need it.

I’ve found that ecoboost engines in particular have a wider range of fuel economy compared to the V6 or V8 engines they replace.  They can get a lot better or a lot worse depending on how they’re driven.

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