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Old 11-25-2008, 01:23 PM   #1
mmiller2002
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Default Does the turbo spin up when the clutch is in or in neutral?

I know, kinda a useless question, but I've been wondering if the turbo only spins up when the engine is under load.
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Old 11-25-2008, 01:32 PM   #2
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Originally Posted by mmiller2002 View Post
I know, kinda a useless question, but I've been wondering if the turbo only spins up when the engine is under load.
yes, but... there are ways to artificially make the turbo spool without a load on the crankshaft. (search for anti-lag) As you can probably guess it does it in a way that your car will not exactly like for long.
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Old 11-25-2008, 01:45 PM   #3
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anti-lag ftw!
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Old 11-25-2008, 01:49 PM   #4
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Are you asking if it is spinning, then yes, it will start spinning the second your engine is started. It won't make boost however until under load.
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Old 11-25-2008, 01:49 PM   #5
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Technically, if the motor is on, the turbo is spinning. It just spins faster under load because of the increased heat and velocity of the exhaust. In regards to making boost, that is not only a function of the exhaust, but also the position of the wastegate.
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Old 11-25-2008, 01:49 PM   #6
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i never understood why the turbo doesnt boost when not under load?

yes the turbo still spins becuase the exhaust gases still have to exit and it goes thru the turbo but why doesnt it create boost?
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Old 11-25-2008, 01:54 PM   #7
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Old 11-25-2008, 02:07 PM   #8
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i never understood why the turbo doesnt boost when not under load?

yes the turbo still spins becuase the exhaust gases still have to exit and it goes thru the turbo but why doesnt it create boost?
The engine RPM increases too rapidly for the turbo to fill it if there is no/little load.

It actually creates a little boost - at least enough to reduce the vacuum or approach zero psi
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Old 11-25-2008, 03:25 PM   #9
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You may also want to do a search for Unabomber's Manifesto on NASIOC. Very valuable information about Turbos.
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Old 11-25-2008, 03:32 PM   #10
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i never understood why the turbo doesnt boost when not under load?

yes the turbo still spins because the exhaust gases still have to exit and it goes thru the turbo but why doesn't it create boost?
Think about an airplane wing. When it's taxiing on the ground air is still passing over it but there isn't enough to provide lift. As the plane accelerates the wings produce lift because there's more air flow over them. It's similar to how the turbo produces boost, its spinning constantly but it has to spin to a certain speed before it starts producing positive boost.

This is not the greatest example or explanation but hopefully it will help you out. Throwing in Bernoulli equations might make this a lot more complicated.
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Old 11-25-2008, 03:34 PM   #11
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^^ Good explanation.
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Old 11-25-2008, 03:38 PM   #12
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SPins when you shut it down for a min too if its a REALLY good ball bearing turbo
http://www.youtube.com/watch?v=pBUpB8v9UDY
Thats mine lol. Spins for like 30 sec after I shut it off.
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Old 11-25-2008, 03:46 PM   #13
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Dave, ask your FXT if it will marry me.
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Old 11-26-2008, 08:46 AM   #14
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Originally Posted by aaronmsadler View Post
Are you asking if it is spinning, then yes, it will start spinning the second your engine is started. It won't make boost however until under load.
What senses load? What if the engine is in neutral and revved to 3-4000 rpm?
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Old 11-26-2008, 08:59 AM   #15
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What senses load? What if the engine is in neutral and revved to 3-4000 rpm?
Nothing in the turbo "senses load". It's just that when the engine is under load, it will burn more fuel and make more exhaust. This causes the turbo to spin faster, and move more air. At the same time, the motor isn't revving up incredibly fast (because of the load) and the turbo is finally able to move more air than the engine can intake. When that extra air starts to back up in the intake tract, it builds up pressure, which we measure as boost.

It's kind of non-intuitive, but boost pressure is really a measure of how much air the turbo can move, but the engine isn't using at the moment. Of course, you can cram more pressurized air into the cylinder than un-pressurized. But the pressurized air that's leftover in the intake manifold isn't doing anything for power. You can make a turbo with a very small hot-side that's very restrictive and it will make insane boost numbers, but not a lot of power. On the other hand, a nice big turbo that's well-matched to the engine can make a ton more power with nowhere near as much boost, because it's not wasting energy trying to compress air on the intake side of the motor that can't get out of the exhaust side because of restrictions.
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