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Had this question on my Engine midterm for one of my Caterpillar classes, and of course, I got it wrong. :rof

At 40hg2 of restriction, at any given rpm, the turbo compressor speed on a 3406 engine will...

A. Increase
B. Decrease
C. Stay the same RPM
D. Not relative


What do you think? I said the turbo speed would Decrease because if the airfilter is a restriction, black smoke would be the result, and the motor would be lugging. My engine teacher said that the fuel is the fire of the motor, and the fuel is still being "pushed" out of the cylinder, where it drives the turbine wheel, so the correct answer would be Increases

My theory is, more air in = more air out, but my conclusion of his answer is, I can go to the track, put a plastic bag ove my intake, and my compressor speed would increase, thus, making more boost. :cookoo[1]:

Am I overthinking this? :rof

This question neeted me a 89% instead of a 90% :rolleyes: :D



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He is talking from the stand point of less air=more fuel which increases speed in diesels.

That's a hard call....I would assume it take more fuel along with more air to increase speed...not taking away air.
 

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I guess it depends on if it is a VVT. The VVT is tuned to speed up when air is not present to stay efficient. I would assume a standard turbo would decrease depending on the velocity of the exhaust gas passing through.
Or maybe I am wrong all together but is sounds good anyway....
 

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Wouldn't more heat be exiting the cylinder in the form of unburnt fuel, so the extra heat should result in increased drive pressure therefore increaseing the compressor speed.
 

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This might be a poor and over simpelfied (not sure if that is a word) take a box fan and turn it on put a piece of cardboard over the intake side,what happens, it speeds up.
 

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Now this interests me. My thinking is also along the lines of smokinlmms, in that a slight restriction / reduction of air is causing more heat to be generated, causing increased turbo speed. On the other hand, I can also see your thinking of the plastic bag over the intake, if restriction gets to high, it MUST start to decrease the speed of the turbo? No expert on this by any means, but you got my curiosity going now! Must get this resolved! Where are the turbo experts? :)
 

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your instructor is right, theres less resistance on the compressor but the exhaust is still going to try to spin the turbo at the same amount of force for the fuel required, so it will increase the compressor speed to compensate for the restriction as long as the fuel being used remains constant
 
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