Is there a problem here or am I just a lousy noob!??!

[AUDI_licious]

Noon question disregard!

[907DAVE]

How about when you're driving? Free reving doesn't really do much for boost testing.

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[AUDI_licious]

How about when you're driving? Free reving doesn't really do much for boost testing.

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It does about the same it'll boot up to 8psi briefly then drop to 0 pretty much no boost nor vacuum.

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[adam044]

You don't boost when revving your engine...

Noob.

[johnruan]

You don't boost when revving your engine...

Noob.

+1 lol

[vvenom800tt]

I want in on this

Noob

[BenMTL]

Big nooooob!

[Forge04]

I thought I had a handle on mechanics... but I'm not that savvy on thungs I haven't learned about, like turbos.

So why wouldn't you have boost while revving? Exhaust is still coming from the engine more with the higher RPM, spooling up the turbo, in turn forcing air to the intake, hence boost right?

I assume I'm missing some valve. The blowoff is normally for when the turbo goes from high RPM to low. I understand our DV does something along those lines.

[907DAVE]

Put simply, a turbo needs heat to create boost. It's the rapid expansion of gasses as they are heated during the combustion process that provides this. A quick free rev cannot do this.

Get us a video of a 3rd gear pull and maybe we can get you headed in the right direction.

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[johnruan]

Isn't using torque app not accurate reading boost?

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[Forge04]

Put simply, a turbo needs heat to create boost. It's the rapid expansion of gasses as they are heated during the combustion process that provides this. A quick free rev cannot do this.

Get us a video of a 3rd gear pull and maybe we can get you headed in the right direction.

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Oh we're talking about a quick gun of the throttle? No it takes time to spool up yeah?

[RakkCity]

Not time, but work done. In physics, work is the product of Force times distance (F • d), meaning in order for work to be done, a mass needs to accelerated by a force a certain distance. In thermodynamics, there's a law stating that the change in heat of a system is equal to the work done on the system.

These are pretty simplified principles but in short, if no work is done then no heat is generated. Obviously exhaust is still hot when idling/revving, because *some* work is being done accelerating the reciprocating assembly and obviously an explosion is going to make heat. However, the total heat energy in your exhaust system while accelerating the car is much higher than the total heat energy when idling or revving, and it's this heat expanding the exhaust gasses that drives the turbine, not simply the airflow from the exhaust. This is why your car doesn't boost while revving.

That being said, a small amount of boost can be made depending on the turbo/engine size etc. My old mk4 GTI would blow off a bit while revving the motor, but the blowoff was a faint whoosh instead of the sharp screech it made under full boost.

As for blowoff valves vs. diverter valves, google it or search the forums, there's many many explanations of the difference. You don't want a blowoff valve for VAG cars, recirculation/diverter valves only.

[Forge04]

Gotcha. That was nicely put in just hair more than layman's terms :)

[AudiTFSI3o3]

i think the reason OP made this thread is because he posted this over in the B8 S4 section.

[14S4GWM]

^ Haha, I replied to that thread too. Whats he thinking?

[Okedokey]

Not time, but work done. In physics, work is the product of Force times distance (F • d), meaning in order for work to be done, a mass needs to accelerated by a force a certain distance. In thermodynamics, there's a law stating that the change in heat of a system is equal to the work done on the system.

These are pretty simplified principles but in short, if no work is done then no heat is generated. Obviously exhaust is still hot when idling/revving, because *some* work is being done accelerating the reciprocating assembly and obviously an explosion is going to make heat. However, the total heat energy in your exhaust system while accelerating the car is much higher than the total heat energy when idling or revving, and it's this heat expanding the exhaust gasses that drives the turbine, not simply the airflow from the exhaust. This is why your car doesn't boost while revving.

That being said, a small amount of boost can be made depending on the turbo/engine size etc. My old mk4 GTI would blow off a bit while revving the motor, but the blowoff was a faint whoosh instead of the sharp screech it made under full boost.

As for blowoff valves vs. diverter valves, google it or search the forums, there's many many explanations of the difference. You don't want a blowoff valve for VAG cars, recirculation/diverter valves only.

Yes, but we are talking about power, which has a time component. Therefore spool time will effect power.