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Help Understanding The Boost Gauge Reading (r33gtsts2)

Torques

By Torques,
in Engines & Forced Induction

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Torques Mentor

Torques

Posted
Posted

Hello there,

I hope this is not a silly question.... (I'm relatively new to the Skyline and turbos)

When I drive the car at say 4500rpm in last gear and with a steady foot at the pedal shouldn't I be reading some constant boost at the build in gauge??

The thing is, that I don't! The boost gauge hovers around 0 to -.

However when I floor it the gauge goes up (to 4) but comes down when a constant speed is reached.

I'm starting to suspect that there might be a leak in the intake system ...

Or maybe I'm not familiar with how boostlevels are maintained.

Any hints are greatly appreciated :)

The Dan Grand Master

The Dan

Posted
Posted
Hello there,

I hope this is not a silly question.... (I'm relatively new to the Skyline and turbos)

When I drive the car at say 4500rpm in last gear and with a steady foot at the pedal shouldn't I be reading some constant boost at the build in gauge??

The thing is, that I don't! The boost gauge hovers around 0 to -.

However when I floor it the gauge goes up (to 4) but comes down when a constant speed is reached.

I'm starting to suspect that there might be a leak in the intake system ...

Or maybe I'm not familiar with how boostlevels are maintained.

Any hints are greatly appreciated :)

Completely normal.

When partial throttle opening is made, the engine will not create a resistance to air flow.

It will only make pressure when the engine is under load.

Torques Mentor

Torques

Posted
  • Author
Posted
Completely normal.

When partial throttle opening is made, the engine will not create a resistance to air flow.

It will only make pressure when the engine is under load.

I see ... it dawned on me after I submitted the post :)

In other words the turbo is not delivering enough pressure to hold the engine under load ..

(Engine is breathing away all the turbo ca deliver ..)

How is it with the larger turbos then?

Do they deliver constant pressure at say 4500?

Cheers and thanks for the help ..

Guilt-Toy Grand Master

Guilt-Toy

Posted
Posted

the turbo will not make boost unless the engine is under load over a certain RPM (Depending on what size the turbo is) the bigger the turbo the higher the rpm the engine can make boost under load

so if your reving the engine at 5000rpm and there is no load on the engine you will have no boost but as soon as the engine loads up you will get boost.

Torques Mentor

Torques

Posted
  • Author
Posted
the turbo will not make boost unless the engine is under load over a certain RPM (Depending on what size the turbo is) the bigger the turbo the higher the rpm the engine can make boost under load

so if your reving the engine at 5000rpm and there is no load on the engine you will have no boost but as soon as the engine loads up you will get boost.

Hi there ...I think I understood ..

So if you rev the engine at a constant 5000 rpm (for example going straight on a highway in last gear) the turbo must still

be working hard and produce pressure, right?

And if you floor it then (at 5000 rpm) the turbo spools up even more thus producing more pressure than the engine can consume.. right?

And that's the moment where the boost gauge comes into positive territory ..

blind_elk Grand Master

blind_elk

Posted
Posted

At a cruise (constant throttle) condition, the engine does not produce enough exhaust gas at a fast enough velocity to spin the turbine at a speed that can produce boost. This is what is termed "low load", ie minimal work being done by the engine. The engine is actually running under vacuum (just like a N/A engine).

When you start to accelerate (increase the load on the engine), the volume and velocity of the exhaust gases increases, causing the turbine wheel to spin faster, thus producing boost. For example, if you are driving at constant throttle setting on a flat road, there is no boost. When you come to an "up" hill, the engine needs to do more work to maintain the road speed. The increase in the load on the engine causes the turbo to produce boost.

Under constant throttle, boost is independent of revs. If you could "cruise" at 7000 rpm, you would still have no boost.

Maybe you should go to a website such as howstuffworks (I think that's what it's called), and study how a turbocharger actually works - lot simpler than us being here writing a "War And Peace" article on how it all works.

Torques Mentor

Torques

Posted
  • Author
Posted (edited)
Maybe you should go to a website such as howstuffworks (I think that's what it's called), and study how a turbocharger actually works - lot simpler than us being here writing a "War And Peace" article on how it all works.

Hi!

HaHaHa ... no war on my side :P

I'll do my homework (though I thought I've done some) but apparently I need to read a bit more on the topic ..

It seems turbo operation is not as straight forward as I though.

The mistake I've made was the assumption that when the engine revs high the turbo is doing the same.

(and that's what you generally read)

So I was wondering why there is no boost reading at cruise level.

Nevertheless you guys pointed me in the right direction .. thanks!

(I'll be back with more 'silly' questions :P)

And btw. I got an answer on a UK site, and this guy had written about 2000 posts!

He claimed I have no boost because the swing valve would be open at cruise ... so how's that ?:P

Good nite then ..

Edited by Torques

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