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How does vacuumn work in a boosted application? 

 

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 Post subject: How does vacuumn work in a boosted application?
Posted: Wed Jan 26, 2011 11:40 am 
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One thing I dont understand about Turbos and Superchargers, is how vacuumn works, obviously in the manifold (particularlly with a supercharger because they dont go off boost) you are gonna have positive boost, so how do vacuumn operated things like the brake booster and the auotmatic climate control, and for that matter (and I geuss more importantly) how does the fuel pressure regulator handle having positive boost instead of vacuumn? Do you need a vacuumn pump like a diesel? what's the go?

Cheers, Gab
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 Post subject: Re: How does vacuumn work in a boosted application?
Posted: Wed Jan 26, 2011 12:14 pm 
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turbo and supercharged engines do make vacuum at idle, light throttle and cruising..
superchargers have bypass valves so if there is any positive pressure created at idle or decelleration it is released when the throttle is shut..
the climate control has a reservoir tank in the inner guard and the brake booster has a one way valve that holds vacuum untill its used, so at anytime when the throttle it shut/decelleration there is manifold vacuum supplied to the booster..
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 Post subject: Re: How does vacuumn work in a boosted application?
Posted: Wed Jan 26, 2011 12:23 pm 
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Is that enough to make it all happy though? what about the fuel pressure reg? I'd imagine after boosting an engine, your brakes wouldnt be as good.

Gab
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 Post subject: Re: How does vacuumn work in a boosted application?
Posted: Wed Jan 26, 2011 12:27 pm 
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fuel regs work with and without vacuum..
at idle the fuel reg will see vacuum and opens up the return line to the tank releasing some of the fuel pressure, under load/ hard throttle there is no vacuum in a n/a and will restrict the return line via spring pressure in the reg causing fuel pressure to rise in the fuel rail.
in a boosted aplication it works the same as n/a untill it sees boost, and the boost will force the reg to restrict the fuel return more as pressure rises raising pressure even higher..
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 Post subject: Re: How does vacuumn work in a boosted application?
Posted: Wed Jan 26, 2011 12:29 pm 
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TROYMAN wrote:

in a boosted aplication it works the same as n/a untill it sees boost, and the boost will force the reg to restrict the fuel return more as pressure rises raising pressure even higher..


I suppose that's a good thing, as the higher the boost you have, the more fuel pressure you want.

Gab
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 Post subject: Re: How does vacuumn work in a boosted application?
Posted: Wed Jan 26, 2011 12:30 pm 
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If you run into major issues you could fit a vacuum storage tank like people do when they run HUGE cams N/A.

 

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 Post subject: Re: How does vacuumn work in a boosted application?
Posted: Wed Jan 26, 2011 12:31 pm 
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possably in extreme hard core conditions, like if you were doing a huge burnout where the throttle is not released at all, and you keep pumping the brakes, you might suffere some brake vacuum issues..
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 Post subject: Re: How does vacuumn work in a boosted application?
Posted: Wed Jan 26, 2011 12:34 pm 
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some fit vacuum pumps :)

also u can get boost referenced fuel regs as well

 

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 Post subject: Re: How does vacuumn work in a boosted application?
Posted: Wed Jan 26, 2011 12:38 pm 
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Gab1 wrote:
TROYMAN wrote:

in a boosted aplication it works the same as n/a untill it sees boost, and the boost will force the reg to restrict the fuel return more as pressure rises raising pressure even higher..


I suppose that's a good thing, as the higher the boost you have, the more fuel pressure you want.

Gab


yes but with factory regs the pressure will rise with boost but its still not enough so supply a safe amount of fuel without bigger injectors and tuning..

thats why some people use 10;1 rising rate regs on std injectors, this means that every psi of boost will raise fuel pressure 10 psi..

im running a factory au vct fuel reg, but i have the larger injectors and the tuning available to supply the fuel needed
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 Post subject: Re: How does vacuumn work in a boosted application?
Posted: Wed Jan 26, 2011 2:20 pm 
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Only thing really required is to redirect the rear tapet cover breather to before the turbo isn't it? Otherwise you will pressurise the crank case too?

And the front has a PCV valve so its not required? (though you fitted another one there inline too Troy?)

Cheers,
Tim

 

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 Post subject: Re: How does vacuumn work in a boosted application?
Posted: Wed Jan 26, 2011 2:27 pm 
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you can still run a pcv as it will close once boost hit it, i got a baxr6t check valve on my pcv hose because the pcv are plastic and can break under boost
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 Post subject: Re: How does vacuumn work in a boosted application?
Posted: Wed Jan 26, 2011 2:36 pm 
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Ah ok then... Makes perfect sense...

And usually the catch can goes in the line from the back breather to before the turbo so oil can not be vacuumed into the turbine blade and destroy it?

This way when under vac conditions it still draws the draught through the rocker cover and feeds blowby back into the manifold? When under boost and rocker PCV closes then blowby is pumped back in before the turbo so you want no oil in it there?

Thats how it makes sense in my mind anyway... :mrgreen:

Not that you really oil in the manifold either... Suppose you could fit two catch cans... One in each line then... But the one for the turbo seems more important (more blowby under boost i guess and like I said it hitting thr turbine wouldn't be real good)...

Cheers,
Tim

 

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 Post subject: Re: How does vacuumn work in a boosted application?
Posted: Mon Feb 07, 2011 8:51 pm 
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TROYMAN wrote:
fuel regs work with and without vacuum..
at idle the fuel reg will see vacuum and opens up the return line to the tank releasing some of the fuel pressure, under load/ hard throttle there is no vacuum in a n/a and will restrict the return line via spring pressure in the reg causing fuel pressure to rise in the fuel rail.
in a boosted aplication it works the same as n/a untill it sees boost, and the boost will force the reg to restrict the fuel return more as pressure rises raising pressure even higher..

In other words, the fuel regulator keeps a constant differential between manifold vacuum and fuel pressure. So a 2.75 bar reg as used in many stock I6's keeps fuel pressure 2.75 bar above the vacuum or pressure in the manifold.

 

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 Post subject: Re: How does vacuumn work in a boosted application?
Posted: Mon Feb 21, 2011 3:55 pm 
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TROYMAN wrote:
you can still run a pcv as it will close once boost hit it, i got a baxr6t check valve on my pcv hose because the pcv are plastic and can break under boost


my pvc hose broke so i have a filter and blocked off the intake side, from this im guessing its a bad idea?
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 Post subject: Re: How does vacuumn work in a boosted application?
Posted: Mon Feb 21, 2011 6:31 pm 
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its not overly bad.. its just breathing to atmosphere instead of being recurculated.. illegal emission wise, but wont really hurt..
although i like to keep the pcv operating,
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