Vaccum Question?

[Harris_EK3]

Okay guys sorta been struggling to get my head round this for ages.

What ive been trying to understand is that on Forced induction engines where does your vaccum for your servo,fpr etc come from?

Asked my one of college teachers this a while back and the answer i got was "its just the way the petrol engines operate" which didnt really answer my question but ive just read this thread (http://www.ek9.org/forum/resource-area/3675-do-i-need-fuelpump-fpr-what-do-fprs-do.html) and the guy talks about the boost pressure holding his fpr shut "more pressure i believe?".

So on factory petrol turbo cars do they run a seperate vaccum pump for the brake servo? Or does it push the diaphram the opposite way giving brake assistance?

Any advice would be appreciated

 

[Vtec6000]

The vacuum source would still be intake manifold. You'll not be braking at wide open throttle(well you shouldn't be!) so once the throttle body flap is closed the intake manifold is under vacuum.

 

[harvey j]

your break servo stays connected to your intake manifold, the split second you take your foot off the accelerator and hit the brakes your no longer creating boost therefore your engine reverts back to a vacuum.

hope this helps

 

[Harris_EK3]

The vacuum source would still be intake manifold. You'll not be braking at wide open throttle(well you shouldn't be!) so once the throttle body flap is closed the intake manifold is under vacuum.

Thanks for your input guys
So there's still the same depression under a closed throttle plate as normal?

I just thought a little boost would sneak past the closed throttle body :/

 

[Vtec6000]

Thanks for your input guys
So there's still the same depression under a closed throttle plate as normal?

I just thought a little boost would sneak past the closed throttle body :/

Yes with all things been equal the vacuum would be the same. Once the throttle flap/butterfly is closed there isn't much air moving through the engine so the turbo won't be creating any positive pressure.

 

[Harris_EK3]

Yes with all things been equal the vacuum would be the same. Once the throttle flap/butterfly is closed there isn't much air moving through the engine so the turbo won't be creating any positive pressure.

I get it now, thanks very much for the advice