Turbos and vacuum lines

[Turbroke]

This is probably a dumb question, but wouldn't it make sense that the vacuum lines on a turbocharged intake do exactly the opposite of creating a vacuum. A turbo creates pressure vs. the engine "sucking" air through the intake. I'm hooking up vac lines today, and was wondering how this affects the vacuum operated systems in my turbo ranger swap. Hmmm.

 

[RonD]

Not a dumb question, I guess they could change the name but if a hose is connected to the intake it is usually referenced as a vacuum hose, regardless of its use.
I.E. some distributors used "vacuum advance" but many would be more correctly called "lack of vacuum advance"

The turbo "pressure hose" is to operate the Wastegate, wastegate is the "valve" allowing exhaust from engine to by-pass the turbo, so it sets a limit on the Boost Pressure, like a 7psi wastegate, "valve" is generally just a spring with known load tolerances, so it is easy to lower or increase max boost by adusting or changing the spring.

Electronic wastegates are better, the spring versions have to start opening early just because of the physics of a spring controlled system, so it increases lag and can vary power output.

Good read here on the different Boost controllers: http://en.wikipedia.org/wiki/Boost_controller

 

[Turbroke]

So if the pressure @ the turbo is identical to the pressure in the intake manifold; how does that effect the operation of the power brake assist, fuel pressure regulator and any other systems that are intended to operate with a vacuum from the intake? I ask this because I swapped a 2.3 turbo engine and intake from an 88' Turbo Coupe into my 1990, 2.3 Ranger. I'm wondering how, and if any of my vacuum operated devices are going to function properly. (I used the fuel rail and regulator from the turbo motor, so this is not a concern, but the rest of it is.) Thanks for the reply.

 

[scotts90ranger]

Simple, you aren't braking under full boost, and the vacuum line is behind the throttle so when not under boost there is vacuum like a normal N/A engine, and there is a check valve in the brake booster so it doesn't see the pressure. On the fuel pressure regulator, it lowers the fuel pressure for idle like normal, but when it's under boost it raises the pressure. The difference is which side of the throttle plate you are on, with a turbo on the turbo side of the throttle plate there is always going to be pressure, but on the engine side of the throttle plate the pressure changes depending on how much load you are putting on the engine (how far the throttle is open)

 

[RonD]

Yes ^^^^

Many Vacuum operated devices(EVAP, EGR, and Climate control) also have a "can" or "bottle" that stores vacuum for use when throttle is open and vacuum is gone on an N/A engine.

 

[Turbroke]

Yes ^^^^

Many Vacuum operated devices(EVAP, EGR, and Climate control) also have a "can" or "bottle" that stores vacuum for use when throttle is open and vacuum is gone on an N/A engine.

That makes perfect sense. Thanks. (I guess I better put the little canister back into the system. lol)

 

[scotts90ranger]

Don't worry about the canister, I don't have one, but I'm not functionally using the charcoal canister either... I think the only functional vacuum components on my Ranger are the fuel pressure regulator, brake booster, and vac/boost gauge, and the wastegate of course...

 

[donfordguy]

Don't worry about the canister, I don't have one, but I'm not functionally using the charcoal canister either... I think the only functional vacuum components on my Ranger are the fuel pressure regulator, brake booster, and vac/boost gauge, and the wastegate of course...

hmmm i thought the vacuum linr went on before the turbo \

 

[scotts90ranger]

On a spark ignited (gas/propane/natural gas) engine, they use throttle plates and the intake vacuum is only behind that point unless the engine is at full throttle (or at atmospheric pressure in a forced induction application) in which case there will be no difference in pressure compared to the atmosphere (ok, so you might have 1ish inches of mercury restriction to account for the air filter and such). There will be a little bit of vacuum before the turbo but not as much as at idle after the throttle plate (as long as there isn't a nasty cam in the equation )