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Old 12-13-2011, 04:31 PM   #13
Bullet Ride
Cars in Perpetual Repair
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Join Date: Nov 2007
Location: Guelph
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Originally Posted by InfiniteDice View Post
Yeah I figured it would release the vacuum at some point, it can't just build vacuum indefinitely.

On some cars you'll see the one line coming off the brake booster, it then divides into two lines... one goes to an open port on the throttle body on the intake side of the TB and plugs into the air boot before the TB. The other line dead ends at a closed off throttle body port.

My system has the one line. Coming from the brake booster it goes into the one way valve, then into a plastic connector, from there the plastic connector plugs into the rubber intake boot and goes to a small port on the TB.

I'm not familiar with the logic of this routing. Why does the booster release air in front and in behind the TB at the same time? I've read that the engine vacuum is what opens the valve, but if that's true then why can I blow through it so easily?

Perhaps the engine vacuum counteracts the air coming from the booster to prohibit the flow from the booster, but since it's one way it can't actually supply air to the booster.

Okay I need a coffee.
The cars with the two line set-up have that second hole in the TB finished, it’s not a dead end. BMW eventually revised the system to the single line on the late model cars and stopped finishing the one hole on the TB. I think the original idea behind the dual line is to help maintain good vacuum to the booster during open throttle conditions (for left foot trail braking while racing) but I don’t know that for a fact.
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