Mechanical boost gauge hook up

[Tim Moland]

My car came with the RPD boost gauge. I was not a fan, so I am going with a mechanical style gauge. Does anyone know which vacuum hose to hook up the boost line to? The lnf has many hoses on it. Lol

 

[Briann1177]

You should be able to tee off the line that the brake booster hooks up to. Just out of curiosity, what is wrong with the digital RPD gauge pod?

 

[Tim Moland]

You should be able to tee off the line that the brake booster hooks up to. Just out of curiosity, what is wrong with the digital RPD gauge pod?

Really! That seems odd to me. Of course I know nothing about it. Would that mean that the brake booster receives more pressure while the turbo is "boosting"? As far as the pod goes, it's kinda gimmicky. I drove my car for a year and a half and only had the boost gauge on display the whole time I have read that the accuracy is questionable. It only shows boost, no vacuum. I wanted something a little more compact for the goblin. Kinda looks out of place.

 

[Ross]

Why are you hooking a boost gauge up to a vacuum line? Wouldn't you want to hook it up to the pressurized air after the turbo? Or maybe after the intercooler if you want to measure denser air.

 

[Briann1177]

The entire intake system from the turbo outlet all the way to the cylinder is pressurized under boost. When you let off the throttle, that same path goes to vacuum.

 

[Tim Moland]

See, this is why I'm confused. I have searched multiple times on how to hook up a boost gauge on a cobalt ss. All the searches come back for supercharged engines, which are different. LNF Cobalts came with an electronic boost gauge instead of manual, so there was little need to hook one up. I have the tubing ran from my gauge, through the tunnel, and back to the engine. I just don't know where to splice into. The brake booster has such a big hose on it, it would be hard to connect the 1/8" gauge tube to it.

 

[JSATX]

I ran mine off the booster line. Any line connected to the intake manifold will work, it’s all the same.

 

[Tony]

The entire intake system from the turbo outlet all the way to the cylinder is pressurized under boost. When you let off the throttle, that same path goes to vacuum.

That's true, but there is a difference between "before throttle" and "after throttle". You want to display the "after throttle" - aka manifold pressure - on a boost gauge. The line to the brake booster is connected to the intake manifold, so that works fine.

Really! That seems odd to me. Of course I know nothing about it. Would that mean that the brake booster receives more pressure while the turbo is "boosting"?

No, the fitting where the hose connects to the brake booster is a check valve, so it only opens under vacuum, while positive pressure forces it closed.

 

[Tim Moland]

That's true, but there is a difference between "before throttle" and "after throttle". You want to display the "after throttle" - aka manifold pressure - on a boost gauge. The line to the brake booster is connected to the intake manifold, so that works fine.


No, the fitting where the hose connects to the brake booster is a check valve, so it only opens under vacuum, while positive pressure forces it closed.

OH ok, that makes sense.