Look ma, I made a boost log!

[g huns]

So after installing a new 034 breather and a new set of injector seats, I had the puter plugged in to clear all the misfire codes from when the stock breather turned to dust. I figured, hey, the snow is off my road, lets do a third gear pull and log it.

So I logged measuring block 115, started at 3000 RPM, stopped at 6000 RPM, took those numbers in Excel, subtracted 1000 for atmospheric pressure and multiplied by .0145 to convert to PSI. This is what I got...



So, what does it mean? She's stock with 130K miles, but damn. less than 8.5 PSI? Is this normal?

[strtdrms]

I'd say that's probably normal for a stock tune. You could always measure requested boost vs. actual boost. If there is a huge difference, you have a leak somewhere, but I doubt that's the case.

[g huns]

Orange line is requested boost, grey is actual.

Something else strange, after installing the 034 breather, if I take the oil cap off, there is a lot of vaccum. That seems odd to me. But the pcv lines on the manifold side of my motor have always been sketchy. This is the first time I haven't had any leaks.

[diagnosticator]

10 to 11 psig is the stock boost specification.

Make sure the conversion from millibars absolute pressure to "pounds force/inch^2" gauge pressure, psig, is correctly calculated.

[g huns]

If 10 or 11 is available, why is the ECU not asking for it?

[old guy]

Orange line is requested boost, grey is actual.

Something else strange, after installing the 034 breather, if I take the oil cap off, there is a lot of vacuum. That seems odd to me. But the pcv lines on the manifold side of my motor have always been sketchy. This is the first time I haven't had any leaks.

If you remove the oil filler cap at idle there should be a slight vacuum. If you are experiencing a lot of vacuum you may have a defective or clogged up PRV or an overly aggressive PCV.

If 10 or 11 is available, why is the ECU not asking for it?

Air temperature affects in air density. Obviously colder air is denser than warmer air. What you will find is that your maximum boost pressures will drop in the colder temperatures. Mine typically drops 2-3 psi between summer and winter.

[g huns]

If you remove the oil filler cap at idle there should be a slight vacuum. If you are experiencing a lot of vacuum you may have a defective or clogged up PRV or an overly aggressive PCV.


Air temperature affects in air density. Obviously colder air is denser than warmer air. What you will find is that your maximum boost pressures will drop in the colder temperatures. Mine typically drops 2-3 psi between summer and winter.

The PCV is the new one from 034. Is the PRV the one up top? I believe I've heard it refered to as the pancake valve.

Good to know about the temp. It was lower 20's when did the log.

[customa4]

If you have the later model B6, I believe late 03 then the PRV would be at the back of the motor behind the valve cover. Yes, the pancake valve.

[g huns]

If you have the later model B6, I believe late 03 then the PRV would be at the back of the motor behind the valve cover. Yes, the pancake valve.

Is there a way to test the PRVs function?