Hi, got a mk1 octavia vrs. Done a raft of vacuum deletes to get rid of a fault code that was plaguing me. Seems to be fine, and I've now fitted a boost gauge. I go into second and floor it at 2000rpm, and watch the boost. Max boost im getting is ~8psi. 

 

Is this normal for a stock one? A lot of places seem to suggest 11psi is what's normal. 

@Saints92 - Are you absolutely certain that your boost gauge is correctly calibrated, and reading peak boost from the turbo rather than manifold pressure post intercooler (which will be lower than turbo exit pressure because of several feet of pipe, and a significantly lower temperature)?

I plumbed it in by cutting the pipe that runs from my DV to the manifold, pretty much exactly halfway along. 

 

Ill double check later but the idle is about -20. How do you check if it's calibrated? 

@Saints92 - To start with, engine off I'd expect a reading of 0PSI (relative pressure) or 15 (absolute pressure). A reading of -20 is impossible because that means that the transducer is being pulled on rather than pressed on!

 

Where did you get this gauge from?

6 minutes ago, KenONeill said:

@Saints92 - To start with, engine off I'd expect a reading of 0PSI (relative pressure) or 15 (absolute pressure). A reading of -20 is impossible because that means that the transducer is being pulled on rather than pressed on!

 

Where did you get this gauge from?

 

 

That's the gauge. Saying -20 is wrong, but it's the 20 below zero at idle. I think it sits fractionally zero when the cars off. 

@Saints92 Ah, any numbers aside from the -20 had been PSI.

 

So what I now know is that that's a relative pressure gauge, calibrated in inches of mercury. In that case, having an induction pressure below 0 at idle revs is entirely normal. With how close you can read the gauge, treat 2" gauge pressure as equivalent to 1PSI.

5 minutes ago, KenONeill said:

@Saints92 Ah, any numbers aside from the -20 had been PSI.

 

So what I now know is that that's a relative pressure gauge, calibrated in inches of mercury. In that case, having an induction pressure below 0 at idle revs is entirely normal. With how close you can read the gauge, treat 2" gauge pressure as equivalent to 1PSI.

 

Yeah, it's not overly easy to keep an eye, but the max boost I can remember seeing is halfway between the 5 and 10. Was wondering if that's right for stock, as I've been told it should be 11.

@Saints92 - 11PSI is equivalent to 22 inches of mercury! Or, in other words, you're seeing about 5PSI boost, which is some way short of the 11PSI (22 in Hg) you expected.

6 minutes ago, KenONeill said:

@Saints92 - 11PSI is equivalent to 22 inches of mercury! Or, in other words, you're seeing about 5PSI boost, which is some way short of the 11PSI (22 in Hg) you expected.

 

Yeah, this is my worry. No fault codes and it doesn't feel like it's underboosting. But it's showing less than what seems to be expected for a Ko3s. May need to just remove the turbo and get it serviced to see if it's actuator related? Changed my N75 and DV already. 

 

This is where It sits when you start it cold and let it idle, slowly drops down to the 20

@Saints92 - That's not unreasonable for an idling reading: In fact, if it was a non-turbo car the vacuum reading would stay in that sector all the time.

 

Next test is when the boost starts to build, but we can do that stationary too.

 

Rev the engine as slowly and gently as you can, and note the RPM when the boost level goes positive (just jumping on the throttle will get the reading to move towards 0 fast, regardless of what the turbo's doing).