boost pressure (ive searched)

[fhh02a]

Hey guys,

Before you get on to me about the search button, Ive used it and I am more confused now:

So my question is :

What is the stock boost pressure range?

I used my Foxpro pro scanner for the real time data collection:

at Idle the boot was 890mbar or 12.9 psi
at 3500rpm it jumped to 13.8- 14.2 psi

Is that about right for a pretty much stock motor?


I am about to change the exhaust to a more free flowing type. I am just afraid of loosing turbo performance and having alot of lag

[Gotpsi2008]

Boost at idle? You should be recording vacuum at idle and under a load is when you will start making boost, as far as the exhaust, you will have a quicker spool due to a better flow of exhaust gasses helping the turbine spin up quicker, and as far as the boost increase that's something controlled by the wastegate so even with an exhaust change you shouldn't see an increase in boost, just more or less a little better throttle response and a different tone. I have no idea what the stock boost is, I'm sure someone will chime in, but at stage 1 I'm surging 18.8 and holding 17

[Der Konig]

Hey guys,

Before you get on to me about the search button, Ive used it and I am more confused now:

So my question is :

What is the stock boost pressure range?

I used my Foxpro pro scanner for the real time data collection:

at Idle the boot was 890mbar or 12.9 psi
at 3500rpm it jumped to 13.8- 14.2 psi

Is that about right for a pretty much stock motor?


I am about to change the exhaust to a more free flowing type. I am just afraid of loosing turbo performance and having alot of lag

Regardless, you wont have a lot of lag with the ko3s. What gotpsi is getting at, is that there should actually be vacuum at idle. A spike of that is pretty high but not that uncommon. I assume a spike to that and then holds more like 10-12 psi?

gotpsi ninja edited, no fair.

[Axis]

I found this usefull

[supple]

I believe my stock KO3 was pulling around 12 psi and Unitronic stage 1 bumped it to 17 psi. Gotpsi2008 is correct that a free flowing exhaust is mostly sound but wouldn't play much into boost holding. You'll have to make sure you're not leaking and your Diverter Valve isn't torn (if it's the old revision).

At idle, you shouldn't have boost since you aren't getting your turbo going, so 0 or vacuum.

Found this on another forum and gives a good explanation of couple things:
"The Diverter valves serve to divert boost pressure air back to the compressor inlets when the throttle is cut under boost. This avoids compressor stall and hesitation in recovery. They are inactive under acceleration or steady state driving. They don't regulate boost, and have no connection with the waste gates.

The wastegates divert excess exhaust gases around the turbines to limit boost. They are regulated by the ECU via a control solenoid valve (N75) to conform (approximately) actual to requested boost."

[Gotpsi2008]

gotpsi ninja edited, no fair.

Like ah boss hah

[fhh02a]

I found this usefull

I used tht
And I was more confused after reading it

[fhh02a]

Sorry for the newb questions

I'm new to boosted cars.


The reason I posted tht number is it was

Boost, actual
I thought it was weird tht it was making boost when there was no engine load but I thought it was normal

[Gotpsi2008]

You should be boosting 10-12 stock. I'm not familiar with the tool your using but I personally IMO wouldn't trust anything but a actual boost gauge, Even though I'm sure there is software and tools that are accurate

[fhh02a]

like i said, the number that was recorded at the moment of idle was 890mbar. Which I guess would be negative? Which after extensive reading is normal.

The tool I was using is a very nice and handy tool.

like i said, im trying to learn as much as i can about boosted cars

[MrBigglesworth]

You've prob figured this by now but essentially at idle is reading atmospheric pressure. Calculate boost pressure by deducting atmospheric from the reading.

[fhh02a]

What I'm looking at

[Gotpsi2008]

To read atmospheric pressure would be to shut the engine off and then take a reading, that's atmosphere pressure, when the engine is running it pulls in air and makes a vacuum until you increase rpms and combustion to create high exhaust flow which turns the turbine which is on the same shaft as the compressor at a different ratio so it creates boost, aka positive pressure

[Charles.waite]

You've prob figured this by now but essentially at idle is reading atmospheric pressure. Calculate boost pressure by deducting atmospheric from the reading.

This. Any reading at idle is showing atmospheric pressure. The stock setup will not measure vacuum at idle, you need an actual boost gauge for that.

Deduct the atmospheric pressure from all your numbers and then you get actual boost in mbar. That's an easy Google conversion to psi. Stock the engine should be creating 12psi (depending on the gear) and holding around 10 until almost 5k rpms. If it's significantly less than that you've got problems.

[Gotpsi2008]

This. Any reading at idle is showing atmospheric pressure. The stock setup will not measure vacuum at idle, you need an actual boost gauge for that.

Deduct the atmospheric pressure from all your numbers and then you get actual boost in mbar. That's an easy Google conversion to psi. Stock the engine should be creating 12psi (depending on the gear) and holding around 10 until almost 5k rpms. If it's significantly less than that you've got problems.

+1