Turbo boost level at cruise.

[Coldcomfort]

Hi all, 2012 3.0CRD. What are you guys getting on your boost gauge (if you have one) when you are cruising at 100kph on the straight and level. I am seeing between 16 and 18. Seems a little high. What’s the wisdom on this? Cheers all, Brian.

[the evil twin]

IMHO... assuming factory setup and not Dawes or Tillix... should be less than that at 100 KPH cruising IE light throttle, flat road, not much wind etc should be 8 to 10 or so and go to 16 to 18 max throttle

[Coldcomfort]

Sorry. I should have mentioned I’m running a Dawes valve and a Beaudesert exhaust. EGR is also blocked. I also have a tig welded inter cooler.

[mudski]

What’s your max boost set at? If it close to your 100kph boost open up the needle valve a touch to bleed a little more air in to slow the spool up which in turn will lower the “cruise boost”.


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[pollenface]

Mine would hover around 8-12 (depending on hills) when the motor was stock.

[phdv61]

Dawes + Needle is a disaster for the "breathing" of your Patrol down low.
The Dawes keeps the vanes of your VNT fully closed until you reach the opening boost it has been set to open at.
And when it opens, it opens in one go. This arrangement transforms a fantastic Variable Nozzle Turbo (V.N.T) into a two stage turbo.

Up until the Dawes opens, you build-up boost ( ie pressurized-hot-air ), but the back pressure it creates at the level of the exhaust wheel prevents fresh air to come into your cylinders. You just loose most of the available torque and power.

If you want to keep such an arrangement, the minimum you MUST do is as follows :
set your dawes so that it opens AS EARLY AS 3 psi. put a second needle behind the dawes to adjust the speed of opening of the turbo vanes as boost is building up.

Only the MAF voltage provides an idea of the REAL quantity of air swallowed by your cylinders. Not your boost gauge.

It it the MAF voltage together with the TPS which are analysed by the ECU to define the level of fueling.
In other terms : little MAF value will imply little fuel quantity, and little power/Torque as a result. In that respect dawes+needle is just a disaster. Apart from the satisfaction of reading a high boost, you have very very little Torque down below 2000RPM.

If anyone tells you otherwise, he is just wrong.
Magic Box VNT is the only device which allows an accurate setting of the turbo vanes to maximize airflow (as measured by the MAF voltage) through your motor. I tested all other systems available before embarking on developping mine.

Only MAF voltage matters, not boost as such.