15 replies to this topic

[garyk220]

Standard VXT will boost to 9.5psi and hold 8.5-9psi

TMS Stage 2 VXT will boost to 15psi and hold 14-14.5psi

TMS Stage 3 VXT will boost to 18psi and hold 17psi

TMS Stage 2 VXR will boost to 17psi and hold 16psi

TMS Stage 3 VXR will boost to 19psi and hold 18psi

I've installed a boost gauge in my car now and noticed that boost is initially peaking at 15psi and then falling off and holding around 12psi. Does this point to a problem with the wastegate actuator leaking boost? It is an AMD map, so perhaps they ran slightly lower held boost values?

This was on track at Knockhill where the intake temps were around 55-60 degrees, so perhaps that had an effect on the held boost pressure.

The car doesn't feel any slower than when I first had it remapped, so I don't think there's a wear and tear problem, but if there's an extra couple of psi boost to be found higher up the rev range, then I want to find them

[Dave]

I had similar problem Originally thought to be wastegate actuator - New Turbo (I think you can get an aftermarket kit to fix it though) But problem was found to be a leaking vacuume hose...tightned up etc and now OK. Dave

[Gouldy]

My standard VXT was boosting to 12psi (ie: higher than expected) but would only hold a boost of 8psi. After a stage1 map it would still boost to 12psi but would hold 10psi. When I asked Thorney about it he said that's just how it is with some turbos and nobody really knows why. Perhaps yours is showing a similar trait?

[VXT Tim]

Was/is JT revising the maps to hold higher boost?

[garyk220]

I had similar problem

Originally thought to be wastegate actuator - New Turbo (I think you can get an aftermarket kit to fix it though)

But problem was found to be a leaking vacuume hose...tightned up etc and now OK.

Dave

Thanks Dave, I'll give that a go

[cheeky_chops]

When I asked Thorney about it he said that's just how it is with some turbos and nobody really knows why. Perhaps yours is showing a similar trait?

depends on which side of the bed they got up i suppose....

[Gouldy]

depends on which side of the bed they got up i suppose....

Ha ha, quite possibly!

I'm no technical genius, I was just informed that some boost higher but can't hold it very well, and others have a lower level of peak boost but can keep it up for longer (as it were).

I'm sure there's someone out there who knows why.........

[d0gz1]

its normal

[Thorney]

Completely normal. Turbos are essentially an enclosed impellar so getting them to spin up quickly requires one type of function (peak or over boost) but having them hold that level requires a different level of engineering. There are a few reasons why boost 'leaks' like this: 1. Friction in the turbo unit, maintained speed in the impellars means the bearing surfaces get hotter and that slows them down. 2. The map itself, ts held boost that kills turbos (makes the turbo work harder for longer period of time) so we've always been quite conservative on the held boost. 3. Actuator, this is basically a spring so its a mechanical part that sometimes need replacing 4. Heat, as heat builds up the ECU will back off the boost to protect the engine 5. The boost controller. The VXT boost controller is a bit crap, it can't seem to hold level boost the further up the tuning level you go so held boost becomes more difficult to map as the ECU doesn't control it well enough. We've been testing with aftermarket boost controllers but nothing confirmed as yet as to benefits. The roller bearing conversion we're running in my car has been designed to deal with all of these, roller bearings are less affected by heat and reduce lag (the delay in the turbo responding to ECU inputs) by 25% so you can run a higher power turbo unit (bigger bascially) without compromising driveability. The guys from Kastle Tuning (I think) from Germany swapped their turbo got a Garret T3 unit at the 2005 German Tuner GP and the car was quick in a straight line but nigh on undriveable in corners as the turbo delivery was too agressive. Ultimate set up (we hope) is our roller bearing Garet turbo unit, an after market boost controller and variable boost control switch on the dash. It should all be ready for the National I hope

[ECM]

It should all be ready for the National I hope

This year's national or the 2010 meeting??

[Jay]

Standard VXT will boost to 9.5psi and hold 8.5-9psi

TMS Stage 2 VXT will boost to 15psi and hold 14-14.5psi

TMS Stage 3 VXT will boost to 18psi and hold 17psi

TMS Stage 2 VXR will boost to 17psi and hold 16psi

TMS Stage 3 VXR will boost to 19psi and hold 18psi

I've installed a boost gauge in my car now and noticed that boost is initially peaking at 15psi and then falling off and holding around 12psi. Does this point to a problem with the wastegate actuator leaking boost? It is an AMD map, so perhaps they ran slightly lower held boost values?

This was on track at Knockhill where the intake temps were around 55-60 degrees, so perhaps that had an effect on the held boost pressure.

The car doesn't feel any slower than when I first had it remapped, so I don't think there's a wear and tear problem, but if there's an extra couple of psi boost to be found higher up the rev range, then I want to find them

In December 2003 AMD fitted a stage 2 remap/exhaust to my VXT. I've noticed over the last 6 months that the car 'feels' down on power and there seems to be a little more turbo lag than there used to. The car generally feels sluggish particularly below 4k RPM.

I finally got round to buying a boost gauge to help diagnose the problem.....

At idle cold, vacuum indicates 22 inHg
At idle warm, the vacuum indicates 26 inHg.
30 inHg (off scale) during overrun.

At full throttle, overboost is 9.5 PSI and sustained boost pressure is 9 PSI pretty much throughout the rpm range. Doesn't seem high for a stage 2 level of tune?? The problem being, I have no idea what the boost pressure has been for the last 5 years so I cannot compare any changes.

All the vacuum hoses and pipes appear to be secure.

Anyone know what boost pressure the original AMD map was designed to achieve? Any other things I should check, ie. Diaphragm?

Any help would be greatly appreciated.

Cheers

Jay

[cheeky_chops]

At idle cold, vacuum indicates 22 inHg
At idle warm, the vacuum indicates 26 inHg.
30 inHg (off scale) during overrun.

At full throttle, overboost is 9.5 PSI and sustained boost pressure is 9 PSI pretty much throughout the rpm range. Doesn't seem high for a stage 2 level of tune?? The problem being, I have no idea what the boost pressure has been for the last 5 years so I cannot compare any changes.

All the vacuum hoses and pipes appear to be secure.

Anyone know what boost pressure the original AMD map was designed to achieve? Any other things I should check, ie. Diaphragm?

Mine is:
At idle cold, vacuum indicates 15 inHg
At idle warm, the vacuum indicates 20 inHg.
21 inHg during overrun.

Sounds like a blockage tbh, vacumn too high and not enough boost. Should be 15+psi (i had a AMD map)

Edit, not much help but also check on astra sport forum, helped me diagnose a split pipe

Edited by cheeky_chops, 10 August 2008 - 08:21 PM.

[Jay]

Mine is:
At idle cold, vacuum indicates 15 inHg
At idle warm, the vacuum indicates 20 inHg.
21 inHg during overrun.

Sounds like a blockage tbh, vacumn too high and not enough boost. Should be 15+psi (i had a AMD map)

Edit, not much help but also check on astra sport forum, helped me diagnose a split pipe

Hi Cheeky,

Great recommendation, I've posted my question on their forum. Cheers.

Anyone else suggest things I can check?

Can I or should there ever be a need to adjust the actuator to restore the higher AMD boost pressures programmed into the ECU??

Jay

[cheeky_chops]

my actuator went - the spring went weak. The boost gauge and dyno printout was wobbling on overboost

[Jay]

my actuator went - the spring went weak. The boost gauge and dyno printout was wobbling on overboost

Guess I need a specialist to diagnose the problem, can see this getting expensive, changing one component after another!!!

[Jay]

For the benefit of others, I believe I have found the problem. The metal heat shield at the back of the block that separates the exhaust manifold/turbo etc from the induction pipe had burnt/rubbed a hole in the induction piping. I only found this after removing the heat shield (PITA). I have used duct tape, as a temporary fix, to cover the damaged area until I can source a replacement pipe. Overboost is now 15PSI with sustained boost of 12PSI which now drops off slowly at high RPM. It's like a different car!! Cheers Jay