T4 2.5TDi boost pressure - what should it be?

[DubDick]

Hi all,

I've made a similar post in the tuning section but it has been un answered so far.

I've got a boost gauge on my T4 and I only get 0.8bar at peak and this tails off to 0.6 at around 3,000rpm.

Is this normal?
Is there anyway to hold the boost at 0.8bar up to 3,000rpm
Is there any way to increase the boost without a remap?


Cheers

Dub;)

[Freshup]

Hi,
Depending on your engine code.
ACV, AJT, AUF: while driving 2nd gear, full throttle 2500 - 3000rpm 0.6 - 0.8bar
AHY: full throttle, 3rd gear from about 1500rpm - 1.75 - 2.08bar
Cheers

[DubDick]

Ah, I'd imagine that's bacause the AHY has the VNT turbo and not the KKK.

So is there any way I can improve the boost from mine without harming anything or tripping limp mode?

Best I can come up with would be to put a bleed valve on the ECU boost ref pipe. That's way the ECU might think it hasn't reached full boost and hold the waste gate in longer.

Problem is that it might not be the ECU that is realising the waste gate, it might be the back pressure on the waste gate that forcing it open.

Next concideration is why does the boost tail off as the revs climb - intentional protection or limitation of the turbo?

[Freshup]

Sorry can't help you there. I'm an old fogey, have enough trouble keeping them running standard, let alone souping them up.

[DubDick]

:biglaugh: I know what you mean. I have recently gone from fixing faults to make improvements on the standard set up.

Now I'd just like to squeeze a little more boost from the standard turbo, that is as long as it does create problems. By problems I don't mean reduced reliability, I mean I don't want to increase the boost if it means the back pressure is increased too much.

What's the point in pushing the air in harder and faster if it can't get away afterwards. That's will just increase wear and tear without giving much back in the form of power increase.

Plus if he boost goes up then so does the heat which may prove too much for the IC.

So i guess I just want to find the limit without is getting costly in turbo and IC upgrades.:(

[onzarob]

Next concideration is why does the boost tail off as the revs climb - intentional protection or limitation of the turbo?

The faster the engine is reving the easier it can pull air in, too much boost would mean a bang!!

You really should look at a remap, rather than fool the system, it will end in tears;)

Remeber the boost is controlled by the ECU and not the turbo itself. ie it doesn't matter how fast its spinning the ECU has overall controll and adjusts the vanes to achieve a measured boost presure;)

[DubDick]

The faster the engine is reving the easier it can pull air in, too much boost would mean a bang!!

You really should look at a remap, rather than fool the system, it will end in tears;)

Rememberthe boost is controlled by the ECU and not the turbo itself. ie it doesn't matter how fast its spinning the ECU has overall controll and adjusts the vanes to achieve a measured boost presure;)

This all confusing to me:confused:

The faster the engine is revving the harder it is to pull air in I thought. The cylinders pull more of a vacuum and if the turbo can manage to even achieve atmospheric pressure in the cylinders then it's doing well.

Yes the boost is controlled by the ECU and it has the power to either let the waste gate spring hold the waste gate closed or is can channel some of the boost pressure through to the actuator thus opening the waste gate and bleeding away the exhaust drive from the turbo.

Thing is I don't know if this is happening. It may just be the exhaust back pressure that's forcing the waste gate open (although I doubt it!). I think the ECU map is tailing off the boost.

Regarding upping the boost. The AXG engine is 150hp as standard and uses a VNT turbo which generates between 1.7 & 2.0 bar (similar to the AHY above). This on the same 2.5 engine as the AJT (mine) and even has the same compression ration of 19.5:1 so I was thinking that it would be okay to up the boost on mine a little.

Question is can the KKK k14 do it?
If so how (without a remap).

I really don't want to get into the whole remappy thing as it shouldn't be necessary. The standard map contains the fuel and timing profiles. I just want to increase the air flow into the engine and then the ECU should detect this and match this increase with the correct fuelling - yes?:D