Turbo lag or design feature

[shining]

I read a recent post that referred to the Euro design rule limiting performance of the TDV6 and this would be overcome by remapping. My symptom is;
I turn right regularly on an uphill stretch. Oncoming traffic flys down the hill so I am careful not to become a T-Bone. I have to lose most of my momentum.
When I accelerate away there is a very distinct flat spot then a satisfying surge of power.
Q: Is this turbo lag or engine design? That is reducing emissions by preventing too much fuel going in that isn't going to be burnt.
Q: Regardless of cause would remapping overcome the issue? I am out of warranty (the disco too ). So less complications there.

Merry Christmas and a Happy New Year to All
Steve
MY07TDV6 HSE

[Neil P]

Keep one foot on the brake and one on the skinny.
It's no different to the old-days of slipping the clutch
on a hill so you're ready to tear off .............


I don't think remapping alters the variable turbo-vanes change rate
from tick-over , but mainly the boost pressure. The engine
still needs to pickup speed to begin with ...........

[WhiteD3]

I wouldn't know as I don't drive a TDV6 but it could be related to this thread.

http://www.aulro.com/afvb/d3-d4-zone...ange-down.html

[Warrigal57]

Likewise with the lag on my 2.7L. Usually not an issue - I think in part because you adjust your driving style and ease on the accelerator earlier - though occasionally it makes you want to scream when you plant the right foot and the engine slowly winds up.

Volvo Marine diesels are electronically limited in the manner you describe in order to reduce emissions ie if you rapidly advance the throttle at low rpm the electronics will limit fuel input to what the motor will efficiently burn, until revs (and turbo) spool up. I assumed the 2.7L was doing the same.

If you're not coming to a complete stop then using Sport mode to manually change down will keep the engine revs and turbo at speed and avoid any lag. Very good for driving through some twisty road....but I usually end up forgetting I'm in manual and wondering why all the revs??

[shining]

Hi Warrigal,
Thanks, I hadn't thought about sport mode. All previous cars have been manuals. I live out of town and often drive in manual to avoid unnecessary kickdowns. But it is so damn quite for a diesel (compared to the MY97 D1 with 350k's ) I often forget to change up too.

[shining]

Thanks Neil... I will remember that, although I am not normally at a complete stop at this turning , just rolling at 5-10kph.

[d3viate]

No lag with my fitted DP Chip. Fullstop.

[Bush65]

I believe you are describing boost threshold not turbo lag.

In simple terms the threshold is when the turbo starts to make effective boost pressure.

The turbine is driven by exhaust heat. At idle there is not enough heat. The engine speed needs to increase under load before it generates enough exhaust heat for the turbo to be able to produce boost pressure.

The fuel mapping can be altered to add fuel earlier, which creates more exhaust heat, allowing the turbo to create effective boost earlier. The increased boost, in turn will produce the extra air to burn the fuel ....

Earlier diesels had single, fixed geometry turbines, and these had a higher boost threshold if they were to perform well at higher speeds.

The variable geometry turbines (as used on disco 3) were developed primarily to produce effective boost over a broader rpm range.

Some newly developed diesels use a small and larger turbo in sequence (low rpm to high rpm) for a broader range than variable geometry.

Some advance this 2 turbo technology and stage (the output of the large compressor is delivered to the inlet of the small compressor for 2 stage compression) the large and small turbos at low speeds, and then sequence to the large turbo at high speed. The 2 stage compression creates higher boost pressure earlier than a single turbo can. I believe some of the latest Land Rover diesels use this technology.

Turbo lag usually only occurs with petrol engines. When the throttle is shut, the pressure in the inlet manifold, intercooler and associated piping drops dramatically, and the turbine/compressor speed is greatly reduced (the shut throttle acts like a brake). When the throttle is opened again, some time is required (lag) to get the turbine/compressor speed back up and to compress the air volume in the inlet manifold, intercooler and associated piping.

[gghaggis]

Unfortunately, the std 2.7 ltr TDV6 suffers from both threshold delay AND lag. The former can be got around with the two-pedal trick. The latter can be somewhat mitigated by forcing the car into a lower gear and then booting it - but you need to know in advance that you need to do this

Some blame the EGR system, some the programming, some the phases of the Moon ..........

Cheers,

Gordon

[CaverD3]

Couple of things can help: a re-map and there is agearbox software upgrade that made a difference with mine.
Also the Vanes can stick; again a software upgrade exercises the vanes to prevent sticking.
This helps but will not remove th lag completely.
I find not stomping on the accelerator gives a better result. Experiment by slowly pressing and you will find it may help.