Thread: VVT Control

Originally Posted by rovercare

Ta for the obvious bit, but to actually correctly match a vnt, according to desired egts is not going to be easy and would vary on each setup, hence the desire for a wastegate

Matching for EGT isn't done in the turbo sizing, it's done through turbo control. The ECU's know how much air and fuel is going through the engine so they have a good prediction of EGT. Some current engines actually have an EGT probe reporting directly to the ECU.

They have a map of engine speed, load and desired boost.

Here's the $1M question. What level of boost should you have for best economy at part load cruise?

Originally Posted by Dougal

Matching for EGT isn't done in the turbo sizing, it's done through turbo control. The ECU's know how much air and fuel is going through the engine so they have a good prediction of EGT. Some current engines actually have an EGT probe reporting directly to the ECU.

They have a map of engine speed, load and desired boost.

Here's the $1M question. What level of boost should you have for best economy at part load cruise?

More obvious stuff, 4bd1 ecu's are a little primitive, so getting match dead eye is not so easy, closed loop control is pretty impressive hey, it's been around a while

Who cares, because in the real world it varies greatly with inclination, altitude, ambient, drag, etc

You copying blacknight with a rambling, followed by a question you know the answer too?

Getting boost levels right at cruise can add or lose 10% to your fuel bill. Getting them right at full load can add or lose a lot of power.
For example, you're running 30psi boost but the fuel you have could be cleanly burnt by at the most a hair over 20psi. You are losing a lot of power and torque to pump that extra air.

The point is, you can do a lot better controlling a VNT turbo than just a pressure can. Reasonably simple pneumatic circuits have a lot to potential even completely avoiding electronic control. If you care so little, why do you keep popping up?

Originally Posted by Dougal

Getting boost levels right at cruise can add or lose 10% to your fuel bill. Getting them right at full load can add or lose a lot of power.
For example, you're running 30psi boost but the fuel you have could be cleanly burnt by at the most a hair over 20psi. You are losing a lot of power and torque to pump that extra air.

The point is, you can do a lot better controlling a VNT turbo than just a pressure can. Reasonably simple pneumatic circuits have a lot to potential even completely avoiding electronic control. If you care so little, why do you keep popping up?

Because low down sucks when the fuel is turned down, like I've posted a few times before, unless I'm going to open the pump, which isn't economically viable, or add a wastegate the choices are limited, nothing to do about my care level, just my experiences on my own vehicle, not information I've gleaned from the interweb

Hands up who has a vnt actually fitted to their 4bd1?

I'd be happy to heed more advice if you actually tried all this in real time dougal, but unfortunately not being a clever dude, I just fit things and see the results

Originally Posted by Dougal

Getting boost levels right at cruise can add or lose 10% to your fuel bill. Getting them right at full load can add or lose a lot of power.
For example, you're running 30psi boost but the fuel you have could be cleanly burnt by at the most a hair over 20psi. You are losing a lot of power and torque to pump that extra air.

The point is, you can do a lot better controlling a VNT turbo than just a pressure can. Reasonably simple pneumatic circuits have a lot to potential even completely avoiding electronic control. If you care so little, why do you keep popping up?

IMHO not only does excessive boost suck power, but so does excessive drive pressure (exh manifold pressure).

Except for the problem with heat (can be overcome with copper signal line) and soot (that can gum up the works), I would be inclined to use drive pressure as part the control.

Originally Posted by rovercare

Because low down sucks when the fuel is turned down, like I've posted a few times before, unless I'm going to open the pump, which isn't economically viable, or add a wastegate the choices are limited, nothing to do about my care level, just my experiences on my own vehicle, not information I've gleaned from the interweb

Hands up who has a vnt actually fitted to their 4bd1?

I'd be happy to heed more advice if you actually tried all this in real time dougal, but unfortunately not being a clever dude, I just fit things and see the results

I have a VNT from the 2.8 litre version of the 300Tdi. I had this on my old 300Tdi, but I consider it too small for my 4BD1T.

Originally Posted by inside

Anyone done this elegantly? I have GT2256V that needs controlling, it works by operating the vanes under vacuum. It seems that there's a mod out there that allows mechanical control of the Patrol 3.0 VVT turbo.

Details here Manual Boost Controller
Kit here Nissan Patrol and VAG TDi

Looks like a cheap solution but am I right thinking this could easily work on the 4BD1 to control a VVT turbo?

Hey Inside,

What do you mean by elegantly? Your link pretty much sums up all you need to know. Just run the hoses so they look nice - is that what you mean?

What position are the vanes set at now? What boost pressure is it getting? What are you hopeing to get from it? Higher peak pressure? An earlier rise in boost with a flatter curve. Or too keep things simple - just better drivability of your 110?

Originally Posted by rovercare

Dougal is never going to get around to fitting that vnt.....

To answer your question, no, it's so quick you can't notice, pretty graphs etc are great to aim for perfection, just that in the real world it don't matter a lick, the Elec over vac systems will just be on/off, I'd suggest the term variable is a little misleading, yes it overshoots a few psi on changeover when going from coast to full load rapidly, but again, in reality it has no I'll effects, except occasional alarms from 30psi overboost on the madman gaugey do dad

Agree, real world matters. **** in equals **** out as a control system can work, some things you can fiddle with in real world to perform - but knowing the theory behind it can certainly give you a starting point, with knowledge for optimising and compromises. Let's go scuba diving some time. Got mask, got fins, got air lets go.... Race you down and up. Sure you might win, but you also might die from the bends without adequate theory Pretty graphs matter a whole lot of licks then. Ok your not going to die from a turbo.... but the turbo might.

Who says an elec/vacuum system for controlling vane position can't be variable? My GT2559V has a linear pot on the vacuum can. In the real world what is that for?