VNT control

[boostjunky]

Hey All. Interested to hear from any of the VNT gurus out there on potential solutions for controlling boost levels. I've got a project on the go (not my 5 or even a Renault actually) where my aim is to retro-fit a VNT turbocharger. The engine in question is a 2500cc turbocharged direct injection housed in a Land Rover Discovery 1.

Now I understand that VNT boost levels are controlled by adjustment of the vanes in the exhaust which are actuated using vacuum rather than boost pressure, vacuum is applied to bring the vanes into their closed position reducing the exhaust a/r ratio - this is gradually reduced as desired boost levels are reached to increase the exhaust housing a/r ratio and continues to be adjusted to maintain it.

So my question to the pros on here: what have you guys put in place to control your VNT's boost levels? I do have a couple of ideas of my own, but would be keen to know how far off the mark they might be before sharing them

[James5]

TD5 standard turbo's use boost pressure (positive pressure) so you will need to use a similar setup if not the same setup as turbo developments used on the VNT's for the R5 or the Big Jim setup which is on Philr5t's 5 but has yet to be seen working.

So you will need Boost pressure actuator and use the actuator rod length to control how far the vanes open if to far it will cause overboost.


What idea's have you got?

[boostjunky]

One of my thoughts was to retain the original VNT actuator, and use a pressure switch or manual boost controller type device to cut the vacuum feed as/when the desired or set boost level is reached. Vacuum would be generated using a simple 12v vacuum pump, sources of those I have found to be the cruise control pump from mid 1990's cars pre fly-by-wire throttle or an electric brake servo assistance pump which is found in more recent cars.

Also considering putting an external WG in place as a safety precaution, the Land Rover Tdi engine doesn't like more than about 18-20 psi boost pressure.

I've seen people using mechanical systems linked to the throttle but I'm not really sure about that myself.

[James5]

One of my thoughts was to retain the original VNT actuator, and use a pressure switch or manual boost controller type device to cut the vacuum feed as/when the desired or set boost level is reached. Vacuum would be generated using a simple 12v vacuum pump, sources of those I have found to be the cruise control pump from mid 1990's cars pre fly-by-wire throttle or an electric brake servo assistance pump which is found in more recent cars.

Also considering putting an external WG in place as a safety precaution, the Land Rover Tdi engine doesn't like more than about 18-20 psi boost pressure.

I've seen people using mechanical systems linked to the throttle but I'm not really sure about that myself.

I am not sure how the boost level is controlled on the TD5 i assume it would be controlled by the ECU. Are you getting a better map for yours??

If your planning doing the above why not just simple turn and mount the actuator up the other way so it works the opposite so then it will push the vanes closed, theoritcally still working the same way it would on a vacum system but using the positive boost to push close and restrict the boost level?

[markey b]

peugeot 407 2.0 hdi 136 has a vnt... i'll see what i can find out...

[boostjunky]

I am not sure how the boost level is controlled on the TD5 i assume it would be controlled by the ECU. Are you getting a better map for yours??

If your planning doing the above why not just simple turn and mount the actuator up the other way so it works the opposite so then it will push the vanes closed, theoritcally still working the same way it would on a vacum system but using the positive boost to push close and restrict the boost level?

It's not a Td5 it's a 300 Tdi, 2500cc four pot with a Bosch VE rotary injection pump. The good thing about this engine/pump is that there virtually no electronic controls whatsoever for the fuelling...it's adjusted mechanically based on throttle position and manifold pressure so it should (in theory) fuel correctly whenever/whatever the VNT throws at it in terms of boost.

I like your suggestion though, effectively replacing the VNT vacuum actuator with a standard turbo actuator and rotating it 180 degrees - is that about right? Would probably need to do some experimentation with rod length to make sure the VNT geometry can be adjusted fully but on the whole this sounds quite promising

[boostjunky]

peugeot 407 2.0 hdi 136 has a vnt... i'll see what i can find out...

Cheers - it's 'probably' controlled electronically with a control unit and series of valves/pumps etc. I've done some research into VAG diesel VNT's and they use this type of system.

Check this out:

[markey b]

there are 2 solenoids that control it

[boostjunky]

The VAG setup uses loads of valves to control the turbo, the EGR valve etc - seemingly quite complex and all ECU controlled which I want to steer well clear of. I will draw up a simple diagram to show my proposal and see if you guys have any comments.

Ben