300Tdi VGT project

[slug_burner]

Turbocharger,

Good to see this thread active again.

All spirited driving results in a thirst, both for the driver and engine.

It appears you have cracked it. Well done. We now want comparative 1/4 mile times

[rusty_wingnut]

The the lever that controls the vanes has some stops that you can screw in (not likely to be here if engine turbo came from is similar size to yours)

I have recently had some problems with my VGT, to try and get more boost I tensioned the diaphragm up more, and as a result I have a greater overpressure but the boost remains around 1bar.

Is it worth me either opening or closing this stop screw to achieve a little bit more?

[Turbocharger]

Probably a good moment for an update on this thread since it's been bumped. I've got a hole in the diaphragm at the moment so I've set it to run fixed geometry (not very exciting performance and a bit 'surgy' on full chat) while I work out where to get a new membrane for a Td5 turbo wastegate actuator.

Mr Wingnut - I'm not sure I understand your question - do you mean 'overpressure' to be the peak in any transients before it settles to steady state? These are a limitation of the mechanical route to control boost, there's lots of clever maths or options with dampers etc to make it behave exactly as you want - or you just have to be careful with your right foot. To get a different steady-state boost pressure you need to change the spring that the diaphragm works against (an extra external spring is easiest) or alter the length or lever ratio of the linkage.

[rusty_wingnut]

I mean the small period when you get shed loads of boost before it settles to it's steady state.

[Turbocharger]

tTo change the steady-state boost you need to change the spring inside the diaphragm, adjusting the preload or fiddling with the linkage just changes the point it starts/stops moving or the response rate.

[rusty_wingnut]

I think I need to fab up a fancy adjustable type thing like the one you have mate!

[Turbocharger]

The steady-state response isn't adjustable unless I change the spring. I drew a graph of the diaphragm position at various pressures, it helped me to understand the effect of different spring stiffnesses, lengths and preload - maybe you should do the same?

If you're using a wastegate diaphragm you'll probably find no movement until it hits 0.9bar, then full extension by 1.1bar (to open the eastegate!) but I found I needed a much more proportional response for the VGT to smooth out silly peaks and give a sensible response.

[Turbocharger]

Inspired by this thread, I've had another look at the boost diaphragm on my VGT again today. As suspected it was leaking, so I replaced the membrane with a sheet of flat rubber from another capsule - not perfect but a passable effort and it seals now.

This is the first time I've had a leak-free membrane and a weak spring in there to open it up almost immediately, to get it away from surging at low revs.

It goes like a rocket, particularly when pulling away. I'd say it's quicker to 20mph than my 1.8 K-series MGF now, and the 285 tyres will chirrup if I'm accelerating from a standstill in low box.

Thanks LR4x4 - I needed a kick up the arse!

[rusty_wingnut]

The steady-state response isn't adjustable unless I change the spring. I drew a graph of the diaphragm position at various pressures, it helped me to understand the effect of different spring stiffnesses, lengths and preload - maybe you should do the same?

I quite agree mate, the unit I have is the standard TGV vain controller, it is very stiff and doesn't move until roughly 0.5barand reaches full extension by maybe 1 bar. I am going to knock up a new unit capable of being adjusted (with different springs) and see if I can get more out of it.

[Turbocharger]

First step is to draw a graph of the boost vs extension you already have - I connect the compressor to the pipe off the inlet manifold, turn down the regulator and then read extension from a tape measure and boost from the dash gauge at 0.25, 0.5, 0.75 and 1 bar.

Mine starts to move at 0.25 bar and is fully extended by 0.5 bar now; if I change the spring again I'd aim for movement starting at 0.4 bar and fully open at 0.75 bar or slightly higher.

[Turbocharger]

First step is to draw a graph of the boost vs extension you already have - I connect the compressor to the pipe off the inlet manifold, turn down the regulator and then read extension from a tape measure and boost from the dash gauge at 0.25, 0.5, 0.75 and 1 bar.

Mine starts to move at 0.25 bar and is fully extended by 0.5 bar now; if I change the spring again I'd aim for movement starting at 0.4 bar and fully open at 0.75 bar or slightly higher.

[Bush65]

I have recently had some problems with my VGT, to try and get more boost I tensioned the diaphragm up more, and as a result I have a greater overpressure but the boost remains around 1bar.

Is it worth me either opening or closing this stop screw to achieve a little bit more?

I quite agree mate, the unit I have is the standard TGV vain controller, it is very stiff and doesn't move until roughly 0.5barand reaches full extension by maybe 1 bar. I am going to knock up a new unit capable of being adjusted (with different springs) and see if I can get more out of it.

IMHO you should try increasing the fuel rate from the fuel injection pump.

[Turbocharger]

2 years on from first installing my VGT, I should give an update.

The turbo itself has been quite reliable, even without the water cooling. I've used various different springs in Lara's special diaphragm housing, and when it works it works very well, but I have had problems with leaks from the capsule and from torn rubber diaphragms. (It can be bodged to run with fixed geometry, albeit without a good response, so failure doesn't mean a tow home!)

I need the rubber diaphragm from a Td5 turbo wastegate capsule to make it reliable again - any clues where I could get one from cheaply, or on alternative materials for a flexible heatproof membrane? I think I've learned enough to avoid tearing another one.

[rusty_wingnut]

IMHO you should try increasing the fuel rate from the fuel injection pump.

Hi John, I have it cracked up quite far, I have a decent EGT gauge and although it never reaches 750F it does get close on long uphills, boot down, making me think there is a leak or the diaphragm isn't performing properly.

[Bush65]

Hi John, I have it cracked up quite far, I have a decent EGT gauge and although it never reaches 750F it does get close on long uphills, boot down, making me think there is a leak or the diaphragm isn't performing properly.

I assume that EGT is a typo!

If your EGT gauge is in fact reading in Fahrenheit, then your EGT is far too low - I'm also assuming your thermocouple is pre-turbo.

[BogMonster]

I think he means 750C

[rusty_wingnut]

Indeed it is! It is preturbo. The alarm is set at 750C, and it can get upto a little over 700 on a long hill.

[rusty_wingnut]

Finally fixed it! the pipe from the actuator has been re-reouted into the back of the inlet manifold, now 1.5bar briefly, before it settles to 1.2bar = happy me

[Turbocharger]

Time for an update - I was always worried about how far out from the block the turbo is mounted. Last weekend that fear proved grounded, and the manifold sheared the weld around the turbo mounting flange. I lashed it back together with straps (it was still making boost!) and drove it home REALLY gently.

Tacked into place:

And welded inside and out.

For the belt and braces approach, more steel was added in a "not pretty but basely functional" sense.

And hopefully reinstalled for another 20,000 miles of trouble-free motoring.

[Turbocharger]

I've had problems at various points with sealing the manifold to the head, which I've always put down to the distance from the head to the weight of the (unsupported) turbo - old photo:

So I made a brace a few weeks back to pass any deflection back down to the (engine side of) the engine mount:

But now it's cracked the manifold (again) on one of the end branches, where the black line is showing:

How to repair it - reliably?

Thoughts:

- it's not the first time I've seen a failure here, the manifold is obviously working very hard structurally though the brace should be helping.

- it's failed in torsion, so the vibration has fatigued it as the turbo has moved up and down

- either it's old damage which has come to the fore, or the assembly is now overconstrained with a brace as well?

- I'll tack it in-situ and then re-weld the crack, but should I brace it somehow as well to spread the stress or will it just concentrate elsewhere?

[Disco-Ron]

Looks to me like you would be better off with a custom made manifold, with a decent suport built into it.......

[Turbocharger]

It is a custom manifold, and my brace should give it the support it clearly craves. How can I see if it's overconstrained?

[dirtyninety]

The design on the manifold, as previously mention in this thread, is terrible.

Perhaps have another manifold fabricated - something closer to block and stronger.

OR, put a brace from the bottom of the block/engine mount that is sleved and threaded so you can 'push' the turbo up to removed the strain from the manifold.

[Gremlin]

Use a disco 200 manifold, thats what the allard kit with the VNT unit uses. Its a great effieciently designed 4 into 1 manifold.

G

[Troddenmasses]

Use a disco 200 manifold, thats what the allard kit with the VNT unit uses. Its a great effieciently designed 4 into 1 manifold.

G

or just use more ratchet straps?