My second T4, operation de-chav

[Activ8]

It would take 5 minutes to swap the pipes over! Although I'd be more inclined to go with an MBC.
Its wrong to compare the pre Volvo turbo experience with the K14 as we're so much further forward.
Just very odd the boosts are identical! The only way you can be loosing boost is through that wastegate.
We could - as a last resort - replumb it up with vacuum control .....

it wont need an MBC - that I am 100% sure of.

I've used the N75 and MBC together to ensure the N75 holds the boost I wanted.
Its helped me map the N75 duty cycle.

Hook the N75 to vacuum?

Not the AJT / ACV N75, I use the 111KW setup and rewrite the maps.
As mentioned previously we'd have to work the pressure / vacuum balance but what the heck - can't be any worse than watching coloured HEX dry!

Lets get this sorted - then plan and move you on to something bigger and better .... I have a few water cooled GT2559's spare in the garage....

They still wastegated?

Vacuum wastegated and a shed load of torque.
Would be nice with a bespoke manifold and 6 speed gearbox?

[regcheeseman]

It would take 5 minutes to swap the pipes over!

Not quite five minutes, intake and boost pipes had to come off before I could even get to the top port

Probably 30 minutes in all. boost pressure plumbed straight to the top port, n75 output still connected to the side port.

And the result?

Steady drive out through 30 and 40 limits and it's obvious there's more there, akin to having the N75 disconnected.

I get to the dual carriageway and give it some loud pedal, it takes off quick, I remember I need to watch the boost, quick glance down and it's pushing 20 psi as I snatch fifth. Few seconds later and I'm doing 70 without really trying so I back off.

I do a few more WOT runs and it hits 19-20 psi and then stops, limp mode a couple times but it only does it when I'm cruising on a light throttle and then go for it, only to get no response as it is already limpng.

It's quick, still rolling coal and obviously not right, but so much better - not that it was slow before, even with only 10 psi it was still much much quicker than the old AJT.

[Activ8]

Not quite five minutes, intake and boost pipes had to come off before I could even get to the top port

Probably 30 minutes in all. boost pressure plumbed straight to the top port, n75 output still connected to the side port.

And the result?

Steady drive out through 30 and 40 limits and it's obvious there's more there, akin to having the N75 disconnected.

I get to the dual carriageway and give it some loud pedal, it takes off quick, I remember I need to watch the boost, quick glance down and it's pushing 20 psi as I snatch fifth. Few seconds later and I'm doing 70 without really trying so I back off.

I do a few more WOT runs and it hits 19-20 psi and then stops, limp mode a couple times but it only does it when I'm cruising on a light throttle and then go for it, only to get no response as it is already limpng.

It's quick, still rolling coal and obviously not right, but so much better - not that it was slow before, even with only 10 psi it was still much much quicker than the old AJT.

OK, we can work on this and get the control of the boost back. If you VCDS code read it I'm sure it would show "over boost "codes,.... as it should.
So pressure to the top port has sealed it shut, I think the boost ceiling on the map is ATM+1.31bar (19.0 psi).

[rjhoy02]

Well done lads. Light at the end of the tunnel

Sent from my vernee_M5 using Tapatalk

[regcheeseman]

OK, we can work on this and get the control of the boost back. If you VCDS code read it I'm sure it would show "over boost "codes,.... as it should.
So pressure to the top port has sealed it shut, I think the boost ceiling on the map is ATM+1.31bar (19.0 psi).

I'll read the codes, I though the boost limit was a little higher on your map and assumed I was still losing some boost.

I cannot see what configuration of plumbing with an MBC will work - I've got a small air regulator that I'll install to vary the pressure active on the top port which will have the same effect as preloading the mechanical spring. That way I will still have the N75 control as intended.

I still think I have N75 control which would explain it pegged at 19 psi

Well done lads. Light at the end of the tunnel

I'm hoping it's not a train coming the other way - there was an ominous head gaskety smell this morning when I pulled up. But I had been enjoying the new boost and things were a little warm, could well be the exhaust wrap as that has the same smell especially on wet roads

[Activ8]

OK, we can work on this and get the control of the boost back. If you VCDS code read it I'm sure it would show "over boost "codes,.... as it should.
So pressure to the top port has sealed it shut, I think the boost ceiling on the map is ATM+1.31bar (19.0 psi).

I'll read the codes, I thought the boost limit was a little higher on your map and assumed I was still losing some boost.

I'll check to be 100% - think I emailed you the SVBL with the v2 map? Its mapped to 2.3bar.

I cannot see what configuration of plumbing with an MBC will work - I've got a small air regulator that I'll install to vary the pressure active on the top port which will have the same effect as preloading the mechanical spring. That way I will still have the N75 control as intended.

The MBC is simply to protect overboosting (if the MAP sensor was at fault) and potential damage to the engine.

I still think I have N75 control which would explain it pegged at 19 psi

You wrote "Probably 30 minutes in all. boost pressure plumbed straight to the top port, n75 output still connected to the side port.
So you T'd off the compressor housing to BOTH the top port AND the N75? Otherwise how is the N75 receiving any pressure to control?
The MAP sensor will be looking at the actual boost figures and limiting it to the SVBL.

I'm hoping it's not a train coming the other way - there was an ominous head gaskety smell this morning when I pulled up. But I had been enjoying the new boost and things were a little warm, could well be the exhaust wrap as that has the same smell especially on wet roads

The MAP sensor and SVBL are working fine so the boost will NOT exceed this maximum.
Where in the boosted air circuit is the boost gauge pressure feed taken from?

[regcheeseman]

The MBC is simply to protect overboosting (if the MAP sensor was at fault) and potential damage to the engine.

I get the why - it's the how? The only conceivable way I could fit an MBC would be as an open bleed on the top port feed - a nasty way to control any turbo.

How did you envisage the MBC fitted?

I've not got one anyway - pressure reg will do a better job.

You wrote "Probably 30 minutes in all. boost pressure plumbed straight to the top port, n75 output still connected to the side port.
So you T'd off the compressor housing to BOTH the top port AND the N75? Otherwise how is the N75 receiving any pressure to control?
The MAP sensor will be looking at the actual boost figures and limiting it to the SVBL.

Yep - Boost line is t'eed to N75, top port on wastegate actuator and boost gauge

The MAP sensor and SVBL are working fine so the boost will NOT exceed this maximum.

Of course - it's not just wastegated, boost map will reign the fuel in as well, good old TDI's.

[Activ8]

I get the why - it's the how? The only conceivable way I could fit an MBC would be as an open bleed on the top port feed - a nasty way to control any turbo.
How did you envisage the MBC fitted?

Why would you need to put an open bleed to the top port of this setup?
We just need to understand whats now happening with boost with the top port under pressure, preferably with a runny log?
We also don't need an MBC, as there's no need. The top port not sealing/being part of the control on your setup is the problem.

I've not got one anyway - pressure reg will do a better job.

A Pressure Reg, OK.

Yep - Boost line is t'eed to N75, top port on wastegate actuator and boost gauge

OK, it wasn't clear the N75 was still part of the control loop. Thats good.

[arfur fox-acre]

runny log....that's funny

[Activ8]

Here's an idea Reg,
for your second runny log , try plumbing the N75 as follows;
Compressor boost feed to N75 as usual,
Boost control to top port,
Boost return / to side port,
The N75 control airflow and pressure changes should then be mimicked by the top and side ports?
It might need the N75 map modifying though.

PS - It would only take 5 minutes to swap over....

[regcheeseman]

Here's an idea Reg,
for your second runny log , try plumbing the N75 as follows;
Compressor boost feed to N75 as usual,
Boost control to top port,
Boost return / to side port,
The N75 control airflow and pressure changes should then be mimicked by the top and side ports?
It might need the N75 map modifying though.

No that wont work at all - not if understand what you are saying correctly - you'll have no control at all - as I have it now there is positive pressure holding the leaky wastegate shut (because the spring is weak not the seat leaking) and then the N75 can equalise this holding pressure and while it cannot fully open the wastegate, it's enough to return it to it's 10psi max state

Why would you need to put an open bleed to the top port of this setup?
We just need to understand whats now happening with boost with the top port under pressure, preferably with a runny log?
We also don't need an MBC, as there's no need. The top port not sealing/being part of the control on your setup is the problem.

No it isn't. Top port is fine - this is evident with the current setup. The problm is as above - insufficient pre load on the wastegate, the fact it ran higher boost with the exhaust back pressure reduced was a sure sign than manifold pressure is lifting the wastegate

You'd need a open bleed - the only way it could work would be to use the MBC to keep a holding pressure on the top port which would also give a constant small boost leak and a spiky boost response.




Meanwhile - first kill today and it's a credible one BMW 840.

Caught it on the B road coming out of hartland, dawdled for a bit and then a T5 was then up my chuff, bit of a straight and whipped past the beemer, which he was obviously not happy with as he upped his pace to stay with me but obviously didn't know the road as well.

We got to the A39 and I'd pulled out 70 - 100 yards, I knew what was going to happen now, there's a roundabout and a near kilometre straight - the beemer is just gonna stretch his legs and blast past, I need to carry as much speed up to and across the mini roundaout as possible, not easy as it's tight and I need to make the second exit.

Leaving the roundabout I nail it, the beemer has spotted the straight and is also going for it, but I'm now nearing 90 and matey is bottling the overtake and has drawn up behind, the T5 is a long way back

By the end of the straight we are back in the twisties this road is famed for - there's no way a sporty beemer is going to keep with a builders van on wangli ditchfinders through the bends and he is history.

Laughed my cock off.

[Activ8]

Meanwhile - first kill today and it's a credible one BMW 840.

Leaving the roundabout I nail it, the beemer has spotted the straight and is also going for it, but I'm now nearing 90 and matey is bottling the overtake and has drawn up behind, the T5 is a long way back

By the end of the straight we are back in the twisties this road is famed for - there's no way a sporty beemer is going to keep with a builders van on wangli ditchfinders through the bends and he is history.

Laughed my cock off.

Thanks for sharing, wish we were there at that roundabout.... go Reg!

Sent from my SM-G901F using Just T4s

[Activ8]

No that wont work at all - not if understand what you are saying correctly - you'll have no control at all - as I have it now there is positive pressure holding the leaky wastegate shut (because the spring is weak not the seat leaking) and then the N75 can equalise this holding pressure and while it cannot fully open the wastegate, it's enough to return it to it's 10psi max state

Yep I understand what you"re saying.... the original design was vacuum top controlled and direct constant pressure to the side port. I reckon I could replicate this with the N75 mapping to balance the control pressure, diaphragm and spring to the top port and surplus to the side port. Your call mate.




Sent from my SM-G901F using Just T4s

[regcheeseman]

Yep I understand what you"re saying.... the original design was vacuum top controlled and direct constant pressure to the side port.

You 100% sure?

Any vacuum to the top port would tend to open the wastegate.

Direct constant (positive) pressure to the side port would also open the wastegate

Manifold pressure will also tend to open the wastegate

And with the weedy mechanical spring the only thing holding the wastegate shut - the wastegate would be always open.

Unless the side port was under direct constant negative pressure??? - which is effectively the reverse of what I have set up.

I reckon I could replicate this with the N75 mapping to balance the control pressure, diaphragm and spring to the top port and surplus to the side port. Your call mate.

Appreciated but there's no need - it works fine with current setup. I'll run as is until I fix the wastegate or fit a new turbo.

[regcheeseman]

Thanks for sharing, wish we were there at that roundabout.... go Reg!

Yep - you should have been there - It was so funny.

Knobber in his BMW convertible 4 litre pride and joy - with his missus/girlfriend by his side and some twat in a van with gay orange wheels catches him napping.

He should have obliterated me - but he turned out to be a bit of a fanny.




Think it may be time for a session on the rollers and a post on the t4 forum for rake.