tuned derv ZS update

[peterzs]

Hope you get it sorted and its an easy fix.

[p_b82]

Right another update i guess is needed...

It is still loosing coolant from the expansion cap when making use of 'some' of the extra torque, so i am pretty sure that the gasket has been compromised, so a strip down will be needed in the near future.

We have got a few ideas from some threads on .org as to what is the root cause, as it shouldnot be the fuelling directly causing the problem (butit might be we dont know)

So back to the update...

The thinking is that the exhaust housing for the GT15 family is far too small for what we are asking from it, and as such, the EMP (exhuast manifold pressure) is rocketting.... with the pressure high in the exhuast manifold it is doing enough to blow\compromise the gasket with the high boost from the inlet side.

So we are going to try and either tap the EM or use the EGR blanked plate and fit a pressure sensor, and just see what is what.

If the EMP is the root cause then there are a couple of options...

Either fit a custom external wastegate, with some pipework and a bit of a flex to join up with the decat - as this would basically show that the internal wastege on the GT1549 we have is not big enough to cope with dumping all the excess exhuast gases so we would be able to bypass the turbo completely and dump the excess pressure that way.

The turbo can still be controlled with the boost readings from the MAP as normal... although i am still thinking of getting a 3bar sensor fitted rather than the 2bar currently in use...

Or i will be going down a larger VNT turbo with electronic boost control, with a adaptor plate for the Exhaust manifold and a custom downpipe.

the later option is last resort, as i dont really want to detune the car (as it stands we think SDI's and remap is the most the turbo housing can take - so peak 250lbs ft and max 150bhp (or around 200lbsft at 4000 rpm), but i also dont really want to have the cost and the hassle of buying a new turbo and trying to sell the hybrid.

If we get the results as expected then i dont think that any-one will want to pay a decent price for a 'pointless' turbo either so it is a bit of a damage limitation excercise now!

So all is not lost, but it seems like it is still a way away from completion....

Any-one know where i can get my hands on a pressure sensor that can cope with up to 1000C, as all the ones i have found stop working after 250c

[p_b82]

Right we have worked out a way to measure the EMP.. just going to use a new blanking plate with a boost guage plumbed into that.... a bit of brake line or something similar to disipate any latent heat then on to normal boost hosing to run it to the cabin... or just something a bit closer if Matt is able to get some testing done on a RR...

Still looking at the various options for once we get the EMP readings - I think i would have to rethink my pipework if i go with the bypass system, as i am almost 100% there is not enough space to join it up with the decat, so the downpipe itself will need to be modified....

external wategate system looks like it would be in the region of £250 for the bits to control and operate that, plus the labour to get it fitted... then the extra cost of getting the pipework plumbed in properly rather than just using a 'screamer pipe' for testing purposes

My concerns with this route is that it is going to be quite hard to control the external wastegate, - As you should see pressure spikes under normal conditions - eg tootling along then stamp the loud pedal when in a rev range that allows max turbo boost) and stopping it opening too early and dumping the boost from the tubo's internal wastegate

If i effect the lag of the system i may as well jsut get a bigger turbo maybe something from the GT20 family...

Still doing plenty of research to try and work out my options.... I will avoid detuning the car if it is the last thing i do

[stamford]

Good to see you are keeping at it, all too easy to throw in the towel.

[p_b82]

Right quick update..

I have come to the conclusion there is almost nothing out there that will give me the daily drivability i am after without needing a lot of extra work to get it to fit...

As VNT is not an option (yet) i have decided on the pressure release system.

However after speaking to Grant (GBE) he has given me a few pointers to try and get this to work correctly...

Firstly he expects to see EMP spiking well above the boost pressure, so as i am running 25-26PSI on the intake side i can expect to see spikes of around 35-45PSI...

Due to this, there will never be any form of boost controller that i will find that will work - as they are all designed to keep boost steady at high rpm not dump pressure at high rpm...

So what we are going to go for a decent external wastegate with a restrictor plate bolted on the exhaust manifold (at the EGR point) - the dimentions of this are going to be a bit trial and error though - so a high temp valve may well be the best bet...

then the same thing on the other side of the wastegate - if the spring on the wastegate is high enough to resist the main spike and the pipework doesn't allow much flow through it. we should be able to dump the excess backpressure.

So the good news is that costs are looking at the £60 for a decent 38mm wastegate and then some pipeing\adaptor plates to be made up...

Other possibly good news is that rally_matt might be able to get his hands on soemthing decent to record the EMP's directly...

If and when the trial and error is all worked out, i will then plumb it into the downpipe so it passes MOT's

reading around some of the TDiclub posts (big VAG tuner forum) i might even see a nice jump in bhp if the balance is got right

[peterzs]

Best of luck Pete, keep fingers crossed for you.

[Jay-ZS+]

Sounds fairly positive then pete all a learning curve for everyone involved

[stamford]

All sounds rather interesting, makes a change from the normal reading.

[p_b82]

In effect we are just running a 'low blow' turbo setup on a car that has high boost pressure.

The challenge we are going to have is to get the restriction small enough that it doesn't dump too much exhuast away from the turbo - but not so small that it is still going to over pressure the EM.

Would be possible to do the same thing with a larger external wastegate - as the problem we have is that the internal one is not big enough to divert enough gas away from the turbine housing....
That however would require a fair amount of pipe re-working so this is the easisest compromise...

just have to get the bits together and then see how it all pans out... (it could still fail but if it stops HGF then in one respect it will be a success...)

[p_b82]

Right car is booked in for another 'Holiday' with Matt next friday.

Going to hook up a boost guage to the Exhaust manifold (where the EGR is blanked) to get some figures as to what it reached achieved when it spits the coolant out.

Also going to try to get something into the coolant system to read the pressure in there to make sure we are getting HGF and not just a general cooling system problem.

Going to check the thermostat just to be sure it is working properly, and also the waterpump.

Pending what is found (but we both expect it to be HGF), the head will come off again and stripped down and rebuilt, then the bypass system will be fashioned.

If we can limit the EMP to be the same as boost then we should be laughing... so around 26PSI

no idea how long this will take, so i am going to be in the little 25 again for a while i think...

still toying with uprating the MAP sensor to a 3bar one so i can get proper boost from the scangauge, but i suspect i will need to get the ECU tweaked a little so just going to get a cheap boost guage to make sure everything is right and maybe get round to that later on.