Warning - for non standard turbos

[944Turbo]

I have a non standard turbo fitted for about a year a couple of weeks back, I was driving to Swansea and as I pulled up steam poured out from under the bonnet. When it had cooled down I discovered the metal coolant pipe on the turbo had fractured below the turbo pump temperature switch (wobbly sensor). This appears to have fatigued through. With the standard turbo this has a flange which bolts to the turbo. The unit I have (K27/K26 hybrid) doesn't have a bolt in the right place, when fitting the turbo I thought it would be ok without it. Wrong!
Around 6 months ago I changed the temp sensor which may have contributed.
I have a replacement pipe (from Porsche apart) and have modified the mounting flange so it is now supported.

 

[944Turbo]

Prior to the trip above I also turned up the boost a little bit - aiming for around 16.5psi on the M4 the car developed a whistle, initially I thought this was down to damage to the turbo from lack of cooling but now I am not so sure. I had driven fairly slowly round swansea with no steam, it was very noticeable as I arrived and stopped.
I had a leak from the vacuum lines by the one way valve? (blue/black circular plastic jobby near rear of engine - anyone got a part number?) and the noise went away(so did the boost)
At the weekend I replaced a load more of the lines with the pluracil kit and the boost has returned to 16psi but I can here a woosh when I change gear, like a vent to air dump valve and I still have a whistle.
I know I have a slight exhaust leak after the wastegate does a wastegate sound like a dump valve?
I think the car feels a bit slower than before the coolant issues.
I can't find any more leaks in the inlet area
Any ideas?
Tony

 

[Diver944]

ORIGINAL: 944Turbo

I had a leak from the vacuum lines by the one way valve? (blue/black circular plastic jobby near rear of engine - anyone got a part number?)

928 537 361 02

I snapped mine when plumbing in my boost gauge. OPC couldn't find one but JZ Machtech say they always keep one in stock. Posted to me for £15.58 inc vat and postage

 

[944Turbo]

Thanks, mine has a little bit left which with the blue hoses just grips, but its not ideal, It is very brittle and was possibly cracked already.
Cheers,
Tony

 

[John Sims]

I know I have a slight exhaust leak after the wastegate does a wastegate sound like a dump valve?

I had a simillar strange noise when one of my exhaust manifold gaskets started to blow, due to loose studs, so it could be exhaust related.

 

[944Turbo]

So I have another reason to buy a Tial, It does sound very Max Power at the moment, Vroom woosh, vroom woosh.
I have a recircultaing dump valve, I am considering removing it so it dumps to air and blanking the hole in the intake boot, so I can really hear that and see if I have two woosh sounds every time I lift off or one - anyone know if this is likely to be a problem? As far as I can see I will be dumping boost through one big hole instead of a ring of smaller ones (as on an off the shelf dump to air type) or am I missing something?
Tony

 

[944Turbo]

When I replaced my water pipe I forgot to do up the intake boot fully - the one that fits onto the throttle body. Once warmed I gave it some boost and it all went nasty!
Whilst I was limping back home 1/2 mile or so the AFM was showing very rich - backed up by the occasional yellow flashes from behind. I made it back mostly on idle and an easy fix, but it gave me a lot more confidence in the AFM. That and the fact the previous boost increase .5 psi approx moved full throttle rich round one segment towards Stoich.

Tony

 

[Diver944]

Do you mean that has got rid of the whoosh, or is it still there?

 

[944Turbo]

No, still wooshing will get the exhaust leaked fixed when the Tial arrives (it's the short pipe from the wastegate). Just considering doing the dump valve mod this afternoon, but I am running out of miles before the service + belts + front oil seals + thermostats +waterpump on the 29th, approaching the 144K mark.

Tony

(aircon can wait)

 

[John Sims]

I have a recircultaing dump valve, I am considering removing it so it dumps to air and blanking the hole in the intake boot, so I can really hear that and see if I have two woosh sounds every time I lift off or one - anyone know if this is likely to be a problem?

Mr Cannell has a non-recirculating dump valve - he shot past me, after a 911&PW Blue Ball meeting, and scared the **** out of me as it wooshed.

I take the view that if it's good enough for Rick it's good enough for me and rather fancy a good old woosh sound myself.

There have been comments that in evacuating the air out of the system you could upset the AFR as you are dumping metered air. I can't see how this would be a problem as the air is metered as it enters the system. If the air is recirculated then the cylinder heads will receive the air later than was metered while the injectors are being timed to receive the air currently flowing though the "Barn Door". Unless Porsche allow some form of overlap I can't see how you avoid running lean after letting off - at this point the injectors will be timed for the minimal air entering the system through the Barn Door whilst the cylinder sucks in the recirculated air - post boost.

If you get my drift, then evacuating the air must be better than recirculating it. If it isn't quite right then the only problem will be a spasmodic over rich mixture - Oh my goodness, this might cause an exhaust flame.[]

Woosh & Exhaust flames - It gets better and better.

 

[944Turbo]

I thought the benefit with recirc was that the dumped air helped to spin the turbo, but since studying the system in more detail there is only an air filter (and I suppose a 'barn door') stopping the boost from going the other way, so I would think no great benefit. My reason for the test is to see if I get 2 wooshes, one from the DV and one from the Wastegate, or jut a louder one. I did find some cracks in the short pipe to the dump valve but they appear to be only in the outer rubbber.
The 'test' will involve moving the DV further from the hard pipe as thats the only place there is room - I am hoping this wont affect its operation too much (only thought about it because SFR mount their DV on the hard pipe).

Tony

John where do you live again? [][][][][][][][]

 

[944Turbo]

Oh forgot to mention Mr C also mentioned a problem with compressor stalling when running high boost (20PSI) and a recirculating DV so thats another good reason to buy an atmospheric dumper, anyone want to buy a Viper motorsport recirculating DV? lovely workmanship - rebuildable for different spring rates, one carefull owner etc. etc.

 

[Fen]

So are you guys saying that with high(ish) boost there is a performance advantage to having a car that sounds like a bus? [:-]

If so can you shut these things up? I really don't want to have to buy a Burberry baseball cap...

 

[John Sims]

I thought the benefit with recirc was that the dumped air helped to spin the turbo,

That might happed as the air can't escape back through the Barn Door as it acts as a one way valve.

As I understand, the dump valve opens to remove air pressure between the Turbo and throttle housing when you come off the gas. Without this pressure relief the back pressure can stall the turbine and even shatter the input shaft. Assuming the air is evacuated from the closed dead end at the throttle side of the turbine, and air continues to be fed from behind, the turbo can continue to spin.

Noting the above, and assuming air is continuing to be pumped through the turbo, we can consider the effect of a recirculating or non recirculating dump valve.

Recirculating - should have little effect on the rotor speed as, being a closed system, any air taken from the output side of the turbine is being replaced with air on the input side. In this scenario any slowing should only be due to surface friction or turbulance within the closed system. No more external air is required, as it is a closed system, and thus no additional air is drawn through the Barn Door.

Non Recirculating - will evacuate the pressurised air between the turbo and the closed throttle to atmostphere but, to allow the turbo to continue spinning, the turbo must continue to pump air. The only way the turbo can now get air to pump is to suck it into the system through the Barn Door. As we know, the Barn Door causes a restriction and will slow the incomming air which will slow the turbo. If we further consider that, by moving the Barn Door, the engine management would think more air is being drawn in which will require more fuel - it doesn't know that the air being sucked in is only being pumped out to atmosphere, not going into the cylinders.


After pondering all the above, and whilst excited by the prospects of whooosh and exhaust flames, I have to conclude that Porsches way of doing it may be better whilst ever we have the restriction of the Barn Door - once we all get MAP that will be a different matter.

 

[944Turbo]

Agreed except I doubt that the barn door is that air tight but if it was could you slow its opening by building pressure behind it?
Isn't theorising fun? [&:]
Tony

Fen, I know you can get especially loud atmospheric DV's but I'm not sure about silent ones.

 

[944Turbo]

For some reason the car didn't want to run with the standard dump valve venting to air - no tick over at all so I put it back as standard and went for a spin. Do atmospheric DV's have a different mechanism or is there something else going on?

I am 90% certain now the woosh is the wastegate as I can here it open as well. I guess when I get the exhaust pipe fixed I will know for sure. Its only a small leak but right next to the wastegate I guess it will make noise.

The car seems a litle more hesitant off boost than it used to but I guess this could just be my imagination, or more go on boost [] making it seems slower off.

Since replacing the vacuum lines the tickover is smoother again, new plug leads was the first improvement, it is rock steady now.

Tony