Getting Exhaust done (and turbo discussions)

[Buller_Scott]

Ill change turbo's when the car reaches 100,000Kms, Ive done 45,000kms so yeah not long.

What Nm are you looking at getting too? I wanna get the little one to around 550Nm

interesting..... i've read about guys' turbos (vnt15 from the pd90 golf mk iv's) blowing at 120k miles etc, and them replacing them then.

I too was thinking that 100,000km's would be a nice round number to replace the current turbo- sure it might be abit early by some peoples standards, but apparently with out pd engines when a turbo blows there's the potential that it will take the engine with it (can someone verify specifics as to why pls?).

i've recently adjusted my thinking into being more concerned with nm rather than kw, and on that front, i think i'd be happy with 320 for the mean time, but once i get to 100,000kms, im thinking of one of two things:

1. upgrading to a vnt17, but with a mild tune (basically, slightly more power as result of bigger turbo, but not pushing the turbo too much). i was thinking a mild tune as straightline power is nice, but i dont like wheelspin and i dont want too much torque steer as i prefer going around bends fast to straighline. also, being a tightass, i was hoping that this would also translate to turbo longevity. the only problem with this is, i think that turbos have to run at to-the-limit boost every now and then, so that everything gets sealed properly?

2. most likely: 315nm under a chippeduk tune, with things like dp and eventually sprayer for smic, will probably produce a few more nm. that, and suspension should see a fun little package. thus, im thinking another vnt15, run it in all over again, and keep it for another 100,000kms.

to anyone who reads this: i readily admit that im unlearned in these things. i still have to research whether or not running a new VNT turbo conservatively (below its true capabilities, boost wise) will be more damaging to the turbo than good. either that, or it doesnt actually matter? not sure. any info would be well recieved.

cheers, scott

[gregozedobe]

but apparently with out pd engines when a turbo blows there's the potential that it will take the engine with it (can someone verify specifics as to why pls?).

If a turbo's bearings get too worn this can lead to turbo oil seal failure (or seals can just fail with good bearings). When the oil seals fail they allow lots of engine oil to get into the intake. This oil burns quite well in a diesel, so well in fact that the engine can just rev itself to death just on its own oil.

Unless you can block off the air going into the engine (or have a really good clutch and can stall the engine in a high gear using the brakes) there is no way to stop the engine. There is no ignition to turn off, no way to restrict the fuel supply (the engine oil), the turbo keeps pumping more air and oil in, so the engine just keeps on revving harder and harder, using up its own oil so lubrication is compromised, until it destroys itself. This situation is often referred to as a diesel engine run-away.

also, being a tightass, i was hoping that this would also translate to turbo longevity. the only problem with this is, i think that turbos have to run at to-the-limit boost every now and then, so that everything gets sealed properly?

to anyone who reads this: i readily admit that im unlearned in these things. i still have to research whether or not running a new VNT turbo conservatively (below its true capabilities, boost wise) will be more damaging to the turbo than good. either that, or it doesnt actually matter? not sure. any info would be well recieved.

Because the VNT turbos have moveable vanes to vary the amount of turbo boost, there is the possibility of them getting clogged with carbon from the exhaust. This is often referred to as sticking or seized vanes. This seems to happen more often with TDIs that are always driven very gently and at fairly low revs, with the result that the vanes get stuck in the angle that maximises boost at low revs. If the engine is then revved above 2,000rpm these stuck vanes can't move to reduce boost at the higher revs, so too much boost is produced. The ECU recognises this situation as dangerous for the engine so it reduces fuel to protect itself - this is often called "limp mode" or "limp home mode". This will be reset next time you switch the engine off, but the ECU usually records an overboost error code.

If a TDI engine with a VNT turbo is regularly given full accelerator pedal from about 1,600 through to 2,500 (say in 2nd or 3rd gear) this usually moves the variable vanes enough to stop them from getting stuck in the high boost position, thus keeping them moving freely.

I have a vague idea it is possible to put too large a turbo onto a TDI and this can lead to turbo surge - which is a bad thing. IIRC there was a thread on this forum discussing this not too long ago, a search will probably find it.

I believe there is quite some science involved in selecting the correct size turbo for any given TDI application (but I am ignorant of the specifics). It is probably worth investigating what other people have done and how successful they were.

[GoLfMan]

If a TDI engine with a VNT turbo is regularly given full accelerator pedal from about 1,600 through to 2,500 (say in 2nd or 3rd gear) this usually moves the variable vanes enough to stop them from getting stuck in the high boost position, thus keeping them moving freely.

well in that case my TDI's turbo has NO CHANCE of the vanes getting stuck

[gregozedobe]

well in that case my TDI's turbo has NO CHANCE of the vanes getting stuck

Nor mine (and my RS's turbo wouldn't either, not that it has a VNT).

[Buller_Scott]

cogdoc, thanks for the detailed reply. thats awesome.

i was aware of the VNT needed a good kick in the pants from time to time to prevent the vanes sticking, and i also read (on this site) that a good way to run in a new car was, once warm, to drive spiritedly out of it- which i do on the weekends (weekdays when the car was new, 2-3 buller trips a week).

thanks for the info regarding the runaway situation on a tdi engine. now i finally know what the term entails.

i think my replacement will be another vnt15.

Cheers!

[Greg Roles]

Scotty, I'm planning on pushing my stock turbo, yet I am not worried about it. Perhaps I'll have to rebuild it early ( you replace "bearings" and the shaft ) and at that point, which I expect to be well over 100k, more like towards 200k, I'll probably look around as to upgrades from the vnt range, preferably with real ball bearings. Garrett indeed have an immense range. Rebuilding a turbo is straight forward really. Few moving parts!

[GoLfMan]

Scotty, I'm planning on pushing my stock turbo, yet I am not worried about it. Perhaps I'll have to rebuild it early ( you replace "bearings" and the shaft ) and at that point, which I expect to be well over 100k, more like towards 200k, I'll probably look around as to upgrades from the vnt range, preferably with real ball bearings. Garrett indeed have an immense range. Rebuilding a turbo is straight forward really. Few moving parts!

cant you say VNT22 and 200+hp 500+nm