VNT's- between a rock and a hard place?

[Buller_Scott]

hi guys, how's yous?

now that formalities are out of the way, im going to get a mufflerectomy tomorrow from the muffler man (thats the name of the shop), but NOT dump pipe.

why not dump pipe? because i still cannot make the decision- here's my thoughts:

no dump pipe: higher egt's= bad for turbo. if it were any other turbo or if i didnt have a tune, i'd get one, BUT!!!

dump pipe= because the vnt's vanes can be prone to sticking (egr fuggin crap), apparently with a tune, as the turbo accumulates crap in it AND without adjusting the vnt actuator rod (which i wouldnt eff with anyway-im clueless), boost creep becomes a real problem, and opening up the exhaust is only going to add to the problem (by way of boosting more freely? i dont know).

so, on one hand there's egts in melbournes lovely 43degree summers, on the other hand there's lowering the egt's but assisting boost creep. with or without dump pipe, it seems my turbo's going to go boom and my car is going to explode and im going to die in a horrible ball of tiny-vnt-will-crush-your-ambitions flames.

so, which is the lesser of two evils, you reckon?

cheers,

scotty

[philthy]

Ported waste-gate, or external?? That could get exxy though.

[Greg Roles]

Well first up you'd be deadset mad to mess with the VNT actuator rod on any car you couldn't live without. I wouldn't contemplate that, as it throws the entire system out, and you're into expensive experimental territory there.

A less restrictive exhaust, that is a dump pipe will actually help lower EGT's. It's all about getting that hot gas out, and I've little doubt the DPF in the GT's and MK6's actually help keep EGT's artificially high. So in my mind a dump pipe would actually help.....but.......

Overboosting on an already tuned TDI would be a major concern. It's all very well to have the hot exhaust gas exiting more freely via your flash new dump pipe, but if the turbo can overboost and produce extra heat anyway, you get the same turbo melting effect.

I'd highly recommend you get a EGT guage, and have it added to your proposed dump pipe right after the turbo. Sure it's on the "colder" side, but drilling the log manifold is precarious, and Gale Banks himself says you just add about 100 degrees and you've got what the turbo is seeing. You can get an electrical EGT guage like i have from E-bay, I've a Swoosh one ( which I won't need shortly as my Snow controller reads EGT's ) and it wasn't very expensive, less than $100 shipped from memory. Let's you keep an eye on things, and there's no reason you couldn't run a crazy tune and just drive to the guage ( and hope like hell a $60 us e-bay guage is accurate!! ) but it's a good indicator of rising or falling temps which is all I care about.

Finally leaving your EGT recycling on will keep EGT's down, and anything you can do on the inlet side to boost the intercooler, drop temps of inlet air and lower the restriction will all help to keep EGT's a bit lower overall. An intercooler spray, even a crude one would be highly recommended, and anyone could rig up a windscreen washer bottle to squirt over the intercooler core at the flick of a switch. Jaycar have lots of temp switch options, and I'm sure you could get your little sister to solder one up for you if you are indeed so "effing useless". Never too late to learn not to be mate, I'm a backyard mechanic with zero formal training in anything mechanical, and had zero knowledge of diesels when I bought the TDI two years ago, and now I am consulted by my mechanic brother on the topic! Go figure....

Get a dump pipe and an EGT guage mate, and boost your intercooler and cold air inlet to the airbox. I've seen pahse one and two snow mater meth kits go on USA ebay for a hundred or two, so there's always that option down the track. I decided to go water meth, as it wll lower EGT's given my plan to ditch the EGR system, put on a big tune, and it seems it'll give me an extra 20-30 hp to the wheels across the entire rev range. Happy days!

[gregozedobe]

Is it possible that you are worrying uneccessarily about the VNT vanes sticking and damaging the engine ?

AFAIK almost all TDIs with sticky vanes are cars that are always driven gently at lowish revs and very little accelerator pedal. This leads to the vanes being in the low revs/max boost position all the time, which allows the soot to build up around them and jam the vanes, preventing them from moving to the high revs/reduced boost position. If the engine is then driven with a bit more enthusiasm the turbo produces too much boost so the ECU goes into "limp" mode to protect the engine (so not much chance of damaging the engine in this scenario).

Of course if the vanes stick in the high revs/reduced boost position then the engine will only get underboosted at low revs, so no possibility of damage from too much boost.

Conventional wisdom says that a TDI that is given full accelerator from (say) 1,600 rpm through to 3,000rpm on a regular basis will be exercising the vanes through their full travel, so they won't stick.

So the only other cause of overboosting would be a faulty VNT actuator (IIRC much less common than sticky vanes), and even here the ECU should still step in if needed and intervene ("limp" mode), thus protecting the engine.

Unless the tune includes a remap which disables "limp" mode when overboosting then I don't see where the (potential) problem is. Or maybe I'm missing part of the puzzle ?

[Buller_Scott]

hey guys thanks heaps for the feedback.

cog i think you're right re me having to man up and start getting my hands dirty. it might f**k with my manicure but as a typical VW driving hairdresser, i've got hook ups. i am sussing out a group buy for polo tdi in the polo section. if the price is right i'll get the dump & cat and then get on the egt gauge.

greg, thanks for bringing that up- you arent missing any part of the puzzle. im so paranoid that i thought, even though i thrash my car once warm on a regular basis with tune, that even then, the vanes will be just as prone to sticking. i DO exercise the turbo so hopefully that's kept that at bay. as for the tune- i dont think they would have disabled limp mode, not that i can really tell. all's i know is the bv39 turbo in the polo is rated good to 4000rpm, and even with my ''track'' tune, it cuts out at 4000rpm just like clockwork. i was happy with that, so i figured that they shouldnt have cut corners with the tunes.

could be missing the point, though.

thanks again guys! dump and cat it is.

[gldgti]

Ahh mate, you make it sound like you think your driving a time bomb! Like greg sayd, you'll be excercising those vanes no end.

Theres absolutely no way in the world you'll increase the chances of having some kind of turbo/engine failure by getting a bigger downpipe. The turbo might spool faster than before, but i'm sure it wont make a big enough difference to cause bigger overall boost numbers.

The ECU is a closed loop controller - it takes measurements and then sends out control signals, then takes meaurements and adjusts, and adjusts, forever more. The control signals for the vanes arent like "positions 1, 2 or 3" - but simply more open or more closed. If the ecu is see's max boost a little earlier than normal, it will simly open the nvanes up earlier to keep the boost where its supposed to be - what it doesnt do is say "at max boost, open the vanes to position x" because this would cause a huge amount of error - the boost that the turbo produces depends upon all of these things:

>fuelling (throttle position)
>load on the engine
>engine rpm
>vane position.

Hope to help

[Buller_Scott]

lol thanks gld. yeah- im slowly getting there, but still very very wet behind the ears.

problem is, even though it's 2007 build, i thick-headedly keep on applying all the horror stories that i read on tdiclub.com about the pre-2004 alh's to my wee polo. and im DAMN paranoid all the time, which hardly helps, lol.

thanks everyone for breaking it down for me! dump pipe is a go!