low-tech conversion of twin-scroll housing to VNT turbo?

[Otis2]

So I came across this simple & ingenious idea recently, that some Mustang guys are pioneering to artificially spool their twin-scroll turbos at low rpms -



There's a thread devoted to the idea here: http://www.turbomustangs.com/smf/index.php?topic=45148.0

I suppose this would be academic for anyone without a twin-scroll turbo housing, but as Dave (935racer) did recently mount a T3 with twin-scroll housing on my AAZ engine, it piqued my interest.  The twin-scroll aspect does nothing interesting for me right now, as it's just mounted on a factory cast exhaust manifold.  It just happened to come available at a decent price when I wanted to try a larger turbo.

So I idly wondered how this gadget would perform on a VW turbodiesel.

Possibly it shoots oil temps through the roof, and shock-loads the cylinders with double the back-pressure when the block-off plate is in place.  And given the huge heat range that the pivot on the block-off plate would have to operate within (say -30 F to +1400 F), I'm sure there would be issues.

But on the other hand, the promise of getting much earlier boost with the bigger turbo housing is there.  I'm mostly happy I have the bigger T3 turbo (a K03 replacement), but as Andrew (libbybappa) has argued several times, there is a real lag penalty to be paid.

I wondered what the turbodiesel hot rodders here thought of the block-off plate idea?  I immediately thought of the slick ideas that Jake & Tintin have used to mechanically control their VNT actuators, and figured something similar could be rigged up here, progressively opening the blocking plate as soon as a boost pressure signal is received by a diaphragm cannister.

[vwmike]

Your 300SD sounds like the Mercedes (not sure what trim level) that my friend had. That car had to have been the slowst car I've ever ridden in. It was a 4cyl NA diesel that couldn't get out of it's own way at lower speeds. I was surprised though, it could do the speed limit on the freeway with the AC on. I was in Canada this last weekend for the Great Canadian VW show and it was quite interesting to see all of the diesels there including one single cab with some short exhaust and what sounded like the little K14. That thing spooled very quickly and I can see how that would be of extreme importance at high altitudes.

[935racer]

Theres a company that makes a twin scroll turbine housing with the built in flap like that, can't remember the name, they use them for the big cummins. Personally I wouldnt use that device, you covered the downsides, money better spent on a properly sized turbo.

[Dr. Diesel]

i don't think you'd have any negative issues you mentioned. You're just putting the exhaust through a small hole to start, much like the late AAZ engines with their baby K03 turbos. I'd say definitely go for it and see what it does.

[DVST8R]

Theres a company that makes a twin scroll turbine housing with the built in flap like that, can't remember the name, they use them for the big cummins. Personally I wouldnt use that device, you covered the downsides, money better spent on a properly sized turbo.

The company is ATS, the turbo they produce in this sort of application is called the Aurora MST http://www.atsdiesel.com/atswebsite/ProductsDodge/TurboSystems.asp Scroll to the bottom of that page for more info.

My personal opinon is that that, It wouldn't be any worse then your stock ko3 for all of the issues you addresed, and as soon as you started to open the flap they would all but disapear, leaving you with a net gain.

[Otis2]

Thanks Dvst8r.  You can see the "flapper" on that commercial unit is a whole lot more beefy than the Mustang boys' home brew.



As I understand this thing, while the flapper is closed, it halves your turbine A/R.  So, since I have a 0.48 AR on this particular T3, with the flapper completely closed, it would be equivalent to 0.24, correct?

I understand that the regular T3 mounted on a 1.6TD has a turbine A/R of 0.36.  I don't know what the K03 has for an A/R factory stock on the late AAZ engines, but a couple of Google hits show 0.26 for some K03 turbos (not sure if they were set up for the AAZ though).

So, with the flapper shut on my turbo, I'd be very close to the A/R of the K03.  If it were possible to rig a progressive boost-sensitive diaphragm actuator (like Jake or Tintin did with their VNT actuator), then as rpm and exhaust backpressure built, the flapper would open progressively.  Ideally, by about 3000 rpm or so, it should open up completely and pour the exhaust through both volutes.  If it were set up to open completely by, say, 5 or 6 psi of boost, then maybe it wouldn't be beating up the turbo too badly.

The first real issue would be to design and build a flapper arrangement that would stand up to the abuse, without leaking exhaust or failing and getting sucked in through the volute.

Does anyone know exactly what the K03 turbine A/R is on late model AAZ engines?  I've searched here without any luck.  Is it 0.26?  If so, that's pretty darn close to the 0.24 that I would get by closing off one of the 2 volutes on this T3...

[RabbitJockey]

rig an old wastegate as an actuator (well, a wastegate is an actuator) actually that wouldn't work well because of how wastegates like to hang shut and then blow open at the proper time