Turbo Compounding (Edit: now gone VNT!)

[Turbinepowered]

I'm in the midst of planning a build for the 2L I5 diesel that's slated to be transplanted into my Quantum Syncro.

While I'm not out for ultimate power or insane levels of boost, I am shooting for good boost low in the RPM range and consistent delivery all the way through the band, kept at a moderate (~15-20 psi?) level for good power.

Seems to me that the best way to get boost early on and later would be to go for a properly sized compounded setup, with a high-pressure turbo that spools up easily enough to practically be spooled up from idle and a low-pressure turbo that really hits its stride at the upper boost limit.

I've gone through the various threads on this site about compounded turbo setups, most of them seem geared for serious power, but I'm more targetting staying in the prime efficiency ranges for the turbos involved for longevity and efficiency.

I already have McInnes' book on the way; any other suggested resources? Thoughts? Am I bat-*** nuts?

[Slave2School]

As crazy as this sounds if you only want 20psi maybe a vnt-17 modified to fit your engine wouldn't be a bad thing.  There are non-manifold integrated versions out there to be had that might be adapted to fit your set up.

[vwmike]

I'd second that. If all you want is quick spool and moderate boost pressure then a VNT is the way to go.

[jtanguay]

to learn more about Jake's VNT rabbit project go here:

http://vwdiesel.net/phpBB/viewtopic.php?t=1306&highlight=vnt+rabbit

its amazing information.  the 1.6 engine made boost at idle even!

check out Named Tintin's VNT controller... closes the vanes as you push the pedal, and a waste gate opens the vanes as the boost rises to the set psi.  pretty neat setup!

http://vwdiesel.net/phpBB/viewtopic.php?t=2848&postdays=0&postorder=asc&highlight=vnt&start=30

[jackbombay]

It would be very hard to fit 2 turbos between the engine and passenger side fender since the engine is pushed to the side a bit with teh side mount radiator set-up.

   I'd just run a VNT 17 or 20, the 20's can be had for a decent price new from KERMA, and hopefully you'd only need an adapter plate to make it mate-up to the stock exhaust mani.

[Turbinepowered]

Yeah, 20 or so PSI is all I'm after. Enough for it to be a good puller, but nothing insane or overly stressing either.

Go VNT you say? I suppose... I thought about it at first, but rigging up a vane controller looked to be bothersome, and I really don't want to add a computer to this thing (Well, I do, but that's a project for another day and time...). Unfortunately, I don't speak French, though TinTin's controller pictures look interesting enough. Have to see if he can explain it to me in English.

What's the difference, overall, between a 15, 17 and 20 VNT turbo? I'm looking for flow maps, but somehow I get the feeling they'll be more complicated because of the mobile vanes within...

[vwmike]

A turbine map would be more complex but the compressor still has a fixed aspect ratio so sizing really isn't anymore complicated. There are some compressor maps available on the garrett site but they should be used as a guidline as not all turbos have the same wheels. Typically they are tweaked by the manufacturer to better suit the specific application.

[jackbombay]

I've seen maps for 15s and 20s, but a map hasn't been released for the 17, I searched for a while...

[rabbid79]

If you have the turbo diesel exhaust manifold, I think the VNT-20 will bolt right up.  I don't think you'll need an adapter.
I wouldn't bother with the 15 or 17, since I've never seen any of them that have the same style exhaust flange that would be compatible with the factory TD exhaust manifold.

[Turbinepowered]

Well, I'll be searching for a new exhaust manifold for this engine anyway; the one that's on it is trashed. Looks like someone took a hammer to one end, big dent just past the #5 cylinder flange.  And it's nastily rusted, too; easier to replace than repair, I suppose.

Reading Jake's thread (And being so oh my god I wish I were here sooner the entire time), it seems like the VNT15 would almost be enough turbo for the boost and performance I want? Boost at idle is a really, really attractive prospect... instaspool!

The VNT has definitely taken forefront in my mind now over the compounds, even with the tales of control issues.

I'm guessing, from the fact that the VNT17 and 20 are bigger turbos, that I would lose some of this low end spooling only to gain more boost at higher RPMs, which would be awesome for power but not really necessary for what I want to do. Am I missing a benefit, or would the 15 really provide what I need even given an extra 4/10ths of a liter in displacement?

[vwmike]

Well, the VNT15 can't really even supply 20 psi reliably on the TDI. The 17 is a popular upgrade and you're going to pay more for it if you buy a used one. I'd consider the 20. As a side note, I would try a different method than Jake took to control that turbo. Not to knock him or anything but I think the wastegate eliminates some of the benefit of the VNT....just my opinion.

[rabbid79]

If you wanted to do something crazy, you could mount a VNT-15 (or 17) with the integrated manifold onto the first 4 cylinders of your 5-cylinder, and then fabricate and weld an extra bit of manifold from the 5th cylinder exhaust port into a hole in the VNT manifold.
BTW, I think the regular Audi turbo gas exhaust manifold is almost the same as the TD, but it has the flange for the Wastgate at the rear.  Perhaps this could be cut off and welded closed.  It might not even need to be cut off as long as it doesn't interfere with the vacuum pump on the end of the engine.

[vwmike]

I would use a block off plate rather than trying to weld up the cast iron manifold. One thing that crossed my mind was running the turbo with the integrated 4 cylinder manifold and plumbing the 5th cylinder in after the turbo. You'd lose some exhaust energy but you wouldn't need it to spool that tiny turbo either. On the other hand that may cause some rough running. Do you happen to know the firing order the 5 cylinder? I think something like that could work if used with a rotational firing order. Then again, why bother? I guess I'm just thinking out loud here.

[Turbinepowered]

1-2-4-5-3, Mike. I consulted the book of Bentley for the car it came out of.

I'd heard about the turbo gas manifolds fitting, and since those are easier to find than turbodiesel manifolds... I was just planning on getting a set of them and making them work. Later, when I have money... custom and tuned, PP style.

Which benefit do you think the wastegate eliminates? Really my goals are the same as Jake's were: driveability and a moderate power boost while broadening the torque band to include some of the lower levels. I'd like a cruiser, not a drag monster. It seemed the wastegate very neatly handled the spiky nature of some of his boost, for sure.

[745 turbogreasel]

I posted this long ago with video of an all mechanical controler.....

http://vwdiesel.net/phpBB/viewtopic.php?t=4555&highlight=

and there is a vid of the VNT control with the engine running here:
http://video.google.com/videoplay?docid=3448331191659563820