OK, so posts 46 and 48 convinced me to go with the Borg Warner (although I was already leaning in that direction). My goals were quick spool, usable low end pull, no smoke, good MPG. I could have almost gone with a new GT1749V/VNT15, but the newer design of the BV39 and the ability to run slightly more boost for just a little more won me over.
Got the turbo, outlet adapter, return hose, new bracket, gaskets and nuts for install. All shipped to my door for under $1000.
I wanted to share a little bit more info. Most of this will pertain to the S7 also as they leave the factory in Hungary as the same part number 54399880083.
Here is the BV39 side by side with the VNT15
Here is the intake side
And here is the hot side
You will note that the turbo is physically the same size as the VNT15 despite comparisons to the VNT17. In fact although the compressor wheel is documented as slightly larger than the VNT15, I found the ID of the inlet and outlet to the compressor to actually be smaller on the BV39. The intake side is necked down inside like a venturi, probably to accelerate the air into the compressor. That does strike me a a bit restrictive though.
Fit and finish was good, no installation problems other than the cold day and the slow old man installing it.
I had done a stage 2 Malone tune back in September. The first version was kind of laggy, hit like a ton of bricks at 2000, but had way too much smoke at spool up and was prone to momentary boost spikes in the mid 20's. We fiddled around with actuator adjustment some. Got boost real steady on original tune but still too spiky and smokey on the tuned file. So, I thought it was a tune problem. Mark kept at it until I was happy with it, but it was still not as smooth as I would have hoped.
Went for a drive with the new turbo and it was very smooth and had no spike at all. First thing I did was reload the first stage 2 tune, the one that left an embarrassing cloud of black smoke and had alarming boost spikes. No smoke and no spikes over 20 with the BV39, just smooth to the requested and stays there. This is exactly what ANut describes in post 46. Less smoke means more air, despite the small size.
So, initial impressions are quite good for what I was looking for. Something with better tech than the 15 but with no lag. Someone has said before that this is what the car should have come with, and it does have that feel like it just belongs.
I will probably lower the IQ until I find the lowest with acceptable smoke. Then I will do some boost logs and make sure the adjustments are good. Then maybe go to a 3 bar map and stage 4 tune, but only if it is consistent with my goals.
