bhodgkiss
Veteran Member
by the way the VB doesn't have a titanium compressor wheel, they're all aluminium on the Garrett range (from VNT 15 to 22 anyway). Titanium is just a myth.
All you need to ummm... "fit" a 17 comp wheel into a 15 housing is a brake hone. Make the inducer bore larger and Voila! you have a 15/17 hybrid! The 17 wheel fits right in there!
But just because it "fits" without interference does not mean it's ideal. You see the EXDUCER tip height on the 17 is smaller than on the 15. This is how the 17 compressor is rated for higher Pressure while maintaining the same "size" 49mm wheel. (you can't always go by the "wheel size"... sometimes the "smaller" turbo is actually an upgrade if you are only considering one dimension)
That leaves a gap of a couple mm between the compressor housing and wheel, inside, where you can't see it. You can't see this discrepancy just by looking at the turbo from the outside, and it is kind of tricky even for a skilled machinist to measure. But the wheel "fits" in there without interference, it's just not a tight fit that you need for a turbo to work like it should. The gap should be measured in thousanths of an inch, not mm. It will "work" but not as well as if it was done properly. So you are essentially getting 80% of what the upgrade should have been if it was a good match between wheel/housing.
The gap can be brought closer but that requires a bit more complicated machining that I doubt was done, especially at that low price. Especially considering the price is below that of the Garrett warehousing master distributor price for a stock vnt15.