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I'm talking about the "independent twin scroll" function of the whole system...
Anyone who has messed with both the S4 and S5 turbo systems knows the turbos produce power differently.
The S5 has a smoother power delivery, because it spools quicker and more linear due to the independent twin scroll.
The S4 will lag a bit and then punch you in the gut when the boost hits around 4kRPM or a little bit after that.
This has nothing to do with boost creep.
I've ported S4 and S5 turbos before, and I've never had a problem with boost creep after porting the wastegate passages.
In fact, I ported the S5 turbo so well, it ended up producing only 5psi of boost with unmolested wastegate vacuum lines, even with no cats.
(We were able to get the boost to hit 10psi with an A'PEXi AVC-R afterwards.)
Oh, and this wasn't with the stock compressor section - it was running an H-trim compressor side.
The S5 turbo parts are not easy to acquire in the states.
In fact, there's a demand for those parts for those who know about it's advantages.
There's a bazillion S4 turbos parts available, and it's easier to stuff an external wastegate on them a whole lot easier.
In the end, you're doing the same thing - remove the independent twin scroll (well, the S4 never had it to begin with) and run an overpriced and oversized external wastegate which, IMO, is not necessary if you know how to port the stock wastegates efficiently.
In the end, I call this kinda project "showing off" just to document the resources you have on hand.
-Ted
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