The same as the ID of the mating surface at the turbo. This was done to accommodate high flow offerings such as the PS2's.
Questions about VTT Aluminum Outlet Testing Results
- Thread starter Rob@RBTurbo
- Start date
The same as the ID of the mating surface at the turbo. This was done to accommodate high flow offerings such as the PS2's.
Yeah our RB Next Gen Plus also has a CNC'd ported compressor housing outlet- which is increased to 1.2" from the OE 1.03". Just was curious as to what the actual diameter was on the adapter.
Thanks,
Rob
This looks like it goes onto the end of the compressor outlet onto the existing v-band feature. If so, it is after the "step" inside the compressor housing that Rob is talking about, isn't it?
Why would that be a better test when the whole point of an upgrade is an upgrade? When you buy an air intake that says 27 percent better flow you don't complain they didn't cut holes in the lid of stock box during comparison. He tested stock unmodified vs his with no games or trickery, he actually did the most straightforward thing he could have done.
Because 1.375" pipes the same length, same bends flow the same amount. It is impossible for for that VTT outlet to do what they claim, especially given the neck down to 2.125" at the merge vs the OEM 2.375" merge.
The turbo flange is 1.1". The OEM outlet has a machined flange that is port matched to 1.1" whereas the VTT flange is 1.4".
ROB isn't wrong in his statements...
Remove both ends and you'll see what the pipes will actually flow efficiently.
Spoiler Alert...
It's about 400 CFM before the air speed becomes turbulent resulting in pressure loss.
There is always going to be that demographic that will fall for shady vendor marketing, oh well as they say you can lead a horse to water but you can't make them drink.
So if his outlets were on stock turbo your saying would flow worse than stock. Then my question is if on gc turbos they would out flow stock?
You may want to thoroughly read this thread along with this one linked below (in particular post #78):
https://bmw.spoolstreet.com/threads/vtt.3368/
In summary the lack of transitional adapter will make no difference on any turbos available, including the Zage (1.0s) or new Zage Rip-Off (2.0s) housings as they all have tiny stock sized outlets which is the entire premise of the transitional adapter ideally remaining intact. Of course by removing the transitional adapter you can get more flow as a COMPONENT on a BENCH, to wow those who are none the wiser about technical matters over the internet... to sell otherwise poorly designed parts.
We'd suggest picking up the PSP pipe if you are looking for an aluminum outlet, as it is the only production aluminum offering that is an actual upgrade.
Rob
Forgive me as I'm not doing the math exactly but it's close enough to illustrate the point.
GC's are flowing 850CFM + to make 750whp. Do you know what velocity of the air traveling through those 2 tiny 1.375" pipes is?? it's over 500mph!! air becomes restrictive and turbulent at 300mph.
2.5" pipe has flow rate of 900 CFM before pressure drop losses associated with air speed/velocity occur, + -
2.5" will support 750whp with an internal flow area of 4.43 sq in. That's a short straight pipe, add length and bends and number decreases rapidly depending on the CLR and number of the bends.
Twin 1.375" pipes have a combined area of 2.97 sq in! add 2 90 degree bends on the rear pipe and 110 degree bend on the front pipe and you're looking at a couple of hundred CFM per pipe efficiently at 300mph. Primaries are the restrictive point in the stock outlet design 2.97sq in vs 4.43sq in.
Any outlet using 1.375" ID pipes will support 380-450bhp efficiently. That's just the math.. Altitude and air temp effect it but that's a good realistic range. Remember you have 2.97sq in flowing into 3.55 sq in and again into 4.43 sq in. The 3.55 is the 2.125" neck down on the VTT that doesn't exist on the OEM version.
If you are using 2.5"OD pipe at the merge ideally you want to flow match the primaries to that area as best you can taking into account losses associated with bends and the available space in the vehicle. A 2.97sq in starting point is missing the mark substantially at 550CFM before bends, Your primary starting point should have a combined area larger than the merge or in this case 4.43sq in. That's a 33% reduction in total area to start!!
Conversely using 1.875"ID primaries have a combined area of 5.52sq in which will flow about 1000CFM +- as a starting point before bend losses.
So.... twin 2" pipes will outflow twin 1.5" pipes by 81% +-
Tell me how a 1.5" pipe will outflow a 1.5" pipe by 63%?
Given the front bend has a lower CLR on the VTT than the OEM there is a benefit there but it's in single digits and once you surpass the CFM capabilities of that 2.25" neck down which is 740CFM you lose those benefits and quickly.
So to answer your question... An OEM outlet with the ends removed and mated to a set of GC's with silicone would outperform the VTT outlet made by them for GC's at their rated power of 750whp.
Both of which are substantially undersized for that power rating.
Just asking not stating but does high temps alter flow at all. Also their silicone outlets dont have these issues correct? How would your outlets compare to silocone flow wise i know they are way more reliable?
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