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Discussion Starter · #1 ·
Many in the Veloster Turbo community have been curious about what downpipe size to run on the oem or stuffed turbos, and the benefits in power for the different sizes. Making this post to shed some light regarding this. This will be discussed specifically around the gen 1 Veloster Turbo on the turbine/hot side of the turbo but can apply to any other turbo setup as well. The measurements are close figures and not exact to keep things simple. Also the discussion is kept generalized for simplicity here although it is very dynamic in how things actually work in the real world. This is to help everyone have a good general understanding of what's going on.

First thing first the more flow out of the turbo into the downpipe the more power that can be made. Best flow occurs with the least restrictions between the turbine and the downpipe opening. The more exhaust that can go directly/straight into the downpipe with the least angle/turning the better flow will be and the more power that can be made.

Posting some pictures to make it easier on everyone reading. To keep it simple, the higher the overlap area is the more flow there can be through the turbine/hot side and thus more power can be made. The higher overlap value means a lesser area of lune 2 in the pic where exhaust has to exit the turbine and make turns before it can enter the downpipe.

Some have come to me saying that a 2.5" dp will make same power as a 3", or has no flow restriction on the turbo, or a 3" may make less power due to be larger than the oem turbo opening. All of this is due to the misinformation they have seen on the internet. I've seen the oem turbo equipped Veloster Turbo gain 3-5 whp going from 2.5" to 3"(even though the 3" tubing is larger than the turbo exit) when pushing the turbo hard in the mid to upper 200 whp area(Pic 3 to pic 4). Imagine the gains from the exhaust side with the stuffed turbo having the higher overlap area(due to larger turbine size combined with a 3" downpipe) and smaller lune 2 area for exhaust to have to exit and make turns before entering the downpipe. Then Imagine what a ported stuffed turbo will gain from the extra overlap created over the non-ported.

The oem turbo example gained 3-5 whp, in the area of 1-2%, from a 10% overlap area increase of going to a larger downpipe on the non-ported turbo housing. The ported stuffed turbo that Qwik Tyme Performance offers has a 15% overlap advantage over the regular stuffed turbos with larger turbine wheel when using the same 3" downpipe(which is best on any oem frame turbo).

Pic 1: illustration of lunes and overlap
Pic 2: oem frame turbo
Pic 3: oem turbo 2.5" downpipe
Pic 4: oem turbo 3" downpipe
Pic 5: stuffed turbo 2.5" downpipe
Pic 6: stuffed turbo 3" downpipe
Pic 7: stuffed turbo ported with 3" downpipe

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Lotta words for

Bigger Pipe = Better Flow = More Power

Seriously though, love that you're one of the few people who posts dedicated analysis like this outside of the big vendors. Never stop ❤
 

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2015 auto VT, 2013 manual VT × 2
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Discussion Starter · #3 ·
Lotta words for

Bigger Pipe = Better Flow = More Power

Seriously though, love that you're one of the few people who posts dedicated analysis like this outside of the big vendors. Never stop ❤
Saying that is the same as any other person or vendor can say which is no better than saying "this is better just because I said so". At that point it's purely a matter of who you trust and does not rely on any data whatsoever. This gives visual and much better explanation of what's going on and why. This is not well documented or documented at all by most vendors for many reasons.

The best any vendor has done on this was posting a video with both accurate and inaccurate information. Par for the course really. Sad for the community though.
 

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2015 auto VT, 2013 manual VT × 2
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Discussion Starter · #5 ·
How much of a lose is there using a catted downpipe? I imagine that would be a large restriction
Power loss or gain depends on every other mod on the car as well and the power made per given flow in a given ambient condition. It can only be said in general that some power will be lost due to a flow restriction.
 
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