TurboXS Dump Pipe and Recode Tuning for Golf R

[Corey_R]

Thanks Tim, that's a great shot. It shows perfectly the turbo opening and the waste gate opening, and hopefully displays why the concept of a divorced downpipe exists.

I'll leave it to the engineers to argue about which is better, but you can clearly see that the "red marked areas" drawn onto the pictures above are not representative of how the turbo lines up to the downpipe.

[Tim]

yeah exhaust gas flow can get pretty technical.
Are there any better pics of the APR setup? It does appear that there is only a very small elliptical opening for the main exhaust gas pipe and that preference is given to the wastegate side of the turbo exit? Im thinking that maybe the black area in the picture above might not show the full story? Always interested to learn some of the theory involved.

[zbeasty]

Haha WTF is with that? Seems like half of it is blocked up!

They have to drop the front subframe to do the DP yeah?

No need to drop the subframe just remove the tailshaft.

[Corey_R]

yeah exhaust gas flow can get pretty technical.
Are there any better pics of the APR setup? It does appear that there is only a very small elliptical opening for the main exhaust gas pipe and that preference is given to the wastegate side of the turbo exit? Im thinking that maybe the black area in the picture above might not show the full story? Always interested to learn some of the theory involved.

Yeah, exhaust flow is certainly WAY beyond my mathematical and physics skills. Just mentioning the topic to the old kart builder behind me has sent him raving about completely being able to dramatically change the torque and HP characterists of an engine by changing the size and shape of the plenum in their exhausts etc.


The photos above aren't too bad, apart from the APR already being soiled by exhaust deposits. The exhaust opening is elliptical, but it has the metal protrusion (seen best in the first two photos) which goes into the turbo's "mouth" to "guide" the exhaust flow from the turbo into the downpipe as early as possible.

The APR exhaust show is specifically for the VW K04.
If you swap to the Garret GT2781R in a Stage 3 kit for example, the divorced design changes to this:


But then that's cause the physical turbo and the placement of the wastegate etc is different.


There was some really good "essays" on this topic in some Subaru forums a few years back, as "divorced vs bellmouth" is also a differentiator between several of the WRX/STI aftermarket designs, but I can't find it right now. Maybe there is some other article about the thoughts behind both designs.

[zbeasty]

yeah exhaust gas flow can get pretty technical.
Are there any better pics of the APR setup? It does appear that there is only a very small elliptical opening for the main exhaust gas pipe and that preference is given to the wastegate side of the turbo exit? Im thinking that maybe the black area in the picture above might not show the full story? Always interested to learn some of the theory involved.

You are correct Tim, there is only the elliptical opening for the main exhaust gas to flow through. The black part between the 2 openings is flat and does not open to anywhere. There is no effective way on the K04 to separate the flow from the turbine and wastegate without compromising the flow of one or the other. In this case the main outlet size is reduced. That is why the red cirle is there on the front on shot. Not only is the opening reduced in size, because the pipe on the other side hasn't been shaped to fit the flow out the other side will just tumble out creating turbulence which will further inhibit flow. You can see the reduction in efficiency in the dyno charts where the APR pipe drops of rapidly after making peak power whereas the TXS one holds power to change up.

TXS have 2 hand made units and have just received their production units. If you're interested give them a call.

[Tim]

Thanks for clearing that up. I was having trouble making out the detail in the photo. The GT28 setup looks very different

[zbeasty]

Thanks for clearing that up. I was having trouble making out the detail in the photo. The GT28 setup looks very different

Sorry, not the best camera or lighting. Yes the divorced wastegate pipe can work on some turbo's like the GT28 but on the K04 the compromise on ultimate flow outweighs the gains from the separation.

[Lazarus7]

Anyone got a pic of the Milltek one for comparison? I've had a search around but can't seen to find one

[Corey_R]

The reason you can't find a picture of the Milltek down pipe is that they don't sell it individually. You need to buy the entire TBE.

You get better results searching for "Audi S3" though, since the DP portion is the same. The new part on the Milltek R exhaust is the catback section, so no one seems to care about taking photos of anything other than the rear muffler and black tips!


Note, this is a catless verison.

[CarbonVW]

An interesting video on the subject. Obviously, every turbo is designed differently and turbulent flow may not be as pronounced compared to other turbo designs.

[Lazarus7]

Great vid, thanks mate.

Interesting the part about the splitter, makes me wonder about the effectiveness of the APR design. However as stated above the type of turbo and its turbulence characteristics will play a fair part in how well or otherwise a design is.

[fuzion]

With all this talk of downpipes. Recently have seen 3 downpipes made for golf r from Liverpool exhausts who have extensive experience in exhaust making even though the name is a deterrent. The quality and design was top marks.

Cost wise was considerably less than most branded ones out there.

Funnily enough on my mk4 which had a custom made downpipe (elsewhere made locally) made more power than any other mk4 with same mods.

Not raining on the parade as I do have a milltek but the turboxs or other custom could and will do the same as a branded one as they also have experience. And let's be honest. They all somewhat copy one another somehow due to it's a simple design as such.

[Fab_R]

Very interesting this thread....

I seem to remember APR before releasing their unit conducted tests using both designs, and found the divorced set up superior.?

[Corey_R]

This is a image of the Borg KKK K04 64 which is what is in our Golf R's and Audi S3's etc.




This was the best image I could find which actually shows the turbine outlet and internal wastegate flapper valve in the turbo.
You can see clearly see from this picture that the APR downpipe's exhaust opening should not cause a restriction as it's still larger than the turbine outlet. You can also see that there is still room to "split" the two outlets effectively.

CarbonVW posted a video from MRT Performance who are a well respected local Subaru and Mitsubishi specialists. In fact, they often compete with (against?) APR in MOTOR Magazine round-ups. This is what they had to say in their video in relation to what they feel is an often overlooked aspect of improving throttle response with aftermarket exhausts, discussing the difference between divorced, split bellmouths, and bellmouth exhausts.

What you need to do is have a splitter plate which directs into the back of the turbo to keep the wastegate outlet and turbo outlet separate because the aim is to when the wastegate comes on boost you want the exhaust gases coming out of the wastegate to go through in the same direction as what the exhaust outlet is going so that when the two flows of gas merge together in the same direction and then go down out through the exhaust. If you don't have this plate here then what happens is when it comes on boost, the exhaust gases come across the back of the turbo outlet and obviously form a high pressure zone which causes a little bit of lag because of course that's where all the gases are coming out of the main stream of the exhaust outlet on the back of the turbine housing itself. But if it's going down that hole there, then obviously you've got two effective areas for the two lots of gases to follow one direction and then merge correctly in a short path down here. Now it doesn't need to be a pipe on its own separately. Those exhausts systems with two separate pipes have no mechanical advantage at all, they just look good, because effectively they don't have the splitter...."

Now obviously, the APR exhaust is a divorced downpipe, but importantly (in MRT's opinion) it also has the splitter.


Anyway, I'm not a fluid dynamics engineer so I'm in really no position to say whether one is better than the other. I just thought we needed to see a clearer picture of what is actually in the turbine housing of the K04 Turbo we've all got, so you can actually see the turbine outlet and the wastegate outlet, and thought that the explanation from MRT on the purpose of the splitter was rather interesting.

[Lazarus7]

Oops missed the splitter on the APR one...well perhaps it is the goods. Nice pictures there Corey, quite helpful.