Is there any REAL advantage to a dual split downpipe?

[supradjza80]

Tissimo - please explain how black soot on the wastegate inlet pipe of the DDP explains that there is turbulence there, you do realize that the dump pipe on a DDP is a much larger diameter than the wastegate hole in the turbo, Right?...I don't beleive you have made a single valid point other then DDPs DO cause creep with the stock size wastegate of the CT26. IF you port it though you can get rid of it.

 

[supradjza80]

you're still not factoring in flow capacity the non-recirculating ddp has flow capacity equivalent to a 4" exhaust ... where as a 3" dp has the well..... you're not an idiot, right?

I think you need to redo your math. One 3" pipe and one 1 or 1.5" pipe does not = One 4" pipe.

 

[carter]

To be truthful I'm kinda glad this discussion came back up, because me and another guy was talkin about this. He's a big Dsm'er and was just tryin to tell me to go with a regular 3" dp instead of using a bic DDP. But then again don't the evo's use a divorced elbow? He claimed it would creep downward as you move to redline. But all in all, from what I remember seeing about the bic ddp, it flows better, less turbulence having the wastegate gasses separated into its own pipe.

But the question I do have, is about there re routed ddp, does anyone have a dyno sheet of this vs a standard 3" Dp?

 

[GrimJack]

But the question I do have, is about there re routed ddp, does anyone have a dyno sheet of this vs a standard 3" Dp?

This has never been done, as far as I am aware. When Randy was doing the initial testing, he hadn't started making re-routed versions yet.

 

[hvyman]

for them dsm comments i would like to see what the ddp on a dsm looks like.

edit: ive read threw 3min of stupid posts on other car forums from google and either they are stupid or smart but none have back to back dyno comparisons on the same car.

 

[TurboStreetCar]

The higher boost is caused by a difference in pressure ratio across the turbine wheel with a less restrictive exhaust system. As far as I'm concerned I don't care how much the boost changes, it's a result of downpipe change not a change to wastegate of any sort.

 

[carter]

here is a picture of the divorced elbow i was talkin about.

And yea I could see that GrimJack, I just didn't kno if someone did dynod and comnpared to normal 3" dps

 

[TurboStreetCar]

^ Would that even really be considered divorced? Its more like a collector.

 

[mecevans]

would a regular DP benefit from a thin divider of some sort in between? would this help with this turbulence?

 

[Poodles]

Yep, been done.

 

[tissimo]

At most there "might" be 5>10 rwhp in it....:nono:

Well within the error margin on most dynos and operators.

Not sure your intent on this post(mocking, or agreeing). I agree there isn't that much to be gained with smoothing the turbulence behind the turbine. Money can be spent else where that would be far more effective. Essentially you're paying for the sound.

Tissimo - please explain how black soot on the wastegate inlet pipe of the DDP explains that there is turbulence there, you do realize that the dump pipe on a DDP is a much larger diameter than the wastegate hole in the turbo, Right?...I don't beleive you have made a single valid point other then DDPs DO cause creep with the stock size wastegate of the CT26. IF you port it though you can get rid of it.

Undirected flow. Instead of going through the wastegate pipe directly (similar to the turbine section) its flowing all around the space made between the wastegate and the wastegate tube (where the divider piece is cutting up), causing the soot to settle on the flange. This high pressure area (back pressure) caused by the undirected flow causing more gases to flow into the turbine causing more boost (boost creep).

 

[kcheng]

Not sure your intent on this post(mocking, or agreeing). I agree there isn't that much to be gained with smoothing the turbulence behind the turbine. Money can be spent else where that would be far more effective. Essentially you're paying for the sound.


Undirected flow. Instead of going through the wastegate pipe directly (similar to the turbine section) its flowing all around the space made between the wastegate and the wastegate tube (where the divider piece is cutting up), causing the soot to settle on the flange. This high pressure area (back pressure) caused by the undirected flow causing more gases to flow into the turbine causing more boost (boost creep).

there is boost creep with a regular downpipe so please explain that as well while you are at it.
old turbos worn out wastegate that cant control boost well does not surprise me.
so tell me why my car with a ddp doesnt have any boost creep? thanks.

 

[IJ.]

Not sure your intent on this post(mocking, or agreeing). I agree there isn't that much to be gained with smoothing the turbulence behind the turbine. Money can be spent else where that would be far more effective. Essentially you're paying for the sound.


Undirected flow. Instead of going through the wastegate pipe directly (similar to the turbine section) its flowing all around the space made between the wastegate and the wastegate tube (where the divider piece is cutting up), causing the soot to settle on the flange. This high pressure area (back pressure) caused by the undirected flow causing more gases to flow into the turbine causing more boost (boost creep).

My "Intent" is that people are getting wound up over something that in most cases can't be measured on a conventional chassis dyno with any degree of accuracy so the entire thread is worthless and a waste of bandwidth....

 

[nctexan]

Why not throw a DDP and traditional DP into some CFD software and give it a whirl.

 

[7M-KDL]

i have seen a ct turbine housing that was already divided. im not sure where it was but that would completely get rid of the turbulence and you could use the ebay ddp without modifying it. i have a BIC(on the way) so that doesnt apply to me but perhaps that is why some of the ddp are made without the divider plate. ill try to find a picture or maybe someone else knows what im talking about.


oops, sorry, its not a ct, its the t61 by CXRacing. for those who dont know, its a bolt on replacement which uses the same dp as stock. it could also use the cheaper ddp without the divider plate.

 

[nctexan]

Ok basic question here, can a DDP be utilized on a sequential twin turbo setup? (Stock 1JZGTE)

 

[Poodles]

It could be built, yes. Space is the main concern though and I don't know on anyone that makes one.

 

[Evilempire1.3JZ-GTE]

There is so much bad information here about back pressure and exhaust dynamics.

First of all if you have a crappy little honda and bolt on a 4-5" exhaust you will not gain HP but loose HP
This reason is not because of the lack of back pressure it is because exhaust piping is like a piece for a musical instrument it haves to be in tune with the engine performance.

If the exhaust is too large there is more turbulences & the gases cool off from too little flow causing the air to get denser making the engine have to work harder to push them out.

So the ideal exhaust would just be long enough to safely let the exhaust out of the car the shortest distance but not so short that the valves get hit by cold air.

Now NA engines need a little back pressure as in the real term for "Back pressure" turbos need no back pressure at all and work best with none at all.

As far as divorced downpipes yes you will get way better performance out of a divorced / external wastegate engine setup then a recirculated/single exhaust.

Cheap bay items are fine its just exhaust you only pay about $120 for the piece a simular US model piece will cost about 10x that and america can not even compete because the raw materials alone could pass the china units up.
So if you buy a china unit and correct any minore imperfections if any like slag welds alignment / ceramic coat it then when you adjust anything to your liking then yea you end up still with a better deal still.

Hell just to make custom flang cut with laser or waterjet will set you back 100+ so its a good deal.

 

[Poodles]

:3d_frown:

Back pressure doesn't exist in any way, shape, or form. It's velocity and the scavenging effect it has that pulls the exhaust out of the cylinders at specific flow levels. As such, yes, it's like a musical instrument and is "tuned."