Dump Pipe Question

[RAP1D]

Forget the maths, there's alot more to designing a good performing exhaust than just working out the cross section size of a pipe.

Dump pipe design, myths and old wives tales have been around for decades, nothings changed for our car, other than using bigger pipes.

For best flow down a dump pipe (front pipe), the wastegate gasses should be kept out of the dump pipe for as long as practical - usually down towards the last bend is a good transision.

The reason for this is the way air exits the turbine, enters the dump, and flows through the dump- its rotating down as it spins out of the turbine, moving very fast, alot faster than gasses exiting an NA header/extractor.

So, you've got rotating air flowing down, and straight flowing gas from the wastegate port... where the gasses from the wastegate port enter this main stream will affect the speed of the air travelling, slower gasses mean slowing (restricting) turbine speed, effecting spool up, spool down. You could say this causes lag, but I dont like to use "lag" as a term, due to the many other factors that can contribe to a turbos responce.

Now looking at this from an XR6T point of view, lets look at the factory dump pipe.

First up, the rear of the turbo, the turbine housing has a main 3inch opening and a wastegate opening of 25mm (? I havnt accually measure it, but the wastegate modders can correct me here... ).

The stock dump has a large opening that encases the whole face of the turbo, so the main gasses and wastegate gasses just blow straight out into a common area, then it collects into a 3inch pipe, running down into the factory cat, and that's your stock dump... not a bad design when compared to the shockers that come on other turbo cars.

So, how do we improve on that? Bigger pipe is a starting point, this will flow more air, make more power, easy.

You could use a 3inch pipe off the turbo flange, and a separate smaller pipe for the wastegate, this will give us the benefits of channeling the wastegate gasses out and nerghing them much further down the stream, resulting is (predicted) better turbo responce, but no improvent in flow volume, so power may not be improved.

Then thers the 4inch dump, which is a 4inch pipe, bent, hammered, and made into an oval type shape to join up the turbine and cover both openings (main 3inch and wasgetae port).

This is basically the same as the factory dump, but where the factory dump merges into a 3inch pipe, this one remains 4inch all the way down, so theres a much greater diameter pipe, allowing greater flow volume.

But again, with this style of dump we have the wastegate issue, where gasses are combined right out of the turbo, so a slowing of gasses will happen, and the natuaral spiral effect of the turbines gasses will be reduced, so turbo responce will be reduced, causing slowed spool up/down.

There are some very intricate dump pipe designs made, mainly one off custom jobs, that combine the benifits for the larger flowing pipe size, with separate wastegate pipes merging down near the end of the dump. But for most, choose one of the off the shelf dumps that suits you best.

[GR8XR6]

Chris,

Is this another item you are looking at doing with your exhausts?? Please do tell what are your plans and what do we have to look forward to. Are you designing a better dump pipe? Are you designing the whole exhaust system? What can we expect from you and I am hoping it will be soon!

Cheers

[RAP1D]

Yeah, Im working on various exhaust solutions to suit a few different budgets and power requirments.

Im testing out a full system at the moment, playing with different mufflers, and cat positioning.

[BAD APPLE]

The reasoning behind using a split dump pipe design is relatively simple, when the wastegate flap opens it bypasses exhaust gases under pressure into the dump pipe directly behind the exhaust turbine inturn creating a high pressure area where you really want a low pressure area to exist. So by using a split dump pipe design high pressure exhaust can be kept as far away from the turbine housing as possible and relieve exhaust back pressure at that point helping mid range power and torque. Not really sure that this will be of noticable benefit on an engine such as the XR6T that creates so much mid range power and torque.

Just my two cents.

[GR8XR6]

Yeah, Im working on various exhaust solutions to suit a few different budgets and power requirments.

Im testing out a full system at the moment, playing with different mufflers, and cat positioning.

Looking forward to it!

[F6_jase]

3 1/2" dump pipe + 2" wastegate pipe = snappier throttle response ( comes onto boost quicker). made a big difference in my FG

[RAP1D]

Looks spot on mate.

[jet_paul]

Turbulence.

I've spoken to a tuner or two who likes the split dumps for the sub 400 region. I spoke to a bloke from QLD who said he went from a 4inch to split and ended up making more power. My friend at pro flow also prefers split dump pipes. Everyone has an opinion...

*actual results may vary

Whose your mate at pro flow?

George?

[straughsberry]

The reasoning behind using a split dump pipe design is relatively simple, when the wastegate flap opens it bypasses exhaust gases under pressure into the dump pipe directly behind the exhaust turbine inturn creating a high pressure area where you really want a low pressure area to exist. So by using a split dump pipe design high pressure exhaust can be kept as far away from the turbine housing as possible and relieve exhaust back pressure at that point helping mid range power and torque. Not really sure that this will be of noticable benefit on an engine such as the XR6T that creates so much mid range power and torque.

Just my two cents.

What car you driving dude?

[straughsberry]

Whose your mate at pro flow?

George?

Yeah Georgy boy. We train together on the odd occasion. You got that yellow T man?