As heading really, whats the differences, other than physical, between the two. One big pipe with the little one fedding in or just the wide open necked pipe.

cheers

 

EddScott,
Can`t believe you`ve asked that question , it was something I was asking myself earlier this morning as i`m looking for one!!! Very interested to know the outcome if anyone can help???

Ross.

 

if the wastegate feeds in a couple of feet down (i guess this is what you mean anyway) there won't be so much turbulence near the turbo and gas should exit faster, meaning faster spool up.

what you really want is an F40-stylee separate screamer pipe

 

Somebody did mention that with the twin dump downpipe, that when the wastegate valve opens it partially blocks off the inlet to the smaller downpipe tube.

From looking at mine, I can see their point. Although both types of downpipe still seem to have pretty good power gains.

 

Andy F's recent WRX project found very little difference, if any, between the two designs. He even tried a splitter to improve the wastegate flow, but any gains, were at best, marginal.

 

So what would the difference be between the two designs of downpipe in question, and the circular neck design that blocks the wastegate, such as on the Megan downpipes?

 

For thoughts:

I have a well tweeked Sti v3 currently @ 407 bhp x 340 lbft.
When i rebuilt the externals on the stock engine for the above, I had a sports 3'' CAT d/p with a dual tube design. The turbo is a TD05 20g from AndyF.
The car was quick (!) and ran great, even passed the MoT nearly as well on immissions as the wife's Yaris.
For the rolling road run, I re fitted my old design Magnex 3'' decat. The turbo collector is an open neck design, though not in the current Very Open neck designs on the market today.
I can say there felt no difference for the change between the two, nothing i could notice at all on the road and the track ( I race the car in hill climbs).

AndyF is someone to listen to with the greatest of respect, and if he could find little difference then that is the answer for me.

When the engine is at full chat, boost rises and needs to be dumped on command of the ecu, the valve is opened and the excess gasses shoot into the mainstream of the turbo exhaust flow (also moving very fast). I personally do not see how the wastegate gasses can seriously disrupt the mainstream to a significant effect in the relatively short time all this takes place. When the pressure is 'off' and the waste gate closes, the turbo is probably on the brink of reaching peak boost again in no time if the throttle position is still wide open.

I guess you could separate the main outlet from the wastegate (done essentially by the popular 'splitter' design) and lead a smaller pipe off the wastegate side to under the car well downstream, ie by the gearbox, so there is zero interference in the 2 gas streams.(?)
This is essentially the turbo type where the waste gate is separate to the turbo, and the w/g is piped off independant to the d/p.

Graham.

 

I run a 3" closed neck which has no problems making 350+bhp.

Was a little unsure before it was all fitted because of the hype of open-neck d/ps but have no reservations now

Bob

 

I would tend to think the other way , the wastegate open`s because the turbo is getting too efficent, to reduce boost, therefore if the gate also interupts flow / creates turbulance, wouldn`t it assist the gate in it`s job ?
Have a goood one
Tim
PS my bro`s got seperate full length gate ex pipe on a vw20vt (ext gate) sounds errrrrr not very sweet :-)

 

IN OUR TURBOS THE WASTEGATE OPENS ONLY BY 30% WITCH MEANS THE GASES FROM WASTEGATE CREATE TURBULANCE IN MAIN TURBO EXIT!

 

JIM , 30% of what ? yes it create`s turbulance but what diference does it make ?

Cant be to spool time as the gate does not open till the turbo has spooled up to create the boost to open it, to create turbulance ?

Have a good one
Tim

 

That was my point too.
With the turbo fully delivering the gas flow from the turbine will be 'full', then the small in comparison flap cracks open and reduces the boost level, but for a short time.

I really wonder if Open/Dual and those in between /splitter make any real difference at all except re invent the Marketing wheel.(?)

Too harsh?

Graham.

 

Graham.[/QUOTE
I really wonder if Open/Dual and those in between /splitter make any real difference at all except re invent the Marketing wheel.(?)

Too harsh?

Graham.[/QUOTE]

Think you have it about spot on there, must admit the single pipe does look nicer than my dual one, but there again it would :-) grass is always greener and all that, more welding on the single so it may crack a little more,

On a diferent note, been changing my 1 box japanese whoever, exhaust cause it scares old people and makes small childen ask their dad "why do you have to drive a vauxhall " (my mate`s kid :-) it was 2 1/2, straight through large box with perferated pipe, no packing, into a 3 1/2 out, very loud, fitted a center section with a small silencer box , no power diference very small decrease in noise, fitted a prodrive rear yesterday , very quiet but lost a lot of power, moved spool up by approx 500 rpm and it sounds like it`s trying to strangle the thing over 6500, any suggestions on s/h free flowing quiet exhaust`s ?
Have a good one
Tim

 

Quiet was discussed here Tim:

http://bbs.scoobynet.co.uk/showthread.php?t=434577

 

I mean wastegate opens by a small amount of 30 degrees against other brand turbos that open even 90 degrees!

 

I should try this