Piper Exhausts turbo downpipe development thread

[surfboardfiller]

You missed the point entirely that the deflector was for a smaller bore pipe and mixing flows is less of a problem with the piper pipe because the bore is bigger, comparing it to the original part is pointless because of this.

You don't get 'violent turbulation' in exhaust gas through a pipe, you get flow separation - The gas can only go in the direction of the pipe as it is the only way out
Any flow from the turbine will cause a lower pressure which will suck the air through the waste gate until both flows are equal speed and therefore equal pressure - this is called venturi effect
Flow from the waste gate is the path of least resistance, giving another physical force in favour of waste gate flow - shortest route & without the turbine
When the waste gate opens it reduces the flow of the turbine it doesn't add any more gas to the equation - both ports a supplied by the same gas flow from the exhaust manifold, it splits the flow and then rejoins

You say the Knoxx pipe is better have you fitted it?

I wrote: If you have problems with over boost then your turbo may need rebuilding if you still have problems then you may want to fit a boost controller but there are cars running with this pipe without problems.
And you said: Ah! So i fixed a bad turbo in it's early state by adapting my downpipe?

I would welcome some reliable data from you but sometimes I don't know what to believe.

Maybe you have "cured" the problem by restricting the flow from the turbine, which you could have done by just leaving the old down pipe on and not buying an upgrade!

[ccb056]

[In my opinion] The Piper design restricts flow through the turbine because the entry angle of the wastegate flow creates excessive backpressure.
All HJ did was improve the entry angle of the wastegate flow to reduce the backpressure caused by the wastegate flow.
HJ effectively balanced two tradeoffs and came out ahead. By improving the wastegate flow he did add some backpressure the the turbine flow, however the net effect was positive and resulted in less overall backpressure.


Introducing turbulent flow into the downpipe via the Piper design is very detrimental to backpressure.
Introducing a deflector is a little detrimental to backpressure, but [I believe] your losses are more than made up because the wastegate flow enters the downpipe more optimally and you don't suffer the loss described above.

[ashm]

Ok, question for those who have installed the downpipe.
How did you tighten the bolt on the lower front turbo/downpipe stud? It's in a recess in the downpipe, and there's too small a gap between the nut and radiator to fit a normal spanner in there.
Do I need some sort of cranked spanner? Crows foot maybe?
Thanks,
Adam

Is this sorted now? Do you have air con?

Yep, sorted. No air con. I shortened the stud a little, and got an obstruction spanner this sort of shape.
I then had to spend some time at the bench grinder, thinning down the spanner ring until I could use it to tighten the nut. Works perfectly once you have a tool the right shape!
Adam

[surfboardfiller]

Good job Adam!

[surfboardfiller]

The Piper design restricts flow through the turbine because the entry angle of the wastegate flow creates excessive backpressure.
All HJ did was improve the entry angle of the wastegate flow to reduce the backpressure caused by the wastegate flow.
HJ effectively balanced two tradeoffs and came out ahead. By improving the wastegate flow he did add some backpressure the the turbine flow, however the net effect was positive and resulted in less overall backpressure.


Introducing turbulent flow into the downpipe via the Piper design is very detrimental to backpressure.
Introducing a deflector is a little detrimental to back pressure, but your losses are more than made up because the waste gate flow enters the downpipe more optimally and you don't suffer the loss described above.

The flow through the turbine cannot be restricted by the waste gate, its too small for the size of pipe it feeds and if it did restrict the turbine there would be no boost creep, the waste gate is supposed to reduce flow through the turbine, that's its only function when it fails to do that there is boost creep.

Waste gate flow cannot cause back pressure it dumps it.

The waste gate doesn't add more gas to the down pipe it just bypasses the turbine, there isnt more gas going to the exhaust pipe there is less from the turbine.

Restricting flow isn't the solution, that was the problem the old system.
Restricting flow of the waste gate - will give you boost creep.
Restricting flow of the turbine - will reduce performance.

He has stopped boost creep by reducing performance, I could do that by taking out the mountain chip or putting back the old down pipe.

[surfboardfiller]

The problem here is with boost creep; too much gas is still going through the turbine even though the waste gate is open, if you have more back pressure you don't get boost creep, it reduces the turbine speed/boost that is what HJ has done with his modification. The piper down pipe is too free flowing for HJ's car.

An external waste gate makes the car illegal and is not worth considering for that reason. It's pointless going back to the same argument when you don't have a down pipe fitted, your opinion is of no use.

Theory is fine to a point but we are at the point when the reality is what's important.
__________________________________________________________________________________________________________

We have cars that are absolutely fine with the down pipe and we have cars that are not? At least 1 so it would be helpful to take stock of what is on HJ's car that isn't part of the standard system?

Size of exhaust pipe, piper?
Chip?
Waste gate port mm?
Standard impeller/hybrid?
Other ECU mods?
Injector?
Boost controller?
Map sensor?

[HJ2]

Restricting flow isn't the solution, that was the problem the old system.
Restricting flow of the waste gate - will give you boost creep.
Restricting flow of the turbine - will reduce performance.

He has stopped boost creep by reducing performance, I could do that by taking out the mountain chip or putting back the old down pipe.

This keeps being an interesting and on-going discussion! (insert Facebook 'Like' symbol here)

1. The area of the core flow of my modified piper at the location where i placed the deflector is still bigger than the OEM pipe + pre-cat housing (= improvement, mainly by faster spooling times, NOT max power
2. The bends of my piper do have less sharp bends than he OEM stuff (=improvement again)
3. The Piper eliminates one gigantic step up / step down in Diameter, namely by eliminating the pre cat cavity. (=improvement over OEM again, my pre-cat housing was empty anyway )
4. with the original PIPER design, the flow of the wastegate is injected at a 90 degree angle into the core flow. Because of the venturi effect you described, velocity of the gasses leaving through the porthole is high. So a high flow, injected angular into another flow, gives turbulence as far as my knowledge goes anyway. You are absolutely right, the total flow does not change, but only the distribution changes. By adding the deflector, the angle at which the 2 flows intermix is flattened, reducing turbulence and increasing flow throug the wastegate. You could say the wastegate flow stalled a little before this addition, with the same result as a to small wastegate porthole. Boostcreep!

Unfortunately i do not have the knox downpipe, so no i have to admit i did not test it. However i know that the design took care of the injection of 2 flows with different speeds. (because you can see it )

However i did buy, perfection internal finishing, tested, modified and drive the modified piper, and i love it.
If you are not sure that this is a performance gain, then you could still use it as access to the radiator & stuff from below is so much easier


I just try to share MY experience so far, as well as explaining MY philosophy why i did certain modifications, not to start a little war here!
I would prefer to combine our knowledge over a couple of beers and discuss improvements together

Meanwhile i will install another Piper With my modification on Peter's car. No way of telling if there i a performance gain where it came from. Ditching the pre-cat or using the piper, and frankly i don't have the money to spend on an in-between dyno.
In the end the turbo can only run @ 0.98 bar @ my setup. (injector limitations..) So the performance gain with my setup is only at noticeable faster spooling times

Last but not least: Due to the language barrier, my text can be a bit harsh sometimes. I can assure you this is caused by my own not so perfect translation. Fine nuances get lost unfortunately and things get more black and white than i would like. Well, keep practicing here is my remedy


***
EDIT: and i do appreciate other people's opinions even it's just theory!

My setup:
1. S2, closed loop
2. Switcher (mainly Everest)
3. Stock turbo in excellent condition, 21.5 mm wastegate port
4. New OEM exhaust manifold
5. reconditioned head + new OEM gasket
6. MY piper (internally flowed and deflector added)
7. 1'st bend is Piper as well (2.25")
8. After 1st bend it is all PECO
9. Stock intercooler + pipes
10. new timing belt + the lot
11. Stock but ultrasonically cleaned injectors
12 All sensors replaced but MAP sensor (so stock)

Did i forget something, Surfboardfiller?

[LotusEnthusiast]

My set up:
Federal- closed loop
Mountain chip- Everest
Stock turbo in good condition. Wastegate is NOT ported
Piper Exhaust 2.25
The rest is stock besides injectors which are the NGK iridium plugs. (Not sure what number)

I have boost creep but hopefully when I port the wastegate to 21mm it will go away, right? I was looking to buy a piper downpipe but since it might not do anything to the performance I'd rather just port the wastegate to eliminate boost creep. All in all my set up is very good, and I love my car! It is much better than stock. Just need to solve boost creep.

[HJ2]

My set up:
Federal- closed loop
Mountain chip- Everest
Stock turbo in good condition. Wastegate is NOT ported
Piper Exhaust 2.25
The rest is stock besides injectors which are the NGK iridium plugs. (Not sure what number)

I have boost creep but hopefully when I port the wastegate to 21mm it will go away, right? I was looking to buy a piper downpipe but since it might not do anything to the performance I'd rather just port the wastegate to eliminate boost creep. All in all my set up is very good, and I love my car! It is much better than stock. Just need to solve boost creep.

Then porting is the way foreward. However, when everything is out anyway ....

[ccb056]

You may be able to go from your 21.5 to 22mm, anything past that may be impossible with the turbo housing.
If you're getting boost creep and you still have room to port the wastegate, you should port the wastegate.

[3 references to theoretical articles removed as irrellevant to THIS thread]

If you do the research, you'll come to the same conclusion that the Knox downpipe is better designed than the Piper because of the divorced wastegate. [Probably no argument on this statement, but irrellevant to THIS thread]

[ccb056]

Restricting flow isn't the solution, that was the problem the old system.
Restricting flow of the waste gate - will give you boost creep.
Restricting flow of the turbine - will reduce performance.

[Acknowledged theory states:-]You can't have one without the other.
The total flow (turbine+wastegate) isn't going to change. These two are in parallel, therefore the dP across them is the same.
Increasing the wastegate flow (better boost control) decreases the turbine flow (lower performance).
Decrease the turbine flow (lower performance) increases the wastegate flor (better boost control).

The problem we have is the Piper is designed so poorly,[I don't like this statement, but it remains so the rest of the content can be kept on this thread and taken in context - perhaps a better phrase would have been "The issue we have is that the Piper design brief was to provide an affordable improvement, at the expence of a totally perfect solution"] there is too much flow through the turbine and not enough through the wastegate.
When run under these conditions your performance goes to zero (overboost).

On a cool day using the stock ECU, a 21mm port, and the Piper 2.5", PCE, no cat, and running the car uphill in 3rd, you will not be able to reach the rev limit without boostcreep. In fact, boostcreep starts at 4000 RPM. You've still overshot the boost even though the wastegate is completely open (0% closed)

3rd stock ecu.png

Place an Everest chip in there and the system is able to control at 0.9 bar without any boostcreep.

3rd everest.png

You're barely able to control to 0.90 bar with the wastegate completely open (0% closed).

Now we're already running running at the ragged edge, the wastegate has be to completely open at 21mm in order to maintain target boost of 0.90 bar near rev limit.

I have created a wiki here to help organize all the data: http://wikilec.9600.org/index.php/Boost_Creep

[surfboardfiller]

Restricting flow isn't the solution, that was the problem the old system.
Restricting flow of the waste gate - will give you boost creep.
Restricting flow of the turbine - will reduce performance.

He has stopped boost creep by reducing performance, I could do that by taking out the mountain chip or putting back the old down pipe.

This keeps being an interesting and on-going discussion! (insert Facebook 'Like' symbol here)

1. The area of the core flow of my modified piper at the location where i placed the deflector is still bigger than the OEM pipe + pre-cat housing (= improvement, mainly by faster spooling times, NOT max power
2. The bends of my piper do have less sharp bends than he OEM stuff (=improvement again)
3. The Piper eliminates one gigantic step up / step down in Diameter, namely by eliminating the pre cat cavity. (=improvement over OEM again, my pre-cat housing was empty anyway )
4. with the original PIPER design, the flow of the wastegate is injected at a 90 degree angle into the core flow. Because of the venturi effect you described, velocity of the gasses leaving through the porthole is high. So a high flow, injected angular into another flow, gives turbulence as far as my knowledge goes anyway. You are absolutely right, the total flow does not change, but only the distribution changes. By adding the deflector, the angle at which the 2 flows intermix is flattened, reducing turbulence and increasing flow throug the wastegate. You could say the wastegate flow stalled a little before this addition, with the same result as a to small wastegate porthole. Boostcreep!

Unfortunately i do not have the knox downpipe, so no i have to admit i did not test it. However i know that the design took care of the injection of 2 flows with different speeds. (because you can see it )

However i did buy, perfection internal finishing, tested, modified and drive the modified piper, and i love it.
If you are not sure that this is a performance gain, then you could still use it as access to the radiator & stuff from below is so much easier


I just try to share MY experience so far, as well as explaining MY philosophy why i did certain modifications, not to start a little war here!
I would prefer to combine our knowledge over a couple of beers and discuss improvements together

Meanwhile i will install another Piper With my modification on Peter's car. No way of telling if there i a performance gain where it came from. Ditching the pre-cat or using the piper, and frankly i don't have the money to spend on an in-between dyno.
In the end the turbo can only run @ 0.98 bar @ my setup. (injector limitations..) So the performance gain with my setup is only at noticeable faster spooling times

Last but not least: Due to the language barrier, my text can be a bit harsh sometimes. I can assure you this is caused by my own not so perfect translation. Fine nuances get lost unfortunately and things get more black and white than i would like. Well, keep practicing here is my remedy


***
EDIT: and i do appreciate other people's opinions even it's just theory!

My setup:
1. S2, closed loop
2. Switcher (mainly Everest)
3. Stock turbo in excellent condition, 21.5 mm wastegate port
4. New OEM exhaust manifold
5. reconditioned head + new OEM gasket
6. MY piper
7. 1'st bend is Piper as well (2.25")
8. After 1st bend it is all PECO
9. Stock intercooler + pipes
10. new timing belt + the lot
11. Stock but ultrasonically cleaned injectors
12 All sensors replaced but MAP sensor (so stock)

Did i forget something, Surfboardfiller?

Good stuff, now we are making progress..

[HJ2]

My point:

Revving up the turbo faster IS a power improvement over OEM stuff.
Every time you step on the throttle you have this benefit. It improves drivability

In terms of extra HP... Nope, with my setup unfortunately not and i am not planning an injector & MAP swap as the car is truly beautiful and balanced as it is now.

Time to get out Elanscan if i am fooling myself or not, Hahaha!

[HJ2]

Meanwhile, on the true Piper front: [This may read strangely now, as I have removed the previous few posts in the interests of 'Moderation' - sorry to spoil your post Henk-Jan ]

I was thinking: Why not guide the wastegate gasses into a tube of a slightly larger diameter diameter than the porthole, say 25mm. Then let it stick at a 90 deg. angle through the core flow (slightly flatten the tube where it goes through the core flow for less core resistance). after this section there is a lot more room to make a large radius and one could join the 2 flows at just a small angle at the end of the piper again. A bit of a hybrid between Piper and Knox ... The deflector can be ditched all together then.
Opinions please! (theory or evidence based )

[Brit-Car-Nut]

I gather you are suggesting a pseudo "divorced" system. I think that "divorced" is the best option (sometimes for more than exhaust systems), but the whole project was to offer an AFFORDABLE pipe that improved flow. Other improvements like large bore exhaust and even the PCE introduced boost creep, so this isn't a new phenomenon, just a continuation of existing design errors or flaws.

Adding another tube section is not an easy design especially for an automated assembly line as the robots must be smaller and smarter to attach said parts. Building them one at a time like Knox did is an expensive prospect and I think would have been viable for a few drivers but not the large pool of people looking for power gains.

Probably, the best solution is to start at the head and design a proper exhaust system that addresses all of the now known issues and quantify the costs to see if it is really something that can be offered without having to port this, polish that and baffle something else.

[HJ2]

I cannot do that.
But i can buy a Piper and adapt that. Either with addition of a deflector or a pipe, the amount of work will not be that different.
For people with a similar setup like me, a modification needs to made anyway, or boostcreep will return, even with a nicely ported wastegate.
It is more about optimizing the Piper. I do not believe that the Knox pipe is still available, so there is only one way forward at this moment, for all set-ups!
(or just stick with everything OEM off course, but who wants that? )

[ccb056]

[In my opinion] The best fix for boost creep is increase the wastegate diameter.
I have found that a car with an everest chip, free-flowing exhaust, and a 21 mm wastegate is operating at the very edge (high RPMs and 0.90 bar boost requires the wastegate to be fully open) with no room for improvement.

If we can establish that wastegate diameters larger that 21 mm are safely achievable, then we may have a chance at using the Piper downpipe in its original state.

If we can't get the wastegate large enough, then we should explore custom routing of the wastegate flow. [either before or after the actual wastegate]

My suspicion is we can bore the wastegates larger than 21mm, but [maybe] not large enough for the Piper [,so maybe need to ensure the flow inside the remaining cast housing is optimised].

I know my machinist was very reluctant to port to 21 mm. Originally he only went to 20 mm and I had to go back, and against his judgement go to 21 mm.

[HJ2]

Not entirely...

A bad design in wastegate flow will effectively give the same result as a reduced diameter of the port, although is is the correct size.
That is what is happening with the piper imho.

[ccb056]

I'd tend to agree. The best path forward for you is to modify flow. Those with stock wastegates and the Piper should port.

[dapinky]

In a bid to stop the cross-Atlantic divide from widening any further, I am 'putting on my moderator hat' and wish to state the following FACTS......

....I believe that the 'best' downpipe ever produced was the ones which Knox produced in very small quantity, and (more importantly) are no longer availlable, and are unlikely to ever be produced again.

As such, there are a number of options availlable to those who seek 'the best' - either go with what you can buy 'off the shelf' and modify it, or start from scratch and design a complete system (this is assuming that a direct copy of the Knox pipe cannot be made either for copywrite or other reasons).

Had Knox made them availlable and AFFORDABLE, then I'm sure they would have sold well - perhaps there is a bit of a geographical divide here - in the UK elans are 'cheap' cars, and spending hundreds of pounds may well be inappropriate to the majority of owners for a small increase - unless the car is being seriously raced - maybe in USA where they are rarer, the improvement is more 'necessary' and 'cost effective' ....

So, Phil approached Piper to see if they could help (they are a well-respected company with proven power-increasing products for loads of different cars, and they certainly have the knowledge and ability to produce something as good as, or even better than the Knox pipe, but as a business, they have to balance price into the equation - with an unlimited budget, I'd go to them any day of the week, but as a realist, I wouldn't want to pay their development costs for a one-off. (I've done it before with them to get an extra 20bhp out of my Dolomite - and it wern't cheap, but at the level I use it, it was 'necessary').

So, we're back to getting an affordable unit, and developing it (either independently or together with the company).

I believe the purpose of this thread is to see how this can be done, NOT to slag off the product, and say that something else is better (especially if the 'something else' can't be purchased), so i would request that we all 'play nice' - as many of us do NOT understand fluid dynamics, and quoting articles from t'internet which may or may not be true don't always help - but are often entertaining.

[/moderation]

Okay, my personal input to the (believed) purpose of the thread.....

I currently run an Everest chip (switcher though, so sometimes more, sometimes less), 2 1/4 Piper with PCE and a ported wastegate - I've never had boost creep.....

I use Iridium plugs, MSD coils, 8mm plug leads, standard (but recently ultrasonically cleaned and tested) injectors.


My question here (to Henk) is "What difference do/did you notice when swapping to the Piper downpipe before and after your modifications".

I ask because I want to know if the Piper is better than the PCE in either it's original form, or in it's modified form??? - and I know you had the PCE before you got this pipe.

I'm not worried about the 'boost creep' issue, as I believe that can be reduced with good porting/flowing, but I am interested in any difference that just the one component can make in the way the car feels/drives (don't really care about absolute top power output either).

As such, unless anyone else has gone from a PCE to a Piper downpipe, then your comments are somewhat irrellevant to my circumstances - I believe that comparing results from different vehicles with different setups is like saying that apples are better than elephants, but results from a single change can be very helpful.