Piper Exhausts turbo downpipe development thread

[ccb056]

Anyway: so I took the Piper out and took it along with the OEM lump for comparison to my colleagues. The general opinion on matters is that the flow of the wastegate enters the main flow to steep, causing impinging problems (turbulence and pressure differences). DUH! The way to solve it is to let both flows mix at a minimum angle of 45 degrees. DUH!
You can't produce a baffle that reduces this to 0 degrees because it will take up too much volume of the main flow (and restrict it again) So I'll have to find an optimum.

My plan now is to dremel out a groove with the desired shape of the baffle. (both sides of the downpipe "head'). The sheet metal baffle is then bent into profile on a bench, inserted in the groove and welded from the outside. I am sorry, but I am not gonna place it back in order to do an Elanscan prior to the work.

We'll see what happens after replacement. I have to be quick as temperatures are rising and chances of boost-creep reduce.
As always, I'll keep you informed. Now go out and drive in stead of hanging around behind your keyboards!

Here's some closeups I took of the wastegate flow. Units are inches. One thing I found very interesting that was difficult to discern in the other pictures I have seen is the wastegate portion acts almost like a nozzle, the cross sectional area at the exit looks to be almost half of the inlet. Also, the flow is diverted downward very dramatically. Looking at this in my hands I would guess there may be some venturi effect between the wastegate flow and the main exhaust flow.

[HJ2]

Good pictures!

Yes, there is a significant speed difference in both flows, also depending on turbine speed and flapper position. That is what is making the joint of both flows complex and that is why the Knox design joins them further downstream, where the speeds are lower and the differences are not so big any more.

I measured the flapper + actuator rod and dimensioned my baffle so it won't come in it's path. The flapper disc diameter is the inner radius of my baffle as in the OEM design, the diversion here is dramatically as well, all be it a little less as there is more room in the head of the downpipe to shape the flow.

I believe i ported to 20.5 mm, but i'll have to measure this to make sure.


Regards
Henk-Jan

[Steve A]

I added an extra securing bolt to the heat shield to gain more support and prevent vibration



As you can see it's an easy mod using an existing bracket

[HJ2]

Finally some progress!

I got a piece of Stainless 310 (for better heat resisting properties), 2 mm.
I bended it into the shape i think works best. Then i marked the shape on the downpipe, drilled a lot of 2 mm holes and finally took the Dremel to finish on side with groove. Now time for lunch, and then start on the other side and weld it up.

To be continued as usual

[HJ2]

Noohoooooo.. I told you!
Rocket science was my former job, now it's just plane aircraft engineering, which is a bit like bike repair

When you've designed bits for stuff that exceeds Mach 3 in the earth's atmosphere, you can call yourself a rocket scientist and not before. And I did warn you 2 years ago.

I Anticipated that i would recieve a relative cheap product that was a good base to start tinkering with...
So far so good, and i am tinkering
Now wait and see if it was worth it (can't make any promises!)

And: Does Mach 4.25 sounds good enough? (old Wind tunnel, now i have access to a Mach 11 wind tunnel )

[HJ2]

... I Just dropped the parts off at the welder,
Tomorrow evening when the temperature drops again i can do a test drive!

[HJ2]

Helaas....

Still boostcreep, now even in second gear @ redline!
No worries yet, i reserved some slack length in the baffle for some serious empiric testing

[ccb056]

The solution may have to be porting to 23mm, removing the washer on the flapper, and welding in a new larger diameter washer.

[HJ2]

... That thought has crossed my mind as well.
However if i can adapt the downpipe, that would be my first choice.
I'll try to get it out again this week and take the grinder (Grin )

I Also thought of introducing a circular restriction in the downpipe as this is easy to install (3 bolts) and see if the boostcreep is gone. Then remove the ring again and replace it for a thinner one etc. to see where the transition point is. Then calculate the corresponding surface areas to see how large the porthole should be.
It still is a bit of a guess, since i do not take into account the cooling effect on the expansion of the gasses and the scaling effects!

To be continued...

[norman lovie]

might be worth tapping into the ex manifold ( say via the recirc plate) and putting a gauge to measure back pressure
the mod's are achieving more boost because of either
a) more efficiency - more flow - otherwise determined by increase in performance for a given boost value
b) more back pressure - more turbulence

recording ex manifold pressure would be a simple way of getting an instant bench mark result to help identify the value of a given mod.
rise in boost directly related to rise in manifold pressure = more psi but no gain in flow = no efficiency gain = mod is not efficient
rise in boost greater than rise in manifold pressure = more useful psi due to increased flow rate = mod is efficient

overall aim is to demonstrate increase in Pressure differential through the head = flow improvement

also if you do a base boost check - to set a base line between mechanics versus control - fit a hose direct from inlet to actuator by passing all control devices - compare this with the result with the boost controller response - worth doing a pressure test of the actuator with this line connected to a pushbike pump- the base boost pressure profile is directly related to the mechanical flow characteristics

[HJ2]

is it not more simple to check with elanscan the time it takes for the turbo to spool up?

[norman lovie]

is it not more simple to check with elanscan the time it takes for the turbo to spool up?

that is a good initial indication of efficiency of the ex gas flow through the turbine- but there should be no contributing flow from the WG at this point
its when the flow is too much leading to bleeding off some via the WG that is causing the creep - and is this causing a choking effect leading to boost rise ( but no actual flow gain) - or boost rise with positive flow gain

[HJ2]

Progress report for today:

In about 1.5 hours i removed the downpipe again, grinded a piece out of the fresh installed baffle and reinstalled the lot (i'm getting the hang of it now)
Of course i went for a spin and.... Boostcreep cured! Finally!

I know the air is hotter than the earlier tests, but the boostcreep occured even in 2nd gear and now it's completely gone. I will be awaiting the winter with a smile on my face now. Ypres Lotus day: Here i come!

Since i now have done all the work for Piper, the next move is to you then!
Piper, are you still with me in this thread !?

[Brit-Car-Nut]

Any chance of some pictures or diagrams describing exactly what you ended up doing?

Looks like you created a divider between the waste outlet and the exhaust outlet. I assume it goes completely across? Did you drill /grind /cut both sides or just one side?

Good job!

[Jeemy]

Ears now fully pricked, meerkat mode. There is a divider inside my downpipe between the two outlets (inlets?). It has a gap cut in it. It doesn't go fully across, maybe 30% across and the first 10% is missing.

I am going to post a picture tomorrow when I get to where the car is laid up. I've been meaning to for ages to ask if it is right.

What you've done, sounds like what I got from Piper. Obviously it won't be (it can't be!), that would be too easy. But I am dying to see what you have ended up doing with this; I can't bring myself to install until I am sure its going to work correctly, and I am very worried about what I see when I look inside the downpipe at the turbo end.

[ccb056]

I'm curious, can the piper downpipe be removed without removing the manifold? The OEM downpipe just barely doesn't have enough clearance.

[cliff]

I'm curious, can the piper downpipe be removed without removing the manifold? The OEM downpipe just barely doesn't have enough clearance.

Yes, comes out easily

[HJ2]

Ears now fully pricked, meerkat mode. There is a divider inside my downpipe between the two outlets (inlets?). It has a gap cut in it. It doesn't go fully across, maybe 30% across and the first 10% is missing.

I am going to post a picture tomorrow when I get to where the car is laid up. I've been meaning to for ages to ask if it is right.

What you've done, sounds like what I got from Piper. Obviously it won't be (it can't be!), that would be too easy. But I am dying to see what you have ended up doing with this; I can't bring myself to install until I am sure its going to work correctly, and I am very worried about what I see when I look inside the downpipe at the turbo end.

???
I would love to see some pics!
Mine will appear tonight i hope

Perhaps Piper has silently changed the design in the mean time? That would be an utter insult to the early adaptors IMHO.

[PiperRS]

Hello Guys,

Sorry if you think that we haven't been paying attention to this thread, we have, I just didn't post a comment as felt i had nothing to add to the conversation.

I would like to see the modification that has been done, It would be good if i was able to implement this into maybe the next batch of downpipes (i still have several on the shelf) But i know that this would affect the overall price of the part. The downpipe we made wasnt made 'cheap' but there is always a compromise to be had and we wanted to price this right in the market.

[Steve A]

Perhaps Piper has silently changed the design in the mean time? That would be an utter insult to the early adaptors IMHO.

It would appear not