With the recent spike in exhaust manifold related threads, I figured I might as well throw up my own. Maybe some will find it usefull...
The manifold that we've used for the past 3 years (fabricator is unknown) that had originally came with the motor was proven to easily support 600 rwhp, which it did on our setup as well... 620 at 24psi on pump w/ meth injection.
Now, we have known since day one that the exhaust manifold wasn't without its flaws, but having recently removed it form the car along with the turbo, we were able to see the whole story... piping that didn't line up correctly, obvious kinks, and a wastegate routing design that'll make you cringe. So, something had to be done.
The turbo was located in a near perfect spot (not a lot of wiggle room with a 42-02) and the 5" downpipe has little if any room to move side to side, so the original mounting location was kept. The original manifold was then measured on all planes, along with the two flanges. The turbo flange matches the actuall port geometry of the turbo itself, which if you take the time to look at is quite a bit different than the port opening of a standard "T6" flange. The resulting overhanging edges are now elimintated.
From there, both flanges are positioned in space, and a routing for each runner is created as so...






There is a bit of work to be done where the pipe meets the turbo flange... this will most likely be done with vertical pie cuts fit between two tapered sections of pipe, which will transition from the pipe ID to the turbo port ID.
Once the runners are set the wastegate routing is then added. The wastegate will merge as close to the turbo flange as possible, with a smooth/gradual exit angle to that of the runners. If you think about what exactly a wastegate does, it becomes clear that this is a necessity. Once a desired pressure is reached, the wastegate opens up to expell additional exhaust gasses from reaching the turbo, which in turn keeps the pressure from rising further/spiking. If the wastegate exits near the engine, the exhaust gas that has already passed the exit, an entire runner length full, is still flowing up through the turbo, which causes pressure to continue rise. If the wastegate is close to the turbo, there is minimal exhaust left in the runner to reach the turbo. This gives much better control or boost pressures... once the limit is hit, the gate opens and additional gasses exit immediately. This is the same principle as a large intake manifold having a supply of reserve air once the throttle body snaps shut... the revs hang for a bit until all air is ingested... just as the pressure continues to climb until all exhaust gas has passed through the turbocharger. To aid in the evacuation of gasses even further, the wastegate routing should be as short as possible.

We also began work on another member's manifold for a 6265 turbo. The smaller T4 frame flange makes the transition a bit easier. Runner length front to back varies by 0.18", and all angles are consistent and square, there are no odd angles, kinks, or bends.
Again, wastegate routing will follow shortly.









All material is 2"sch10 piping (.109 wall) 304 stainless. As others have said, 321 is simply not necessary for most applications. The runner ID on the current manifold is 1.92", which we have found out is actually smaller than the exhaust ports on our motor. Stepping up to a 2.15" will only help in our case. Truthfully, having measured stock exhaust ports on a few engines, I can say that I wouldn't hesitate to run this size pipe on a smaller T4 setup as well.

Screen captures of the wastegate routings will follow, along with the actual fabrication process.

 

Where do you guys get the thicker 304? Burnstainless only has 16gauge that i can find. And all I can find on mcmaster is straight tubing??

 

^ Type in pipe on the search bar, click stainless steel pipe, then elbow, then choose 90 degree or 45 degree, then butt weld x butt weld

 

Here are a few more of the manifold complete. This manifold uses a 40mm gate, which will eventually route back into the downpipe.
Next step is obviously cutting everything out... all pipe pieces will be cut on Mazak rotary laser, and all elbows will be cut on an IGM HD plasma robot.

 

looks like it might have enough clearance to fit an FC !

 

The turbo and supporting cast... Flanges and pipe sections to be cut this week.

 

The T4 flange manifold may not have a problem, but we've found some boost control problems with a 40 mm wastegate on the Tial V-band hotsides. I'd recommend doing a bit more blending on the wastegate port into the flow of the manifold. We've moved up to 60 mm wastegates on the Tial hotsides.

my $0.02
-Trent

 

Here is the transition to the wastegate outlet as modeled in SW. Excuse the oversized pics, I've tried resizing them over and over...





The merge and divider at the turbo flange:



The wastegate dump:

 

A few in progress...







And a mock up of the runner to T6 flange merge (GT4202). Almost perfect...

 

Looking really good. Great set up work.

Care to weigh in on why back filling isn't necessary?

 

The photos show the manifold being tacked together, once everything is in place the flange is capped and each runner is purged for full penetration. More pics to follow...

 

A few photos of the manifold complete.



Equal length runners.










Note transition to wastegate outlets.

 

Very nice.

thewird

 

how did you weld the divider to the flange? through the flange then grind smooth?

 

Right on. Once the flange is on, the welds and the overhang (because the twin scroll openings are not identical to the ID of the pipe) are ground to form a smooth transition.

 

awe yeah... I see my manifold and turbo!

Thanks Casey!

 

Due to a new larger intercooler we've switched gears with our manifold and have redesigned it to place the turbo just far enough forward that we can clock the compressor housing in the appropriate direction (end tank inlet and outlet now on top vs. bottom as before). The result is below. Excuse the junk pics, they've been compressed one too many times...

 

Nice!

 

A few of the manifold in the car after the runners have been welded up. Flange positioning is right where it needs to be. I'll post up a few more of the turbo mounted up once my phone gets it head out of its ***.

 

 

holy crap that's a big turbo, I had the measurements for my midpipe but seem to have lost them. I'll send you an email tomorrow.

 

A few finished pics, minus wastegate dumps..

 

Very nice .. I like a lot..

 

Sweet mani!

 

I want to thank jdmfantasy for first showing this artwork and how and why they did it. I also want to especially thank him for not succumbing to the temptation of actually answering all of the posts that had to be deleted asking when he was going into production and how much they cost.

Reading this thread shows you how to do it yourself. It's unbelievable that this group has shown every "secret", the build drawings and the final product. If they decide to pursue actually selling this stuff, I imagine they'll do the Group Buy route and all of the attendant rules and fees that go along with that....or it could very well be they just wanted to share a very special piece and its build history with us, and that was it.

Please. No more replies asking how much. Leave this a tech thread as it should be.

Mario III.