patsmx5

iTrader: (16)

Yeap, exactly. Hope the two gates will be enough if I port both, if not I'll put a 50 or 60mm gate up front.

patsmx5

iTrader: (16)

I'll got get the mounting system done and then post a few pics.

patsmx5

iTrader: (16)

Drilled/tapped top of CHRA for 1/4" NPT so I could use a fitting without using the two bolts on the CHRA. Then used those bolts for a mounting system, since it's basically holding it in the CG of the turbo more or less.

Mounting system has silicone vibration isolators/flex pieces so that the turbo can bend/move a bit. To allow the exhaust system to flex a bit without cracking the exhaust.

Basically you bolt the turbo to the mount (2 bolts to CHRA, then install it into the car. The front lands on a tab to hold the weight, then raise the rear in and bolt it together.

hornetball

iTrader: (4)

With two inline turbine wheels . . . I wonder if you need mufflers at all?

ihiryu

Well that was fast. I'm surprised you got it done so quickly

patsmx5

iTrader: (16)

I dunno, but my gut feeling is yes. Going to only use straight thru muffler for best flow. Going to build it with 1-2 glass packs between cat and second turbo, and see how it sounds. Then fab rear exhaust based on sound.

Thanks. I'm behind schedule actually, goal is to be driving it on 2/12/2016.... But crap happens. I'm hoping now that the turbo is home, the rest won't take so long. Working on boost pipe to front now. Turbo outlet is a weird size (3.375") and I just sanded/filed it down to 3" so I can connect to it.

codrus

So the rear turbo is hanging on the oil feed studs? Is that strong enough?

What do you plan to do for control? Two PID loops for the two WGs? For ideal spool you're going to need to close the little WG as you crack open the big one -- synchronizing that sounds tricky.

--Ian

patsmx5

iTrader: (16)

It's a pair of M8 bolts, high grade, over 2.5x the diameter of engagement. Should be plenty strong. This isn't like a traditional setup where it's hanging on one end, bolted to a vibrating engine. I've seen people run huge turbos this way on drag cars without issue. I do plan to wire those bolts together though just in case.

Working on how to route boost pipe right now, trying to find the best path that won't drag the ground when I launch.

Leafy

iTrader: (1)

No, well just a muffler for the rear ewg would be my choice. Once thing I know from other rear mount twin charge setups is that you do not want to have a cat or muffler between the turbo unless you make it easily replaceable.

patsmx5

iTrader: (16)

When I first hook it up, I'm going to run each turbo at 12 PSI boost with a simple MBC for each. That should make ~34 at the intake manifold. Will run it that way and fix any problems that arise, then go from there regarding fancy boost control. I think ideally I'd have the small turbo shoot up to say 20-25 PSI in the midrange to get the extra torque and mass flow. That would mean more torque sooner, and more mass flow to help spool the big turbo. Then manage the transition to getting both to the same pressure ratio as the big one spools. Not sure how I'll do that, will just run 12 PSI from each at first and go from there.

patsmx5

iTrader: (16)

codrus

Why use a silicone 180 like that instead of clocking the compressor 180 degrees so it points forwards?

I guess the 12 psi thing will probably work, so long as it's a 2-port wastegate so you can reference it off the compress inlet charge instead of atmospheric. I think you'll get 24 though, not 34, because a mechanical wastegate is additive, not multiplicative. I think you'll also need a much stronger WG spring to hold against the higher exhaust manifold pressure.

--Ian

18psi

iTrader: (76)

why not just clock the compressor so you don't have to make a silicone u

*edit:
Ian beat me to it lol

patsmx5

iTrader: (16)

Also to add to this, a lot of rear mount turbo setups I see don't support the turbo at all, and use the exhaust pipe to support it instead. Given this is a big turbo, I didn't like the idea of that at all. My exhaust system will have hangers too, this will just be extra support. Also makes removing the exhaust a lot easier to service stuff, since the turbo doesn't have to be removed.

18psi

iTrader: (76)

what about movement in the exhaust? flex bellows?

exhaust moves a whole lot during hard launches and such

patsmx5

iTrader: (16)

I tried too, the other end of the turbo hangs down wayyyy too low if I do that hurting ground clearance worse than this. The outlet of that compressor is 3.25" OD and way on the outside.

If I could weld aluminum, I'd cut that thing off, weld a 2.25" pipe to it, clock it, and bamm.

EDIT: Those U-bends also transition from 3.25" to 2.25" BTW.

patsmx5

iTrader: (16)

If it ever cracks, I'll do a flex. Read about some of them can deteriorate, which if so would go right into the turbo. The mounts I made in the back are adjustable, it flexes a lot if you don't pinch the bolts down too tight, the holes are ovalized to allow it to move forward/back over 1/4". And I don't have a flex section on hand and I got a self-imposed deadline to meet.

Also I have AWR motor mounts and poly diff mounts.

patsmx5

iTrader: (16)

I'm not following. Why would it be 24 and additive?

codrus

Yeah, I guess the big A/R ratio makes it spiral out a lot further. The silicone looks like it sticks way down as well, though?

Perhaps rotate it 90 degrees so that it points up and use a single 90 degree silicone adapter to point forwards?

--Ian

codrus

The big turbo has a 12 psi (80 kpa) WG can, so it's taking in 100 kpa atmospheric air and putting out 180 kpa into the intake of the small turbo.

The small turbo also has a 12 psi (80 kpa) WG can, with the "atmospheric" side of it connected to the outlet of the first turbo. Since it's a diaphragm and a spring, it's going to regulate the WG to produce a fixed delta pressure above the inlet pressure. So it takes 180 kpa inlet air, adds 80 kpa to it and gets 260 kpa, or about 24 psi of boost.

At least, I *think* that's the way a mechanical WG can works?

--Ian