I just accidentally ALL OVER MY PANTS from bmw's N55 now must tiny twin scroll - Page 2 - Miata Turbo Forum - Boost cars, acquire cats.

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Old 03-10-2011, 07:22 PM   #21
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Quote:
Originally Posted by Sean View Post
equalizer pipe to make sure both sides of the mani have even pressure
Completely defeats the purpose of twin-scroll. You end up with cross-contamination from the pulses and you lose the divided effect. There's a good reason that real twinscroll manifolds (i.e. Full-Race) have two EWG hookups.
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Old 03-10-2011, 07:26 PM   #22
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Quote:
Originally Posted by fooger03 View Post
You have read correctly. You bolded my version of the quote, which is what "should have been" written. In both scenarios, we're comparing the GTA wheel with the inconel wheel, the only difference is, the original quote gives no baseline for comparison.

Now, that being said, we understand what "the new part is over 50% lighter than the old part" means; but it's mathematically incorrect - try solving for the weight of the new wheel mathematically using only the information provided in this statement, understand that you must multiply the difference between two quantities (some unknown quantity - the weight of the old wheel) by 1.5 in order to solve it.

I know I'm only confusing the matter more by editing with following information, but:

q = some unknown quantity
o = weight of old wheel
n = weight of new wheel

q-n = (q-o)1.5
assume o = 100

q-n = (q-100)1.5

assume Q = 110
110 - n = (110 -100)1.5
110 - n = 15
-n = 15-110
n = 110-15
n=95
New wheel = 95g, 50% lighter than old wheel relative to 110

Assume Q = 200
200 - n = (200 -100)1.5
200 - n = 150
50 = n
new wheel is 50g, 50% lighter than 100g relative to 200g

Assume Q = 50
50 - n = (50 - 100) 1.5
50 - n = -75
125 = n
new wheel is 125g, 50% lighter than 100g relative to 50g

The problem is: "Q" is a mathematically undefined variable in the original quote.

TL;DR: over 50% ligher than != less than 50% of the weight of.
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Old 03-10-2011, 07:29 PM   #23
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Originally Posted by JasonC SBB View Post
Sav:

AFAIK VNT control is still pneumatic - IOW they still use the same wastegate actuators our "normal" turbos use.
The 997TT is all electronic - it uses the vanes for response and overall boost control. You could do pneumatic control pretty easily, though. I wonder if EGT/abuse is still a concern for high performance aftermarket use?
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Old 03-10-2011, 07:33 PM   #24
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Originally Posted by fooger03 View Post
The problem is: "Q" is a mathematically undefined variable in the original quote.


Come on, guys. It's implied that they are referring to the Garrett Inco wheel when they say "50% lighter". Kind of like how your stock portfolio goes up 10% a year - it's not 10% relative to the GDP of China, it's relative to your portfolio.

It's not hard to figure out what they meant, especially when you look up the mass of GammaTi vs. Inconel.
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Old 03-10-2011, 09:22 PM   #25
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Originally Posted by Jeff_Ciesielski View Post
The Holset he351VE uses a fairly sophisticated servo based system to control its VNT functionality.
Got a linkie?

FWIW the old Aerochager miata kits used the same old wastegate actuators we have.
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Old 03-10-2011, 09:23 PM   #26
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Quote:
Originally Posted by Savington View Post
The 997TT is all electronic - it uses the vanes for response and overall boost control. You could do pneumatic control pretty easily, though. I wonder if EGT/abuse is still a concern for high performance aftermarket use?
Well FWIW AFAIK dem Porsches can take track abuse.
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Old 03-11-2011, 12:21 AM   #27
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Sav's on point here re: twin scroll and VNT. One correction, the BMW and Mitsu internal wg draws from both scrolls, not just one. They're done right.

EFR looks really nice. Hope they hit the ground soon. Turbine housings look nice. Ti-Al wheel is its single biggest perf benefit. Curious about the wheels' heat tolerance though.

Porsche's is the only VNT capable of handling gasoline EGTs. That, and the Garrett motorsports VNT on the Audi R15 LeMans car, but that's pretty much unobtanium. Borg sells the Porsche VNT in the aftermarket though...

Many/most VNTs use a rotary electric actuator for vane position control.
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Old 03-11-2011, 12:24 AM   #28
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Also, the fucktards in this thread arguing about the ******* Ti-Al / inco weight verbiage need to get the **** away from mt.net and return to m.net.
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Old 03-11-2011, 12:29 AM   #29
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Quote:
Originally Posted by Savington View Post
real twinscroll manifolds (i.e. Full-Race) have two EWG hookups.
You can use a single gate too. Just need to keep the two feeder pipes separate all the way up to the wg's valve. This is deceptively non-trivial in terms of keeping the divider wall from splitting/breaking but can be done.
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Old 03-11-2011, 12:58 AM   #30
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Is the benefit of dual-scroll from the scavenging or from effectively a more efficient turbine?

If the former, I don't get it, don't you get the same benefit from longer manifold runners? IOW, the gas pulses mix in the turbine blades, so the pulses are kept separate only for the additional length of time it takes to go through the turbine:

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Old 03-11-2011, 02:21 AM   #31
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Quote:
Originally Posted by JasonC SBB View Post
Is the benefit of dual-scroll from the scavenging or from effectively a more efficient turbine?

If the former, I don't get it, don't you get the same benefit from longer manifold runners? IOW, the gas pulses mix in the turbine blades, so the pulses are kept separate only for the additional length of time it takes to go through the turbine:
I don't think it's really scavenging. You just want to get the most exhaust flow possible to the turbine and pressure in the manifold of course restricts this, by keeping the exhaust gas pulses separated until they reach the "inner scroll(?)", where the pressure is going to inevitably increase due to the turbine flow restriction, you are creating a lower pressure and less restrictive path resulting in increased gas flow to the turbine and therefore quicker spool.
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Old 03-11-2011, 02:28 AM   #32
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Quote:
Originally Posted by JasonC SBB View Post
Is the benefit of dual-scroll from the scavenging or from effectively a more efficient turbine?
Yes.

See:
http://blogs.insideline.com/roadtest...alkaround.html
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Old 03-11-2011, 02:50 AM   #33
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Quote:
Originally Posted by JKav View Post
Ah, talking about the pressure more so than the flow (which is just dynamic pressure) makes it much more clear. To summarize, the pressure that would be "cross-contaminating" and creating backpressure in the manifold is instead being utilized by the turbine because the separation causes the pressure to be "used" in moving the turbine.

edit- It's really a more efficient turbine housing and manifold design that gets the pressure to the turbine better instead of allowing it to restrict flow in the manifold.
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Old 03-11-2011, 03:31 AM   #34
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Quote:
Originally Posted by JKav View Post
You can use a single gate too. Just need to keep the two feeder pipes separate all the way up to the wg's valve. This is deceptively non-trivial in terms of keeping the divider wall from splitting/breaking but can be done.
I feel like the appropriate way to do this would be machining a custom split valve seat from nitronic 60, although the thought of machining something even tougher and more wear resistant than regular 304 makes me shutter...
but you can get away with using a more common alloy as a wall that's just clearanced far enough from the valve? Realistically, even though I realize your post was just saying it can be done, it seems safer and more effective in terms of both cost and performance to just run two wastegates.
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Old 03-11-2011, 12:01 PM   #35
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Quote:
Originally Posted by JasonC SBB View Post
Got a linkie?

FWIW the old Aerochager miata kits used the same old wastegate actuators we have.
http://www.superturbodiesel.com/std/...tronic-control
http://forum.diyefi.org/viewtopic.ph...&t=199&start=0

I shouldn't have said 'sophisticated' as its just a servo, however it seems that there are a lot of variables that go into controlling it. i.e. it isn't just boost pressure. EGT/AFR/Throttle position/etc are all accounted for in the factory system from what I've gathered.

I'm really thinking about running one of these on my 320i as I have access to one locally for pennies (if I can fit the bastard between my frame and block). My thoughts were to remove the stock control system and replace it with a standard internal gate actuator ala aerocharger. I was thinking that if it were supplemented with an external WG and plumbed both of them together behind a boost control solenoid controlled by the MS2, the results could be rather nice.

Quote:
Originally Posted by JKav View Post
Also, the fucktards in this thread arguing about the ******* Ti-Al / inco weight verbiage need to get the **** away from mt.net and return to m.net.
Woah killer. I just wanted to be sure I didn't need to hang up my reading hat and head over to cr.net to chat about my hellatightflushtaintsteez.
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Old 03-11-2011, 12:56 PM   #36
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Quote:
Originally Posted by Jeff_Ciesielski View Post
http://www.superturbodiesel.com/std/...tronic-control
http://forum.diyefi.org/viewtopic.ph...&t=199&start=0

I shouldn't have said 'sophisticated' as its just a servo, however it seems that there are a lot of variables that go into controlling it. i.e. it isn't just boost pressure. EGT/AFR/Throttle position/etc are all accounted for in the factory system from what I've gathered.
I don't get it - why can't a simple pneumatic actuator + the usual EBC do it? After all, you want to regulate boost in our gas engines. (maybe that complexity in the links is for diesel apps)
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Old 03-11-2011, 01:03 PM   #37
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Quote:
Originally Posted by JasonC SBB View Post
I don't get it - why can't a simple pneumatic actuator + the usual EBC do it? After all, you want to regulate boost in our gas engines. (maybe that complexity in the links is for diesel apps)
It can, see the rest of my post. Its been done before by a couple of DSM guys.
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Old 03-11-2011, 08:36 PM   #38
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I was just thinking, for NA motors, the most efficient scavenging is when only 2 cylinders are paired? E.g., for a 6 cylinder, you have 3 exhaust pipes all the way to the back?
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Old 03-11-2011, 08:37 PM   #39
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Originally Posted by Jeff_Ciesielski View Post
It can, see the rest of my post. Its been done before by a couple of DSM guys.
So Sav's comment that the control system is a hurdle for VNT, isn't correct?
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Old 03-11-2011, 08:39 PM   #40
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BTW anyone with a link to the history of the evolution of the blade shapes for compressors and turbine wheels?

In the days before CFD, how did the big brains come up with such an organic, complex shape?
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