I just accidentally ALL OVER MY PANTS from bmw's N55 now must tiny twin scroll
 

In addition to Valvetronic, Direct Injection, and a map controlled oil pump, BMW's N55 (which im just now reading about) also has this:
http://www.bmwblog.com/wp-content/uploads/n55_eng_3.jpg

My goal is to have 300+whp and the most immediate response possible. Engine's at builder's with 84.5mm Wiseco's, M-tuned rods from 949, and ACL Race bearings, but I'll be using a 3" exhaust, VVT head, +1mm valves (good/bad idea for the street? exhaust only?), and attempting to copy hf-mx5t's dual plenum intake :3

I'm thinking GT2860RS and this ATP twin scroll housing. I'm curious as to how exactly I should go about this though.

Option 1) Cylinders 1&4 are divided to one scroll and 2&3 to the other. *oops, had that mixed up at first...

Option 2) All cylinders feed together undivided into the flange, but there is a "quick spool valve" which blocks one scroll until it needs to open.

Option 1.5+) Design a setup which all goes into one scroll and then divides 1&4 from 2&3 when the 2nd scroll opens.

Option 3) STFU and get a TiAL full v-band housing because that ATP shit is going to break as soon as you take it on the track; your bitchboy turbo will be plenty responsive anyway.

I'm not concerned if the "QSV" will be smooth, because I can always just set up something to open it if needed for track driving etc.

What do you guys think? (i feel like i will see a lot of option 3 "suggestions"...)

BTW, even though the off/on throttle response I'm after can't be shown on a dyno here's a chart from a "62mm billet GT35r(.84 T4 turbine) on stock 7MGTE [3.0L inline 6] with SAFC on stock ECU" w/ a QSV
http://www.echowavepro.com/supraphotos/dyno/qsv2.jpg

Forget about the QSV. They grenade under track abuse.

300whp and response-minded? You should really press the pause button until a couple of people get EFR6258 setups together.

back to life, back to reality

I've been thinking about something similar but with a proper 1&4, 2&3 twinscroll manifold (option 4?). I thought about making my own QSV but like Andrew said I'd be weary of it grenading into my turbine. You can ask ATP if they have this turbine in GT28XX for a little less money:
http://www.atpturbo.com/mm5/merchant...egory_Code=GTH

Your 3 options could apply to the BW EFR turbos with their divorced turbine options.

What's a QSV?

Why would you want "on/off" throttle response (if I'm understanding you right)

Pairing should be 1&4 and 2&3 as TurboTim implied, not 1&2 and 3&4.


---------------
Now what's the theory why twin-scroll turbines improve spool?
Until what point do the gas paths remain separate?


Response and power - have the VNT and variable vane turbos not moved on yet and become more reliable?
I don't see how BW can improve on wheel aero to challenge VNT/VV in terms of the spool/flow tradeoff.
Why haven't Honeywell released a complete line of VNT and VV turbos to the aftermarket? Maybe if BW are enough of a threat they finally will.

quick spool valve

http://www.spracingonline.com/images/news/15.jpg
mostly found on supras with small animal/baby eater turbos.. supposedly helps spool the turbo up faster.. one dyno i saw showed the power came on 700 rpms sooner with it..

QSV = Quick Spool Valve - basically a plate with a flapper that you stick between the twinscroll turbo and the single-scroll manifold. When it's closed you get half the A/R you normally would, which means faster spool. Until it just comes apart and ruins the turbo.

Exhaust gas pulse separation. They remain separate until they touch the turbine wheel, ideally - a good twinscroll setup uses two external/internal wastegates so the chambers remain totally separate. (Or janky ones like BMW/Mitsubishi use a single internal gate on one half of the twinscroll.)

With single-scroll, you reach a point where the exhaust pulses arrive right on top of each other, and their effect is essentially negated. With twinscroll that point is moved way up in the RPM range since you're only trying to stack two pulses vs. stacking 4.

Once you spin the motor up high enough, the benefit goes away, but the low end benefit is enormous - typically you run a much larger turbine A/R to pick up some flow up top, while still getting good spool via the twinscroll housing. Borg will do a .83 A/R single-scroll turbine or a .92 A/R twin-scroll turbine, and I'd bet money that the .92 TS would spool faster.

Jason, I bet the hurdle for VNT is control. How many of Garrett's customers have an ECU that will control a VNT setup? How many of them are using reflashed Honda/Suby/Mitsu ECUs?

You should read up on the new titanium aluminide exhaust wheels that BW is using - crazy, crazy stuff.

double post fail

I don't tjink a qsv applies to track use eitehr becuase unless you drive the whole track in 6th gear you will always be above boost threshhold.

My guess is garrett has no afgtermarket VNT because not enuff ppl would buy em becus of complexity.

OP just get a 2871 .63 or a uh .4 T2 3071 and be happy. Actually if 2876 came with a .4 housing and T2 I soulx get that because baby turbines and huge compressors are awesome.

Why not just build a good twin scroll mani with 1,3 and 2,4 hooked together with a equalizer pipe to make sure both sides of the mani have even pressure and run your waste-gate off of the equalizer pipe. This will still spool the shit out of a turbo simplify your set up and run with it. If not just run a single scroll mani and deal with it. My experience with a quick spool is one on track cars they blow up two you only need one if you are running some huge huge turbo as in if you have a gt42R with a 1.1 a/r exhaust then yea it would be a good idea for what you want just run with it. SIMPLE is better in all cases.

Love this thread. I've been wanting some chatter on these subjects. Also, is the theory behind a QSP similar to an inline twin turbo setup?

Yes the QSV is similar to that in a way but not at all in other ways. They hit the market big time on supra's trying to run massive turbos and they work well on street cars but people think hey that guy ran it on his street car for 5 years it will work on my track car. Difference is that the abuse most street cars especially supra's see in a year is equal to what most track cars do in a couple full speed laps. There is a reason you can build a turbo kit for the street for $1000 and get away with it and almost every track car has that in a turbo alone.

I had a feeling that little piece of stainless would eventually end up in the turbine, maannn... Oh well, the divided setup seems more pr0 anyway.

The EFR6258 looks perfect though! Slightly smaller turbine, slightly larger compressor wheel, and a higher A/R with twin scroll + hybrid ceramic bearings and it appears to just simply be superior in construction too. My only concern is, and this maybe just from reading this forum too much, will I be alright on track without v-bands? I'm assuming BW housing is higher quality and warps less?

Oh right, that makes sense since the firing order is 1-3-4-2 and the point of the twin scroll is to separate interfering exhaust gas pulses. late night assumption, heh...

I said "off/on" (ha, if that makes a difference?) in reference to the "lag" I guess attempting to differentiate between the when (at what rpm) the turbo starts making power under a full throttle condition as opposed to getting on the gas mid-corner. I think I made it more confusing, but the terms kind of blend together sometimes. Essentially, I'm referring to the throttle response that's so good with N/A or supercharged in comparison to the slower response of a turbo setup and trying to minimize that.

I'm interested in VNT/VV, it looks like it's still more of an OEM thing though possibly due to cost of making it a reliable setup and only having enough market by supplying it as an OEM product. Even though there are plenty of people doing aftermarket turbos, I don't think there would be enough demand because they'd be pricey and as Sav was saying, most people wouldn't be able to control them without having a capable standalone or some auxiliary form of control which would make them even more costly.

The "Gamma Titanium Aluminide" wheel of the new EFR series is "over 50% lighter than its inconel counterpart". so awesome.
I think this, coupled with a twin scroll housing, hybrid ceramic bearings, and proper manifold will be very responsive.

Sav:

AFAIK VNT control is still pneumatic - IOW they still use the same wastegate actuators our "normal" turbos use.

The Holset he351VE uses a fairly sophisticated servo based system to control its VNT functionality.

lighter relative to what? relative to the moon? relative to the equivalent garret turbine housing?

Had this been "The 'Gamma Titanium Aluminide' wheel of the new EFR series is 'less than 50% of the weight of its inconel counterpart'", then we assume you mean less than 50% of its weight relative to zero, or "less than half"

Hypothetical examples:

a. Turbine wheel = 50 grams
"Over 50% lighter relative to 51 grams" = new wheel < 49.5 grams.
"Over 50% lighter relative to 60 grams" = new wheel < 45 grams.
"Over 50% lighter relative to 100 grams" = new wheel < 25 grams.
"Over 50% lighter" = Mathematically meaningless.
"Over 50% lighter relative to 40 grams" = >55 grams. (WTF!? IT GOT HEAVIER!! the 50g turbine wheel relative to 40 grams is -10g (negative 10) lighter than 40g. If we mulitply the difference by 1.5 (thus increasing the relative "lightness" by 50%) the new difference, relative to 40 grams is "-15g lighter" "OMG!")
"Less than 50% as heavy" = Weighs half as much relative to no weight

I worked in camera sales briefly, and when my co-workers said "the 10x zoom makes things look like they're 10 times closer" I was tempted to strangle them.(because mathematically, this is meaningless, does the object appear 10 times closer relative to the moon, or 10 times closer relative to that car 1 mile away?.....10 times closer relative to something that was between the object and the viewer would actually make it look farther away than it actually is.) To be mathematically correct, a 10x zoom makes things look like they're "1/10th as far away" (because that is relative to the actual distance of the object being viewed)

/off-topic rant

I'm not sure which one of us is retarded so I've bolded the relevant statement here. If I can read correctly, it is comparing the weight of the advertised wheel to the weight of the inconel version of the exact same wheel.

Have I been huffing too much glue today?

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.

haha, yeah, I hate lack of actual quantification as opposed to random numbers, which is why I left it in quotes =P however, I checked some numbers like I shold have before and:

Densities:
Gamma TiAl 4.0g/cm³
Inconel 8.14g/cm³

btw, I alt + 0179'd those ^3s instead of copy and paste B) aw yeeeee

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.

TL;DR: over 50% ligher than != less than 50% of the weight of.

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?

:jerkit:

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.

Got a linkie?

FWIW the old Aerochager miata kits used the same old wastegate actuators we have.

Well FWIW AFAIK dem Porsches can take track abuse.

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.

Also, the fucktards in this thread arguing about the fucking Ti-Al / inco weight verbiage need to get the fuck away from mt.net and return to m.net.

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.

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:

http://www.blogcdn.com/www.autoblog....07/6653491.jpg

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.

Yes.

See:
http://blogs.insideline.com/roadtest...alkaround.html

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.

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.

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:giggle:). 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.

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.;)

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.

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?

So Sav's comment that the control system is a hurdle for VNT, isn't correct?

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?

This twin scroll on a 4-cyl stuff suggests that the twin scroll acts like having 2 separate turbines on the same shaft, is more efficient.

If it's due to "pulse energy", it suggests that a turbine would operate more efficiently powered from 3 cylinders than 6, or from 2 cylinders than 4.

Would a turbine reach higher effcieincy powered from 1-cylinder than from 2? After all, you can't get any more discrete "puffs" than that.

Just curious which ones you've seen fail? I'm not really a SP fan but I know a couple people that have them on Supras that see some track use.

WHOA BRO! YOU MEAN QUAD SCROLL?!

If inertia/mass and friction and all that poo stuff was gone, I think 2 smaller separate turbines might be more efficient?

The argument is that the pulses interfere with each other in a manner that causes static pressure in the manifold as opposed to against the turbine blades. If the pulses aren't interfering though, I think there actually is some level of scavenging effect.

^^^:vash: GOD DAMNIT YOU BEAT ME!!!

Not a real answer, but I'm sure if you run 'em fat enough and keep the EGTs low you might be alright. Apparently with turbos though sometimes running rich can increase your EGTs? The only experience I have with EGT tuning though is from playing with the 38mm carburetor of a 2-stroke 125cc GP bike with a huge bridged exhaust port so it wouldn't surprise if it's a little different...

drawing on more past experience, and knowing turbo EGTs can get up to and even past 1800F, stainless will definitely get soft (and bend and break in a moving part) around 1600-1800F. They made us do science fair projects in 10th grade so I did a valveless pulsejet (nice video of it glowing around 1800F) and instead of using proper "block clamps" I was like hurr hose clampz is cheap and the 16 gauge 304 stainless tubing deformed to a bit of a D shape.

I was thinking of just making a super-gnar one that was MELTPROOF like a fucking ball valve or something excessive and bulky, but was curious as to how in the hell I would make a seal similar to what's on the turbine side of the turbo shaft. Similar curiosity over at SP I guess because the black soot that covers the outside of their valve shafts confirms they're leaky, F that S...

Probably, but then you lose it all in turning a second set of wheels.

A quad-scroll turbo would be interesting. Probably really hard to cast, though.

I didnt know this about the porsche until now, but having driven one for about 20 minutes I couldnt for the life of me figure out how it made scary power with such little lag. It was pretty impressive to say the least. Im liking this twin scroll stuff now...

Dann

What they're talking about, and what you primarily felt was the VNT in action.

The naturally aspirated version is not a slouch either.

:confused: :facepalm: :noob:

Look if the naturally aspirated version makes 300 something hp, it's not like the turbo version is going to be slow as a bag of dicks before the VNT turbo extraordianaire spools up. Who knows- porsche might have set up the VNT to ramp up boost gradually instead of OHSHITWEAREINBOOSTNOWOMGI'MGOINGSIDEWAYSTHISPORSCH EISAPIECEOFSHIT

I do...

Having throttle by wire and electronic boost control it was surprising that if you drove it gently it was quick but just like a decent v8 family car and you had to get your foot past 3/4 before it boosted, but once youd done that it was extremely responsive and powerful, it just transformed into a monster, then if you drove it gentle for 10 seconds it went back to grandma mode.

And thanks to Nagase for pointing out to me it is the VNT helping what i felt... lol

Dann

I was not suggesting such a system, merely a thinking out loud trying to understand why twin scroll is better than single scroll.

Let me rephrase my question another way.

Would an optimized turbine, designed for a single cylinder engine, be more efficient than that for a 2, 4, or 6?

Another question:

Does having your exhaust puffs in discrete puffs, produce a more efficient turbine, than if you passed the puffs through an ideal, theoretical lossless entropy-constant "puff homogenizer", so that the energy in the exhaust stream were in a continuous high temperature, high pressure flow like steam entering a steam turbine?

If so, is it because there is more kinetic energy in having the exhaust in puffs and there is inherently energy loss if you passed said puffs through said ideal "homogenizer"?

ME's? M@? Jay?

I like to just state a concept here to discuss.

A 45 IDA webber is often used in pairs on 4 cylinders and rotors that make 250hp and they arent too big at all for that application infact starting to get a bit small, but on a v8 you can make much much more power with the same carbies and they still arent too small. The reasoning is supposedly that having multiple cylinders means that the air and fuel is being drawn through 100% of the time not just for 260 degrees (just pulling an intake cam duration out of my head here) out of a 720 degree cycle.

Perhaps it could be similar with spooling turbos when it comes to feeding them?

Dann

It's not.

Cheers...

Do you mind explaining why or pointing my to a thread containing so explanations as to how a turbo it spooled efficiently with either single spaced pulses versus a single flow?
Also why do big power engines (drag...f1) use hugely long runners? it isnt for this effect?

Dann

The "homogenizer" is like an ideal equal-length manifold collector, right? Separating the pulses out so they never converge except at the turbine blade? This evens out the pressure and prevents spikes and dips that kill overall flow.

I know that twin-scroll setups will outspool a perfect collector like that, and I'm fairly sure the kinetic energy of the "puffs" are what make the difference. You can use that energy at lower RPM to puff against the turbine wheel and spin it just a little quicker. I guess there's no high-RPM gain because the "puffs" blend together and you lose the additional effect - that's why most twin-scroll housings use larger A/Rs to split the benefits between spool and top-end flow.

This is the answer as far as puffs vs flow:

http://www.full-race.com/img/article...comparison.jpg

It's covered more in page 22 of: http://www.full-race.com/articles/efrturbotechbrief.pdf

If you're curious about turbos at all, it's a good read.

Integrate momentum with respect to velocity, KE is basically defined as 0.5mv^2, so with the higher velocity you have these exponentially higher energy pulses which translate force onto the turbine wheel more effectively especially when the turbine is at low speed.

A pulsed flow is superior, because if you have a constant flow there will be less static pressure. Think of it kind of like a small explosion, I guess, next to turbine blade. The hot gases expand against the turbine blade and against the surrounding static pressure. With pulsed flow the exhaust gases slow down (decreased dynamic pressure, increased static pressure) between pulses and create that higher static pressure for the pulse to work against. Of course, as speed increases this effect fades.
(This is mostly assumption, but it seems right to me. Corrections are appreciated!)
Definitely a great overall read, they didn't really go that in-depth on twin-scroll though. I wish there was more data and resolution of the image for that matter with those FoMoCo open/divided flow graphs.

ALSO, MY DEMANDS! Apparently the 0.92a/r twin scroll is large enough to where the 0.64a/r single scroll is just as responsive on the miata. I really want a 0.76-0.83a/r twin scroll housing without an internal wastegate. Any chance that will be available?

edit- lol@ Earth Friendly Race Ready EFR^2 then Earth Friendly Racing for EFR. I get that they mean earth friendly because of the efficiency increase, but unless they were trying to market to the people who wrote the CAFE laws "Engineered For Racing" is a much better use of the acronym EFR.
Ooo, and the abradable coating stuff was neat. I remember hearing that the newer RX-7s had that. That would definitely add more baller status to the EFR line in addition to the ceramic bearings and Gamma-Ti turbine wheel. Even if gains are minimal, mad sluts be gettin wet for the abradable coating...

They go in depth enough to answer the question, which is really why I linked it in response... to the question. I know, not enough tech, but if they went into deep tech, that'd be a 1000 page document no one that they want to read would read (shop owners/people with EFR spending money).