JasonC SBB

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.

njn63

iTrader: (4)

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.

NickC

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.

mx5autoxer

iTrader: (1)

^^^ GOD DAMNIT YOU BEAT ME!!!

NickC

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 ******* 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...

Savington

iTrader: (31)

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.

nitrodann

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

Nagase

iTrader: (6)

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

Faeflora

iTrader: (2)

The naturally aspirated version is not a slouch either.

Nagase

iTrader: (6)

Faeflora

iTrader: (2)

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

nitrodann

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

JasonC SBB

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?

nitrodann

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

Nagase

iTrader: (6)

It's not.

nitrodann

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

Savington

iTrader: (31)

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.

Nagase

iTrader: (6)

This is the answer as far as puffs vs flow:



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.

NickC

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 ***** be gettin wet for the abradable coating...

Nagase

iTrader: (6)

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).