what's the difference between twin screw, centrifugal, single turbo and twin turbo?

[Ammonia]

Originally Posted by Hanni_0176

Why is a twin turbo worthless on our platform? From what I've read about boxer engines, wouldn't a twin scroll design provide the greatest efficiency with minimal lag while retaining good top end power?

I'm not the most knowledgeable person when it comes to auto mechanics, so I'm not saying you're wrong. I guess what I'm asking is, can you explain why twin turbos are worthless on our platform?

I came in here as well to ask the same thing. I loved my twin turbos on my BMW, because the lag was nearly non-existent, response was amazing, power easily made.

But then again that was on an I6, and this is a 4 cyl boxer. I'm just curious.

[xjohnx]

Originally Posted by Ammonia

I came in here as well to ask the same thing. I loved my twin turbos on my BMW, because the lag was nearly non-existent, response was amazing, power easily made.

But then again that was on an I6, and this is a 4 cyl boxer. I'm just curious.

The 135i had a twin scroll turbo, not twin turbos, no? There's a distinct difference. See above.

[AVOturboworld]

There is single scroll turbo, twinscroll turbo, twin parallel turbo, and twin sequential turbo. I've actually owned OEM versions of 3 of these 4. I've owned 2 twin sequential turbocharged Legacy 2.0's, a twinscroll Legacy 2.0, and several single scroll turbocharged vehicles (many of which were originally n/a).

The twin sequential turbo was a great idea on paper, but had a big flaw in execution on a 2.0-liter motor. When the turbo system switched over to the larger secondary, it opened valving to feed all the air to said secondary - leading to a loss in boost referred to as the Valley Of Death (VOD). And yes, I coined that term on NASIOC many, many years ago. Basically, imagine a motor that has to spool up twice, the second time from about 3300rpm to 4000rpm.

Mainly, the issue has to do with 2.0-liter motors (or smaller). There isn't a lot of exhaust gas to work with. And it's exhaust gas that turbo's generate power off of. Putting two turbo's in just lowers that efficiency too much, which is why even a parallel system wouldn't work all that great (but would on a 3.0-liter).

All in all, it's about efficiency. If we were talking about turbocharging a 3.0-liter or larger, it would be a lot easier because there would be so much more to work with.

[jc1993]

Originally Posted by Tansey86

Turbo wins in pretty much every aspect aside from price and install time.

no doubt that turbo makes more power but wen it comes to over heating which would be safer???

[jc1993]

Originally Posted by Splat

Thanks, that is why I want twin screw...I am happy with the high end revs and power.

like wise just want that low end torque dip vanished lol

[ft86me]

I def love my centrifugal vortech. The car feels like it has a bigger motor and the distribution of the power feels really equal all throughout the power band. I can rip through the canyons without a problem without worrying about power kicking in all of the sudden. I personally feel the car is much more predictable with my kit. plus i still get the blow off sound HAHA. just my .02. not bashing anyone or anything. hope this helps

[AVOturboworld]

Originally Posted by jc1993

no doubt that turbo makes more power but wen it comes to over heating which would be safer???

Overheating from what, specifically? From a hotter engine bay? Due to a FMIC being in front of the radiator core? Or due to the engine making more power, burning more fuel, thus making more heat? Or from heat soak on the intake path due to lack of intercooler?

"Overheating" from a <insert FI option here> is a loose term that's thrown around without much actual understanding of it. People were quick to blame FI for overheating at the track, for instance, then it turns out the car in n/a form ran too hot at the track.

If you FI a car, it will run hotter. The engine will always run hotter the more power it develops. Find a way to make it make the same power in n/a form, and it will likely run as hot.

Put an intercooler in front of the radiator, and it will not get as much cool air, leading to higher temps. So what will matter the most there will be the efficiency of the FMIC core and radiator core, the FI option pushing the air through the intercooler won't matter.

[fenton]

Originally Posted by xjohnx

The 135i had a twin scroll turbo, not twin turbos, no? There's a distinct difference. See above.

N54 is twin turbo. N55 is twin scroll. They switched to twin scroll or "twin power" as BMW calls it. In about 2012 I think... Maybe 2011

Sent from my HTC One using Tapatalk 4

[xjohnx]

Originally Posted by fenton

N54 is twin turbo. N55 is twin scroll. They switched to twin scroll or "twin power" as BMW calls it. In about 2012 I think... Maybe 2011

Sent from my HTC One using Tapatalk 4

Ahh gotcha, knew I was missing something.

[Hanni_0176]

I just read up on it again, and it looks like I was wrong in assuming twin scroll meant two single scroll turbos. I appreciate the info, thanks guys.

From http://www.modified.com/tech/modp-09...n/viewall.html

Back in the day, most aftermarket and factory turbocharger systems featured simple log-style exhaust manifolds. But just like on normally aspirated engines, where exhaust manifold design has become recognized as a critical element to maximizing horsepower and torque output, there has been increasing attention paid to turbocharger and turbo manifold design. Divided or "twin-scroll" turbos and manifolds have emerged as the preferred design of many of the top tuners and even OEMs, showing up on high-performance models like the Mitsubishi EVO, Pontiac Solstice GXP and JDM Impreza STI. But what exactly are the differences between single-scroll (or constant pressure) turbo systems and twin-scroll (or two-pulse) turbo systems and how do these design differences impact overall engine performance?

Single-scroll systems have been in use for a long time, and for good reason. These systems are generally compact, inexpensive and extremely durable under the high heat they're exposed to. So from a simplicity of design, packaging and reliability standpoint, a single-scroll, constant-pressure turbo system is quite appealing-especially to the OEMs that must consider more than just power production. Although log-style or simple unequal-length turbo manifolds used by the OEMs can be tweaked for improved performance or replaced by a more sophisticated equal-length aftermarket manifold, this doesn't change the fact that there's a single exhaust gas inlet to the turbo's "hot side" turbine (which powers the "cold side" compressor, force feeding a denser and therefore more oxygen-rich air charge into the combustion chamber from the intake side). Because of this design limitation, single-scroll systems are not particularly efficient at low engine speeds or high loads. This decreased turbine efficiency contributes to turbo lag, something we've all probably experienced while driving a stock turbocharged vehicle.

One of the biggest limitations of most factory single-scroll turbo system is the restrictive nature of its log or compact unequal-length exhaust manifold. Keep in mind, the purpose of this manifold isn't just to channel exhaust gases to the turbocharger's turbine wheel; the manifold must be designed to allow exhaust gases to exit the combustion chamber of each cylinder quickly and efficiently. Also keep in mind that these exhaust gases do not flow in a smooth stream because the gas exits each cylinder based on the engine's firing sequence, resulting in distinct exhaust gas pulses. Next time you fire up your car, place your hand lightly over the exhaust tip (before it gets hot!) and you will feel these pulses. With a log-style or compact OE-style, unequal-length runner exhaust manifold like you'll find on SR20DET or USDM STI engines, the pulse from one cylinder can interfere with subsequent exhaust gas pulses as they enter the manifold from the other cylinders, inhibiting scavenging (where the high-pressure pulse draws the lower pressure gases behind it out of the combustion chamber with it) and increasing reversion (where exhaust gas flow is disturbed so much that its direction of travel reverses and pollutes the combustion chambers with hot exhaust gases). The trapped and wasted kinetic exhaust gas energy from poor scavenging and too much reversion also means higher combustion and exhaust gas temperatures, necessitating less aggressive ignition timing and reduced valve overlap as well as richer air/fuel mixtures (and higher NOx emissions).

Twin-scroll turbo system design addresses many of the shortcomings of single-scroll turbo systems by separating those cylinders whose exhaust gas pulses interfere with each other. Similar in concept to pairing cylinders on race headers for normally aspirated engines, twin-scroll design pairs cylinders to one side of the turbine inlet such that the kinetic energy from the exhaust gases is recovered more efficiently by the turbine. For example, if a four-cylinder engine's firing sequence is 1-3-4-2, cylinder 1 is ending its expansion stroke and opening its exhaust valves while cylinder 2 still has its exhaust valves open (while in its overlap period, where both the intake and exhaust valves are partially open at the same time). In a single-scroll or undivided manifold, the exhaust gas pressure pulse from cylinder 1 is therefore going to interfere with cylinder 2's ability to expel its exhaust gases, rather than delivering it undisturbed to the turbo's turbine the way a twin-scroll system allows.

The result of the superior scavenging effect from a twin-scroll design is better pressure distribution in the exhaust ports and more efficient delivery of exhaust gas energy to the turbocharger's turbine. This in turn allows greater valve overlap, resulting in an improved quality and quantity of the air charge entering each cylinder. In fact, with more valve overlap, the scavenging effect of the exhaust flow can literally draw more air in on the intake side while drawing out the last of the low-pressure exhaust gases, helping pack each cylinder with a denser and purer air charge. And as we all know, a denser and purer air charge means stronger combustion and more power, and more power is good!

But the benefits of twin-scroll design don't end there. With its greater volumetric efficiency and stronger scavenging effect, higher ignition delay can be used, which helps keep peak temperature in the cylinders down. Since cooler cylinder temperatures and lower exhaust gas temperatures allows for a leaner air/fuel ratio, twin-scroll turbo design has been shown to increase turbine efficiency by 7-8 percent and result in fuel efficiency improvements as high as 5 percent.

Combine these benefits with a well-engineered tubular equal-length manifold and the design strengths of a twin-scroll approach can pay even bigger dividends. "Equal length" simply refers to the length of the primary exhaust manifold tubes or runners that the cylinder head exhaust ports breath out into, which should ideally be of equal length before merging at a narrow angle at the collector so that the gases flow smoothly together into the turbine inlet. This helps maintain exhaust gas pulse energy, resulting in better boost response and overall higher turbo efficiency.

Designing a high-performance twin-scroll tubular manifold like those available from top tuners like Full-Race is no simple task. Fitting equal-length primaries into the tight confines of a turbocharged car's engine bay while maintaining proper radius bends and strong exhaust gas flow characteristics is a serious design challenge. Determining the best length and diameter of the primaries and angle of the merge collector also requires a lot of R&D, as does choosing the best wall thickness and material for the tubing itself. That's where Full-Race's team of highly educated mechanical engineers and years of constant refinement of their designs comes into play. According to Geoff at Full-Race, "Because of the increased turbine efficiency found in twin-scroll systems, twin-scroll manifolds can often use a smaller runner than a single-scroll design. However, due to the complex shape of the runners and the requirement for a second wastegate and dumptube (one for each side of the divided turbine) there's more mass and more parts which adds expense and complexity. Plus, twin-scroll turbos are physically larger than their single-scroll equivalents, so it's more difficult to make them fit our cramped engine bays." Overcoming these challenges means developing extremely robust manifolds that make smart use of the available space, something Full-Race does with the help of computer programs like SolidWorks and other proprietary processes.

All this hard work does translate to serious performance gains in the power-delivery department, particularly at spool-up and peak torque where sophisticated tubular twin-scroll manifolds properly matched to a twin-scroll turbo deliver superior airflow to single-scroll or OE twin-scroll designs. According to Geoff, "Our twin-scroll turbo kits have a higher average cylinder pressure and turbine efficiency, while single-scroll systems tend to have a higher peak cylinder pressure and exhaust backpressure. We have found the twin-scroll systems have higher backpressure at low rpm (which is good for turbo spool-up) and lower backpressure at high rpm (which is good for top-end performance). On the other hand, single-scroll systems have lower backpressure at low rpm (bad for spool-up) and higher backpressure at high rpm (which hurts top-end performance)." In order to realize the full benefit of a top-shelf twin-scroll system like one of Full-Race's, the manifold design and A/R ratio of the turbo must be spot-on, so it's best to get the help of a professional when choosing a turbo for this type of system.

It's certainly possible to generate huge power and great high-rpm performance with a single-scroll turbo system. There are plenty of examples of very high-horsepower, single-scroll turbocharged engines out there, but with single-scroll systems spool-up and response are much slower than with a twin-scroll design, yet twin-scroll systems still provide excellent top end performance. Although switching from single-scroll to twin-scroll can be expensive, for hard-core boost junkies who want much faster throttle response without giving up any top end, there is no better solution. With the added benefits of higher turbine efficiency, lower cylinder temps and EGTs which allow more aggressive timing and fuel mapping, and the freedom to run more overlap,twin-scroll turbo system design is really a perfect match for the high specific output engines featured in many of our favorite sport compact machines.

[mike the snake]

Originally Posted by Frs300

Twin scroll isn't twin turbo..twin scroll has two holes that blow air over the exhaust wheel. One is open at low rpms to increase air velocity, at higher rpms second one opens up to help out the top end. Twin scrolls usually spool at low rpms and are tq monsters.

It was my understanding that twin scroll turbos had two holes, but they were not different in size. The two holes were used to split the exhaust pipes up so the exhaust firing order pulses didn't oppose each other.

I had a BMW 135 twin turbo, the newer ones had the twin scroll, so I had to look that one up

[Floggin Tires]

Exhaust manifold runners are combined (in 4cyl's case paired) together based off firing order.

Doing this separates the interference of the exhaust gas pulses you would have from runners just all merged together.

These runners (that are joined together) stay separated from other runners that are joined together.

Then they run into the turbine inlet flange which is divided.

The turbine housing has two separated scrolls. (hence twin scroll)

These "pulsing" gasses are delivered smoothly, with increased efficiency. Also improving exhaust scavenging.

[Ammonia]

Originally Posted by xjohnx

Ahh gotcha, knew I was missing something.

Yea I had an 08 with the N54. Damn near bulletproof motors, 700+ reliable whp on stock block is impressive. Mine had 400+ and I miss it lol




On topic, basically our little 2.0 wouldn't produce enough exhaust to make a twin set-up viable is what you're saying @AVOturboworld ?

[circuithero]

Always such a dangerous topic! Ill give my personal experience as I used to play the turbo game... But first, my own small rant:

//RANT//

There is a lot of bias coming from the guys trying to sell you boost. I have nothing against them but take everything with a grain of salt and do your research!

1. First and foremost: F1 is not going turbo because that is what the teams and manufacturers want to improve performance. It's a silly regulation change to develop a better perception from the outside and make the sport seem more green. On the one hand with F1 developing technology this could trickle down to the OEMs, with more and more cars going OEM FI. Aside from that, I do not see it as an advantage at all and is another bonehead move by the regulators combined with a lot of politics in the background.

2. The McLaren is faster than a 458 for maybe two laps, before it starts pulling timing because of heat saturation and to protect the car. I believe Motortrend ran into this in a 3 car comparo. Ultimately, in a time trial the McLaren is a superstar, need to go the distance? Nada.
I assure you the Italia v8 cost a lot more to R&D and build. I suspect McLaren went with boost because that is all they could afford as they are not a giant like Ferrari. But that is just that, speculation.

3. Im sorry but an NA engine making the same power with the same cooling will no way in hell generate as much heat. With a blower you are compressing air which is what generates the heat and how much heat is a function of efficiency and how much air you are compressing. The NA engine will cost 3X more to build and will never have the torque but it will certainly run cooler.

//RANT//

My personal experience is with turbo miatas. I had the chance to purchase a well sorted, NA bolt on 1999 Miata or a boosted 1990 track monster. I went the fast and furious route and lost 1-1.5 years of possible and proper race experience and coaching. Mind you this is from the perspective and POV of a guy who likes the racing more than the wrenching and tuning. I sure as hell don't spend my time on highways doing "pulls".

Turbos do have a lot going for them and have come a long way in the last 3 decades. Way better compressor ranges and efficiency, easy map switching (Piggy Backs are the worst, ask me how I know), launch control, flat shifting...etc, etc. They will make you the most hp/$, without a doubt.

Example: Only with a turbo can you make 200whp/200lbft out of a 1.6l miata motor. For the same money, NA you would be lucky to get 140/100. BUT! And this is a HUUUUGE BUT: its not all fairy land and pure numbers, there is a lot more especially depending on what you want to do. Common scenario from miata world, might sound familiar: "Hey guys, love the car, so much fun to drive but could use a bit more power - so I have 4k and Im looking for 200whp". Universal answer will be boost and you will hit your power level. Done. Easy.

But then, you need a clutch. Car is also running a bit hot in traffic, so need a bigger radiator, maybe patch up some ducting. Tuning is a bit rough could use some dyno time. Boom, your 4k proposition is now 6k if you are lucky. If I was to boost my car and I didn't love trackdays and autox so much, I would definitely be going turbo. You get the great Jeckyl and Hyde where offboost you can be sipping gas and getting stock mileage with no extra attention and one downshift and you leave all traffic 2 blocks behind in a couple seconds. Plus, that torque hit is what boostheads love and nothing hits as hard as a well sized turbo. On the other hand, torque brakes stuff.

God forbid you try to track your 6k (if your lucky) proposition. Get ready to: overheat, blow oil, exhaust manifold is loosening (I melted a dipstick, with a heatshield in place), intercooler piping coming off...etc, etc, etc. You are in for another 3-4k just to get her to survive a 20 minute session in moderate heat. Most of the miata guys quickly learned to save the boost only for the street cars, some spent megacubic dollars making their cars reliable on track and most that like the racing invest in a low power, miata race car that costs them much less to run. You eventually get used to any power and quickly learn that it is all relative. I would rather drive my car 10/10ths the entire time and progress as a driver than get faster with parts and be driving the car between 8-10/10ths because its too damn hard to drive consistently at the limit. You would see these boosted miata guys, with more than double the power, better suspension components getting walked on by caveman spec miatas with 100whp and cheap suspension components.

And that is the crux of the matter. I have nothing against boost as long as you are aware it is always a larger financial commitment then you expect unless you have been down the road a couple times and know to take your estimated cost and double it when all is said and done. You want to be top dog, the fastest and chasing big dogs down? You will need boost and you will certainly pay to play. Remember you are adding more points of failure, more heat, more weight and more torque. That all requires higher maintenance and parts will wear out faster = $$$. If I had a dedicated race car and 8k laying around my street FRS would be running a nice <insert vendor> turbo. Would I try to track a boosted FRS? Hell no, been there done that. Better buy a racecar and it will be just as fast, more reliable and I won't ruin my daily and go through months of headaches.

For track and autocross I personally do not like turbos. Aside from being financially inefficient - non-linear torque makes it difficult to drive at the limit, consistently and all the time. I have never driven a turbo car in anger that I was comfortable pushing to the limit off the bat. You need to know the car and the course like the back of your hand, otherwise you are not extracting the maximum from either or you are lying to yourself. First time I raced a beast of an SM E36 BMW (twin screw), with slicks, in the rain - I was pushing that car. Despite what everyone from turbo camp will tell you, properly sized turbo or not, as the boost develops (lag) you will have non linear torque coming on. Sometimes in autocross all I need is 0.5-1 seconds of throttle and I want the power to be consistent and predictable which is not what you will get with a turbo car. For that application I prefer the positive displacement motor, the boosted all aluminum I6 just felt like a race V8.

If you look up comparo reviews of these Porsches, you will see similar thoughts: GT3 (NA) vs GT2 (FI). Ultimately the GT2 is always faster but it is less approachable, consistent and the GT3 always wins overall.

I will leave you with one last thought: Good tires and Coilovers should be worth roughly 3-6 seconds on a 60 second course and cost you <5k. What do you think is cheaper/easier to replace, shocks or motors?

PS. I am taking the Porsche RS philosophy with this car. Take out 100-150lb without making it uncomfortable, get it to 200-220whp with minor bolt-ons and enjoy my giant killer on track. Its such a great platform, I would just prefer an ITR instead of a GSR