Cadillac News: Cadillac Unveils New A Twin-Turbo 3.6L V6 For The 2014 CTS

[regfootball]

Most cars today have high belt lines to meet crash standards. GM and Chrysler tend too keep the low roof and smaller windows where Ford lifted the roof on the Taurus and look like a SUV or Checker.

getting sick of the bunker cars. a lot of the public dislikes the problems created by it also.

[dwightlooi]

I read only the twin turbo CTS will get the 8-speed, which is sort of sad since even a Hyundai Genesis Coupe 4-cylinder has an 8-speed transmission. I see no reason as to why every Cadillac doesn't have a standard 8-speed on everything, at least on their rear drive vehicles.

The reason was that GM suspended its 8-speed transmission development during the bankruptcy. GM, today, does not have an 8-speed transmission. I suspect that the CTS's 8-speed is an Aisin sourced transmission (the ratios are exactly the same which is highly unlikely for an indigenous transmission).

But, here's my basic take on transmissions... Small, less powerful, engines especially need 7 or 8 speeds to meet fuel efficiency and performance targets. Big engines do not need as many gears, but can use a wider spread. Beyond 7 speeds the benefits are really minimal -- spread is more important. A 7.00 spread on a 6-speed would benefit an ATS-V or Corvette, more than a 6.71 spread 8-speed from a performance and/or MPG standpoint.

[Drew Dowdell]

I think the 8-speed Cadillac is getting now is just a hold over until a GM designed/built 8-speed is done.

[dwightlooi]

GM did patent this logo back in 2007-2008, so they were seriously working on something until the sky came crashing down. When they re-started and how close to production they are at this point is anyone's guess.

[dwightlooi]

Anyway, transmission aside, I was kinda disappointed that they used a traditional bi-turbo setup. A reverse flow single turbo design would be better.

A reverse flow design will place the exhaust on the inside of the Vee. This allows you to use a single turbo instead of two smaller ones. This is both more economical and superior in terms of performance -- because larger turbines and compressors also tend to have higher efficiencies. Hence, a single large turbo is always more thermally efficient and more responsive than two smaller ones of equivalent technological content. Given that GM is using an air-water intercooler this can also be place in the Vee allowing for a very compact package. Emissions is also superior.

The reason V6es traditionally use two turbos is that they are typically adapted from designs that do not easily allow for the intake and exhaust ports to be reversed. Two turbos are hence a necessity because the exhaust ports of the left and right banks are so far apart. If you rout the exhaust from one back to the other there will be a tremendous loss in efficiency.

BMW's V8 bi-turbos for instance is a reverse flowed version of the NA 4.4 V8. They also went from two turbos to a single one in the I6es -- albeit more for emissions that anything else.

Edited March 21, 2013 by dwightlooi

[hyperv6]

Most cars today have high belt lines to meet crash standards. GM and Chrysler tend too keep the low roof and smaller windows where Ford lifted the roof on the Taurus and look like a SUV or Checker.

getting sick of the bunker cars. a lot of the public dislikes the problems created by it also.

Sorry some people dislike but I like mine and I am not alone.

I am sure they all will get 8 speeds in time as they ramp up production. Even the Malibu has the 4 cylinders on the 4 speed till they got production to the point to support all.

They don't have much time, Lexus had an 8-speed transmission in 2007, Hyundai even has their own in house built 8-speed. When Cadillac first got 5-speed autos in the CTS and STS the other guys went to 6, when Cadillac got 6-speeds, Mercedes, Infiniti, Lexus, BMW starting using 7 or 8. If the ATS gets an 8-speed on the 2017 refresh, BMW will probably be on a 10-speed by then.

With all the chapter 11 delays on product GM has the late 8 speed is the least of their problems.

Anyway, transmission aside, I was kinda disappointed that they used a traditional bi-turbo setup. A reverse flow single turbo design would be better.

A reverse flow design will place the exhaust on the inside of the Vee. This allows you to use a single turbo instead of two smaller ones. This is both more economical and superior in terms of performance -- because larger turbines and compressors also tend to have higher efficiencies. Hence, a single large turbo is always more thermally efficient and more responsive than two smaller ones of equivalent technological content. Given that GM is using an air-water intercooler this can also be place in the Vee allowing for a very compact package. Emissions is also superior.

The reason V6es traditionally use two turbos is that they are typically adapted from designs that do not easily allow for the intake and exhaust ports to be reversed. Two turbos are hence a necessity because the exhaust ports of the left and right banks are so far apart. If you rout the exhaust from one back to the other there will be a tremendous loss in efficiency.

BMW's V8 bi-turbos for instance is a reverse flowed version of the NA 4.4 V8. They also went from two turbos to a single one in the I6es -- albeit more for emissions that anything else.

While I will not dispute anything you said I so want to add some more info here that is relevant.

[hyperv6]

Anyway, transmission aside, I was kinda disappointed that they used a traditional bi-turbo setup. A reverse flow single turbo design would be better.

A reverse flow design will place the exhaust on the inside of the Vee. This allows you to use a single turbo instead of two smaller ones. This is both more economical and superior in terms of performance -- because larger turbines and compressors also tend to have higher efficiencies. Hence, a single large turbo is always more thermally efficient and more responsive than two smaller ones of equivalent technological content. Given that GM is using an air-water intercooler this can also be place in the Vee allowing for a very compact package. Emissions is also superior.

The reason V6es traditionally use two turbos is that they are typically adapted from designs that do not easily allow for the intake and exhaust ports to be reversed. Two turbos are hence a necessity because the exhaust ports of the left and right banks are so far apart. If you rout the exhaust from one back to the other there will be a tremendous loss in efficiency.

BMW's V8 bi-turbos for instance is a reverse flowed version of the NA 4.4 V8. They also went from two turbos to a single one in the I6es -- albeit more for emissions that anything else.

I would like to add some other basic Turbo info here. Generally the use of two turbo or bi turbo is that larger engines like a V6 and V8 for the street need two smaller turbo's to cut down on lag. One large turbo will often produces more lag as it takes too long to spool it up to be effective. Two smaller turbo's tend to spool faster and reach peek boost faster and at lower end on a street car while moving the same amount of air as a larger single. In some rare cases they have also used progressive where there is one small and one large to provide less lag. Now in racing where the revs are up and the throttle is down lag is less of an issue with a large single turbo but on the street it is a rare sight to see a single anymore just do to the low end lag of the large unit. We deal with large racing turbo's at work and if used on the street they would be a major disappointment but coming off the line at near the red line they build boost before they launch.

Also packaging in todays small engine compartments are difficult and two smaller units can often be fitted in on the sides or below an engine. Some kits we have even package a pair near the rear axle.

Smaller engines like my 2.0 use a single but they it is a modern duel scroll that helps eliminate much of the lag with a two passage air system in the housing that keeps air flow up and progressive. Also with only 2.0 liters it does not have as much demand for boost as the engines demand for air are less so it is a much smaller turbo vs. the needs of a V8 or V6. Note do not have any kind of lag like a GN.

BMW has the single but they are also working on a Electric Turbo charger. This is not one of the E bay rip off deals but it is a Electric turbo to supplement their single exhaust fed unit to eliminate the lag on the larger turbo at low end. They expect once it is read for market it would make for a much smoother performing system with no lag. They have not given all the details but the info is out on what they are trying to do.

turbos are an are even few car guys really understand unless you spend some time reading up on it as things are changing fast in this area as companies spend more and more money on them,

[David]

Anyway, transmission aside, I was kinda disappointed that they used a traditional bi-turbo setup. A reverse flow single turbo design would be better.

A reverse flow design will place the exhaust on the inside of the Vee. This allows you to use a single turbo instead of two smaller ones. This is both more economical and superior in terms of performance -- because larger turbines and compressors also tend to have higher efficiencies. Hence, a single large turbo is always more thermally efficient and more responsive than two smaller ones of equivalent technological content. Given that GM is using an air-water intercooler this can also be place in the Vee allowing for a very compact package. Emissions is also superior.

The reason V6es traditionally use two turbos is that they are typically adapted from designs that do not easily allow for the intake and exhaust ports to be reversed. Two turbos are hence a necessity because the exhaust ports of the left and right banks are so far apart. If you rout the exhaust from one back to the other there will be a tremendous loss in efficiency.

BMW's V8 bi-turbos for instance is a reverse flowed version of the NA 4.4 V8. They also went from two turbos to a single one in the I6es -- albeit more for emissions that anything else.

I agree with you on what I have read about a single larger turbo, what do you think about a twin scroll single turbo? Do you still keep all the efficiencies of a large turbo but have the gain of the small section to keep a wide flat torque with minimal turbo lag?

Lot's to learn still on Turbo's, I have always been a supercharger guy. I felt the 3800 SC V6 engine was awesome and still think they should have done this for the ATS, CTS and XTS

[dwightlooi]

hyperv6, on 21 Mar 2013 - 18:59, said:

I would like to add some other basic Turbo info here. Generally the use of two turbo or bi turbo is that larger engines like a V6 and V8 for the street need two smaller turbo's to cut down on lag. One large turbo will often produces more lag as it takes too long to spool it up to be effective. Two smaller turbo's tend to spool faster and reach peek boost faster and at lower end on a street car while moving the same amount of air as a larger single. In some rare cases they have also used progressive where there is one small and one large to provide less lag. Now in racing where the revs are up and the throttle is down lag is less of an issue with a large single turbo but on the street it is a rare sight to see a single anymore just do to the low end lag of the large unit. We deal with large racing turbo's at work and if used on the street they would be a major disappointment but coming off the line at near the red line they build boost before they launch.

Also packaging in todays small engine compartments are difficult and two smaller units can often be fitted in on the sides or below an engine. Some kits we have even package a pair near the rear axle.

Smaller engines like my 2.0 use a single but they it is a modern duel scroll that helps eliminate much of the lag with a two passage air system in the housing that keeps air flow up and progressive. Also with only 2.0 liters it does not have as much demand for boost as the engines demand for air are less so it is a much smaller turbo vs. the needs of a V8 or V6. Note do not have any kind of lag like a GN.

BMW has the single but they are also working on a Electric Turbo charger. This is not one of the E bay rip off deals but it is a Electric turbo to supplement their single exhaust fed unit to eliminate the lag on the larger turbo at low end. They expect once it is read for market it would make for a much smoother performing system with no lag. They have not given all the details but the info is out on what they are trying to do.

turbos are an are even few car guys really understand unless you spend some time reading up on it as things are changing fast in this area as companies spend more and more money on them,

Actually, I think you bear two misconceptions here:-

(1) Two smaller turbos are not more responsive than a single larger unit. In fact, the reverse is true in ALL parallel arrangements. A larger turbo is more responsive than two smaller ones because it has higher turbine efficiency. Sure, the larger unit has a bigger and heavier rotating assembly with a greater inertial. However, a turbo with twice the flow capacity does is not twice the diameter and does not have twice the wheel mass -- it has less than twice, more like 1.5~1.6 times. Also, if you look at turbos from ANY manufacturer, the larger units always have higher turbine and compressor efficiencies. This has a lot to do with aerodynamics of the wheel. As wheels scale in size they become more efficient. Without going into the math, let's just say that it has everything to do with the fact that air molecues are the same size and pressure is pressure even as an object scales. It is easier for a car to go 60 mph than an ant (assuming its shaped just like a car) simply because it is bigger. This is true in aeronautics too. When you scale a wing to 1/4 the size or 1/16th the size for wind tunnel testing you need to adjust the Reynolds number otherwise the result will not be accurate -- not even close.

The only time when two turbos are more efficient is when the exhaust routing is horrible -- like when you have the turbo on one side of the engine and have to pipe half the exhaust through a long contorted pipe from the other bank (sometimes even adding a catalyst in between ala Subaru's WRX) -- or when it is a sequential setup. A sequential setup is when ALL the exhaust goes through the smaller turbo first, then as it approaches the limits of its efficient flow capacity, the waste gate opens and dumps all the extras through a larger unit. The only reason a sequential setup is more responsive is that 100% of the exhaust goes through one turbo first until the first waste gate opens. In parallel arrangements typical of V engines where 50% of the exhaust goes to each turbo there is zero responsiveness advantage. This is why you never, ever, see a parallel bi-turbo in an Inline-4 or Inline-6. A parallel Bi-turbo is simply a convenient compromise to easily route exhaust in Vee engines.

A reverse flow engine puts all the exhaust in the same place and allows a single turbine to be used with no routing penalties. The larger turbine, being more efficient gets better response compared to two parallel turbines of a smaller size (always). It is perhaps not as good as a sequential twin turbo design. But sequential twins are NOT typically implemented non-reverse flow on V6es or V8es anyway because of the same routing problems with getting all the exhaust to one side then the other. Hence, a reverse flow single turbo is almost always more efficient and a non-reverse flow twin turbo design.

(2) A Twin Scroll turbo turbo is not more responsive because it keeps airflow "up and progressive". The twin scroll turbine housing has ONE purpose and one purpose only -- to keep exhaust from a cylinder which is just opening its exhaust ports from pushing exhaust back into another cylinder which is near the beginning of its intake stroke and into the intake mannifold. During this instance, one cylinder near top dead center has both valves open (overlap period) and if the exhaust back pressure from the cylinder just opening its exhaust valves is not segregated, it forces exhaust (which is at a higher pressure than the intake air) into the intake. This is horrible for volumetric and scavenge efficiencies. The solutions are to either uses almost no overlap in the intake and exhaust cams (which is also inefficient but not as bad as if you let exhaust back flow into the intake. The other is to segregate the exhaust flows from two cylinder from the other four in an Inline-4.

It is important to note however that this is the essentially an Inline-4 problem! An Inline-3 for instance does not have two pistons at TDC at the same time. Neither does and I-5, V6 or V8. Hence, a Twin Scroll Turbo has ZERO benefits in I3s, I5s, V6es and V8s. Zero, nada, zilch!

Edited March 21, 2013 by dwightlooi

[dwightlooi]

Sorry just read my own post again and realized all the typos I made... which really confuses anyone reading it! LOL.

A Twin Scroll turbo's benefit is that it keeps exhaust leaving a cylinder near Bottom Dead Center (BDC) from back flowing through the exhaust valve(s) of the cylinder at Top Dead Center (TDC). This severely impacts volumetric and scavenge efficiency by preventing the intake charge from entering the cylinder at the beginning of its intake stroke and pushing out the last remaining exhaust gases.

A Twin Scroll Turbo is useful only in engine layouts where you will find a cylinder at Top Dead Center while another is at Bottom Dead Center at the same time. Generally, this means an Inline-4 and an Inline-6.

[Robert Hall]

Funny thing....I'm listening to the latest Autoblog podcast and they are discussing the next CTS and this engine.....two of guys on the podcast are having the same debate we saw here w/ Camino---about the gas mileage and comparing the TT V6 to a V8....

[hyperv6]

No matter how you spin it larger single turbo's have greater inertia and this leads to lag in street cars. Yes I agree that the larger turbo has efficiencies at higher RPM and top end performance but that seldom comes into play in a street car. Also the lag in a race car is a non factor since in many cases they launch at high RPM and can build boost sitting still. But that is not something some one will do in a ATS at a street light.

While duels are much better for street use and decreasing lag at low end they do suffer at the top end. This is where the Sequential comes into play. It worked well in everything from a 959, Supra and even a Ford Diesel. It as you point out and I agree address the low end and top end both.

Also another version is the Staged Turbo system. It is a Sequential taken to the next level where similar turbo's will move pressure from one to another to build pressure a it goes. I have seen this one mostly in aviation and it is pretty much impractical for cars.

There are factors to all these systems and can affect how they work and what they do as there are no absolutes but generally duel and sequential are the systems that have the best low end in most street cars and often are what we see. Now if you were racing a Grand National in drag racing one large would be your best bet for over top end performance where street driving is not a factor.

Though John Lingenfelter was racing a TT V6 Cobalt for us when he suffered his crash and If I recall was dipping in the 6 second 1/4 mile even with the TT set up. He was beating many of the single turbo cars at the time.

Duel Scrolled turbo systems are prized by OE automakers today. I will post this link as it better explains the truth of single scroll vs. duel. http://www.modified.com/tech/modp-0906-twin-scroll-turbo-system-design/viewall.html

But with any turbo system there are qualifications to each that need to be addressed. On turbo or system is not a one fits all in the OE segment or racing. Most OE system will be limited in total possible power but they have to give a little for better drivability. In racing it is all power and street drivability be damned. This is not unlike cam shaft choices as there are compromises that must be made for the sake of the street vs. over all power output or use.

While I agree with much of what you state there is still much you do not address as for a specific purpose of each set up tune. There are adjustments and compromises that are made to address the use. The fact is two small turbo's would better serve a OE CTS on the street and better meet the needs and drivability of the owners vs.. one large turbo. Now I would agree with you if the owner was running the quarter mile or on Bonneville.

[hyperv6]

Funny thing....I'm listening to the latest Autoblog podcast and they are discussing the next CTS and this engine.....two of guys on the podcast are having the same debate we saw here w/ Camino---about the gas mileage and comparing the TT V6 to a V8....

Are they addressing all aspects or are they just addressing pure numbers?

Too often people do not address the marketing aspect or the fact GM wants to take these cars globally where customers thinking is much different than it is here. Many places a V8 is not look upon as it is here. Also there at tax factors in play in other counties too. Just as Cadillac needs a Diesel overseas they need to address the gas engine to fit the wants and needs of the customer too.

[Robert Hall]

Funny thing....I'm listening to the latest Autoblog podcast and they are discussing the next CTS and this engine.....two of guys on the podcast are having the same debate we saw here w/ Camino---about the gas mileage and comparing the TT V6 to a V8....

Are they addressing all aspects or are they just addressing pure numbers?

Too often people do not address the marketing aspect or the fact GM wants to take these cars globally where customers thinking is much different than it is here. Many places a V8 is not look upon as it is here. Also there at tax factors in play in other counties too. Just as Cadillac needs a Diesel overseas they need to address the gas engine to fit the wants and needs of the customer too.

Not really...one of the guys is from Michigan and his view is always that a V8 improves anything.

[hyperv6]

Here is a good general common sense tech article from Turbonetics. It is not so much twin vs single but it addresses large vs. small turbo and how you plan to use it. http://www.turboneticsinc.com/choose_turbocharger

While Turbonetics supply most of the top racers today it kind of splits this down and better explains that one turbo or system does not fit all. Addressing the OE market is a challenge into itself.

[hyperv6]

Funny thing....I'm listening to the latest Autoblog podcast and they are discussing the next CTS and this engine.....two of guys on the podcast are having the same debate we saw here w/ Camino---about the gas mileage and comparing the TT V6 to a V8....

Are they addressing all aspects or are they just addressing pure numbers?

Too often people do not address the marketing aspect or the fact GM wants to take these cars globally where customers thinking is much different than it is here. Many places a V8 is not look upon as it is here. Also there at tax factors in play in other counties too. Just as Cadillac needs a Diesel overseas they need to address the gas engine to fit the wants and needs of the customer too.

Not really...one of the guys is from Michigan and his view is always that a V8 improves anything.

That is the problem as if Cadillac wants to grow and expand they need to take a global view and not just a Midwest view. I think with a good mix of technology engines and the V8 they will remain strong here but also start to draw interest overseas if they can under cut the price of the locals there.

If anything comes of the Vette with the two boost gauges that could lead to a interesting engine for the LTS. It would be a case where it would meet the demands of both TT V8? We will have to see what comes of the duel boost gauge Easter egg GM left.

[Drew Dowdell]

Why the assumption that boost gauges on a Vette mean it has a turbo? The CTS-V has boost gauges right now too and nary a turbo in sight.

[Lamar]

Why the assumption that boost gauges on a Vette mean it has a turbo? The CTS-V has boost gauges right now too and nary a turbo in sight.

Boost gauge for the supercharger then?

[Drew Dowdell]

I think a supercharged Vette would be far less surprising than a Turbo V6. I'm not saying a Turbo-V6 Vette is impossible... just ... lets not jump to conclusions over the boost gauges.

[hyperv6]

Why the assumption that boost gauges on a Vette mean it has a turbo? The CTS-V has boost gauges right now too and nary a turbo in sight.

Well I did some more digging and here is what GM's reply was to the Duel Boost gauges as of 3-14-13.

They claim they programed the TFT display with things for future models and they just did not shut it off. The TFT can be and will be used in some new models and they can turn on what they want. They did not go into detail to say if it was the CTS or other models. These models had it on as they were test cars and some of the TFT options were left on.

The Stingray is the first to use the TFT system and we will see it used in more cars.

This is like a advanced system of what is in my Terrain info center. I know someone who has jail breaked his Terrain and has all sorts of engine and car info at his disposal. He can now read tranny temps, engine oil temps, pressures and many other parameters that are not shown or offered in the stock configuration.

This system seems to be similar but has much more it can do for many cars. While the shape of the dash may change I suspect the type of dash we see in the Stingray will be common to many GM cars.

Edited March 22, 2013 by hyperv6

[Robert Hall]

Who knows? Maybe some day the words of Sir Mix A Lot will be prophetic.. 'Got it goin' like a turbo 'Vette'

[riviera74]

I would like to know the answer to this Q: Does GM currently have a supercharged 3.6L V6? If so, in which vehicles? If not, why not? Would a supercharged 3.6L V6 not be better than a TT3.6?

[hyperv6]

No SC 3.6. The 3.8 is also gone

There are advantages to both induction and in this case where you are looking to increase power in a smaller engine as they will in the future the Turbo tends to be better suited for it on several levels.

1 Turbo engines are demand pressure where the Supercharger is all ways there. and often can take up to 70 HP to drive. Granted the new Eaton units are greatly improved but there are still some issues with weight, efficency and drag.

2 Supercharged engines drive pulleys are set for max boost at specific RPM and will deliver less power at lower RPM when a Turbo is more flexible and can deliver more power at lower levers and under different loads.

3 DI injection, VVT and the new computers have solved many of the issues with past turbo's where it was hard to control them for the needs of the engine. DI thrives on Turbochargers.

4 Superchargers are difficult to mount in many smaller engine compartments and with the new hood clearance laws for crush space. They could go to a mount on the side of an engine but many compartments lack room there too.

Turbos are flexible in where they can be mounted. While it can make for more work on piping they can go on, infront, beside , under an engine and some today even mount them near the rear axle.

5 Superchargers still have an advantage with heat as they do not introduce as much heat but they still do add heat to an engine compartment.

Few companies are working withy SC anymore Ford is said to be dumping it for turbo's in the Shelby due to space.

I have owned several SC engines and they were fine and reliable. My Series III was even flexible on fuel choice as it could run prem or reg at the cost of around 20 HP. I now own a 2.0 Eco with the GM turbo upgrade and if given a choice between the turbo and the Series II the Turbo engine would be my choice. It is just a much stronger engine and so much more torque with much better MPG. The lag is not an issue and the only problem I have is traction as in a FWD car it is difficult to hook up even at speeds over 35 MPG in the dry.

Either system has advantages and disadvantages but both are pretty good system. The fact is today most Auto engineers for reason they have determined the Turbo is better suited to meet the goals of power, MPG, Emission and fitting on many of todays engines. I know many will want to argue one way or the other but the Automakers are going with what works best for their needs and doing a pretty good job with the Turbo today. I know some non engineer here will pop in and disagree with the auto company engineers but it is what it is and those who build the cars have made their best choice.

[Drew Dowdell]

Why the assumption that boost gauges on a Vette mean it has a turbo? The CTS-V has boost gauges right now too and nary a turbo in sight.

Well I did some more digging and here is what GM's reply was to the Duel Boost gauges as of 3-14-13.

They claim they programed the TFT display with things for future models and they just did not shut it off. The TFT can be and will be used in some new models and they can turn on what they want. They did not go into detail to say if it was the CTS or other models. These models had it on as they were test cars and some of the TFT options were left on.

The Stingray is the first to use the TFT system and we will see it used in more cars.

This is like a advanced system of what is in my Terrain info center. I know someone who has jail breaked his Terrain and has all sorts of engine and car info at his disposal. He can now read tranny temps, engine oil temps, pressures and many other parameters that are not shown or offered in the stock configuration.

This system seems to be similar but has much more it can do for many cars. While the shape of the dash may change I suspect the type of dash we see in the Stingray will be common to many GM cars.

That makes a lot of sense. I know that even the current monochrome DIC in the current cars has the ability to switch on and off different pages. The ZL-1 has pages the Verano does not.

[dwightlooi]

No matter how you spin it larger single turbo's have greater inertia and this leads to lag in street cars. Yes I agree that the larger turbo has efficiencies at higher RPM and top end performance but that seldom comes into play in a street car. Also the lag in a race car is a non factor since in many cases they launch at high RPM and can build boost sitting still. But that is not something some one will do in a ATS at a street light.

It's not a spin. It's a simple fact. Larger turbos are more efficient and do not have higher lag compared to two smaller ones in parallel. They have higher inertial, but you are also feeding it twice the exhaust flow to overcome the inertial. If the efficiencies are the same it'll be a wash -- no better, no worse. But because they have better efficiencies, more exhaust pressure is converted to angular velocity and more angular velocity is converted to boost instead of heat.

The ONLY reason they may be less efficient is that if you have a large turbo on one side of a Vee-type engine, getting the exhaust from the far bank over to it is highly inefficient. A reverse flow engine where the exhaust exits the center gets rid of this condiition

[dwightlooi]

Let me give you an of example...

BMW N54 3.0 I6 (2007 thru 2010) used two turbochargers in parallel. It made 306 hp @ 5800 rpm & 295 lb-ft from 1400~5000 rpm.

BMW switched to a single larger turbo for the N55 3.0 I6 (2010 thru present). It made 302 hp @ 5800 rpm & 300 lb-ft @ 1200~5000 rpm.

Not only did the torque go up slightly, response is improved with maximum torque arriving 200 rpm earlier than before (1200 vs 1400 rpm)

[hyperv6]

The only spin here is on the turbo.

Read the following from Turbonetics one of the largest Turbo suppliers for racing.

www.turboneticsinc.com/choose_turbocharger

Sorry but they do not agree and I could bring up others like Gale Banks and others that will also not agree. Sorry if I have to choose between you or the Turbo MFG I will have to side with them. If they say a larger turbo has more lag then I suspect they know a little more then you do. As stated there are variables that can offset some of this but in the end it is a compromise. It is simple smaller turbochargers are better for street use and more fun to drive due to the less lag time. Duels help supply.

The other reason for a duel set up is more air flow as while a smaller turbo has less lag it also works as a restriction in the system. The duel opens up more flow while still keeping the ability of a small turbo to spool up faster.

It is simple physics like a fly wheel and it all comes down to inertia. Sorry but even you and you way of thinking can not over come the simple physics.

The fact is most MFGs have abandon one large turbo for the street for 2 on most V6 and V8 applications and in the case of the Veyron they went to 4 smaller turbo chargers vs. one or two larger ones. This is how they keep the air volume up and better low end response.

You sure like to post numbers but you always leave out the rest of the story. You may fool some but I am sorry I can go to MFG and show they disagree with you. It is not my opinion it is the facts stated by the people who build these system.

There are a lot of variable to a turbo system and compromises. The key like Turbonetics state is to choose wisely. You must chose what best fits your application. If you are racing 1/4 mile or at Bonneville one large turbo is fine as you have ways to spool the turbo up before launch or you have time to get it up to speed. On the street mass and inertia take over and prevents the turbine to spool as fast.

Gale Banks

Lingenferlter

Callaway

Honeywell and others all work with smaller and duel systems for better low end and less lag on the street. Most diesels can go single just do to the greater torque.

[dwightlooi]

Is it really that hard for you to comprehend?

• A larger turbo always have more lag compared to a smaller one at the same exhaust flow.
• However, a larger turbo does not have more lag (it actually has less) when fed twice the exhaust flow.
• A twin (parallel) turbo design feeds each turbo with 50% the available exhaust flow.
• A single turbo design feeds the turbo with 100% of the exhaust

A 2.0 I4 engine with one large has worse lag and efficiencies compared to a 2.0 I4 with one small turbo. Therefore, to get the most responsive engine you want to use the smallest turbo that meets your power goals. Using a larger turbo will allow you to hit higher boost levels or flow rates without "falling off the map", but using a larger turbo also negatively impacts response and lag. However, if and when you want to hit higher power levels, you are always better off using one bigger unit than two smaller ones in parallel.

The reason most V6 and V8 designs use twin parallel setups is because it is impractical and/or inefficient to run exhaust from both banks to a single turbo. It is also impractical and/or inefficient to run a sequential bi-turbo setup for the same reasons -- because you need to get ALL the exhaust to the first turbo, then dump the output from the first turbo into the second.This is the reason Vee type engines commonly use bi-turbo setups and Inline engine (where the exhaust ports are in one place) use either a single larger turbo or two unequal sized turbos in a sequential dual setup.

A reverse flow head design allows you to use a larger single or twin sequential design.

Edited March 24, 2013 by dwightlooi

[hyperv6]

You just like to hear yourself talk don't you? Did you really read your statement above? The first two comments are nuts and you are changing things again to fit what you want to say. Here we speak of a TT 3.6 and comparing the two system to it with the same flow. What you state is like saying that Nome is just as warm as Death Valley if they are the same temperature. I am sure they would be but in the real world that is not likely and is the rare acceptation.

First off your statement that a larger turbo has more lag at the same air flow is the whole point. But to get the wheel moving even with the added flow from a larger turbo still takes time. It is no different than trying to spin a larger tire wheel combo vs. a smaller tire wheel combo with the same engine.

The same engine with the same size with the same conditions has more lag than a smaller turbo. This is the whole point of this exercise here since we are basically speaking of street cars.

The whole idea of the 3.6 TT having two turbo's is that they will be better in low speed street driving conditions as they will provide better low end and better performance where a CTS is going to be driven. Sure you can use a turbo and not have any lag like a Drag Car but few people will want to launch their CTS at 7,000 RPM like my customers do a the track.

As I also pointed out the failing of a small turbo is air flow as it can become a restriction to the exhaust at higher RPM and the second turbo can be used to also increase more exhaust volume at high speed.

I do agree with the impractical part but that is subjective to the application.

I know you make it a habit of fooling people with a lot of points but you always leave out enough to make them fit your analysis. This often leads you to making statements that even the lead engineers at the automakers do not agree with. In this case your statements are true to a point but in the reality with all the facts put into the analysis they are not what the Turbo MFG state or claim.

Sorry but I will respectfully base my views on what the Automaker and the Turbo companies I work through state and have taught me. I think they may just know more of what they are doing and they need no convoluted explanations to try to get it cross.

Like I stated before your argument is not with me all I present is what the MFG state. This is why I posted and recommended the links as they can explain what I was try to state better than I could and more consistent and accurately than you could. Turbonetics and others are much better suited and informed to explain this as are others like Honeywell and others. You may want to go to their sites and brush up.

Honeywell has a new system now that is a single feed impeller with two compressors on each side. I would no be surprise to see this system come to the OE market at some point. It allows for better placement and still makes for a very street able charger with less lag. The fact is a lot of money right now is being sent to the development of Turbochargers with the explosion of them in the OE market. We will see more new innovations and more variations soon. Many will be fit to special needs that will crop up with the new engines and the size of engine compartments.

The advent of better oils, bearings and now electronics with Di injection have made this all come about. I expect some real innovations are soon to come. We have come a long way from a Buick T Type to today.

I

[Drew Dowdell]

Regardless of where the best location for the turbo-charger(s) is, there is no way GM was going to redesign the 3.6 to be a reverse flow engine in turbo-charged form.... just wasn't going to happen..... so the whole debate of where the turbo-chargers would be installed is purely academic.

[Robert Hall]

Agreed it is pointless to argue about turbo count or installation configuration--GM has figured out what is appropriate for their usage of this engine in various models. As far as the '14 CTS goes, it looks pretty cool in the new teaser photos out there today...what do you all think?

Edited March 24, 2013 by Cubical-aka-Moltar

[ocnblu]

A real jaw-dropper, Moltie. Full of swagger and moxie... in other words, fully appropriate for a Cadillac.

[hyperv6]

I think many will be shocked at how much was covered buy the Camo in the spy shots. There is a lot more detail on the car than most expect.

The standard car will be much more aggressive in styling than expected in standard form.

I think unless Lincoln does something different and soon there will only be one American luxury car maker left in Cadillac. I think that GM finally have figured out how to finally take on the world. There will be some things that still need fixed but they will finally be on even ground as the others are far from perfect too.

This will be the car that will transform the present Cadillac look from just being different to owning it's own look and style.

Edited March 24, 2013 by hyperv6