Cadillac News: Rumorpile: Cadillac ATS-V Could Pack A 3.2L Twin-Turbo V6

[William Maley]

William Maley

Staff Writer - CheersandGears.com

November 13, 2013

We know that Cadillac is hard at work on an ATS-V, but no one has been able to nail down what will be under the hood of it. Reports say it could either be a twin-turbo V6, possibly the new TT 3.6 found in the CTS and XTS VSport, or a V8 engine. According to a new report from Automobile, the ATS-V will likely have a twin-turbo V6, but not the 3.6. The report says the twin-turbo V6 will be a 3.2L and will be capable of producing of more than 500 horsepower.

This TT 3.2 V6 has a bit of interesting story to it. The engine is based on GMs’ High Feature V6 engine architecture which was supplied to Alfa Romeo in the later half of the 2000's. Alfa Romeo fitted its own set of twin turbos and direct-injection system, thus creating the 3.2 JTS engine which was available on the 159, Brera, and Spider.

Source: Automobile

William Maley is a staff writer for Cheers & Gears. He can be reached at [email protected] or you can follow him on twitter at @realmudmonster.

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[G. David Felt]

Sounds Like if they go with the 3.2 TT V6 it would be due to tax from the stupid Euro Zone rather than a solid TT engine. Euro zone auto rules will kill off auto companies at the rate they are going.

[Drew Dowdell]

I doubt this would be a direct lift from the Alfa Romeo.... more likely, it is just the current 3.6TT with a slightly shorter stroke and the boost turned way up.

[ZL-1]

I doubt this would be a direct lift from the Alfa Romeo.... more likely, it is just the current 3.6TT with a slightly shorter stroke and the boost turned way up.

Yeah. My guess is that, if the rumour has some truth in it, it'll be a variant of the 3.6L block but I guess with a smaller bore. I think the rationale is that a smaller displacement engine using the 3.6L block would have thicker cylinder walls and it would withstand higher boost pressures.

Edited November 13, 2013 by ZL-1

[aurora97]

Will there be a real manual transmission to go with it?

[Drew Dowdell]

I doubt this would be a direct lift from the Alfa Romeo.... more likely, it is just the current 3.6TT with a slightly shorter stroke and the boost turned way up.

Yeah. My guess is that, if the rumour has some truth in it, it'll be a variant of the 3.6L block but I guess with a smaller bore. I think the rationale is that a smaller displacement engine using the 3.6L block would have thicker cylinder walls and it would withstand higher boost pressures.

Smaller bore would make sense too. I seem to remember that the HF engines were capable of taking cylinder sleeves to adjust bore size, so the block itself would actually be the same but then they could sleeve it down to the displacement they wanted it to be. With no sleeve, the displacement would be 4.0 liters, but it would have to be a relatively slow, all torque/no rev, engine.

[Z-06]

IIRC Dwight had given the max displacement for the HF engines somewhere around 4 litres. The 3.2L would make perfect sense as it would be less engineering involved and yet be a unique Caddy engine.

[Carguy]

I hope they also do a lower boost turbo version of the 3.0L V6 to replace the NA 3.6L in the regular ATS,CTS and even XTS models! Then they could also build that 4.5L DOHC 4VPC Turbo V8 to use in the upcoming large Cadillac and the next CTS V in different stages of tune! An all DOHC 4VPC Turbo Cadillac engine lineup would be properly competitive in todays premium market!

[G. David Felt]

Still Think Cadillac should have a family of V4, V6 and V8 engines based on Corvette V8 DNA engines for their lineup.

These engines could all be Twin Turbo'd and maxed out and then use detuned versions for the other departments.

[Drew Dowdell]

the HF 3.0 was never a particularly compelling engine... if they did do a 3.0, it would/should be a new design.

[Carguy]

the HF 3.0 was never a particularly compelling engine... if they did do a 3.0, it would/should be a new design.

The only issue the HF 3.0L V6 had was it was competing with larger more torquey 3.5L/3.7 V6s from other beands! With twin turbocharging it could become something special for Cadillac replacing todays NA 3.6L V6! And remember it was putting out 260HP using a unique from the 3.6L high compression ratio but with a lower compression ratio its economy would improve significantly as well as its power with turbocharging!

[regfootball]

My guess is if Caddy rolls with a 3.2 turbo, that it also might become a replacement for the 3.6 in some cars. For example, as the step up motor in the CTS and XTS. CTS motor lost them the C/D comparo in the recent issue. A 3.2 turbo 6 would upgrade over the 3.6 and then they could spread it around the lineup and to the ATS. It could even end up in say the Impala or LaCrosse.

[hyperv6]

The pressures in this engine will be greater than the 3.6 TT so we will see the bore shrink just as we did in the ZR1.

We saw hints of this engine coming over a year ago and it is no surprise.

Even on the Ecotec they went to 2.0 liters to add more pressure for durability so it s very simple to see what they are doing. Now while I do not have the boost numbers I am speaking of numbers that would bury a T type.

My GM tune on my 2.0 eco puts out 23 PSI of warranty coverage. With the TT it may not be a high but it will spool up low down and hold it for a long time when called upon.

We deal with many Supercharger companies and Turbo companies at work and our customers. Bock damage and blown head gaskets are very common in adapted engines. Ford Small Block suffer the most with only 4 head bolts around each cylinder. With out O ring head gaskets they almost always fail.

Block strength, head strength and head bold or studs are also a factor. Just look at the failure alone of the Ford Diesels and their head bolts from a couple years ago.

I expect that the 3.2 may show up else where as the High Performance Option. The 3.6 Turbo may not be the performance engine as we though it may just be the normal TT engine and the heavy grunt work will go to the 3.2 TT.

The real question is will the TT set up on the V6 and V8 be held as the Cadillac trademark engine to set them apart. The non Turbo and Supercharged V8 may be left to Chevy.

While GM may not be able to make a Cadillac engine the TT hallmark could make the engine that GM makes special just to Cadillac. In this segment technology sells and if they want to sell in Europe and Germany they need to address this over there. It is like Americans love NASCAR and Indy car but Euro people love F1 for the technology and not so much for on track passing. Just see how BMW and Benz sell their cars over there as they detail the technology no matter if it is performance of safety over there before anything else. They buy things not for what image they depict but for the technology they demonstrate.

Cadillac is going to be global in 10 years and you need to start building a global image now to do that later.

Edited November 17, 2013 by hyperv6

[Drew Dowdell]

It should be pretty easy to do a 3.2 TT High Output and a 3.2T Standard Output

[G. David Felt]

The pressures in this engine will be greater than the 3.6 TT so we will see the bore shrink just as we did in the ZR1.

We saw hints of this engine coming over a year ago and it is no surprise.

Even on the Ecotec they went to 2.0 liters to add more pressure for durability so it s very simple to see what they are doing. Now while I do not have the boost numbers I am speaking of numbers that would bury a T type.

My GM tune on my 2.0 eco puts out 23 PSI of warranty coverage. With the TT it may not be a high but it will spool up low down and hold it for a long time when called upon.

We deal with many Supercharger companies and Turbo companies at work and our customers. Bock damage and blown head gaskets are very common in adapted engines. Ford Small Block suffer the most with only 4 head bolts around each cylinder. With out O ring head gaskets they almost always fail.

Block strength, head strength and head bold or studs are also a factor. Just look at the failure alone of the Ford Diesels and their head bolts from a couple years ago.

I expect that the 3.2 may show up else where as the High Performance Option. The 3.6 Turbo may not be the performance engine as we though it may just be the normal TT engine and the heavy grunt work will go to the 3.2 TT.

The real question is will the TT set up on the V6 and V8 be held as the Cadillac trademark engine to set them apart. The non Turbo and Supercharged V8 may be left to Chevy.

While GM may not be able to make a Cadillac engine the TT hallmark could make the engine that GM makes special just to Cadillac. In this segment technology sells and if they want to sell in Europe and Germany they need to address this over there. It is like Americans love NASCAR and Indy car but Euro people love F1 for the technology and not so much for on track passing. Just see how BMW and Benz sell their cars over there as they detail the technology no matter if it is performance of safety over there before anything else. They buy things not for what image they depict but for the technology they demonstrate.

Cadillac is going to be global in 10 years and you need to start building a global image now to do that later.

So then TT would be the Trademark of Cadillac and leave the same 3.2 T for chevy?

[dwightlooi]

Honestly, rumors are just that, rumors... I wouldn't put too much faith in rumors.

But, just on the technicalities. I doubt they will use the Alfa engine -- it's OLD! If it's the GM HF block the logical thing will be a reduction in bore, not a shortening of the stroke. Reducing the bore has two disirable effects. Firstly, it strengthens the cylinder walls allowing it to better withstand increased working pressures. Secondly, it makes the engine more resistant to detonation because it shortens the distance from the spark plug to the furthest corner of the combustion chamber. Reducing the stroke does not do any of the above. The only thing it does is reduce the piston speed which permits a higher redline. With turbocharged engines it's easier to crank up the boost to get more power than it is to have a turbo system able to keep up with the airflow at very high rpms (say 7000~8000 rpm) while also being responsive at low rpms off idle.

Edited November 19, 2013 by dwightlooi

[regfootball]

could they get about 350hp with a 3.2t v6? That would be to me where a mid level CTS would spec out nicely.

Edited November 19, 2013 by regfootball

[hyperv6]

could they get about 350hp with a 3.2t v6? That would be to me where a mid level CTS would spec out nicely.

Hell that would be the entry level engine.

The 3.2 TT will do so much better than that. My 2.0 is at 300 HP and has no issues on pump gas and holds the full GM warranty.

[hyperv6]

The pressures in this engine will be greater than the 3.6 TT so we will see the bore shrink just as we did in the ZR1.

We saw hints of this engine coming over a year ago and it is no surprise.

Even on the Ecotec they went to 2.0 liters to add more pressure for durability so it s very simple to see what they are doing. Now while I do not have the boost numbers I am speaking of numbers that would bury a T type.

My GM tune on my 2.0 eco puts out 23 PSI of warranty coverage. With the TT it may not be a high but it will spool up low down and hold it for a long time when called upon.

We deal with many Supercharger companies and Turbo companies at work and our customers. Bock damage and blown head gaskets are very common in adapted engines. Ford Small Block suffer the most with only 4 head bolts around each cylinder. With out O ring head gaskets they almost always fail.

Block strength, head strength and head bold or studs are also a factor. Just look at the failure alone of the Ford Diesels and their head bolts from a couple years ago.

I expect that the 3.2 may show up else where as the High Performance Option. The 3.6 Turbo may not be the performance engine as we though it may just be the normal TT engine and the heavy grunt work will go to the 3.2 TT.

The real question is will the TT set up on the V6 and V8 be held as the Cadillac trademark engine to set them apart. The non Turbo and Supercharged V8 may be left to Chevy.

While GM may not be able to make a Cadillac engine the TT hallmark could make the engine that GM makes special just to Cadillac. In this segment technology sells and if they want to sell in Europe and Germany they need to address this over there. It is like Americans love NASCAR and Indy car but Euro people love F1 for the technology and not so much for on track passing. Just see how BMW and Benz sell their cars over there as they detail the technology no matter if it is performance of safety over there before anything else. They buy things not for what image they depict but for the technology they demonstrate.

Cadillac is going to be global in 10 years and you need to start building a global image now to do that later.

So then TT would be the Trademark of Cadillac and leave the same 3.2 T for chevy?

You miss the point of the TT set up. They use two turbo's not for power but more so for less lag as the two turbo's will hold the volume of one large turbo but they will spool much faster for much less lag. The TT has none of that GN lag you used to get and with the VVT adjusting for low end torque what lag you have is not any where as detectable.

A single turbo would not move much volume and would have a lot more lag. If you want a detuned Caddy engine you put two smaller Turbo's on it or you just hold down on the boost. In the Cadillac you can afford to make the engine Premium required and run a 3 bar T Map but on the Chevy GM likes to run a Premium Recommended rating that give the owner the option but a little less power.

Turbo charging is one of the greatly misunderstood things today with all the changes we have seen in the last 5-10 years. DI and VVT along with the better turbo units and computers have totally changed this game. I was as anti turbo as you could get years ago and now that I have learned the new ways I really can appreciate the changed and how well they can make these smaller engines perform. The new engine with the torque curves that are flat as a table from 1800-5300 RPM in my engine are amazing. I have not seen torque like that since a 428 Pontiac.

GM will not use an Alfa engine in a Alpha. Though the T maps in my HHR are from a Alfa LOL!

Edited December 19, 2013 by hyperv6

[hyperv6]

I did forget to also mention that two smaller duels are at times easier to package in some V6 compartments.

I believe it is Honeywell that is working on a new Duel Boost Turbo that is a single housing. It is smaller and more efficient with many advantages. Check it out as you will see this as the next step for most gas powered engines.

[Lamar]

As far as the concerns with lag, I wonder why GM doesn't try supercharging.

[hyperv6]

As far as the concerns with lag, I wonder why GM doesn't try supercharging.

Simple it take power to make power with a supercharger. Also packaging can be difficult or expensive in some cased.

Turbo engines do not have any drag on them to run a turbo where as a SC engine has to use power to make power. In a larger V8 this is not as much an issue as it would be in a smaller engine where you are working to make power but not take on any power loss with drag or loss in MPG that you are trying to gain.

Also packaging can be difficult with a SC where as you have to have a drive system where a Turbo can take power from anywhere in an exhaust system. You can mount a turbo high, low, in front, back or even at the rear axle as one system does today.

Also todays Direct Injection engines love turbo charging and react to it very well. Add to it Variable valve timing and the new improved turbo units and drag is pretty much reduced to a point that many do not notice it.

With my own turbo the lag is small and the torque is instant so you really do not miss it and if anything it make it more drivable as with 315 FT LBS of torque available at 1800-1900 RPM it can be tricky on in the snow. To be honest most automatic transmissions have more lag in the down shift than most modern turbo engines.

Having owned several 3800 SC versions including the last Gen III and a Eco Turbo with the GM upgrade kit I would take the Eco Turbo hands down every time over the 3800 SC. I liked the SC engines but they just do not have the pull or acceleration the Eco has. I can kick it down and spin the tires at 50 MPH and I never could do that with any of my FWD 3800 SC engines. The first time it happened I thought something broke as the power cut, the waste gate popped and I had dash lights that I finally noticed they were for the traction control.

[Lamar]

So I guess my question is this... if, say, GM were to built a 3.2L V6S with 350 or so HP, how much power would be lost in running a normal-sized (whatever "normal" may be) blower? And would it really be that consequential in an compact sport sedan?

Also, how do Audi, Jaguar, and Porsche make the supercharged V6/V8 worth the effort? (and I know I'm forgetting a brand or two)

Edited December 21, 2013 by Lamar

[dwightlooi]

So I guess my question is this... if, say, GM were to built a 3.2L V6S with 350 or so HP, how much power would be lost in running a normal-sized (whatever "normal" may be) blower? And would it really be that consequential in an compact sport sedan?

Also, how do Audi, Jaguar, and Porsche make the supercharged V6/V8 worth the effort? (and I know I'm forgetting a brand or two)

With the 6th Generation (TVS 4-lobe) Eaton Superchargers, the rough rule of thumb is 0.1hp per horsepower. In otherwords, it takes about 0.1 horsepower in parasitic drag to drive the blower for every horsepower the engine puts out. We are assuming modest boost levels of about 9~11 psi. A 3.2L engine will probably run the 0.9L or 1.05L blower. A 350 hp 3.2L application will actually burn enough fuel to make about 385 hp, 35 of which is consumed by the supercharger itself.

The upsides to supercharging are that:-

1. There is no turbolag at all and the throttle gives the driver a direct connection to the output of the engine, which is preferred in spirited driving. Supercharged engines typically feel and drive like a larger displacement normally aspirated engine.
2. The Supercharger is actually better for emissions because there is no turbine between the exhaust ports and the catalyst to soak up heat and slow catalyst light off in cold starts
3. The supercharger typically packages neatly into the engine Vee and costs less, whereas a turbo setup will typically require two turbos and a bunch of piping to take air to them, from them to IC(s) and finally to the engine.
4. Superchargers also have better reliability and/or require less hardware to make reliable because they do not subject oil to thousands of degrees of heat in the turbine bearing section -- heat which in modern applications typically calls for an electric water circulation pump to keep the turbo cooled after the engine shuts off, mandate more frequent oil change intervals or high temperature synthetics

#3 is predorminantly why Audi and Jaguar went with the TVS R1050 blower on the 3.0V6 even while they prefer turbochargers for their inline-4 applications.

Onw problem with GM's HF V6es is that they are 60 degree engines. In general, a supercharger is easier to package with a 90 degree engine with a wider valley for the blower to fit in. With 60 deg engines the blower sits high

Edited December 22, 2013 by dwightlooi

[Drew Dowdell]

GM has also engineered much of the lag out. There is still some, but we're not talking 80s Saab here.

[dwightlooi]

The pressures in this engine will be greater than the 3.6 TT so we will see the bore shrink just as we did in the ZR1.

We saw hints of this engine coming over a year ago and it is no surprise.

Even on the Ecotec they went to 2.0 liters to add more pressure for durability so it s very simple to see what they are doing. Now while I do not have the boost numbers I am speaking of numbers that would bury a T type.

My GM tune on my 2.0 eco puts out 23 PSI of warranty coverage. With the TT it may not be a high but it will spool up low down and hold it for a long time when called upon.

We deal with many Supercharger companies and Turbo companies at work and our customers. Bock damage and blown head gaskets are very common in adapted engines. Ford Small Block suffer the most with only 4 head bolts around each cylinder. With out O ring head gaskets they almost always fail.

Block strength, head strength and head bold or studs are also a factor. Just look at the failure alone of the Ford Diesels and their head bolts from a couple years ago.

I expect that the 3.2 may show up else where as the High Performance Option. The 3.6 Turbo may not be the performance engine as we though it may just be the normal TT engine and the heavy grunt work will go to the 3.2 TT.

The real question is will the TT set up on the V6 and V8 be held as the Cadillac trademark engine to set them apart. The non Turbo and Supercharged V8 may be left to Chevy.

While GM may not be able to make a Cadillac engine the TT hallmark could make the engine that GM makes special just to Cadillac. In this segment technology sells and if they want to sell in Europe and Germany they need to address this over there. It is like Americans love NASCAR and Indy car but Euro people love F1 for the technology and not so much for on track passing. Just see how BMW and Benz sell their cars over there as they detail the technology no matter if it is performance of safety over there before anything else. They buy things not for what image they depict but for the technology they demonstrate.

Cadillac is going to be global in 10 years and you need to start building a global image now to do that later.

So then TT would be the Trademark of Cadillac and leave the same 3.2 T for chevy?

You miss the point of the TT set up. They use two turbo's not for power but more so for less lag as the two turbo's will hold the volume of one large turbo but they will spool much faster for much less lag. The TT has none of that GN lag you used to get and with the VVT adjusting for low end torque what lag you have is not any where as detectable.

A single turbo would not move much volume and would have a lot more lag. If you want a detuned Caddy engine you put two smaller Turbo's on it or you just hold down on the boost. In the Cadillac you can afford to make the engine Premium required and run a 3 bar T Map but on the Chevy GM likes to run a Premium Recommended rating that give the owner the option but a little less power.

That is one of the widely propagated myths... Vee engines do not employ twin turbos for less lag. In fact, using one turbo would have produced less lag. One larger turbine with twice the flow capacity being fed twice the exhaust volume would spool at the same rate if all else are equal. In reality though, a larger centrifugal turbine or impeller is ALWAYS more efficient than a smaller one. This is immediately apparent when you look at the turbine and compressor graphs of smaller turbos vs larger ones. Hence, a single turbo engine will have better response and better efficiency.

Vee type engines use two turbos in a parallel arrangement because it is highly inconvenient and lossy to pipe exhaust from one bank of cylinders to the other. They accept the slight loss in efficiency and response from the twin turbos as necessary compromise. The only alternative is to have reverse flow heads which exhausts into the Vee instead of the flanks. The problem with that is that most turbo engines are derivatives of naturally aspirated counterparts which are not reverse flow. Also, with a reverse flow engine the turbo will be right on top of the engine under the hood. This is sometimes deemed unsightly and has the very practical need for extra shielding to prevent the hood paint from cooking, In 60 degree Vees, the turbo also necessarily ride very high requiring a hood bulge in most cars. Still, certain engines which are designed from the ground up to be turbocharged powerplants (only) have reverse flow heads. BMW's 4.4 Bi-turbo V8 and the GM Duramax 6.6 Diesel comes to mind.

The only time two turbos reduce lag is when they are in a sequential arrangement with two unequal size turbos. All the exhasut goes to one initially allowing to spool faster, once the capacity of that turbo is maxed out, the wastegate opens to dump all the flow to a second larger turbo which supports the engine to higher rpms and maximum power. This however is never the case in convential V6 or V8 turbos. You'll need a reverse flow Vee engine or an inline engine to implement a sequential turbo setup, because you need all the exhaust to converge on one turbo first. Even then, it is highly debatable whether the complication and costs are worth it. BMW's Inline-6 3.0 turbo used to use a sequential twin turbo setup, but they went to a single dual scroll turbo and ended up with better response and (more importantly) better emissions. The only other sequential twins in historically had been the Toyota Supra 3rd Gen (2JZ-GTE engine) and the FD RX-7.

Edited December 23, 2013 by dwightlooi

[hyperv6]

Bla Bla Bla.. So you still think you know more than GM some things never change. LOL!

Merry Christmas Sheldon!

[Z-06]

Hyper - tell us in what way he is incorrect. I am interested in learning the other side also.

[dwightlooi]

Bla Bla Bla.. So you still think you know more than GM some things never change. LOL!

Merry Christmas Sheldon!

Well, let me give you a real world example... The CTS V-Sport engine (LF3) makes 420 hp @ 5750 rpm and 430 lb-ft @ 3500 rpm. It does so with two turbos and at less boost than the 272 hp / 260 lb-ft ATS 2.0T engine (LTG). Despite the lower boost, lower specific torque (120 lb-ft / liter vs 130 lb-ft / liter) and lower specific output (117 hp/liter vs 136bhp/L), the LF3's peak torque arrives 1800 rpm later. Look at the official power/torque graphs for yourself. I think it is apparent to anyone that boost (hence torque) rises faster (LTG) 2.0T and the torque plateau is wider. Does that show that two smaller turbos spool faster or does it show the reverse?

[hyperv6]

Hyper - tell us in what way he is incorrect. I am interested in learning the other side also.

There are no absolutes as there are always an acceptation but the fact remains a smaller turbo unit in street trim will spool faster. To make up for the lack in volume they use two. But when it comes to the type of engine, use of engine and how the plumbing has to be run can all be factors.

Case in point here is in a street car such as a v6 CTS the TT is much easier to spool up with two smaller units vs. one large mass unit for street driving. This is also why Callaway also chose this for the Corvettes they built.

Now if I were doing a 4 Cylinder with lower engine volume and no packaging issues the single will do just fine as you will never approach the size of turbo with a smaller engine that would incur so much lag to spool it up.

Now racers like in Drag Racing where they launch at high RPM and often are holding the RPM at the line have no lag as they have already built the boost. This is why so many of the Mustangs and import cars use one single unit. This is not practical for street use.

Think of it this way. Take a car and put 33" wheels on it and then do not change the gear in it while running a 3:07 gear. You will find it take more time and effort to get the car to speed faster than if you had smaller diameter wheels. It is simple physics.

Now with a turbo you can not just change a gear ratio here either so you have to compromise the top end to gain a less lag with the smaller units. But in a street car with a V6 or V8 once up to speed there generally is enough power to maintain good performance.

The sequential units try to bridge the gap buy giving you low end with the small unit but still retain the higher volume of the larger unit.

Now engine size and air volume along with how and where the engine is plumb can affect this but the general rule for a V style engine of moderate size a duel system tends to decrease the lag on the street.

Here is some info on Turbo units that is helpful

http://www.turboneticsinc.com/choose_turbocharger

Here is some on the sequential units.

http://www.dieselpowersource.com/en/news/twin-turbos-vs-single-turbo/

Here is some info on parallel and sequential

http://www.carsdirect.com/aftermarket-parts/the-benefits-and-drawbacks-of-twin-turbos

I should make it clear that there are no absolutes here as there are many factors involve. But some as posted here have tried to make it like there is one way and one way only. GM and others have their reasons for using the systems they use and for street use and packaging with a V style engine the two smaller units generally provide less lag. Much of any use of Supercharging and Turbocharging is a compromise anyways and you have to set the goals of what kind of performance you want and what you want to accomplish.

I just get tired of someone here who likes to throw out a lot of numbers to make it look like he has the only answer. The reality is he often leaves out the whole story and only likes to support his view only. This is not a case of me or him being right or wrong but a case that there is a lot more to this than he likes to present.

Case in point he last post. He takes two different engines with two different needs of air volume and with two different plumbing packages. The difference is the volume needed here for each engine and the packaging of each.

Now if he would take a single turbo unit on a 3.6 and a TT 3.6 and compare them with equal volume that the units can move the TT unit will spool up a little faster but the large single unit if you could find a place to put it would give you more top end.

The bottom line is GM did not just add TT just for fun and bragging rights as they found it to produce the better driving experience along with the much easier packaging. If they could do It that easy with one they would have done so as I am sure it would save cost.

So to be fair I will not say he is totally wrong but he still does not take into account all the factors in play here. I am not trying to prove I am right as so much as I would like to just show that he is no giving the full disclosure. I hope you can see my point.

[dwightlooi]

LOL... let me put it simply...

(1) Two smaller turbos do not spool faster because, while each has lower inertial, each is also getting half the exhaust flow (hence energy) with which to operate the turbine. To make matters worse, smaller centrifugal turbines and compressors are less efficient than bigger ones.

(2) GM didn't put two turbos on the LF3 for fun or for bragging rights. They put two on there because they don't really have a better choice. The other alternatives would have been to totally redo the architecture of the LFX engine such that the exhaust exits in the valley of the engine, or ineffciently pipe exhaust from one side to the engine all the way to other. The former is financially uneconomical, the latter is worse in performance and response than using two turbos (they tried it actually with the 3.0 Turbo used in the SRX 2.8L Turbo (LP9).

(3) If you want the most efficient turbocharged engine, you'll want to get the exhaust out into the same space and you'll want to use a single turbine that is fed all of it. A good example of that is the N55 3.0L engine in the 535i. It gets to 330 lb-ft from 1200~5000 rpm. If they had gone with two tiny turbos the kind of turbines available would have turbine efficiencies in the mid-60% range and compressor efficiencies in the low 70% range -- about 5~7% and 7~9% behind the larger twin scroll unit. If they had done that, they could never have achieved that kind of performance,

[G. David Felt]

So it would seem that we could have very efficient performance v90 V6 and V8 engines with Superchargers or totally re-engineer the V6 and V8 engines to send the exhaust to the center of the engine where you would mount a single more efficient turbo that can handle all of the exhaust but that would require major re-engineering of the engines or at least the top end of the engines.

Personally, I will take a larger V8 engine over smaller turbo engines. I loved the 3800 SC in the Buick, was a blast to drive. Loved the Supercharged Cobalt as it was also fun to drive and while many here say Turbo's are very reliable in high mileage cases, I have not seen that yet myself and after yesterday where a kid in his Civic all turbo'd out tried to cut me off on the highway and my Trailblazer SS only needed a nudge to jump ahead and get away from the idiot driver. I am sold on my pushrod V8 Corvette engines for long life, solid performance and a total fun factor that 4 and 6 bangers just do not seem to produce for me yet.

Happy Holidays all!