3.6 Twin Turbo or 5.5 Pushrod for ATS-V?

[dwightlooi]

You may assume that the Twin Turbo V6 is ~80 lbs heavier and ~$2500 more costly.

Fuel Economy numbers assume a 3,500 lbs curb weight & Hydramatic 6L80 6-speed automatic transmission.

Edited April 17, 2010 by dwightlooi

[loki]

just some things that come to mind....

that's a low redline for the V6.

think the weight/cost issue would only come into play if it's pushed into another's price range too much.

yo umake the 5.5L premium for the power or because it's a cadi so it doesn't matter?

[Drew Dowdell]

how comes the torque happens so high on the RPM scale with a DI small block?

[loki]

how comes the torque happens so high on the RPM scale with a DI small block?

isn't that kinda typical of all NA engines? why would the peak move lower just cause of DI... shouldn't the torque curve just move up, maybe flatten in the lower ranges...

[Drew Dowdell]

isn't that kinda typical of all NA engines? why would the peak move lower just cause of DI... shouldn't the torque curve just move up, maybe flatten in the lower ranges...

Well, Dwight posted a torque range for the 3.6, but didn't with the small block. On the DI Ecotecs without turbo the torque curve is fairly flat and the peak is at 4900.

[dwightlooi]

Answers:-

(1) Turbocharged engines using torque computing electronic boost control generally have a torque plateau as opposed to torque peak. Basically, the torque limit is reached and held until the ECU determines that boost should be reduced gradually to keep the turbocharges "on map" and prevent over spinning them to an early death.

(2) The low red line on the 3.6 TT is because there is little to be had from reving beyond 6000 rpm or so. The GT20 series turbo are sized to generate boost fast and early, they start to run against rpm and efficiency limits in the 5000+ rpm range. It is very much like winding an LNF (2.0T) beyond the mid-5000 rpm range simply makes noise and slows down the acceleration times of the car. The transmission will probably shift at 5600~5800 rpm for best acceleration, allowing the motor to wind to 6800 rpm is moot. The unfortunate reality of single stage compressors -- even ones with very modern aerodyanmics -- is that they can keep only about 3000 rpm worth of torque plateau at moderate boost levels (eg. 12 psi). You can size them up to get them to do this through say 3200~6200 rpm, but that costs your lag time and efficiency at low loads.

(3) The LS3 makes its peak power and torque at 5900 rpm and 4600 rpm respectively. A de-stroked version displacing 5.5 liters with the same bore with make power slightly higher in the rev range -- hence 6200 and 4800 rpm. This is a reality of the physics of moving air. Same bore + shorter stroke = same amount of air pumping at higher rpms. Direct injection does not change the amount of air you move with each intake stroke.

(4) Both engines run on premium to maximize output. The understanding is that anyone forking out cash for a 400+ hp compact sport sedan isn't exactly looking for the lowest fuel tab.

[dwightlooi]

BTW, the redlines are not the maximum engine speed. That's the fuel cut speed. The redlines are the basically the indicated shift points.

When the transmission is being shifted by the driver via paddles or switches on the steering wheel, a shift light comes on at the "redline" indicating that shifting should be inititated then or shortly thereafter for maximum acceleration performance. This should be the purpose of a "redline". The common, but misguided, practice of using the redline to indicate rev limit is flawed because when you bump the rev limiter, it is too late to do anything about it!

[Drew Dowdell]

Thank you for your very detailed clarification Dwight. After hearing that, my vote goes solidly in the TT3.6 side. I like my torque way down low.

[CanadianBacon94]

Thank you for your very detailed clarification Dwight. After hearing that, my vote goes solidly in the TT3.6 side. I like my torque way down low.

my vote goes to the V-8 because i like my IBC powerful engine note.

[Camino LS6]

Thank you for your very detailed clarification Dwight. After hearing that, my vote goes solidly in the TT3.6 side. I like my torque way down low.

Agreed on the torque issue, not so sure about casting my vote just yet.

Higher price and more weight are serious concerns, but I do see the TT 3.6 fitting into Caddy's portfolio better.

Tough call.

[smk4565]

Twin-turbo DOHC V6 would be my choice. It works for the GT-R. The next M3 is going to be an inline six, so that seems like a good way to do. The 5.5 liter pushrod sounds like something in the Silverado, thus not something that should be in a Cadillac. Notice Mercedes never put the Hemi V8 from the Ram into an E-class.

In an ideal world, I think the ATS would have a straight six and they would copy BMW's engine as closely as possible. GM's 3.6 V6 and Infiniti's 3.7 V6 still lag behind the BMW and Benz in refinement and smoothness. A Cadillac straight six would be more refined than the 3.6 and then Cadillac would also have an exclusive engine to offer.

Although I'd still like to see a twin turbo DOHC V8 the most, and a V12 Cadillac would be nice. Even if they did something like a 4-5 liter twin turbo V12. The Ferrari F40 only had a 3 liter V8, a 4 liter V12 is possible. The F50 had a 4.7 liter V12 that weighed 435 lbs, which is right in line with what the LS-series engines weigh and less than the Northstar.

Edited April 18, 2010 by smk4565

[Camino LS6]

Wait. You want them to copy BMW's straight six in order to have an "exclusive" engine?

[Sixty8panther]

Very cool, the styling is quite awesome.

[smk4565]

Wait. You want them to copy BMW's straight six in order to have an "exclusive" engine?

Exclusive from the rest of GM.

The BMW straight six (gas or diesel) is the world standard for that class, and straight sixes are smoother than V6s.

Now my 4.4 or 4.8 liter V12 idea would be really exclusive.

[Camino LS6]

Very cool, the styling is quite awesome.

That's DF's "ZTS" chop, one of the coolest things you missed in your absence.

[Lamar]

my vote goes to the V-8 because i like my IBC powerful engine note.

+1.

That sort of engine sound is characteristic of this class of car, no matter who's building it.

[regfootball]

BMW sure is working hard to retain their ultimate driving machines, by adding 1/4 ton of weight to the 5 series, by making front drive and three cylinder cars going forward, and other driver centered things.

[dwightlooi]

SIDE NOTE: The two engine proposals are intended to represent two directions Cadillac can take...

• Join the bandwagon of the force induced DOHC sixes (eg. Audi 3.0 Supercharged DI V6, BMW turbo straight sixes, Ford Ecoboost 3.5, etc.)
  
• Carve out a unique identity with the American tradition of big displacement, push rod V8 albeit one loaded with contemporary technologies.
  

The output will be roughly equal. In this case it is set at 420bhp, which gives the ATS-V a power to weight ratio superior to the C63 or M3 and in the same class as the Nissan GTR.

The Turbo V6 has a slight (city) fuel economy advantage. It also has the advantage of incurring lower taxes in countries where new cars are taxed based on the displacement of the engine.

The V8 is lower in costs, complexity and weight. It also has the advantage of providing a more direct response due to the absence of turbine induced lag.

The pushrod 5.5 V8 and DOHC 3.6 V6 are roughly equivalent in the weight and size of the engine itself. The additional mass (est. 80 lbs) of the V6 setup comes from the two turbochargers, their manifolds, their plumbing, the air-to-water aftercooler, the water-to-air coolant radiator and the associated pumps and accessories.

Edited April 18, 2010 by dwightlooi

[dado]

You may assume that the Twin Turbo V6 is ~80 lbs heavier and ~$2500 more costly.

Fuel Economy numbers assume a 3,500 lbs curb weight & Hydramatic 6L80 6-speed automatic transmission.

Looking at competition I think it should aim close to 500 HP (Mercedes c63 AMG with sport pack offer around 480 hp). I don't know if V6 TT from GM can offer that much HP and keep warranty,reliability etc. Maybe 5.5 l v8 with forced induction would be better choice.

I wouldn't be suprised if AMG put their new 5.5 lv8 TT in next gen. C class.

[FAPTurbo]

Caddy has been tearing up the track and shutting out the competitors using their 6.2L in the CTS-V. I think continuing that trend with a 5.5 in the ATS-V is the best way to go. Everyone is using twin-turbo setups in their cars; Caddy would continue to offer something distinct. Plus, vehicle weight is a concern, so why not save a few pounds going with the V8, and be rewarded with a mean engine note?

[67impss]

Caddy has been tearing up the track and shutting out the competitors using their 6.2L in the CTS-V. I think continuing that trend with a 5.5 in the ATS-V is the best way to go. Everyone is using twin-turbo setups in their cars; Caddy would continue to offer something distinct. Plus, vehicle weight is a concern, so why not save a few pounds going with the V8, and be rewarded with a mean engine note?

I agree why limit your top HP with a topped out V6. The smallblock can always be bumped with forced induction and the V-series has this tradition of V8's be they S/B or N/S after all it's American send the few that go to Europe with the 6 pop.

[dwightlooi]

Looking at competition I think it should aim close to 500 HP (Mercedes c63 AMG with sport pack offer around 480 hp). I don't know if V6 TT from GM can offer that much HP and keep warranty,reliability etc. Maybe 5.5 l v8 with forced induction would be better choice.

I wouldn't be suprised if AMG put their new 5.5 lv8 TT in next gen. C class.

Actually, I feel that while it is easy to get giddy with horsepower the appropriate positioning of the V-series ought to be:-

• ATS-V: 420hp / 3500 lbs / compact - 3.6 V6 TT or 5.5 V8
  
• CTS-V: 550hp / 4200 lbs / mid-size - 5.5 V8 Supercharged or turbocharged
  

As far as the C63 is concerned, that is a 3900 lbs car and exactly what the ATS-V should beat it terms of weight. Shooting for 3500 lbs with a pushrod V8 or TT V6 is not unrealistic. It'll put the vehicle in the same size and weight class as the previous (W203) C55 AMG. 420hp in a 3500 lbs car is roughly equivalent to 468hp from a 3900 pounder -- I'll say it is "competitive". Besides, it'll be easier to make a 3500 pounder handle well.

I agree why limit your top HP with a topped out V6. The smallblock can always be bumped with forced induction and the V-series has this tradition of V8's be they S/B or N/S after all it's American send the few that go to Europe with the 6 pop.

I won't consider a 420hp 3.6 twin turbo V6 "topped out". A topped out DI Turbo will make around 150hp/liter or about 540hp for a 3.6 liter powerplant. That's what the Japanese market WRX STis and Lancer Evolutions do. At 116 bhp/liter for 420hp, we are shooting for an engine that has very minimal turbo lag and better response than the 260hp 130hp/liter 2.0T (LNF). 116hp can be done with undersized turbos with very fast spool times and with moderately high compression ratios for improved cruise economy.

Edited April 18, 2010 by dwightlooi

[dado]

What would be the length differences between v6 TT and 5.5 l v8 ?

I assume v8 would be longer (bigger bore and more cylinders). I know that wouldn't be such problem when engine is longitudinally mounted (like the engine in CTS is mounted and most likely in ATS)but i think it would present difficulty in cars such as XTS. I mention that car because there is rumors that it could get v6 with TT and about 420 hp, so maybe this is the engine that GM is already planning to put in ATS-V also.

So GM could use V6 TT for V version of ATS, between model of CTS (between 3.6 with 300 hp and future V model with 5.5 l v8 and forced induction) and top engine in XTS (i'm not sure if XTS can acommodate V8)

[hyperv6]

4 Eco Turbo and TT 3.6 for the ATS and leave the V6 and V8 for the larger CTS. If there is a V8 at all.

The key with the TT turbo is technology sells in this class. People who buiy these cars like the exotic things. The Chevy V8 by many no matter how good is still a Chevy truck V8. We know that it is good but the snobs you need to buy this car need to get something they will think is a cut above and not something you will find under the hood of a truck.

Image and not just real world performance means a lot to non GM fans and needs to be considered. There are may who dis the CTSV because of the engine. Yes a very good engine still gets snubbed by many who drive German cars.

[FAPTurbo]

People who diss the CTS-V's engine would never buy a Cadillac in the first place, and are really just trying to justify their preference for a Merc or BMW. AKA, grasping at straws.

At first, haters pointed to the first generation CTS' lesser performance compared to the Germans, and now that Caddy's current CTS has whipped their 'Teutonic' butts, the criticism has changed from how quick the vehicle is around the Nurburgring, to how 'refined' , and 'technologically superior' DOHC is compared to 'pushrods.'

Obviously DOHC is far more advanced because it's an acronym, unlike the archaic, agricultural pushrod!!

At the end of the day, Haters gonna hate, and Caddy shouldn't be chasing that crowd. Caddy needs to forge its own direction, like it did with the CTS.

[RjION]

Caddy has been tearing up the track and shutting out the competitors using their 6.2L in the CTS-V. I think continuing that trend with a 5.5 in the ATS-V is the best way to go. Everyone is using twin-turbo setups in their cars; Caddy would continue to offer something distinct. Plus, vehicle weight is a concern, so why not save a few pounds going with the V8, and be rewarded with a mean engine note?

Agree and I'll add no need for all the added parts to fail.

[67impss]

Amen sir

[smk4565]

Agree and I'll add no need for all the added parts to fail.

Porsche is #1 in long term reliability, and they only make DOHC engines. It isn't really the number of parts, it is how well it is made.

Really it doesn't matter if the ATS-V has a million horsepower, Cadillac has an image and reputation problem. They are struggling to be the 4th best selling luxury maker in the USA, and they are nothing overseas. Cadillac needs to focus on build quality and turning around their image. Cadillac is still a brand that you have to justify why you bought one rather than a BMW, Mercedes, or Lexus.

[dwightlooi]

4 Eco Turbo and TT 3.6 for the ATS and leave the V6 and V8 for the larger CTS. If there is a V8 at all.

The key with the TT turbo is technology sells in this class. People who buiy these cars like the exotic things. The Chevy V8 by many no matter how good is still a Chevy truck V8. We know that it is good but the snobs you need to buy this car need to get something they will think is a cut above and not something you will find under the hood of a truck.

Image and not just real world performance means a lot to non GM fans and needs to be considered. There are may who dis the CTSV because of the engine. Yes a very good engine still gets snubbed by many who drive German cars.

The Identity issue goes both ways. A TT 3.6 puts it in the same class as the BMW, Nissan and Ford TT sixes. That's both a good thing and a bad thing. It is a good thing in that there is certainly certain demographics of the car buying public which subcribe to the Turbo DOHC = sophisticated + refined school of thought. A TT 3.6 hence will win their favor.

The flip side is that from a product differentiation standpoint you end up with a less differentiated product because it is "yet another DOHC twin turbo". The product is less unique and less desired by people who either want a more "special" car or simply subscribe to the American V8 traditions.

[Lamar]

Cadillac is still a brand that you have to justify why you bought one rather than a BMW, Mercedes, or Lexus.

Possible justification: "Because I liked it and because BMW and Mercedes are annoying as crap to service." Works for me.

[Sixty8panther]

Cadillacs are all about the V8.... if not a 16 or a 12 any "exotic" Cadillac worth it's weight in salt should have at least 8 cylinders under the hood.

[Camino LS6]

I'm still not ready to vote...

[CSpec]

People who diss the CTS-V's engine would never buy a Cadillac in the first place, and are really just trying to justify their preference for a Merc or BMW. AKA, grasping at straws.

Good point.

[hyperv6]

Agree and I'll add no need for all the added parts to fail.

GM and most other OHC engines have few failures anymoe. GM no matter what engine has a great record right now on drivetrains.

[hyperv6]

The Identity issue goes both ways. A TT 3.6 puts it in the same class as the BMW, Nissan and Ford TT sixes. That's both a good thing and a bad thing. It is a good thing in that there is certainly certain demographics of the car buying public which subcribe to the Turbo DOHC = sophisticated + refined school of thought. A TT 3.6 hence will win their favor.

The flip side is that from a product differentiation standpoint you end up with a less differentiated product because it is "yet another DOHC twin turbo". The product is less unique and less desired by people who either want a more "special" car or simply subscribe to the American V8 traditions.

Most of the industry is going to small engines and OHC. It is not going to be just another DOHC engine or twin turbo as technology is advancing on all of them at a fast rate. Many new things are being applied and there will be a race to see who can come up with the best, most powerful and economical engines.

No one just said it was just anothe V8 back in the 60's when they made up 84% of the market. They all marketed the tech features and advancements to seperate them. We still have Ford Chevy wars just on v8 engines alone reguardless of what car it is in.

Technology and how it is marketed will make or break who has the best engines. Right not the Ecoboost has the upper hand on marketing. This is about a lot more than just engineers.

[hyperv6]

I'm still not ready to vote...

Even though I expect you to vote V8 I am proud to see you are at least thinking about it and not just in a rush to check a box.

Thank you for at least keeping an open mind.

[Lamar]

Cadillacs are all about the V8.... if not a 16 or a 12 any "exotic" Cadillac worth it's weight in salt should have at least 8 cylinders under the hood.

Agreed.

[Camino LS6]

Even though I expect you to vote V8 I am proud to see you are at least thinking about it and not just in a rush to check a box.

Thank you for at least keeping an open mind.

Thanks for the compliment.

You might be surprised to know that I am leaning in the direction of the TT V6.

But I am still mulling the idea over. There are some factors that have me debating with myself.

- Alpha is going to be package-protected for a V8 last I heard.

- The V6 adds cost, weight, and complexity

- The positioning relative to the CTS-V concerns me (it has to be just right)

- The Camaro is likely to share quite a bit of the "dirty bits" with this car.

- the snob factor of DOHC

I keep running scenarios in my head which don't net me a clear winner.

[Lamar]

- The positioning relative to the CTS-V concerns me (it has to be just right)

With the numbers Dwight posted, it seems there's a lot of space between the ATS-V and CTS-V. Space for the ATS-V to increase in power.

Is supercharging the ATS-V a la the CTS-V off the table?

[Camino LS6]

I almost feel as if I'd need to drive prototypes of each formula before I could decide.

[regfootball]

GM and most other OHC engines have few failures anymoe. GM no matter what engine has a great record right now on drivetrains.

the high feature v6 had some issues when it first came out. have those been corrected?

AFAIK, the basic 4 cyl. ecotec has been pretty reliable.

[dwightlooi]

the high feature v6 had some issues when it first came out. have those been corrected?

AFAIK, the basic 4 cyl. ecotec has been pretty reliable.

A few minor issues here and there. The assumption is that by 2012 they'll be taken care of. The basic premise though is that with two turbocompressions, additional plumbing and an air-to-water aftercooler circuit there are more things on the TT V6 to go wrong with than with the NA V8.

Power from both engines are equal. The V6 probably has more torque area under the curve. The V8 is simpler, cheaper, lighter and has more "character". Fuel economy is going to be pretty close -- the DOHC valve train, back pressure from the turbos, reduced compression and increased weights on the V6 hurts economy, but it makes up for it in having two less cylinder walls and a smaller displaced volume. In the end, contemporary engines point to a 1 mpg advantage to a 3.5 liter class TT V6 vs a 6 liter class Pushrod V8 in the urban cycle, and a draw in the extra-urban cycle.

[regfootball]

well ford can get 17/25 epa on a 4400 pound awd tt v6 sedan. Pontiac GXP G8 rwd only was like 13/20 with a pushrod v8. So i would tend to think the tt v6 might have a similar mpg advantage, even in an ATS.

[Lamar]

well ford can get 17/25 epa on a 4400 pound awd tt v6 sedan. Pontiac GXP G8 rwd only was like 13/20 with a pushrod v8. So i would tend to think the tt v6 might have a similar mpg advantage, even in an ATS.

While I agree with you to an extent, a better comparison would have been the GT (more similar power numbers).

But what gets lost in your statement is that very few people who shop a V-Series, much like those who shop an M, AMG, or RS, aren't making their purchases based on fuel economy. It's just a perk.

Edited April 21, 2010 by Lamar

[dwightlooi]

well ford can get 17/25 epa on a 4400 pound awd tt v6 sedan. Pontiac GXP G8 rwd only was like 13/20 with a pushrod v8. So i would tend to think the tt v6 might have a similar mpg advantage, even in an ATS.

Actually, a better comparison would be a Camaro SS 16/25 with the 6.2 V8 and 6-spd Auto. The Camaro is ~500 lbs lighter, but it also makes do without the Ecoboost engine's direct injection system. The SHO is essentially FWD until the wheels slip and the haldex clutch engages the rear differential and wheels.

Another example that lower displacement and cylinder count does not automatically translate to better economy is the W203 2000~2006 Mercedes C-Class AMG cars. The C32 AMG was 14/19 using a 349hp 3.2 liter Supercharged V6. The C55 AMG was 16/22 using a 5.5 liter (5.439 actually) 362hp SOHC-3v V8. Both cars use a 5-spd auto and weigh within 40 lbs of each other. The latter car gets between 17.5 and 19.5 in my daily driving.

Edited April 21, 2010 by dwightlooi

[RjION]

Again ............... I'll take the 5.5L small block without the turbo, and the added fat.

[Z-06]

Dwight, I have following questions:

• Is there any way to fudge more in the engines to get better fuel economy without sacrificing the power? I know we can have displacement on demand, but before we take that option can the engine be tuned for more fuel economy?
• Can the peak of the torque curve for the V8 be made higher and the curve flatter without sacrificing other salient features.
• What would be implications of going regular unleaded for the V8?

[Robert Hall]

It will be interesting to see what engines the competitors in the compact super sedan market will have in a few years.

Audi currently has a V6 in their S4 IIRC, BMW has a V8 in the M3 but the next will be back to a 6 from what I've read, Merc has a V8 in C-class AMG63, and Lexus currently has a V8 in the IS-F.

[regfootball]

While I agree with you to an extent, a better comparison would have been the GT (more similar power numbers).

But what gets lost in your statement is that very few people who shop a V-Series, much like those who shop an M, AMG, or RS, aren't making their purchases based on fuel economy. It's just a perk.

it still doesnt cover up the fact that those v8's are thirsty. er.

[Lamar]

it still doesnt cover up the fact that those v8's are thirsty. er.

Well, it's a given in that segment... much like the full-size pickups.