dwightlooi

Well, let me re-state this again... The CVT does not, in any way, make possible a lower cruisin RPM than an automatic or manual transmission. That has nothing to do with the CVT or its infinite ratios. It has to do with the the final drive gear. Period. For example, you can be at 1000 rpm at 60mph with ANY transmission. I mean ANY manual, automatic or CVT transmission. All you have to do is to select a final drive to match the tallest ratio of that transmission that will make the engine turn at 1000 rpm when the wheels are covering 60 mph. The only question what ratio your 1st or lowest gear will be when you do that. If it is very tall then the car will be really sluggish off the line from a stand still. The ONLY thing that affects your 1st or lowest ratio when your tallest makes 1000 rpm at 60mph is the ratio spread of the transmission. Ratio Spread = lowest ratio / tallest ratio. A transmission with a ratio spread of 7:1 will have a 1st gear that turns the engine 7 times faster at any given speed than its tallest gear. The CVT, currently does not have the widest ratio spread. The traditional automatic does. Aisin hit 7.5:1, ZF hit 7.01:1. The Nissan's CVT is 5.4:1 and Audi's is 6.0:1. GM's 6-speed 6L45 and 6L50 Autos are 6.06:1

For the Flagship, I have always been a proponent of doing a 7.2 liter V12 based on the 3.6 DI V6, but with a new double length block casting and crankshaft... Name: Cadillac Symphony V12 Type: 60 deg V12 Valvetrain: Chain Driven DOHC 48-valve; Dual VVT Construction: Aluminum block and heads Fuel Injection: Direct Gasoline Injection Bore x Stroke: 94 x 85.6 mm Capacity: 7128 cc Bore Center: 103 mm Compression ratio: 11.3:1 Power Output: 600 hp @ 6200 rpm Torque Output: 550 lb @ 4800 rpm Maximum Engine Speed: 6200 rpm Fuel Grade: 91 Octane (Recommended); 87 Octane (Required) Transmission: GM Hydramatic 6L90 (6-speed Automatic) Differential: 149hp Rear Differential Motor/Generator* Fuel Economy: 16 mpg (City) / 22 mpg (Hwy) (5300 lbs Cadillac Flagship) * Derived from Chevy Volt Main Propulsion Motor. Provides an additional 273 lb-ft @ 0 mph and 149 hp at 70 mph. Energy supplied by and recovers to a 4 kWh Li-Ion Battery Pack. In Eco Mode, the motor can provide electric only propulsion at low throttle for up to 5 miles.

(1) The last CVT I sampled was in an Altima Hybrid. I wasn't impressed. The same 2.5 liter QR25DE engine was less obstrusive and has better perceived refinement when paired with the previous generation's 4-speed Automatic. (2) I have also driven the Audi A4 3.0 Multitronic, the Ford 500 CVT and the Nissan Murano CVT. None were as good as the newest 6-speed, 7-speed and 8-speed autos. (3) Planetary CVTs in Hybrids like those in the Prius, HS250, Fusion Hybrid, Volt, etc. aren't CVTs at all. In fact, they are not really transmissions at all. What they are is a work splitting device; more like a differential. Imagine a reverse differential, where you connect each wheel to a separate engine, the drive shaft then becomes the output. The engine and the motor drive the sun and ring gears. The planet carrrier drive the wheels. The more torque either one puts in the faster that device spins an the lower its gear ratio, conversely the ratio on the other becomes higher and its rpm becomes lower. The ratio is directly proportional to the input torque from each. To reduce the increase for one, the other must do more work. This allows driving force to be split between to independent propulsion sources. It only works when you have two motors. It only works well when the two are similarly powerful but at optimized for different rpms. (4) EPA highway economy really has nothing to do with CVTs or automatics or even the ratio spread. The test is done at highway speeds with practically no shifting and very little change in speed. Essentially only the top gear ratio matters. You can have minimal ratio spread and still have a tall cruising ratio hwoever you'll sacrifice off tthe line acceleration. With a wide ratio spread you can have both. Right now the ratio spread for CVTs are between about 4.2 to 6. The ratio spread for conventional autos are between 5.4 and 7.5. The advantage goes to automatics. The reason for the difference lies in the fact that autos can have 2 or 3 planetary sets in sequence. CVTs typically only have one variator. Even though the effective ratio it can achieve with one is wider than that which is achievable with one planetary gearset, it is narrower than can be hit with 2 or 3 of them. What's important here is that lets say both the CVT and the automatic has the same top gear ratio, the automatic is more efficient in cruise because it does not have to waste power driving the hydraulic pump to keep the variable pulleys functioning.

I look at it differently. I don't think the Caddy V8 should try to ilk out another 20~30 horses over the Corvette engine. I mean really, whatever the Corvette engine puts out, it'll be "enough". What I'll like to see is additional features that enhances refinement in the Caddy engine. This can be a balance shaft in the oil pan. It can be an acoustic skirt around the block -- a perforated honeycomb sandwich like those used in the engine casing of commercial turbofan engines comes to mind. It can be a dual length intake. Or, even something simple like switching from a composite intake assembly to a cast magnesium or aluminum one (metal ones are quieter). Also, the engine should -- dressed up or not -- look different from the Corvette version.

There are reasons why most adopters back outed of CVTs -- Audi, Ford, Nissan, you name it. They... well... uh.. sucked! Primarily the problems were three fold:- (1) CVTs have limited torque ratings -- about 100~120 lb-ft on compression (Van Doorne) chain designs abour 200~240 on tension chain ones. (2) CVTs reduce refinement -- by causing the engine to drone at one RPM. Some designs simulate discrete ratios, but doing so reduces the efficiency. (3) CVTs are NOT more efficient in service than contemporary automatics -- infinite ratios are nice, but both chain and toroid designs have narrower ratio spreads than leading automatics. This leads to higher freeway cruising rpms or inferior off the line acceleration or some combination of both. On top of that, because CVTs sandwich the variator chain with pulleys at high compression forces, it requires a constant supply of high hydraulic pressures. This in turn require the constant operation of a powerful hydraulic pump. Think 2~3 A/C compressors worth or parasitic drag. These practically eliminates any efficiency gains from the CVTs and frequently actually made mileage worse.

Of the various (relatively affordable) transmissions and drive technologies being developed, or can be developed, what will you see most as a standard feature on GM vehicles? The keyword here being "most", hence you may only choose one.

BTW, if case I sounded like 8-speed trannies are never going to happen. Let me say that the following is going to be going on a car near you. The only question is when. It won't be 2011 or 2012, but it'll happen.

Actually, I don't think you need to beat the 3-series in every measure to beat the 3-series. You just need to make the car a more compelling buy. For instance, it is not important to have a turbo six just because the 3-series has a turbo six. It is more important that in styling, in perceived refinement, in overall handling and interior quality you appeal to the buyer more than the 3-series. In this regard, going with a 4 cylinder - 8 cylinder lineup may not be a bad one. The mainstream car offers a 4-cylinder turbo with V6 class performance and refinement. The V8 CTS-V is priced to run against a 335i (~$45K), beating it (and the E90 M3 for that matter) in both cylinder count and in performance. The amount of cost you save from not having a twin-turbo six can do wonders for the interior and the standard amenities. Even 270hp in the 2.0T I4 and 420hp in the Pushrod V8 -- which is on the low end of what's possible -- will be just fine.

~290 I think, but torque was over 300. However, that is a tuner kit engine. General production power plants will have more conservative margins. In any case it does have more lag to peak power than the standard 260hp engine. To preserve the same knock margins, you generally lower compression as you specify a higher boost level. That is predorminantly what causes a reduction in fuel economy. Remember, 99% of cruising on the freeway is done in vacuum not boost.

I have never sampled the 3.9, so I cannot pass judgement on it. The 3.5 liter wasn't bad though... it was smooth and quiet. At 221 hp / 220 lb-ft with 22 (city) / 32 (fwy) mpg (pre-2008 EPA standard) it was also reasonably competitive with the 2.8 ~ 3.2 DOHC V6es of the period. Not class leading for sure, but good enough to be mid-pack.

Here are the practical realities given the intent to introduce the ATS in 2012 as a 2013 model It is unlikely that GM can, or will, do a new family of transmissions in time. This leaves us with the 6L45, 6L50, 6L80 and 6L90. You can easily bring the 2.0T to 300hp. But, if you do so, expect somee degree of turbo lag and reduction in fuel economy. A low boost 3.0T will be roughly the same output as a high boost 2.0T. A high boost 3.0T will be about 400hp. If GM does a low boost 3.0T they'll probably keep it at or under 315hp / 332 lb-ft to be compatible with the 6L50 transmission. If they do a low boost 3.0T they'll probably NOT do a high boost 2.0T and use the 220hp or 255hp versions in the Regal instead. If they do a high boost 3.0T @ ~400 hp that'll probably be the V engine in lieu of a 420~470hp Pushrod V8. If GM is to revamp its transmissions to either a hybridized drive or a 7~8 speed unit, it'll probably be a mid-life ATS update.

My experience with the HF V6 seems to indicate the following:- So far I have sampled the HF V6 in the Malibu, Lacrosse, CTS, SRX and Camaro. All were rentals. None of them are particularly refined -- acoustically they have a grainy, gritty, groan. None of them are particularly fast revving -- revs are lethargic compared to similar V6es others (especially Honda). The DI versions seems to be coarser and less refined than the port injected versions. Independently of the engine, some applications have more insulation than others make the V6es less obtrusive. Others like the Camaro is down right crude sounding. By that I mean, the engine sounds and feels less refined than the 2.4 Inline-4 in Malibu. Even in a pretty well insulated vehicle (SRX 3.0) the engine comes across as coarse, groanny and not particularly eager. If the Toyota 2GR-FE (Lexus ES350) is a 10 and the Honda J32A (Acura TL) is a 9; I'll give the LF1 (3.0) and LLT (3.6) engines a 5 in refinement. In fact, the 3.5 Pushrod V6 in the last generation Malibu & G6 seemed to be a bit better. Not more of a revver, but somewhat quieter and smoother.

Here's one big problem for GM to solve. The current 3.6 and 3.0 DI V6es have pretty good specfic output... But, they are also:- Some of the roughest sounding V6 in service with anyone -- worse than the Pushrod 3.5 (REALLY!) Below average in fuel economy ratings Possible Solutions? Precision crankshaft balancing Piston & Rod weight matching Add a balance shaft in valley of engine block Switch from plastic to aluminum valve covers and intake tracts Add external ribs and webs to stiffen block Improve engine mounts Add sound absorbing / canceling devices (Helmholtz's, perforated honeycombs, mastic sandwiches, etc) Use active noise cancellation in cabin (through stereo system) Replace DOHC valvetrain with SOHC or Cam-in-cam valve train Use a single cam lobe for two valves to reduce friction Implement a cam switching system to switch between Otto t& Atkinson cycles (ala Honda) Add mild hybrid system Go from chain to belt drive (detrimental to service intervals though)

Cam-in-cam was used in the Viper 8.3 V10 by (then) Daimler-Chrysler. A company called Mechadyne out of the UK holds the patents and has functioning systems. GM can readily license it if they want. Mechadyne Cam-in-cam (aka Concentric Cams) is the most straight forward and efficient way to get independent intake & exhaust VVT onto a pushrod engine like the Gen V small block. It also opens the door to replacing the current DOHC heads with SOHC heads while preserving Dual-VVT. Except for the lack of independent VVT, SOHC designs are superior in fuel economy, compactness and is equivalent to DOHC in performance up to about 7000~7500 rpms. Cam-in-cam removes that and makes SOHC superior in every way. GM has reportedly tested the system in the Small Block V8. It is unclear at this point if they will incorporate it or simply stick to synchronous VVT. What is clear is that Cylinder Deactivation and Direct Injection will make it onto the next generation of Pushrod engines.

It's more than that... Let's consider the GM 3.6 DI V6 (LLT) in RWD applications. It makes 302~312hp @ 6300~6500 rpm and 270~278 lb-ft @ 5200, with a maximum engine speed of 6700 rpm. The GM 6L50 has the following ratios 4.06 - 2.37 - 1.55 - 1.16 - 0.85 - 0.67 If the TCU shifts at 6700 rpm in each gear the rpms after each shift is as follows:- 1st - 2nd: 3911 2nd - 3rd: 4382 3rd - 4th: 5014 4th - 5th: 4909 5th - 6th: 5281 Basically, the engine speed is already where is ought with six speeds. Now, lets consider the same engine fitted with a ZF 8HP45 (4.7 - 3.13 - 2.10 - 1.67 - 1.29 - 1.00 - 0.84 - 0.67) 1st - 2nd: 4462 2nd - 3rd: 4495 3rd - 4th: 5328 4th - 5th: 5175 5th - 6th: 5194 6th - 7th: 5628 7th - 8th: 5344 8-speeds may not even be of value in terms of performance. As you can see, in three of the gears the after shift rpm is actually above the 5200 rpm torque peak. That is not ideal because an engine pulls the hardest in ANY gear at the torque peak. You want to shift to where the torque peak is or a few hundred rpms before it arrives. You don't want to shift to a point after it and waste the meatiest areas under the torque curve. Performance aside it is also detrimental to seat of the pants feel. After each shift, will you rather have the driver feel an increase in the rate of acceleration as the needle climbs towards the torque peak? Or do you want him to feel the acceleration forces immediately start fading since you have landed just past the peak and it's all downhill from there? That is why some 8-speed trannies sometimes skip gears during upshifts.

Well, let's compare the facts surrounding the two transmissions shall we? Facts, after all, are not subjective... GM Hydramatic 6L50 (6-speed Automatic) Max Input Torque Rating: 332 lb-ft (450 nm) 1st: 4.06 2nd: 2.37 3rd: 1.55 4th: 1.16 5th: 0.85 6th: 0.67 Rev: 3.20 (-) ZF 8HP45 (8-speed Automatic) Max Input Torque Rating: 332 lb-ft (450 nm) 1st: 4.70 2nd: 3.13 3rd: 2.10 4th: 1.67 5th: 1.29 6th: 1.00 7th: 0.84 8th: 0.67 Rev: 3.30 (-) As you can see -- using the same final drive ratio -- both transmission will wind up having the same cruising rpm. The difference here is that the 8HP45 has a 4.7:1 1st gear compared to a 4.06:1 1st gear on the 6L50, hence it'll put 15% more torque to the wheels off the line resulting in slightly better acceleration. This also actually result in slightly worse fuel economy in the city, which is why the transmission typically starts in 2nd gear downshifting to 1st only if the driver aggressive stomps the pedal at a stoplight or at very low speeds (0~15 mph). It can afford to do so because the additional speed steps enables it to have a 2nd that is not too tall (between the 6-spd box's 1st and 2nd). On the flipside, the 8-spd does not hit 60mph in 2nd and the additional shift may actually cost it 0.1~0.2 sec in the "revered" 0-60 mph tests. You typically see rapidly diminishing returns in performance and economy as you ratchet up the number of speeds a transmission has. Huge difference between 3 and 4. Big difference between 4 and 5 speeds. Small difference between 5 and 6. Tiny between 6 and 7. Anything over 7 speeds may not even register any tangible fuel savings -- at least not with MPG measured only to 2 significant figures on the window sticker. That's based on the benefits of ratios alone. If we consider the fact that 7 to 9 speed boxes probably need to add one additional planetary gear set which increases parasitic losses in any given speed, the rate of diminishing returns may be greater. Point to ponder: What gives you more tangible fuel economy and performance gains? Replacing the torque converter with an electronically controlled multi-plate clutch (ala M-B AMG) or adding two speeds to the 6-speed Automatic?

Actually, I disagree on this one... on the question of how many speeds you need, more is not always merrier. Let's take it to the extreme and consider a 24-speed transmission. It'll actually make the car slower due to all the shifting that's taking place. In fact, most of the 7 and 8 speed trannies do not go through all its speeds from stop to freeway cruising speeds. Instead, many start in 2nd and only goes to first in sport mode or when you floor the gas at a stop or at creeping speeds. Heck, even the M-B 5-speed starts in 2nd. Some skips 4th and/or 6th on upshifts, and use those gears only during part throttle downshifts at certain speeds where they go down one gear instead of two. When it comes down to it, I think what is "enough" is enough ratios and spread to do three things:- Get to 60 mph in 2nd with a low enough 1st to optimize performance. Have a high enough top ratio such that the 65 mph cruising rpm is at or under 2000 rpm. Have enough ratios such that each upshift puts the rpm at or near the torque peak. We can already do all of those things with 6 ratios and a 6~6.1 ratio spread. More ratios really do not do much for performance or economy although it may make gear changes less perceptible under some situations or offer an alternative starting gear for sport and comfort modes. All it all it doesn't help a lot. But, surely it can't hurt can it? Well, actually it can... in two ways. Firstly, 6-speeds is practically the limit you can do with two planetaries. More speeds require three planetaries. More planetaries in the same case size means higher parasitic losses from free spinning gears. It also means narrower and weaker gears. In short, a weaker transmission that is less efficient at any given constant speed. Secondly, it is a matter of money and where is goes. If you spend $1000 on an extra 2 or 3 gears, thats money you cannot put into a flywheel integrated motor. Overall, the economy gains from 3 additional speeds is probably less than you'll get from mild electrification. So, this becomes an opportunity cost and a bad trade off. For me, I'll rather see a 15hp electric assist system than 3 additional speeds.

The ATS is probably GM Luxury's most important car of the decade. If GM is to go for broke it'll probably be with this vehicle. Here are a number of things that can happen... Mild Electric Hybridization being standard on all 4-cylinder models 15~20hp Belt-Alternator-Starter (BAS) or Flywheel-Integrated-Generator/motor (FIG) 0.5 kWh / 115.2 Volt air cooled Lithium Ion Battery Pack Idle Stop control Regenerative braking Mild power assist Gen III Ecotec Engine (ATS 2.4 & 2.0T) 200~220 hp 2.4 liter Direct Injection Naturally Aspirated Inline-4 270~300 hp 2.0 liter Direct Injection Turbo Inline-4 Intake Port Mounted Throttle Butterflies Intake Cam Switching system affording part time Miller & Atkinson Cycle operation 0W20 Low Friction Synthetic Lubricants Gen V Small Block Engine (ATS-V) 420~470 hp 5.5~6.2 liter Direct Injection Pushrod V8 Cam-in-cam Dual Independent VVT Cylinder Deactivation Clutched Automatic Transmissions 6-speed Planetary Automatic with electro-hydraulic clutch pack instead of torque converter Advanced Refinement and Amenities Double Glazed Acoustic Glass on front and rear windows Electrochromic glass all round (Real Time Auto and Manual tint control) 99.9% UV A/B proof glass (Asian Markets) Sound Absorbing Perforated Honeycomb Sandwich engine cover and skirts Noise Cancelling Audio System Magnetorologic Shocks Advanced Unibody Structure High Strength Steel Unibody Aluminum hood and Selected Panels Cast Magnesium Firewall Cross member Laser seam welding Quiet Steel Elastomeric Sandwich firewall and underbody pan

(1) There is no such thing as a 6L40 to begin with and there is no way the Lacrosse will use a "6L" transmission. There is the 6L45, 6L50, 6L80 and 6L90 -- there is no 6L40 in existence. All the 6L transmissions are for Longitudinal, Rear Drive, applications. Hence, the "L". (2) The 4-pot Lacrosse uses the 6T40 transmission -- 6 speed, Transverse, torque rating 40. This transmission is rated for 180hp / 177 lb-ft and is used in the Lacrosse, Equinox and Terrain. The V6 Lacrosse uses the 6T70 tranny with their 3.0 and 3.6 V6 engines. (3) If you are interested, the ratings for all the aforementioned GM Hydramatic Transmissions are as follows:- 6L45 -- 6-speed, Longitudinal, Up to 278 hp / 258 lb-ft / 7000 rpm 6L50 -- 6-speed, Longitudinal, Up to 315 hp / 332 lb-ft / 7000 rpm 6L80 -- 6-speed, Longitudinal, Up to 469 hp / 439 lb-ft / 6500 rpm 6L90 -- 6-speed, Longitudinal, Up to 555 hp / 550 lb-ft / 6200 rpm 6T40 -- 6-speed, Transverse, Up to 180 hp / 177 lb-ft / 7000 rpm 6T70 -- 6-speed, Transverse, Up to 315 hp / 280 lb-ft / 7000 rpm 6T75 -- 6-speed, Transverse, Up to 315 hp / 300 lb-ft / 7000 rpm Note: The 6L45, 6L50 and 6L80 are also sold to BMW for use in the 3-series and 5-series. BMW buys GM trannies because their traditional supplier (ZF) did not have a suitable transmission to support the "xi" AWD models. The 6T70 model is jointly developed with Ford and is also used in the Ford Fusion, Lincoln MKZ and other Ford vehicles. (4) The ratings have pretty conservative built-in margins. Generally, you can exceed them by a bit with absolutely no ill effects. In fact, GM routinely does that. The Equinox and Terrain for instance puts 182hp through the 6T40 even though it is rated at 180hp. The CTS-V exceeds the 6L90's ratings by 1 hp and 1 lb-ft. (5) Yes, an engine can be a "mild" Atkinson and lose only 10% of its original power rating. It all depends on how late you close the intake valves. A typical Atkinson engine closes them about 25~30% into the intake stroke, losing a similar percentage of power. You can close it a mere 10% into it and lose 10%. But, you'll also not reap as much efficiency benefits. I don't think this is the case here though... 182 hp --> 180 hp is so trivia that it is probably from small variations in the exhaust, air box or things of that nature.

(1) At 180hp (as opposed to 182) I am pretty sure it is NOT Atkinson. An Atkinson cycle engine loses between 20~30% of the compression stroke to regurgitation through the intake valves -- they have cams that are ground to keep the intake valves open for the first 20~30% in of the compression stroke. This causes a similar 20~30% decrease in power output compared to the same engine were it to be operating with a regular Otto cycle*. If the 2.4L were to be Atkinson cycle, one will expect the output to drop from 182hp to about 127~146hp. (2) There is a way to get the best of both worlds. You can switch between Atkinson Cycle and Otto Cycle Cam lobes if you implement a cam switching system (ala VTEC). The engine can operate on Otto mode during hard acceleration and revert to Atkinson mode during idle, cruise and light throttle situations. It's not a free lunch of course. Using same pistons and heads, there is a dramatic difference between the compression ratio of the engine in Otto and Atkinson modes. For instance, if the engine is normally 11.2:1 (Eg. GM's "LAF" DI 2.4L), an ideal Atkinson cam will drop the effective compression to 7.8:1 -- that's pretty darn low. If you want to keep the effective compression at around the Prius' 9.5:1, the compression ratio under Otto mode will have to be a staggering 13~13.5:1. Even with premium fuel, that is a bit too high. Hence, some kind of compromise has to be struck. Either the Atkinson mode is not as deep as a dedicated Atkinson engine would use, or the Otto mode compression is higher than typical calling for premium fuel usage, or a combination of both. An engine that does Otto-Atkinson switching is the Honda Civic's SOHC R18A 1.8 Liter -- it makes 140hp and uses a rather "mild" Atkinson grind during low load situations. (3) I do not believe the GM 2.4 is using a cam switching system. The current heads are not designed to accommodate it and if they switch the head architecture to a completely new one, I am sure they'll trumpet it. * Eg. The Toyota Prius' 1.8 liter engine (2ZR-FXE) has a geometric compression ratio of 13.0:1. It keeps the intake valves open for the first ~27% of the compression stroke. This ejects about a similar percentage of the intake air before the valves close and compression begins, resulting in an effective compression of about 9.5:1 in Atkinson mode. The Prius's engine (2ZR-FXE) makes 98hp compared to 138hp the non-Atkinson version in the Corolla (2ZR-FE). A 29% output loss to (similar) 27% compression stroke reduction.

It'll do well efficiency wise -- because you'll have 12 valves instead of 16, 3-cylinders instead of four. But, it'll be somewhat lacking in refinement. A 3-potter is 1st order unbalanced. You can cancel most of that out with a balancer. The key word here is most, a because two rotating shafts (the crank and the balancer) cannot match and cancel a non sinusoidal reciprocating mass shift 100%. 3-potters are tolerable unbalanced up to 1.0~1.3 liters. A balancer may make a 1.3~1.8 liter somewhat palatable. I am not so sure about a 2.1 liter-- especially one based off the Vortec 4200 which has a pretty long 103mm stroke. But really though... if we want to shoot for minimum parasitic efficiency losses, I'll go SOHC or Concentric Cam before I build a very big 3-pot. It's a lower hanging fruit. I'll also make a 1.5 or 1.8 3-potter based off the HF V6 rather than a 2.1 liter based on the I6.

It's not loud, it's just that its a crude groan even if its a muted one. It just sounds like a buzz saw and a garden blower heard from behind double pane windows. I try to rent different vehicles when traveling just to check them out; took out the V6 Camaro with the 3.6 DI V6 (LLT) in Phoenix, AZ, while attending Intel's FST event.

How does the engine sound? In the CTS Sedan, it's a muted but unimpressive groan -- gritty, coarse and almost a prolonged agony given the rather slow revving nature of this engine (for a 60 deg V6). It's a good thing it's very well muted, because in the Camaro the engine probably competes well for the least refined V6 in existence -- it's worse than GM's departed 3.5 pushrod V6, Ford's Duratec 3.5 or Chrysler's 3.8 and definitely a class below the Honda/Acura 3.5 or the Toyota/Lexus 3.5. I know the DI V6 engine delivers good performance numbers, but refinement is somewhat lacking.

A few things... (1) First of all, I fail to see why getting from 2.4 to 2.5 liters is that important that GM needs to bend over backwards to do it. The power/torque difference between a 2.4 and 2.5 mill is negligible. (2) If they REALLY want to do it without a completely new block (different bore centers) they can probably bore the engine out from 88 to 89mm (7mm wall thickness; same as LS7) and lengthen the stroke from 98 to 100 mm. This will yield a displacement of 2.488 liters. (3) If it's me, I'll actually drop the displacement from 2.4 to 2.1 liters. The resulting engine -- in NA and turbo trims -- can then be used to replace the 1.8, 2.0, 2.2, 2.3 and 2.4 liter power plants. I'll use the following dimensions:- Bore Center: 98 mm (+2mm) Bore x Stroke: 89 mm x 85.6 mm (Same bore size as 3.0 DI V6; same stroke as 3.6 DI V6) Displacement: 2130 cc (Good median displacement for replacing 1.8 through 2.4 engines) Compression Ratio (NA): 11.7:1 (Same lofty compression ratio as 3.0 DI V6 using 87 octane) Compression Ratio (Turbo): 9.7:1 (0.5 points higher than LNF 2.0T) (4) The idea here is that the pistons, valves, valve springs, lifters, seats and guides are the same ones as those used in the 3.0 DI V6. The connecting rods are shared with the 3.6 V6. This offers a great degree of logistical commonality. Using the same piston and combustion chamber geometry as the V6 also means that we can achieve a very predictable output from the engine with minimal R&D. This will be pretty decent at between 84 and 90 bhp per liter on 87 octane naturally aspirated -- more than enough to be competitive. Add a turbo and you will be pushing 300bhp easily. NA Power: ~185 bhp @ 6800 rpm NA Torque: ~170 lb-ft @ 4800 rpm Turbo Power*: ~320 bhp @ 6000 rpm Turbo Torque*: ~280 lb-ft @ 2600 rpm * Premium 91 Octane Recommended (not required)

2mm bore increase or 5mm stroke increase or some partial combination thereof. 2mm bore increase is practically out of the question. The 96mm bore center means that the cylinder walls will be a mere 6mm thick. That's really thin, even the current 8mm is considered thin -- too thin for any significant amount of forced induction. 103 mm stroke is OK, but with an 88 mm bore it'll also make for a very long stroke engine. hp/liter will be poor, energy recovery might be better but if that is what you are trying to achieve an Atkinson cycle cam is probably the better way to go.