dwightlooi

Wow, I stepped out for a couple of days and this thread exploded. Anyway, let's clear up a few misconceptions shall we? (1) All else being equal a DOHC engine is always bigger and heavier than a Pushrod engine. This is simply because the heads are much bigger and they have four times as many camshafts. If a DOHC engine of similar displacement weighs less it is a testament to its construction technology not the layout. With the same construction the Pushrod will be even lighter. (2) Smaller displacement does not equal better fuel economy. The biggest determinant of fuel economy is vehicular weight, followed by gearing. Engine efficiency comes in third. And, engine efficiency is as much a function of internal friction as it is pumping losses. A DOHC 4-valve engine has higher internal friction and lower pumping losses. (3) In general Pushrod engines have only one performance disadvantage compared to 4-valve DOHC designs -- they have smaller valve areas and do not breathe as well at high rpms. This disadvantage does not show itself until about 5300~6300 rpms. Below that, there is no performance disadvantage. (4) The DOHC design has only one decisive advantage over pushrod engines when they are not tuned to deliver peak power at 6500 rpms or higher. Due to the lighter valvetrain mass, they tend to be be more refined at higher rpms. This affects consumer perception and consumer perception is often much more important than performance, economy or even cost.

Not sure, but the 3-valve Single In-Block Cam design was actually tested but rejected for the LS3. The reason being that the increase in performance is not significant and not worth the additional complexity. The added valvetrain mass also lowered the redline. More valves do not necessarily add power. It is increased airflow that makes more power and more valves simply facilitate that at high rpms. The problem is that a 2-valve head with lift at LS3 levels is adequate in supplying air at 6000~6300 rpms (which is where the power peaks in the LS engines). Going to a 4-valve or 3-valve head doesn't do much good unless you also optimise the cam profile for higher rpms. Herein lies the problem... the 6L80 transmission (which can handle 468hp/439 lb-ft) has a maximum shift speed of 6500 rpm. The 6L90 is even lower at 6000 rpm. Hence, if you want to have an engine which makes proper use of the advantages of a 4-valve head you need to develop a new tranny to allow it to rev to 7000 rpm or higher -- like GM's own LF1 3.0 liter V6 which makes 270hp @ 7000 rpm (90 hp / liter). Otherwise, a 4-valve head is just more bulk, more weight and more costs for very little benefit. Think about it for a second a Camry V6 makes 268 hp out of 3.5 liters at 6200 rpm. That's 76.5 bhp/liter and not worth while using a DOHC-4v design for! An LS7 is already at 505 hp @ 6300 rpm out of 7 liters. That's 72 hp per liter. With DI we can probably get to about 75 hp/liter. Close enough. And not using DOHC saves globs of mass by eliminating the big DOHC heads, and three camshafts. You also make the engine smaller dimensionally so you can fit it into a smaller bay.

A few things... (1) A 5.3, 5.7 or 6.0 liter small block (the currently existing ones) are not lighter than the 6.2 and the 7.0 is not heavier either. They all hover around 198~212 kg. If you want to make the block lighter in general you want to make it smaller, that means you need to ditch the small block's 111.76 mm bore centers. Increasing or decreasing the stroke and bore do not change the weight tangibly, in fact it is accessories and the like which affects the model to model weight difference. (2) A V-8 will be shared with trucks and other "muscle" cars like the Camaro. A V-12 will be shared with Caddy's STS replacement, etc. A V-12 is not particularly expensive if you use off-the shelf parts from the 3.0 V6 and simply mate two end to end. It'll may be add $3000~4000 more to the price of the car with the same profit margins. An S600 costs $120K not because the V-12 costs $40K more but because it's an S600 and they can charge $120K. (3) In general, an in block cam V-8 has better power to weight or power to size ratio. A V-12 has higher power to displacement ratio, not to mention superior civility and prestige. (4) Making the C7 slightly smaller and paying attention to mass will probably get it to ~3000 lbs (200 lighter than today). Adding DI and VVT to the LS3 will get you another 10% more output.

Which engine will you prefer in the next Corvette?

I happen to think that a smaller "Menu" is better. Acura had the TSX and the TL. They both had one engine. They both had has two trims -- with or without the Tech Package. There are no option boxes to check. IMHO, that is not a bad strategy. You keep the the logistics and inventory simple which frees up a few bucks to spend on quality. A technologically competitive 3.0 V6 with 270~300hp is not a bad place to start. There is really no need to complicate the lineup and customer choices with a 4-cylinder or a bigger V6. If the customer is really about saving every last penny on gas they'll be at the Chevy dealership looking at a Cruze. If they are really tree huggers they'll be looking at the Converj. If they are true enthusiasts there's the ATS-V.

I don't think that's true. Really. I drive a C55 right now, so I am no stranger to the desire for power and torque. However, if we are to limit ourselves to one engine for a luxury RWD compact we don't need to go overboard with on power and/or torque. People buy C240s and 328s. In fact, they buy more of these than C350s and 335s. 300 hp from a free revving, engine with a flat torque curve delivering 90% of its peak 228 lb-ft from 2000 rpm to 7500 rpm is no sham. For hard core enthusiasts, we can always defer them to a small block powered "ATS-V". The Alpha can be smaller and lighter than the current 3-series or c-class, more like the previous generation 3 and C. If it is not under 3550 lbs it'll be an engineering failure. 3350 is actually quite a reasonable goal -- that is about how much the previous C240 weighed or 328 weighed empty, and neither is a paragon of extreme weight reduction. And, GM can produce light weight vehicles if they make it a priority -- the Corvette is very light for a 6.2 liter RWD car of its size (~3200 lbs). Price wise it is not unreasonable to want to keep it at the level of an IS250 or TSX. Afterall, you don't really want to price it the same as a CTS. Features can be sacrificed as long as quality is kept high. In an entry level Caddy, I'll gladly trade a power sunshade, xenon lights, dual zone electronic climate control, multiple seat position memories, headlight washers, parking assist sensors, rain-sensing wipers, magnetologic shocks, etc for better switch gear feel, posh interior finish and better quality leather. I am also a believer in the Acura model of option pricing. There is basically a base version and a tech package -- no options, they build them one way to keep costs down by reducing logistic complexities. Cost can also come out of the platform by ditching advanced suspension configurations for simple struts front and back. Benchmark an E36 M3, improve on the interior materials and quality -- its not a bad car.

Hybrid or not Converj is a beautiful car. Such a beautiful design is too good to waste on a niche vehicle with a small sales volume. Here's a concept of the an Alpha Platform vehicle adopting the Converj's lines. Notable changes include:- The front wheel is moved forward. The chassis is stretched to make it a sedan. A second set of doors is inserted. 2012 Cadillac ATS Front Engine, Rear Drive, Rear Mounted Transaxle, 4-seats, 3350 lbs, 48%(F) / 52% (R ) weight distribution. 3.0 liter V6 (LF2) with 300 hp @ 7500 rpm & 228 lb-ft @ 6000 rpm, 6-speed Hydramatic (6L50S) Automatic. One all-inclusive trim, no-options, $32,000.

It looks like they'll introduce a Compact RWD after all. It won't be the RTS but the ATS it seems, but thats all well and good.

Yes, except that capacitors are big, heavy and have an exponential discharge curves. The last is very problematic because an electric motor cannot be powered by an exponential discharge -- the motor will just blow up and not go anywhere. This means that you need a big, bulky, power conversion circuitry to convert exponentially falling voltages to relatively linear voltages. Power density of Capacitors also fall between 1/100th and 1/1000th that of a battery.

I am sorry, but I cannot be a cheerleader for bad engineering. The whole point about unibody crossover SUVs is that they are lighter and in most sense more civil in ride quality than body-on-frame truck derivatives. A vehicle on the SRX's size in unibody construction ought to be LIGHTER than the larger body-on-frame predecessor it is replacing. Being heavier is unconscionable And 4500 lbs is doubly unconscionable. The RX is as light as 4178 lbs. Being 350 lbs heavier with a smaller and lighter engine cannot be justified -- even if lightweight construction hasn't been GM's forte. And, I believe that isn't really true. The Cruze is around 2800 lbs. That isn't so far off the Civic's 2750 lbs or the Corolla's 2811 lbs.

That is like saying GM will never build a good car. If you believe that, then there is no point in doing anything. The fact of the matter is that 3350 lbs is an engineering possibility, and one without resorting to exotic materials or processes. In fact, it has been done before in perfectly civil cars... The E36 3-series was about 3219 lbs with an iron block 3.2 liter inline-6 in the M3. Models like the 320 and 325 were lighter yet. The W203 (2000~2007 C-class) was 3423 lbs with the 3.2 V6 and all the amenities expected today. Part of the reason the CTS is that heavy is that it is big and it has a 113.4" wheelbase. The CTS is already has the "I prefer a roomier car" crowd covered. The current A4, C-class and 3-series are all about 3400~3700 lbs because they are bigger than the previous generation. I am suggesting that we go back to the size these cars were at at the turn of the millennium.

Whether 223 lb-ft is sufficient in a 3350 lbs car is debatable. However, the LF1 is so linear that even though maximum torque arrives at 5700 rpm, it's largely irrelevant because 90% of that (~200 lb-ft) is available from 1500 rpm to 7000 rpm.

OK, let me summarize the formula... $30K base price 270hp DI V6 power 3350 lbs RWD w/rear mounted transaxle 6-speed auto 108" wheel base W203 C-class size Keep it simple, light and affordable. Keep it high on material and assembly quality, but not necessarily high on amenities and features.

I think that is besides the point. The point is that the 3-series sell very well. The C-class sells very well. The IS250/350 sells very well. They are all smaller than the CTS. And, the buyers chose these vehicles their respective manufacturers also have larger offerings. It shows that taken as a whole, there is a big market for compact luxury cars. This market is -- overall -- larger than that of the mid-size or full-size luxury cars combined. To not have an offering in this segment is a huge mistake, and Cadillac should make bring out an compact entry a higher priority than a new full-size, mid-size or exotic sports car.

IMHO the 3.0 (LF1) is in many ways a better engine than the DI 3.6 (LLT). Specific output is higher (90 bhp/liter), refinement is better (shorter stroke = lower 1st order vibrations) and compression is higher (11.7:1 vs 11.3:1) meaning that thermal efficiency should be slightly better. The engine also has various innovative features like an exhaust manifold that is integrated into the cylinder head. Fuel economy numbers are expected to be ~ 2mpg better on the freeway and 1 mpg better in the city. I do not know if a 7 or 8-speed is warranted at this point. The 6-speed has a 6~6.1 ratio spread. That is plenty. Too much shifting actually slows you down. What I'll focus on is doing something different for the segment -- like mounting the transmission under and in between the rear seats for better weight balance. The hardware is already in the parts bin. The Corvette uses a rear mounted transmission arrangement.

The way I see it, while Cadillac may be leading GM's brand renaissance it has two problems:- (1) Lack of a Globally relevant, unified product portfolio. (2) Lack of a Compact Luxury (3-series/C-class) offering. The first is quite apparent. You have the Escalade which is a US Suburban derivative. The SLS which is a China only S-class competitor which Caddy won't bring to the US and EU because it believes that it has decided to surrender to the S-class and the 7-series rather than risk additional funds to try and market a so-so product. The BLS is yet another derivative, this time an Opel, and a flop in the EU where they just wanted to bring out something for the sake of having something, anything in its segment. The DTS is, well, a last generation straggler renamed. The second is a Critical Problem. The luxury compact is the key bread and butter car Caddy has to have, yet it has nothing in the US and the lack luster BLS in Europe (which is a joke). It is a Critical problem because this is where the money is! If you look at BMW sales figures (for cars; not including SUVs), the 3-series is 60.2% of the sales volume, the 5-series 29.8% and the 7-series a mere 10%. To have nothing in the compact luxury segment is suicide. This should be Caddy's priority, not a flagship, not another V-car, not anything else. A world class flagship won't make a lot of money, neither will a dominating sports sedan. What these thing do very well is elevate the brand prestige and image and help to sell the rest of the portforlio. But, that is all moot if you have nothing to sell into 60% of the market! The RWD Alpha (or whatever it ends up being called) should be the #1 thing on Cadillac's plans. It'll do well to produce an approximately 3350 lbs car with an ~108" wheel base and an interior volume very much like the departed W203 C-class or E46 3-series. The engine can be as simple as the excellent 270hp (LF1) 3.0 V6 or the 260hp (LNF) 2.0 I4. The transmission can be the 6L45 6-spd auto. The platform can be relatively unsophisticated -- maybe the Kappa's unequal length arms out back with struts in front. Just keep it relatively light, keep the interior at the same grade as the CTS and get it out on the market FAST! FAST is key because Cadillac is not in the game until the Alpha is on the market -- when you cede 60% of the market, even if you are competitive in the remaining 40% you are still nowhere.

Well... in retrospect, there was a very similar reduction in brands and lineup. They kept Buick, but otherwise it was close. There is also continued overlap between GMC and Chevy trucks where I would have preferred if Chevy get out of the truck business altogether and leave it to GMC. Finally, wasn't a reduction in power train lineup, however which IMHO they could have implemented. But, all it all, Government Motors is leaner and more streamlined than GM was. Let's hope that this company can turn itself around and take the company back to non-government ownership ASAP.

Not necessarily... A larger, single turbo is not less efficient or more laggy than two small ones. The reason twin turbocharged engines are favored traditionally for Vee configuration engines is that it is difficult to route exhaust from one side of the engine to the other, and when you do that you also invariably introduce thermal losses which negatively impact turbo response and performance. Regardless, there are many examples of dual bank engines using a single turbo. The Subaru EJ20 (2.0l) and EJ25 (2.5l) H4s do that, and so does the GM LP9 (2. engine in Saabs. However, if one reverses the cylinder intake and exhaust ports such that the air enters the engine on the sides and the exhaust exits in the Vee of the powerplant, one can then mount a single turbocharger in the valley of the engine without the exhaust routing woes. Some european diesels already do that. A single Garrett GT 35 medium frame turbo will do just fine for 600 hp.

Let's sum it up simply... (1) The gas turbine is attractive for its mechanical simplicity, light weight and small size. A 100 hp unit can be about the size of a 100 pcs stack of CDs. (2) A gas turbine is only feasible as a daily driver engine if it is used in a series hybrid drivetrain. This is the only way to make irrelevant the 5-10 sec throttle lag and also allow the engine to always operate at its peak efficiency (at ideal speed and load). (3) The problem with series the turbine-electric series hybrid is not the turbine but the battery. Constant charging and discharging shortens the battery life and batteries are extremely expensive today ($10,000~16,000 for the Volt's 40 mile range pack).

Well... the short anser is that it will make HCCI easier to achieve and maintain. However, HCCI employment will also yield much less efficiency improvement in a series hybrid compared to a parallel hybrid or conventional power train. The long answer is that the HCCI's principal goal is to make a gasoline engine more like a diesel engine to increase its efficiency. A diesel engine is more efficient for three reasons... The spontaneous conflagration achieved in a diesel engine's burns fuel more efficiently than the spark triggered flame front light off in a gasoline engine. The diesel engine has higher compression ratios (18~22:1 vs 9~12:1 for Naturally Aspirated engines) The diesel engine runs has no throttle body choking the engine at any time and operates simply by running the same air charge lean at part "throttle", hence affording lower pumping loses. In a Series Hybrid, the engine can be designed to run at full load, WOT or not at all. As such, the ability to eliminate throttle butterfly induced part power pumping losses is moot. And, since gasoline HCCI is currently unachievable at full load running conditions the benefits may only be in increasing efficiency during the brief periods when the engine revs up and down from its optimal, constant operating speed. Another alternative is to use a larger displacement engine and only operate it at 20~40% power, but in HCCI mode. However, the larger displacement engine is also bigger, heavier and thirstier to begin with. So in the end it may not be worthwhile to implement HCCI in a series hybrid like the Volt. If ultimate in efficiency is the goal, just run a series hybrid with a real diesel engine! If gasoline fuel is a must then an Atkinson or Miller Cycle power plant makes sense.

No, GM is not responsible for all that went down. In fact, they have done a great deal in bring their product line back to a competitive level. Solstice, G6, G8, GMT900s, Aura, Traverse, CTS and especially the Malibu -- you name it, all huge steps forward. However, I will rather see a 3 brand GM -- Chevy for mainstream cars, GMC for all SUVs and trucks, Caddy for Luxury stuff -- than a continuation of this 10 brand mess. We need more good cars, not more brands of cars. I don't see a need to expend resources developing body styles of the same vehicle, promote these different products and share the marketing pie over multiple overlapped brands. Heck I think that even Toyota has one too many brands with the addition of Scion.

(1) Noise from turbine engines, very much like noise from any other exhaust producing motors, depends largely on exhaust velocity. Reducing the former is the job of the muffler. In the case of the turbine engine, this job is actually easier because the exhaust is not pulsatile. Expand the cross section and if necessary dilute it and it'll sound like a turbocharger on boost -- which is quite pleasant by any measure. (2) It is always a trade off between efficiency, complexity and mass. Simple turbines are about 25~42% efficient depending on how advanced it is (how high a compressor pressure ratio and turbine inlet temperature you can get). For small, single-stage, single shaft, turbines tend to be close to the 25% mark whereas large 60,000hp units on ships are near the 42% mark (eg. GE LM6000, R-R MT30). To go above that you need to recapture the energy in the exhaust heat. The simplest way to do this is with a recuperated turbine. Here, the exhaust is passed through a heat exchanger and is used to heat up the intake air between the compressor output and the combustor. This earns you another 5~10%. A Combined Cycle engine uses the same exhaust heat to boil water and run a steam turbine. Because of the efficient air-water heat exchange interface due to the high thermal conductivity of water, and the high amount of heat which can be captured due to the specific latent heat of vaporization of water, the combined cycle unit is much better at capturing wasted exhaust heat energy than the air-to-air recuperated turbine. It is usually good for 10~20%. (3) The secondary Rankine cycle turbine is often idle when the primary turbine is operated a partial power. However, in the case of a series hybrid, we can always design the turbine to operate at full power or not at all to achieve maximum efficiency. Unlike a parallel hybrid or direct drive setup, a series hybrid simply uses the turbine to generate electricity. Given the presence of a battery, there is no reason to operate the turbine at 1/4 power or 1/2 power when you can operate it at full power for 1/4 or 1/2 the duration.

I am sure HCCI is possible, but it may not be practical on an OHV engine. HCCI is tough enough to achieve with carefully designed, highly symmetrical combustion chambers of a 4-valve cylinder head. And, even so it only works in a narrow rev and load range (up to about half loads at up to 55mph in top gear), and requires a cam lobe switching variable valve lift system to be incorporated (a GM first) in the 2.2 liter demonstrator engines. Try to do it on an OHV V8 and you'll need to fit VTEC style dual lobes, dual lifters and dual push rods per valve. You'll also probably end up with an even narrower HCCI operating envelope. At some point the added complexity, costs and compromises in operable envelope makes it impractical. Yes, HCCI works best at a constant load and engine speed. I guess there is enough developmental risks on the Volt and enough efficiency margins over conventional hybrids that GM does not want to debut HCCI on it (yet). And, that makes sense. If you are looking for a "breakthrough" powertrain for efficiency, there are other things as well. Try a recuperated gas turbine for instance. 30~40% thermal efficiency (comparable to contemporary spark ignition engines) but the entire 100 hp engine is probably small enough to be integrated as part of the MUFFLER! Weight is the biggest robber of fuel economy. making the engine basically disappear saves a lot of weight. It also saves a lot of space which in turn saves even more chassis weight. All the disadvantages of a turbine -- horrendous response time, poor economy at part loads, inability to idle slow, unable to start quickl -- are pretty much retired by decoupling the engine directly from driving the wheels through a series hybrid arrangement. Want even more efficiency? Rout the heat from the exhaust to a heat exchanger and use it to boil water for a secondary closed loop steam turbine. Do that and you can try to break the 60% efficiency barrier. That's how the natural gas power stations and high efficiency cruise ships do their generation.General Electric -- with COGES arrangements like the General Electric MS7001H or LM2500+STM)

I think there are a few misconceptions here... (1) Smaller displacement -- in and of itself -- does not equal better economy. Smaller displacements = smaller pumping losses. However, a larger number cylinders = a larger number of cylinder wall area, valves, etc. -- all of which increase mechanical friction and reduce economy. (2) In general the maximum specific power output and fuel economy is achieved by using the fewest cylinders for a given displacement that you can stay under the knock threshold. A 1-cylinder 2 liter engine -- if you can stand the vibrations and prevent it from knocking -- will be more powerful and more economical on fuel compared to a 4-cylinder 2 liter engine. The Mazda 1.8 liter K-series V6 is neither powerful (130hp) nor economical (29mpg on the freeway) compared to other 1.8 liter engines of the period such as the Honda B18C. (3) 5.2 liters was suggested because it was a convenient displacement with a 94x94mm (bore x stroke) engine. This allows the engine to share the 3.6 V6's bore spacing and bore diameters which makes it easier to build both engines on the same line even if they have different V angles. It is also a displacement which allows the engine to get close to LS3 power levels without radical cams or forced induction. (4) As far as torque is concerned, more is not always better. 375hp is plenty fof a 2,900 lbs car. Any more will simply equal more wheel spin in 1st and second,.

Well.... let's remember why the push rod OHV engine was originally invented. It wasn't that SOHC or DOHC designs didn't exist -- most WWII V12 fighter engines were SOHC 4-valve per cylinder powerplants, the German ones largely featured direct gasoline injection too! It was the desire to produce a smaller and lighter Vee-configuration engine that let to the incarnation of the OHV push rod V6 and V8 engines. Daimler Benz DB605 -- 35 liters, 48-valve, inverted V12, with Bosch Mechanical Direct Gasoline Injection