Should the Corvette never again offer a six-cylinder?
Americans have a long-established love affair with the V8 engine, and with good reason: almost all of the coolest cars that Detroit has produced have had huge V8 engines. Those engines were able to propel the large muscle cars that they were encased in to very high speeds very quickly, all the time burbling away a deep, throaty exhaust note that was music to the driver's ears. We have no problem at all with V8 engines, which will likely still be installed in vehicles for quite some time. What we do have a problem with is the guzzling of gasoline and the accompanying exhaust which pollutes our roadways. A well-designed V8 engine, especially when equipped with technology such as cylinder deactivation and direct injection can provide an abundance of power and reasonable fuel mileage. The same can be said of a well-designed six cylinder with forced injection. Ford has announced that we'll be seeing plenty of such engines from the blue-oval-brand in the coming years, and other manufacturers are sure to follow. The question that is on some writers' minds, though, is whether those high-tech engines should be used in performance cars like the Corvette. We can understand that purists want to see nothing but V8 engines in their favorite sports cars, just as Harley riders want their air-cooled V-Twin. But the notion that there is no other power plant which can provide the necessary power is just plain wrong. Tell the Evolution driver that his four-cylinder engine is holding back performance.
Gallery: 2008 Detroit: Corvette ZR1 LS9 engine cutaway
[Source: Manny Lopez / The Detroit News]
Reader Comments (Page 1 of 2)
GenWaylaid 8:30AM (2/18/2008)
For marketing reasons, I doubt the Corvette could ever offer anything other than a V8 engine. Still, there's nothing preventing GM from making much smaller, higher-revving V8 engines. Such engines have been used in race cars for decades.
Add forced induction and there are plenty more ways to cut emissions under normal driving. Maybe the Corvette of 2020 will drive around town on four unboosted cylinders, but once the driver floors the gas all eight cylinders come to life with supercharger boost and more aggressive cam timing. Since the majority of Vettes are sold with automatic transmissions, a computerized CVT could further accentuate such a split personality by selecting appropriate RPM ranges.
I suspect most sports car and performance car buyers would be happy if their cars behaved normally most of the time, but just like Michael Knight they could hit the "turbo boost" once per episode.
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mike 9:20AM (2/18/2008)
Electric Motors give you Maximum Torque at 1 RPM. The V8 is DEAD. Dumping money into V8's, yesterday's tech, is a Waste of Money.
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siry 10:20AM (2/18/2008)
hmm...I feel uniquely qualified to offer an opinion since I regularly drive an EVO, a corvette, and an electric car.
Although you can get an extraordinary amount of power out of a turbo inline 4 like the EVO, it is a totally different experience than the performance and sound you get from a V8. I don't prefer one over the other necessarily, but they are totally different. I love the sound of the turbo and the feeling of boost coming on but the nearly absent low end torque can get annoying. With the V8, the sound and low end torque is great fun but it isn't as precise or exciting as the EVO. Great for cruising around. Similar comparisons can be made between my CBR600 and my Ducati S2R1000.
Also - the mileage in my EVO is miserable. There is no free lunch. Performance = CO2 - there is no way around that except lower weight vehicles. Some engines are more efficient than others but there is no magic bullet here with ICEs.
That is where electric cars come in. Huge torque, great acceleration and zero emissions. Driving the Roadster is by far the most fun. granted, it is a totally different set of noises and feelings, but you get to know them as a unique driving experience.
So what will the future bring? I think V8s will become specialty engines just like V12s are today. I-4s and V-6s will become the norm as they started to do in the late 70s and 80s. Electric vehicles and electric assisted ICEs will grow in market share over time.
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DC 10:38AM (2/18/2008)
The 3.6L V6 has a nice engine note, a biturbo version of it would be Corvette worthy.
Otherwise I'd expect mild parallel hybrids and electrified accessories, since the Corvettes etc. get pretty strong highway fuel economy performance already.
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jim 10:39AM (2/18/2008)
Rumors of a diesel Corvette. 300HP, 500ft/lb of torque. Is that a smile on your face or your cheeks falling behind your chin due to the acceleration.
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why not the LS2/LS7? 11:37AM (2/18/2008)
I don't have any qualms with a V6 Corvette. But I don't see any reason to make one right now. It's already making better mpg than any other sports car anywhere near its class. It makes better mpg than the 4-banger Lancer Evo!
But if times get really tight, and even better fuel economy becomes important, then yeah, they could go down to a V6.
But don't expect miracles, a turbo is not an mpg panacea, as the Lancer Evo shows.
jim:
Acceleration comes from torque at the wheels. The lower redline of a Diesel means you can't gear it as low, which robs you of torque at the wheels, which is why Diesels accelerate slower than gas cars. You need to look at engine HP, not engine torque, to get an idea of how fast the car is, and Diesel offers less HP in a much heavier package. Not a win for a car which GM has worked so hard to take weight off of.
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Whopper 12:11PM (2/18/2008)
LS2/LS7; Not necessarily so. "High Speed" diesels which generate peak HP at 3000 RPM or higher are not unusual. The rear wheels don't care what the source of torque is as long as sufficient tractive force is being applied. Therefore, if the engine delivers 300 ft-lb at 2800 RPM or 550 ft-lb at 1800 RPM a different final drive ratio is all that is required. In the case of a SI (spark ignition) Vs CI (compression ignition) engine, the CI engine may require more gear ratios (anyone want a Roadranger in their Malibu?) but that is not out of the realm of possibility.
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Dave 12:12PM (2/18/2008)
Sorry - but what's the point again? Somebody who is driving a Corvette cares about the mileage?
If I ran GM, I'd never take the teeth out of the Vette. If it gets a 6 - it would have to be a hell of an engine, normally aspirated, and cause enough of a weight loss for the entire vehicle that _performance_ improved.
Sorry folks, if you want a gas sipping sports car, you're going to have to go to a smaller vehicle. If Vettes were the size of Miyatas (and maybe they were that small at one point?) then fine, a 6 will do. But let's make it inline, not V (see BMW, early Vettes)
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Whopper 12:27PM (2/18/2008)
Dave,
You see an advantage of an inline 6 over a V configuration? I guess I'm not sure what that would be. The inline 6 being longer and, unless we cant it over like the old Chrysler slant 6, it has packaging issues. It has to be heavier than a V6 because the longer crankshaft has torsional rigidity problems and needs more main bearings and a longer block. The V6 is a more compact powerplant and should be capable of equivalent power. I don't yearn for the return of the Corvette "Blue Flame" 6.
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why not the LS2/LS7? 1:39PM (2/18/2008)
Whopper:
3000 RPM isn't much.
The problem here is the Diesel is giving 500 ft-lbs of torque at 3,000 RPM while the gas engine is giving 400 ft-lbs of torque at 6,500 RPM. So the gas engine is delivering 70% more torque to the wheels and thus goes all that much faster.
Diesel cars will be as fast as gas ones when they make the same HP. Right now, most Diesels are far behind in HP and the ones that even begin to match up are enormous engines with piles of geegaws on them to make the HP, thus making them expensive and heavy.
Chevy should look at HCCI for performance cars first, then maybe Diesel if HCCI doesn't pan out. HCCI will have much smaller, lighter motors at equivalent HP and if we're lucky, cheaper too.
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rgseidl 1:51PM (2/18/2008)
Turbos with intercoolers are great for fuel economy, but they do introduce lag - especially on throttled gasoline engines. In the context of downsizing a V8, the lag can be minimized by adding a second turbo stage to a six-cylinder engine, as BMW has already done for its diesels. Another option is to combine an efficient detachable supercharger (e.g. Integral Powertrain's SuperGen) to eliminate lag and deliver high static boost at low to medium RPM with a large single turbo that boosts power at medium to high RPM. VW has done this for its 1.4L TSI inline 4 but not (yet) for a six-cylinder engine. Note that superchargers and turbos both alter engine sound in ways that many purists dislike.
An alternate way to downsize a big V8 is to use a flat crankshaft, as is always done for race cars (e.g. F1) and also for certain European sports cars (e.g. Ferrari). This eliminates the exhaust manifold crosstalk that gives cross-plane V8s their characteristic burble at the expense of ~15% less rated power. It also permits the use of much smaller counterweights, so V8s with flat crankshafts will rev up very eagerly. As a result, they do not need to be designed for high torque levels to deliver the desired power.
The downside of a flat crankshaft is the rotating inertial force of the second order. It can be eliminated with a pair of compensation shafts, something that is expensive but necessary above ~3.2L total displacement. Four valves per cylinder and overhead cam shafts are pretty much required to exploit the full RPM range. The combination of firing fully on all cylinders and revving high gives flat-plane V8s a cleaner, more aggressive sound than cross-plane designs.
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Chris 3:56PM (2/18/2008)
GMC knows they can make a Turbo-V6 that out performs the NA-V8. They've done it before and in respectable sales numbers. Check out the 1987 Grand National and Regal T-types (3.8L). Faster than the '87 Vette with almost 2 Liters (119 cubic inches to be exact) less displacement and better fuel economy. They did it again in 1989 with the Pontiac Turbo Trans-AM (still 3.8L).
Want more? Check out the all wheel drive 1991-93 GMC Syclone and Typhoon that were also Turbo-V6 (4.3L) and in Corvette territory.
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brian 4:23PM (2/18/2008)
I drive a C6 Corvette and I also drive a turbocharged 4 cylinder Audi. I don't drive the Corvette for the gas mileage. It's a sports car, and everything is designed as such. Would I commute to and from work daily in it? No, that's where the other vehicle come in. I'll tell you on thing thoguh, i've owned 10+ vehicles over the years, and NOTHING has come close to the pure enjoyment I experience driving the Corvette. I've owned turbo 4 cyl's, turbo 6's, etc, and it is a completely different beast. The sound, the acceleration. It isn't something technology can replicate or replace at this point. So for me, I would not purchase a Corvette with anything other than a large growling, gas guzzling V8.....
With that said, I hope my next daily driver is a plug in electric.
http://www.tagsum.com/news/10532/Should-the-Corvette-never-again-offer-a-six-cylinder
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why not the LS2/LS7? 4:19PM (2/18/2008)
rgseidl:
Flat-plane V8s idle like crap even though they have to idle at 1,000rpm or more. This high idle makes it tough to meet emissions with them and hurts fuel economy. I think if you look at the LS2/LS7 and look at Ferrari's flat-crank offerings, you can see flat-crank isn't a path to better mpg. Adding 3 spinning camshafts to an engine robs power output too, and that's before you add balance shafts.
GM showed a Saab supercharged/turbocharged/variable displacement engine about 8 years ago. Maybe it's time to bring that technology to production.
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Dan 5:21PM (2/18/2008)
A big reason for the weak torque of turbo engines off boost and low efficiency is the low compression ratio. BMW has more or less cracked that problem in the 335i with direct injection, sequential twin turbos and a high 10.2:1 compression ratio. The VW/Audi 2.0T has an even higher 10.5:1 ratio. Compare that to the 8:1 compression ratio of an Impreza WRX, or, going really old school, the 6.5:1 ratio of a 1976 Porsche 930 Turbo.
The Ford Ecoboost is more or less the same idea: direct injection, high compression turbocharged engines.
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MikeW 5:51PM (2/18/2008)
Get F- out of here. Flat plane cranks HAVE to idle at 1,000rpm or more.
Why would 2 four cylinder engines suddenly have to have their idle speed increased by 50% or more.
They wouldn't.
And it would be stupid to run the exhaust without sonic equalization. Porsche 911-that means you.
I was hoping Honda would do something like take 2 x R20A I4 engines and [add VTEC, taking out the inverse half economy VTEC] make a 325hp V8 for the Acura RL.
or if the market demands a vehicle smaller than the odyssey, say an odyssey lite (mazda5 sized) Honda could scale up the R20, for a 225hp hp 3 liter Inlin6.
or possibly a series of 2.4, 2.7, 3.0 liter Inline6 for future US accords. The US market will still demand a wide car, which will have room for a compact transverse inline6.
Flat plane cranks!
http://www.youtube.com/watch?v=vZBMvkK5a7A&feature=related
http://www.youtube.com/watch?v=df4vG67CPsI
the exhaust manifold of the V4 bank did not compensate for the different length
http://video.google.com/videoplay?docid=-1022006688444014313&q=W8+straight&total=13&start=0&num=10&so=0&type=search&plindex=0
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MikeW 6:50PM (2/18/2008)
Isn't Audi making a 'tri-charger' V6 for the replacement of the V8 in the S5 & S4? 3 liter V6 350hp/350ft-lbs.
Air goes to the Roots TVS supercharger, then into 2 turbos, then the charge coolers, then the engine. The supercharger is bypassed when the turbos are good and ready.
BMW's turbocharger arrangement in the 335i/535i is NOT sequential. It is purely parallel.
http://gallery.audiworld.com/gallery/q7v12/Q7060140_large?full=1
Lets look at acceleration from 2000-4000 (and equate that to acceleration from 50-100mph). at 2K you are at 56.9% of maximum power. At 3K you are at 85.4%. At 4K you've topped out-and diesels don't take to overrev [not overreving the maximum engine speed, but the race track concept where you wind the engine out without shifting-see yamaha] power drops off precipitously.
At 500rpm over, you make the same power as 1000rpm under [you should upshifted already for faster acceleration]. At 250rpm over, you make the same power as 500rpm under.
So for the approximately the same power output, 505hp LS7@6300. (again equated to accelerating from 50-100mph)
50% power at 3150rpm, about 83% at 4725rpm.
and 500rpm over is about the same power as 500rpm under.
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why not the LS2/LS7? 6:48PM (2/18/2008)
Well, MikeW, I guess I'm wrong. You could instead increase the size of the flywheel significantly, to keep the idle smooth and working at low revs.
Of course, no one does that because they make it a flat-crank in the first place to get the ability to increase revs rapidly and adding mass hurts that.
Either way, by the time you get done taming a flat crank for the street, the engine is not terribly fuel efficient. So what's the real point?
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MikeW 6:54PM (2/18/2008)
Vette engines
http://picsorban.com/upload/gmgraph.jpg
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MikeW 7:29PM (2/18/2008)
I don't get your reasoning to come to that conclusion.
Are you watching dumbass kids cold start their parents 360 modena or F430. The EPA almost mandates elevated idle speed to hasten catalytic converter warmup.
I bet if BMW went to a flat plane crank, they could take 4-6 lbs out of the crankshaft. Commensurately, why would BMW add to the flywheel? They wouldn't, seeing as the extra inertia of the balance shafts would almost make that up.
http://www.edmunds.com/insideline/do/Drives/FirstDrives/articleId=124806
I'd like to see a return to V12s, a nice rip roaring 3 liter for the BMW 3 series. 70mm bore x 65 mm stroke [I can dream]
you can make even firing 90 degree V12s, not only by just spliting the journals, but by increasing the axial offset and inserting the counterweight between connecting rods. (hey what is an extra 1/2" of engine length between friends)
10 liters:105mm bore x 96mm stroke, 1,000hp @7500, 800ft-lbs@5000rpm, perfect for the Veyron2, especially with an 8 speed double clutch.
http://www.youtube.com/watch?v=IDnp3tsTzpM
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