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Old 12-28-2012, 10:16 AM   #1
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Motor Trend C7 LT1 article

Just got a new Motor Trend with a two page spread on the new LT1. Here are some excerpts:

Billed as the biggest change to the venerable small-block V-8 in its 57 year history, the Gen 5 edition retains the trademark bore spacing, overhead-valve/cam-in-block valvetrain, and other key details, but the engine bristles with high-tech fetures. Direct fuel injection? Check. Variable-valve timing? Got it. Two starter bolts, a piston pin, and a retainer bolt or two are all that remain of the LS3. Chevrolet expects 0-60 mph performance for the base C7 to be under 4 seconds, with efficiency to make it among the least-thirsty 450 hp vehicles extant. That's right, Chevrolet expects at least 450 hp at 6000 rpm and 450 lb-ft at 4000 rpm, yet with a 26 mpg-plus EPA highway number.
The LT1 will be the first pushrod engine with gas direct-injection, and a key enable to the power-efficiency equation is cylinder deactivation, but with the car's rear transmission, it was an NVH nightmare in four cylinder mode. Chevy claims those problems have been overcome, with a system optimized for a wide operating range in the 3.1 liter V-4 mode. Smaller displacements reduce the amount of time the engine can operate as a four-banger, so bigger displacement, like 6.2 liters, can save more fuel. With its 6600-rpm fuel cutoff, this is the highest-speed valvetrain with deactivation, cutting cylinders one, seven, six and four. The LT1 will offer wet and dry-sump lubrication.
The LT1 also comes with a "radically new combustion system with 11.5:1 compression ratio" that improves power and efficiency, says Jordan Lee, chief engineer and program manager for small-block engines. The high-strength aluminum pistons are shaped like those in supercharged engines, with a high-compression pop-up. another factor contributing to the high compression is maximum in-cylinder cooling from the direct fuel injection and extensive air-fuel mixing dynamics. The high-flowing intake and exhaust ports are twisted to direct air for peak tumble. Intake and exhaust valves have swapped sides, which gives slightly better flow and better enables the spark plug to be centralized for peak ignition efficiency.
Chevy claims its naturally aspirated LT1 is a match for some top turbo engines on the market. BMW's 4.4 liter, twin-turbo V-8 produces 400 hp and 450 lb-ft. It weighs 503 pounds and stands 29.6 inches high. With 50 more horses, the LT1 weighs 465 pounds and is just 25.3 inches tall.




More to come later
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Old 12-28-2012, 11:01 AM   #2
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After the base C7 coupe goes on sale in the first half of 2013, the convertible is next, followed by the Grand Sport, then the Z06 replacement and finally, the ZR1. Rumors persist that a 5.5 liter version of the small block, which many of us car journalists (guilty!) had reported as the expected displacement of the LT1, remains in the product plan. The rumor has the 5.5 liter Gen 5 powering a new entry model that revives the Stingray name, to launch in the timeframe between the Z06 replacement and the ZR1.
The problem is, the rumor contradicts engineers' assertions that 6.2 liters with cylinder deactivation - making a 3.1 liter V-4 in highway cruising mode - is the optimum size for power and efficiency in the sports car. The Z06 and ZR1 engines probabaly will have their displacements cut for efficiency, while they get power boosts commensurate with the "base" LT1. The ZR1's supercharged LS9 will probably lose 0.2 liter, to 6.0. The Z06, which may be renamed Z07, may go on a displacement diet, too, from the LS7's 7.0 liters. The LT1 is a good candidate for Cadillac's coming Mercedes S-Class fighter.
There is no costly dual-clutch transmission planned, at least for the short term. Chevy hints that the new small-block has been protected for a start/stop system, even though it will not have the feature at launch. A 5.5 liter Stingray would seem the ideal car to introduce the system. don't rule out a 3.6 liter DOHC V-6 for Corvette some time during the C7's life cycle, particularly if needed for CAFE. GM is holding the V-6 C7 as a "provisional entry".
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Old 12-28-2012, 12:14 PM   #3
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I don't think that the ZR1 will see a displacement reduction, and also do not see the Z06 getting a displacement reduction either.

For the simple reason, they have been selling about 1,000 Z06 Corvettes a year and 1,000 ZR1 Corvettes a year. This has no impact on GMs CAFE rating, doing things to improve the fuel economy of these models does nothing to help GMs CAFE and doing things to reduce their fuel economy does nothing to hurt GMs CAFE.

The whole notion of down sizing the Corvette engines is something that purely comes from automotive journalist and some on this forum. The 5.5L engine rumor was completely made up by people who strongly believed that the Corvette engines would shrink. It has been known for a long time that smaller displacement V8s do not run as well in 6 or 4 cylinder mode. This is because of the addes mass of still having to spin around 8 cylinders with only 4 firing. If they went with a 5.5L V-8 engine it would be 2.75L in 4 cylinder mode, its more efficient to have a larger displacement engine (able to produce more torque) spin the mass.

So as I stated many times, it was the blind belief that the Corvette would go to smaller engines (even TT V-6). Also fed by the fact thatthe C6R GT2 car was running a 5.5L engine, though this was not a Gen V engine but more a gen 4.5. However in thinking that the LT1 would be 5.5L people ignored some important facts. One is the belief that they would want to tie the race car into the road car via engine size. When the C5R program started it used a 6.0L engine making 600BHP, at the time the street car ran a 5.7L engine making 345BHP. The C5R engine was then enlarged to 7.0L while the street car still used a 5.7L engine. When the sixth generation Corvette came out they went to a 6.0L engine and the Z06 was planned with a 6.4L engine. The goal was 6.4L and 450BHP to compete with the 450BHP Viper however the Viper got a power bump to 500BHP so that changed the Z06 engine from 6.4L to 7.0L. When the Corvette went to the GT2 class (now call GT) the max engine size at the time was 6.0L and that is what they used. Its important to note that while the race car had a 6.0L engine the street car had a 6.2L engine. Then a rule changed which brought the engine size limit from 6.0L to 5.5L and that is how we got a 5.5L engine size in the C6R.

So the 5.5L rumor was created based on two false premises, I hope the next time people want to believe in such a rumor they will read this and think about it first.
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Old 12-28-2012, 12:58 PM   #4
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my 5.3 in my old Impala SS ran in 4 cylinder mode... no problem or vibration so i don't really buy the argument... unless you want to force it to run in 4 cylinder mode most of the time. And the 6.2 in the Trucks run in 4 cylinder mode already so nothing new on that front either. Problem is that they don't run in 4 cylinder mode very much.
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Old 12-28-2012, 01:47 PM   #5
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Originally Posted by dobrenyr View Post
my 5.3 in my old Impala SS ran in 4 cylinder mode... no problem or vibration so i don't really buy the argument... unless you want to force it to run in 4 cylinder mode most of the time. And the 6.2 in the Trucks run in 4 cylinder mode already so nothing new on that front either. Problem is that they don't run in 4 cylinder mode very much.
I agree. I had an '08 Silverado with the 5.3 that ran in 4 cylinder mode at highway speeds. The transition was pretty much undetectable and it ran just fine. And the Silverado weighed a lot more than a Vette. I'm just not sure what their concerns are with a 5.5 liter running on 4.
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Old 12-28-2012, 04:01 PM   #6
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MT and C&D are both stuck on the 5.5l.the only reason it exists is the class restriction in Lemans. It also has little in common with the GenV or did last season anyway.
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Old 12-28-2012, 04:58 PM   #7
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my 5.3 in my old Impala SS ran in 4 cylinder mode... no problem or vibration so i don't really buy the argument... unless you want to force it to run in 4 cylinder mode most of the time. And the 6.2 in the Trucks run in 4 cylinder mode already so nothing new on that front either. Problem is that they don't run in 4 cylinder mode very much.
They are talking about with a rear mounted transmission, also I know that they had issues in the past with manual transmissions for said engine.
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Old 12-28-2012, 04:59 PM   #8
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I agree. I had an '08 Silverado with the 5.3 that ran in 4 cylinder mode at highway speeds. The transition was pretty much undetectable and it ran just fine. And the Silverado weighed a lot more than a Vette. I'm just not sure what their concerns are with a 5.5 liter running on 4.
Their concern is this.... there is no 5.5....
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Old 12-28-2012, 05:19 PM   #9
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I swear to god these journalists just make this shit up, lol.

I call bull on the V6 and lower displacement V8. Few buyers would want them, it would hurt the Vette's image, and it wouldn't help GM's cafe that much.

I also call bull on the article's statement that the GS will come before the Z06. I doubt GM would introduce the wide-body style on the GS instead of on the Z06.

I could however believe that the Base, Z06, and ZR1 models might all come with the same 6.2L displacement. I don't think 7L is necessary for the Gen V to make 525 hp. I predict that rather than going to 7L to differentiate the Z06 GM has instead de-tuned the Base LT-1.
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Old 12-30-2012, 06:33 PM   #10
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Technically they could do a 5.5l DOD motor but it would use an odd bore more than likely. The new genV 4.3l will have DOD. With the marginal gains they would have if consumption I doubt they would do a 5.5L and drop HP from the previous 6.2L.
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Old 12-31-2012, 11:02 AM   #11
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They are talking about with a rear mounted transmission, also I know that they had issues in the past with manual transmissions for said engine.
Exactly. It was a harmonics issues with the direct connection between the motor (clutch) and the rest of the drivetrain. Autos don"t have this issue because of the fluid in the TQ converter dampens these harmonics.
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Old 12-31-2012, 02:23 PM   #12
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that may be correct, but i believe harmonics issues can be "tuned" out... that can take some time. We are really debating a dead issue since there is no 5.5 anyways... but i suppose that there might be... the big point is, if they were to make a block design that is yet still lighter and more compact than this current 6.2, how big would they go? A 5.0 that is 100 lbs lighter and puts out 430 hp would be a good target. The point is to create a smaller and lighter and more compact block... that that results in performance gains due to it's size and lighter weight. A true win...win...
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Old 12-31-2012, 04:33 PM   #13
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that may be correct, but i believe harmonics issues can be "tuned" out... that can take some time. We are really debating a dead issue since there is no 5.5 anyways... but i suppose that there might be... the big point is, if they were to make a block design that is yet still lighter and more compact than this current 6.2, how big would they go? A 5.0 that is 100 lbs lighter and puts out 430 hp would be a good target. The point is to create a smaller and lighter and more compact block... that that results in performance gains due to it's size and lighter weight. A true win...win...
I do not see them making a new block just for an engine or two. They could make an even smaller small block with a max size of 5.0l. However the chevy small block is so small and light that with the last generation it sqw use from 4.8l all the way to 7.0l. It looks as though with generation five the 4.8l truck engine is gone at least for the tine being. The trucks will have so far 4.3l all new v6 based on the gen five engine. 5.3l and 6.2l will be produced at launch for the new silverado and sierra.
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Old 01-01-2013, 04:41 AM   #14
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Well, according to that guy on ls1tech (Bigg_Gunz that says he works at GM)the planned sizes are 6.2, 5.3 and (V6) 4.3L.

Then he talks about a "bigger" engine, but at the same time mentions that one shouldn't be too hooked on cubes. That probably means blown 6.2 though.

For a while I haven't heard anyone (except some car rags..) talk about a 5.5L - it's most likely that since they spun that BS back before we knew anything, they can't just stop spinning it cause it'll show how little they know. When the new engine comes out, people will have forgotten all the 5.5L debacle OR they'll just insert a "but GM changed their plans due to <insert random junk here> and decided to go with 5.3 and 6.2L as their V8 sizes on the new engine". Meaning it doesn't matter what they spin, they'll just make it sound like they were right all along but GM changed their plans...

// Stefan
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Old 01-01-2013, 09:40 PM   #15
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If Gm is were going to down size i only hope that they resurrect the 5.7l (350ci)

Personally i think the new LT1 have a lot more potential and GM is not saying.

I am under the impression that this engine will love to rev And with some minor modification it could rev high or higher the LS7
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