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GM has a new DOCH flat-plane crank engine for the Z06

Roc Doc

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Seems like a pretty cool engineering exercise. GM Announces 5.5L LT6; 670HP, Four Cams, And A Flat-Plane Crank



GM Announces 5.5L LT6; 670HP, Four Cams, And A Flat-Plane Crank​


By GREG ACOSTA OCTOBER 26, 2021
We’ve all heard the rumors of a dual overhead camshaft V8 engine for the Corvette. Some lost hope when the 2020 Corvette debuted with the LT2 variant of the Gen-V direct-injected small-block Chevrolet. Some speculated that the Cadillac Blackwing’s 4.2-liter DOHC engine would be the basis for the upcoming Z06’s new architecture. Those hopes seemed to be dashed when Cadillac dropped the DOHC powerplant for an LT4 based option.
Not all hope was lost, however, as Chevrolet teased that the 2022 Z06 would feature a flat-plane crankshaft. That feature alone didn’t confirm or kill a dual overhead camshaft arrangement, but sparked interest nonetheless. However, at today’s Corvette Z06 reveal, we got our first look at the car’s new powerplant — The LT6 — and it has four cams.
Here you can see some of the details of the all-new LT6 engine. Chain-driven dual overhead camshafts, active intake manifold butterflies, and an exhaust with an incredible amount of engineering in it are just a few of the incredible features of this new engine. Photos by Dave Cruikshank

5.5-Liter LT6

While all of the details and specs aren’t yet available, what we do know is pretty amazing. The engine is rated at 5.5 liters of displacement — or 333 cubic inches — thanks to the 104.25mm (4.104 inches) bore diameter and 80mm (3.150 inches) stroke. The clean-sheet block design retains the standard 4.400-inch bore spacing, meaning the bore, as delivered, is close to, if not the absolute limit.
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The engine will feature forged-aluminum pistons connected to forged-titanium rods — a combination we’ve seen from GM before in the LS7 — but what is all-new for GM is the 3.15-inch stroke flat-plane crankshaft. “With a flat-plane crankshaft, the mass that is moving the fastest, is much lighter. That allows the engine to accelerate much more rapidly than any small-block before it,” says Dustin Gardner, Assistant Chief Engineer, LT6
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Another all-new feature (for an LT-platform engine, at least) is the dual overhead camshaft cylinder heads. The four camshafts are chain-driven and use a mechanical finger-follower setup to translate cam motion into valve motion, with dual valvesprings controlling the whole affair. The four-valve-per-cylinder design features 32 valves (16 titanium intake valves and 16 sodium-filled exhaust valves, similar in construction to the LS7’s), and incredible efficiency, with our good friend Billy Godbold of Comp Cams running the numbers and noting an estimated 95- to 98-percent volumetric efficiency at peak horsepower.
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Looking into the intake manifolds, the level of effort to achieve that efficiency is obvious. Each bank has its own plenum and throttle body, with each cylinder’s intake runner having its own bellmouth to smooth airflow into the cylinder, as well as an active intake airflow management system (no, not DOD or AFM). Direct injection is almost a given in today’s world, and the ignition system appears to be a fairly traditional coil-on-plug system mounted to the valve covers.
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How Much Power Does The LT6 Make?

With SAE power certification testing just recently completed, the engine is rated at 670 horsepower at an amazing 8,400 rpm with 460 lb-ft of torque at 6,300 rpm. The maximum RPM limit in the production vehicle will be 8,600 rpm, which while impressive, isn’t surprising, given how oversquare the engine is. “It makes power all the way up, so even in the upper RPM range you can still feel it pulling,” explains Cindy Molnar, Vehicle Performance Engineer, Chevrolet Performance Cars
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The LT6 makes peak power at 8,400 rpm and is rev-limited to 8,600 rpm. The highest engine speeds of any factory Corvette ever.
“An Engine of this nature is truly playing in the exotic space, Gardner explains. “It is a low-volume, hand-built, precision engine. The manufacturing tolerances in this engine are racecar tight.” What that all amounts to is the most powerful naturally aspirated V8 engine to ever grace a production vehicle. A crown the team at Chevrolet hopes to wear for a considerable amount of time.
 

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Pt_Ranger_v8

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So, when they say flat plane, what are they referring to?

The rest of it I understand, and it's marketing-speak :laughing:
 

Roc Doc

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So, when they say flat plane, what are they referring to?

The rest of it I understand, and it's marketing-speak :laughing:
It's the design of the crankshaft.

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What Is A Flat-Plane Crank?​

There are two crank designs available when picking one for your next V8 project: cross- and flat-plane. For the most part cross-plane cranks dominate, especially in American V-8 engines, while flat-plane cranks typically show up in high-end Euro exotics and full-on race cars. Cross-plane cranks give American muscle its distinctive rumble while flat-plane cranks have a tell tail high-rpm whine. But, there's more to these cranks than just their exhaust notes.
Flat-plane cranks, in V-8 and V-12 engines, used to be fairly rare and only seen in uber-expensive super- and hypercars. They're the reason you can always tell a Ferrari is ready to crest the hill at a track day. Just like the name states a flat-plane crank has all its crank pins in a single, flat plane. This is much like an inline 4-cylinder crank, but with more space for more rods.
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Do Flat-Plane Cranks Have Vibration Issues?​

Flat-plane cranks, no matter what firing order they have, will always alternate from bank to bank. This yields optimum exhaust scavenging and thus doesn't require the more complex header primaries that have to cross over from one bank to the other. Due to their design they don't need huge counterweights, which is why they weigh less and rev up so quickly. The downside is that they suffer from secondary vibrations.
Chevy solved the vibration issue with LT6 engine by minimizing piston speeds, by opting for a large 4.11-inch bore and short 3.15-inch stroke. The result is a 103-mph peak piston speed at redline (for example a the 5.2L in the Shelby Mustang has 114 mph piston speed). Vibration was also helped by the use of titanium piston rods from Austria-based Pankl Racing Systems. Even the aluminum harmonic balancer helps in the battle to solve flat-plane crank vibrations. There are still some vibrations, but nothing detrimental to the car, the LT6, or the Corvette Z06's mission to be baddest Corvette ever built.
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4-2023-corvette-z06-ls6-c8-details-dohc-flat-plane.jpg
 

Jackie Treehorn

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It’s nice to see gm one-up ford’s 5.2 flat plane engine. Now let’s see them give it forced induction and go after the hellcat.
 

fvs

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Maybe the manufacturers are giving it their all so when everyone is sick of their electric cars they can point to these engines.
Most manufacturers aren’t complete idiots. They will pander to the EV craze but even they realize it isn’t feasible at this time.
 

bunk

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When i went to school in the 90's, most auto mfgr's designed drivetrain components to last 200k. I wonder what they go for now.
 

MChat

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What's the purpose for the butterfly valve controlled connection between the plenums? I'm assuming it's part of the "active intake airflow management system" but what is the purpose? Low RPM cross flow? High RPM? Something else?
 

87manche

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What's the purpose for the butterfly valve controlled connection between the plenums? I'm assuming it's part of the "active intake airflow management system" but what is the purpose? Low RPM cross flow? High RPM? Something else?
because intake runner length affects how the cylinder fills at different RPMs because of resonance in the air flow caused mostly by the frequency of intake valves opening and closing.
Alter the intake runner lengths and you can use the mass of the air that is suddenly stopped at one intake valve to "force fill" the adjacent cylinder.

at least that's how the BMW technical manual explains their variable intake runner system.
 

Norm

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It's a different beast from past GM designs, it will be interesting to see if they hold up. 8500 RPM redline :eek:


At 90k for base model, it's not going to be cheap. Wasn't the c8 base price supposed to be 60k :confused:
 

Landslide

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GM finally catching up to fords coyote engine with DOHCs, everyone ooooo and aaaaaaa :flipoff2:

The Getty up of the coyote 5.0 DOHC is very impressive just in my truck. Down side is I have to replace the cam gears and sensors as they are fucking up. I’ll change out the timing chain assy same time I’m in there.
 

MChat

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because intake runner length affects how the cylinder fills at different RPMs because of resonance in the air flow caused mostly by the frequency of intake valves opening and closing.
Alter the intake runner lengths and you can use the mass of the air that is suddenly stopped at one intake valve to "force fill" the adjacent cylinder.

at least that's how the BMW technical manual explains their variable intake runner system.
That makes sense. So it's a way of "tuning" the intake runner length (virtually, without physically changing the actual length of the runner) based on RPM. In this case though it's working with plenum volume/pressures to accomplish the same idea.

It makes you wonder what the real effect is on the HP/Torque curves; how much time, energy and R&D costs went into that "extra 10hp". :laughing:
 

plym49.2

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Flat-plane V8s are awesome. They rumble like a AA/FD at idle. I had one in a Ferrari.

GM should have made this a 327 instead of a 333.

The intakes have a straight shot at the intake valves, just like a 1953 Buick Nailhead! :)

It is amazing that modern engines are as fuel-efficient as they are with all the extra twirly bits as opposed to a traditional, 2-valve engnine without overhead cams.

Oh, and the starter is in the valley! LOL.
 

flexy flatty

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It’s nice to see gm one-up ford’s 5.2 flat plane engine. Now let’s see them give it forced induction and go after the hellcat.
The ZR1 is going to be a turbo version of this motor, and supposedly the top level Zora will be the ZR1 plus a hybrid electric system with four digit hp.
 

plym49.2

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Too bad they changed the bellhousing bolt pattern. New generation of transmission adapters coming in 3.............2...............1...............
 

87manche

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That makes sense. So it's a way of "tuning" the intake runner length (virtually, without physically changing the actual length of the runner) based on RPM. In this case though it's working with plenum volume/pressures to accomplish the same idea.

It makes you wonder what the real effect is on the HP/Torque curves; how much time, energy and R&D costs went into that "extra 10hp". :laughing:
well in BMW land the difference between a 328 and a 330 is the intake manifold, and installing the variable intake manifold and software is good for like 40 horsetorques all over.

I can certainly feel when the DISA does it's thing at 4500 RPM.
 

Weasel

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GM finally catching up to fords coyote engine with DOHCs, everyone ooooo and aaaaaaa :flipoff2:

The Getty up of the coyote 5.0 DOHC is very impressive just in my truck. Down side is I have to replace the cam gears and sensors as they are fucking up. I’ll change out the timing chain assy same time I’m in there.
Should LS sawp it then you'd really be impressed.
 

Bebop

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When i went to school in the 90's, most auto mfgr's designed drivetrain components to last 200k. I wonder what they go for now.
I cannot give you specific numbers but it's not 200k.
I can however tell you that it's less than that. At least for the OEMs I work(ed) for.
 

bunk

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I cannot give you specific numbers but it's not 200k.
I can however tell you that it's less than that. At least for the OEMs I work(ed) for.
Under 100k i imagine for crossplane engines. probably 80 afaic.
 

ThePanzerFuhrer

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well in BMW land the difference between a 328 and a 330 is the intake manifold, and installing the variable intake manifold and software is good for like 40 horsetorques all over.

I can certainly feel when the DISA does it's thing at 4500 RPM.
But I took all mine out lol.
 
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