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Old 12-23-2016, 10:19 PM   #1
 
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Default DOHC V8 coming to 2018 Chevy Corvette

Fire up your rumor machines.

DOHC V8 coming to 2018 Chevy Corvette according to GM Document - Autoblog

Well it looks like the rumors are real. The Chevrolet Corvette will drop pushrods and adopt dual overhead cams in 2018, at least in one application. According to a document on the GM service website, an engine with the code designation LT5 and a 6.2-liter displacement is among the General Motors list of 2018 powerplants, and the application corresponds to the Corvette.

The LT5 name is no coincidence. It's the same as the last DOHC Corvette engine, a Lotus-designed, Mercury Marine-built V8 found in the 1990 to 1995 ZR-1. Our highlights of the GM pdf, seen below, show that the new LT5 is all aluminum and does not seem to have any form of forced induction. As The Drive points out (via Reddit), that suggests the engine is unlikely to go in the rumored upcoming ZR1. The logic being that the ZR1 is supposed to out-power the Z06 (as it did in its previous iteration) and it's difficult to top LT4's 650 horsepower in a 6.2-liter engine without turbo- or super-charging.



Which inevitably leads to the mythical mid-engine Corvette. The specific advantages overhead cams have over pushrods work naturally with the idea of a Ferrari- or Ford GT-fighting supercar with the engine behind the seats. DOHC engines can hit high revs more easily, and can adopt independent valve timing (and even lift) for the intake and exhaust valves. That suggests a screaming, high-rpm engine in place of the classic low end torque characteristics of the traditional Chevy small block. DOHC engines are typically larger and heavier than pushrods, though, so everything comes with a price.

We did not reach out to General Motors for comment because, come on, they're not going to talk about this. They never do.
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Old 12-23-2016, 11:54 PM   #2
 
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This should have been done in the C5's.
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Old 12-24-2016, 07:37 AM   #3
 
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Valve wizardry coming to Corvette soon!
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Old 12-24-2016, 08:40 AM   #4
 
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Valve wizardry coming to Corvette soon!
close this up nothing more needs to be said in here.
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Old 12-24-2016, 09:57 AM   #5
 
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What's the upside to all these valves and whatnot? They've doing just fine with push rods.
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Old 12-24-2016, 10:07 AM   #6
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more precision control and actually variable timing to better meet certain conditions
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Old 12-24-2016, 10:11 AM   #7
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The Merc design motors had a in cab timing adjustment. I bet they are wanting to also give the driver more 'control' over the car... Push of a button and you have a mean lopey idle..
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Old 12-24-2016, 10:24 AM   #8
 
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The Merc design motors had a in cab timing adjustment. I bet they are wanting to also give the driver more 'control' over the car... Push of a button and you have a mean lopey idle..
HA! Try explaining that one to an LS fanboy

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Old 12-24-2016, 12:17 PM   #9
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Default DOHC V8 coming to 2018 Chevy Corvette

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more precision control and actually variable timing to better meet certain conditions


Technically certain LS and new LT motors have variable cam timing, but of course it's nothing like separate cams with individual cam timing


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Old 12-24-2016, 12:33 PM   #10
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Technically certain LS and new LT motors have variable cam timing, but of course it's nothing like separate cams with individual cam timing


But it could be. The Viper uses a concentric cam in cam design to offer independently variable intake and exhaust phasing.

https://www.mechadyne-int.com/products/duocam

It doesn't get you variable duration though. That requires VTEC, or something like FIAT's Multi-Air system.

Personally, I think once Freevalve hits mainstream we are going to see a huge upswing in performance. I also see problems with Piston to Valve contact if someone holds the valve open too long.
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Old 12-24-2016, 12:36 PM   #11
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GM does have a VTEC-like system on their 2.5L based 4 cylinder cars like the Malibu and 4cyl impala. It's literally just like VTEC with 2 cam lobes and 2 sets of lifters per valve and they just switch which rocker is active via oil pressure.

But you're right, freevalve is going to be the future. The holdup I'd imagine would be the next level programming and processing power to make it all work. But manufacturers will eventually need to switch just due to the potential of lowered emissions and cost savings of raw materials that the engine no longer needs
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Old 12-24-2016, 09:15 PM   #12
 
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Please Please Please GM dont fuck this up and put it in a mid engine vette badged as a cadillac....

Hope this engine stays more C4 ZR1 and not some mid engine vette badged as a cadillac and this being used as the successor to the northstar.

The LT5 designator gives me hope GM will keep this out of the Cadillac line up and I hope this goes in a mid engine VETTE not anything else.
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Old 12-24-2016, 10:05 PM   #13
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I'm going to bet that this motor gets twin turbos for the Mid Engine
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Old 12-24-2016, 10:17 PM   #14
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But you're right, freevalve is going to be the future. The holdup I'd imagine would be the next level programming and processing power to make it all work. But manufacturers will eventually need to switch just due to the potential of lowered emissions and cost savings of raw materials that the engine no longer needs
boy i can't wait until those hit mainstream shit box cars that are produced as cheap as possible and not maintained properly.
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Old 12-24-2016, 11:12 PM   #15
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But will it be flat plane like the voodoo?
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Old 12-25-2016, 07:31 AM   #16
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Theoretically, a freevalve engine could change firing order any time it wants now that I think of it
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Old 12-25-2016, 08:50 AM   #17
 
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But will it be flat plane like the voodoo?
doubt it will be fpc and i doubt itll spin to 8k maybe 7k or 7500ish redline?

over 6 liters is like a giant coyote.
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Old 12-26-2016, 05:23 PM   #18
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Theoretically, a freevalve engine could change firing order any time it wants now that I think of it
I don't disagree with you but would there be any performance benefits to that? 4-7 swap for high rpm harmonics
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Old 12-26-2016, 05:37 PM   #19
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I don't claim to be an expert on the matter, but I'm fairly confident that every engine layout has advantages and disadvantages based on RPM range and emissions. Perhaps changing firing order on the fly could help that
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Old 12-26-2016, 06:24 PM   #20
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All changing the order would do is move the stress point around. One of the reasons the Gen1,2 changed to the Gen3 and up firing order was better harmonics. Since you can't change the crank on the fly, there are only a few combinations you can take there.

You can swap (1/6), (8/5) in addition to the changes they already made. How that affects the harmonics I can't say. But I think if any other changes were to be made, they would have made them when the Gen3 debuted.

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A Flat-plane sound awesome, and is great for scavenging exhaust. Thats the real reason to do it. But it also throws the engine out of balance, so you then have to deal with the vibration. And the longer the stroke, the more extreme the vibration becomes.

Even the GT350 doesn't quite use the same flat-plane as you would find in a Ferrari. There are some extra counterweights on the crank, increasing its weight. Its still 180°, but there are extra counterweights in locations to help with balancing it all out.

The tradtional flat-plane is Up, Down, Down, Up

The GT350 uses Up, Down, Up, Down.

https://www.edmunds.com/ford/mustang...voodoo-v8.html

In any case.

From a harmonics standpoint a Cross-plane crank has WAY better balance, and will deal with higher RPM better than a traditional flat-plane. But you lose out on scavenging.

So the way more costly and heavier alternative is to use a cross-plane crank, with 180° crossover exhaust primaries.

There is no reason that GM couldn't build a 6.0L DOHC engine capable of revving to 8000rpm in todays age. But they'll probably go supercharged like they have on everything else. Even though I think turbocharging is the more effective solution.
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Old 12-27-2016, 01:24 AM   #21
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I'm super excited for this I just wish we got to see what an LT7 would be capable of as well. 7L + DI + VVT would be sweet.
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Old 12-27-2016, 06:25 AM   #22
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I'm pretty sure you're not going to see anything over 6.6 liters and even that is probably stretching it.
Just remember a couple years ago was a twin turbo V8 on the gimbal/g-force dyno.

There is a replacement for displacement but I don't think it will be a supercharger with the new fuel economy and Emissions standards
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Old 12-27-2016, 06:27 AM   #23
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The one thing with freevalve it would allow you to switch between four cycle and 2 and 5 cycle...

Could you imagine programming your car's ECU to make your V8 a 2 stroke with twice as many power strokes per Revolution under wide open throttle while maintaining the fuel economy and emissions of four stroke engine for the rest of the time
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Old 12-27-2016, 06:46 AM   #24
 
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So many LS fanboi's are so butthurt by this!!!
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Old 12-27-2016, 07:36 AM   #25
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holy shit this thread stayed on topic. im impressed.
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