DOHC V8 coming to 2018 Chevy Corvette

Mook

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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.

oTBq6Ik.jpg


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.
 

Thirdgen89GTA

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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


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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.
 

Stink Star

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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
 

Rent Free

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Please Please Please GM dont fuck this up and put it in a mid engine vette badged as a cadillac....:fu:

Hope this engine stays more C4 ZR1:fth: 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.
 

bikrboy128

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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. :fu:
 

Thirdgen89GTA

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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.

SBC FO = 1843 6572
LSx FO = 1872 6543


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/mustan...-gt-more-insights-on-the-gt350-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.
 

Turbocharged400sbc

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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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