Very interesting read, thanks for sharing.

Tom

 

I'll bet that any HP gain (if any) on the base C6 will be extremely small for 08. I just don't see GM wanting to up the HP on a base car when "most" owners are happy with the current power. If they aren't going to bump it to 425 or 435 then why bother? How many owners are going to trade a 06 or 07 to gain a couple HP? Not to many IMO but that's my take on it. If you want a vette just go buy one and stop worrying about what may or may not happen with GM. If you wait for the latest and greatest vette you will never own one..........

 

I'll expect you to come back in a month and edit this.

 

It takes about 7 hp to push the C6 down the road at 55 MPH. Another 10-12 to run the engine accessories. That leaves 380 horses eating but not working. The LS2 is not a diesel, you can't just keep cutting back on the fuel and expect it to keep running. There's a minimum AFR you have to maintain in each of those 8 cylinders for the mixture to light and burn cleanly.

But if you shut off 4 of them, you don't have to feed them at all. By closing the valves to those 4 deactivated cylinders, you also nearly halve engine pumping losses. So end result, when in DoD mode, you save up to half the fuel you'd have to burn if the engine didn't have DoD. But within 5 milliseconds of demanding more power, all 8 cylinders are back on line pulling their weight. You can't even feel that delay. It is roughly the time it takes your computer or TV screen to refresh once, and you don't see that flicker.

Of course it only saves you fuel when you're not accelerating. If you're demanding more power, fuel consumption goes back to what it would be without DoD. But most people run steady speed or decelerate for much longer periods than the time spent accelerating, so the overall fuel savings is significant, with no performance penalty. It is a clever idea, and in its current incarnation it works very well.

The old Caddies with the first generation DoD didn't have modern computer controls. Don't judge DoD by them. This new system is slick. It works seamlessly to effectively vary engine displacement according to load demand. Go drive a Yukon or Impala that has it, you won't be able to tell it is working unless you notice the light on the dash coming on and off.

 

AHH YES,I think it was called the 4-6-8 motor back in the 80's.

 

Yes. It had several problems, trying to do 4-6-8 was one of them. A V8 can't run smoothly on 6 cylinders. That's why the new system doesn't try to do that. Trying to run on 6 made the Caddy engine shudder, causing an unpleasant vibration in the passenger cabin. Another problem with the old Caddy system was that the engine used throttle body injection. Not having all the cylinders working caused serious problems with fuel/air distribution in the intake manifold. This caused the engine to stumble. Modern engines use port injection, so this isn't an issue. Also, the old Caddies weren't drive by wire, so the computer couldn't compensate for the surge when switching. New cars do have drive by wire, and can modulate the throttle to smooth the transition between 4 and 8 cylinders.

 

At the Corvette Corral over the weekend at Sebring, Tom Wallace's staff was emphatic that there will NOT BE displacement on demand on the Corvette. The reason given was the placement of the transmission at the rear axle, and that a driveline resonance set up during the transition from 8 to 4, or from 4 to 8, could not be overcome.

Sounded like good news to me, in spite of shopdog's correct thermodynamic justification for using DoD.

 

Good info. So far Rick Conti is batting .333 as he already said no DOD. I would be willing to bet on his 425 - 435 hp ratings also.