I like this thread.

Why? Because I finally don't disagree with IZ28 here.

:-D

 

LOL, cool!!

I think we can all agree that this can be a good thing.

 

Thanks for the breakdown!

Obviously, (almost ) noone maintain 100mph on the freeway, so DOD should work well at normal highway speeds, and even if you are going fast enough at a constant speed where 4 cylinders won't cut it, I'm assuming the computer will bring 2 additional cylinders online and fire on 6 to maintain enough power to keep the speed. And if that is not enough, it will bring all 8 cylinders online...

As GM has said, it is 'seemless' so , I'd think the computer is setup to account for all of these situations!

 

:chuckle: Me too!

 

Thats 2!! Keep them coming.

We've agreed on some things before guys. Its just that we disagree mostly.

 

A constant 80mph in a Cadillac STS (big, heavy and boxy... not the slipperiest car in the world) took about 72hp in 1993.

We were doing measurements at the time to provide a look-see at what happened when the engine went into "limp home" mode due to coolant loss, and how the transmission could help it out.

What we found out was that the engine was capable of running indefinitely on 4 (alternating) cylinders at 70mph without much throttle input.

At that point, even though I was not a GM employee, I started cooking up a way in my head to physically break the motor in half at the crankshaft and have it run as a V4 on one half and completely shut down the other.

See, even the GM DOD system wastes energy by spinning the deactivated pistons. This is 100% wasted effort.

What I came up with conceptually was a magnetic clutch that was capable of switching fast enough to re-align the crankshaft into the proper phasing if one half was at 6000rpm and the other was at rest. The half of the crankshaft at rest would be progressively "dragged" up to speed and the clutch would switch on and off quickly enough to allow the the crankshafts to "slip" relative to each other until they came into phase. Firing order and cam timing would be varied to assist the "dead" half in spinning up.

I proposed the concept to my boss (VP of R&D at the company I worked for) and even came up with some concept sketches, but he figured it was beyond our scope to pursue.

Oh well.... I still think about it though.

 

I know Im pretty excited about this.

 

Just nitpikin' here but 2 things posted are wrong.

The DOD is a 8-4 mode---there is no 6 clyinder mode--like there was on Cadillacs 8-6-4 system.

At a cruise rpm 2700rpm I doubt your engine is making 150hp.

Why? That sounds like a hp figure at Full-throttle.

But I get your point.

 

Yes, after doing some additional reading, I believe you are correct... it'll be firing either 8 or 4 cylinders...

Thank you for the correction.

 

Just trying to make a very rough stab at how much hp is possible at a given rpm/mph. With D.O.D., the throttle is a fly by wire like the Vette, the PCM opens the throttle further in 4 cylinder mode. The engine operates at a much higher volumetric efficiency than in 8 cylinder mode with a slightly opened throttle.

This is one reason that diesel engines are so efficient - they are always operating at W.O.T., because they have no throttle blade.

 

The Caddy limp home scheme alternately shuts off the fuel injectors for the cylinders. The valves continued to open and close, the engine continues to pump air through the cylinder.

With D.O.D., the wasted energy is primarily the friction of the piston rings. The valves are closed, and no air is actually pumped through the deactvated cylinders. The air is trapped, and just compresses and expands, and acts as a spring, storing and releasing energy.