Variable displacement V8 - thoughts?

[roflwaffle]

Originally Posted by cr45

Just disconnecting the four FIs will not work as the oxygen sensor will pick up on a lean AFR and the engine management will try to adjust by adding extra fuel.

Remove the O2. Closed loop versus open loops shouldn't result in a huge difference in fuel consumption.

[Big Dave]

The GM AFM system works very well, but required enormous engineering resources and two decades to develop.

You think you can DIY, you are kidding yourself.

It would be far easier and cheaper to find a 5.3 GM engine and swap it in.

[autoteach]

positive thoughts, dave, positive thoughts.

[some_other_dave]

Chances are it won't see the kind of gains that the factory setup did/does. It may not even work. But much will be learned. Hopefully the knowledge will be shared with us.

So it won't be a waste, no matter what, and it could be really very cool. As long as the expectations are reasonable, and it's an enjoyable thing to put together, I fail to see a downside.

Even blowing up a motor usually teaches you something; and it's not exactly as if Dodge V8 motors are that rare. And odds of that happening are pretty small if you pay attention to what the motor is actually doing.

-soD

[SlideWRX]

The OEMs see a 5% improvement because they hardly use the cylinder deactivation. They don't use it at idle, or under moderate load. Mostly just during cruising. An ecomodder would use it much more often.

They deactivate the valves so that they can run the 4 cylinders with the best balance, so that the customer only sees a little vibration at certain rpms. They have to keep the air from coming in or out of the chamber so it doesn't mess with sensors.

On my Mustang, there are separate O2 sensors for each bank, so I could turn off fuel injectors from one bank, fake the signal from the O2 sensors, and the ECU would stay happy. The air from each bank joins after the sensors, so O2 from the one bank shouldn't get to the other bank. Honestly, the only problem I see is how bad the vibration is.

For your project, what you are looking at I think is basically individual throttle bodies, maybe sealed up better. The 3 valve 4.6l has flaps inline (Charge Motion Control Valves - Tumble generators) that could be turned into full fledged valves/throttles.

[5speed5]

I didn't realize you already had the 3.55 gears. I say go for the cylinder deactivation if you feel you are up to it. It sounds like you have the skill set needed, and what a feeling of accomplishment it would give you to finish it and have it work.

SlideWRX has a good point about the OEMs under-utilizing it. They have to be very conservative to prevent the owners from thinking something is wrong with the engine, whereas an ecomodder is much more forgiving.

[Frank Lee]

I sure wish I could see results of "motoring" an engine- reverse dyno'ing it by spinning it with an electric motor and measuring power requirements to spin it. Data that shows how much power it takes to move that piston with valves going and with valves disabled would be most useful.

[some_other_dave]

That would be cool! I bet the OEMs do it, at least every once in a while.

It could be inferred from how much current it takes for a given-sized electric motor to spin the combustion engine to a given RPM. A motor intended for small EVs might be ideal.

You would, ideally, want to have the engine parts at their operating temperatures. You could run the engine for a while until it got to operating temp, then shut down the fuel and ignition and let the electric motor go.

This is sounding like something that a resourceful person could do at home...

-soD

[Frank Lee]

The OEM I used to work at did that for the entire driveline.

[autoteach]

Originally Posted by some_other_dave

That would be cool! I bet the OEMs do it, at least every once in a while.

It could be inferred from how much current it takes for a given-sized electric motor to spin the combustion engine to a given RPM. A motor intended for small EVs might be ideal.

You would, ideally, want to have the engine parts at their operating temperatures. You could run the engine for a while until it got to operating temp, then shut down the fuel and ignition and let the electric motor go.

This is sounding like something that a resourceful person could do at home...

-soD

Do you mean something like a starter motor with a disabled ignition and injection system? Yeah, its on the motor already.