Variable displacement V8 - thoughts?

[Frank Lee]

That wouldn't get the engine anywhere near cruise rpm, but it might give useable results.

[bestclimb]

Originally Posted by 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.

Could one derive the energy needed to spin an engine from comparing coast down tests engine off but spinning verses transmission in neutral?

[Frank Lee]

That should be an indicator of engine drag while it's "motoring".

[t vago]

I think, in trying to figure out how much drag is induced inside the engine, we're not seeing the entire point of deactivating cylinders.

The idea is the same as with going to a taller differential gear, in that you want to lower the vacuum inside the intake manifold while reducing pumping losses past the throttle body. Taller diff gears accomplish this by allowing the engine to rev at a lower speed. Cylinder deactivation accomplishes this by physically removing the airflow from 1/2 the cylinders in the engine, and forcing the remaining cylinders to suck in almost twice as much air to develop the same power output to the wheels as before.

In both cases, the throttle plate in the throttle body will have to open up more, reducing the drag loss imparted by the throttle plate to the incoming air. Opening the throttle plate will also cause more air to be sucked into the intake manifold, which, in turn, raises the average pressure inside the intake manifold. More of the pumping work done by the engine goes to sucking in air/fuel mixture, and less goes to developing a vacuum.

[t vago]

I've also thought of testing a related idea, of using a pair of throttle bodies in a staged configuration. The primary throttle body would open first, and would have a rather small bore diameter. The secondary throttle body would start to open once the primary opened fully, would have a larger bore diameter, and would provide additional air to the engine as needed.

This idea uses the same principle as the warm air intake that seems to be popular here. Get the throttle plate to open up more, thereby reducing drag loss past the throttle plate, while maintaining the same engine power output. It isn't going to do much to reduce intake vacuum, but it's better than nothing.

Before you write off this idea as being half-baked, consider that the 1989-1992 Ford Probe 2.2L I4 and several Mazda models used this exact configuration in one form or another. Note that in each picture, the primary has a smaller moveable surface area than the secondary. With the Probe throttle body, the secondary consists of a single larger diameter bore. With the Mazda rotary throttle body, you can see that the secondary consists of two more throttle plates.

[Frank Lee]

You are correct in that it isn't the entire point. But I think when dealing with such a small potential for improvement, one can not afford to throw away any of that improvement by spending it on pumping losses. Still, I look forward to seeing how it goes w/o valve deac.

[autoteach]

How about mating two four cylinders together through a clutching mechanism so that you can shut down the entire engine, with no motion from it. There ya go, problem solved. Or maybe if there were a way to manage the volumetric efficiency of an engine, so that when you dont want air entering the engine, it acts like a 2.5 litre, and when you do, it acts like a 5 litre. I might patent this system of variable volumetric efficiency. I will call it a Turbo.

[Frank Lee]

I like the siamese engine concept and have thought about it much. The biggest hold up for that one is probably NVH: if you've ever run/been in a twin engine plane with the engines out of synch you'd know how GD annoying anything less than perfect synch is.

The other hold up I've considered is that of the deac cyls cooling down too much, so that they aren't at operating temp when called upon. I think that one could be largely overcome via a shared cooling system.

[bestclimb]

It can be nice when they are way out of sync, you get kind of a vibratory back massage thing going. It works better on freight flights as passengers get worried/whine when the plane vibrates enough to shake their seats.

how about 4 clutched v twins. The clutches could be designed to slip just a little bit with electronic pins that engage when the rotational difference is reduced enough not to shear them or they could be electronically controlled and the computer could closely match RPM then let the pins slip in negating the need for a clutch. The pins and holes could be located so as to reduce harmonic vibration...or what ever. Just begs for straight pipes out the hood, with flappers on them so you know how many pairs are running or nice mufflers under the rig with a set of lights on the dash if noise ordinances get you down.

[mechman600]

Originally Posted by autoteach

I might patent this system of variable volumetric efficiency. I will call it a Turbo.

LOL...you will make millions!

Seriously, yank the 4.7 boat anchor and install a small turbocharged four banger. All the OEMs are starting to do this in various vehicles (smaller than normal engines with turbos to make up the difference) because they have re-realized that turbos are the easiest and most effective way to vary volumetric efficiency. Sure, variable valve timing and variable displacement do this too, but to a MUCH smaller extent than a good old turbocharger. Plus, thanks to the magic of variable geometry turbochargers, turbo lag is eliminated and torque curves are flat as a pancake all the way down to 'just above idle' RPMs. Hmm...seems like a magical recipe for ecommodding to me!

Oh, and don't forget to attempt to freeze your slushbox. Torque converters ruin most economy attempts.