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...why not just use single cylinder ignition coils and disable 4 of them...?

From what I've read and seen, most of the existing Variable displacement engines Lock the valves closed (by disengaging the associated valvetrain) and shut off the injectors to the "Off" Cylinders.





The air trapped in the cylinders then acts as a sort of Gas Spring aiding in the engine's rotation.





I don't know if the systems disable the ignition on the Off Cylinders, but I don't think it'd matter if the plugs still fire anyway..





I also read of one design that had a clutch setup in between two V-4 engines.


Sounded too complicated and Fragile to me..

DEI makes several CO2 systems for cooling the intake charge. They call it "Cryo2", as in Cryogenics. Check out their website for info.


The centrifugal superchargers with a clutch are also used by BMW. You can find them on ebay from time to time. The reason that all the clutched superchargers have been of the centrifugal type is because your engine can still suck air through them when they are off. I've heard of racers driving their centrifugal supercharged race cars to the track with the belt off and then putting it on when it was race time.


VCT, or Variable Cam Timing, could be incorporated to deal with the compression issue with the Roots SC. The valve events are changed to run the engine decently in half a range at a time, with each specific mode. Decreased duration while NA to raise compression some, combined with timing being advanced by the ECU (lower RPM). Turn on the blower and the cam timing changes back to a little more duration (higher RPM) and ignition timing is retarded.


As for knocking while NA because of low compression, knock is usually caused by too low of octane, ignition timing too advanced, or too much compression for the octane of fuel used. This is of course ignoring any physical causes such as hot spots in the cylinder.


I have figured out a way to make the on/off supercharger (Roots) work but again it is too involved, very costly, and the gain, while seemingly cool, would not be quite as impressive as one would hope because of the parameters required to make the engine run decent in both modes. Engines need to be built to how you are going to run them, and then it can be built well. Try to make it work in two different principles, and due to laws of physics as it applies to compression and air flow, the engine won't be able to do either way very well.


Personally, I love a challenge, but in this case success would not be too sweet.


Steve

The best way would be to disable every other cylinder according to the firing order. Not front, back, right or left. There would be no point disabling individual coils unless fuel flow were also shut off to those cylinders.


I don't think compression is that big of an issue because you only lose about 4% power for each compression point lowered. It's been proven with dyno testing. So reducing say a 400HP engine from 10:1 to 8:1 would only lose 30-35HP.


Variable cam timing doesn't actually change duration. The valve remains open for the same amount of time but they open & close earlier or later which has an effect on dynamic compression. Retarding a cam 4 degrees reduces DC and shifts the power range up about 300rpm higher.


Retarding ignition is easy. The technology has been used in nitrous applications as far back as I can remember. It's something that can be triggered manually, preset automatically or by using a knock sensor. There are also ignition boxes available with dual advance curves that have been used on flexible fuel engines like propane-gasoline hybrids.


I have a couple designs that don't require expensive parts or complicated electronics. The question is, what would be a reasonable price if a kit were available?
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[div]Cadillac V-8-6-4 was terminated after just one year.[/div]
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[div]Variable Displacement: Fuel efficiency by cylinder deactivation http://www.automedia.com/Variable/Displ ... 050601dd/1http://www.automedia.com/Variable/Displ ... 050601dd/1[/div]
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[div]http://f1.grp.yahoofs.com/v1/IAVYRt7BCv ... Timing.jpgVariableCamTiming.jpg[/b]

Cadillac 4 valve latest technology [/div]
[div]http://f1.grp.yahoofs.com/v1/IAVYRt7BCv ... Timing.jpghttp://f1.grp.yahoofs.com/v1/IAVYRt7BCv ... Timing.jpg[/div]

http://www.popularhotrodding.com/featur ... echnology/





How GM currently does their cylinder deactivation.

Thanks mfpmax, that's the article I remember reading but didn't have the link handy. It's easy to see why Displacement on Demand, when done correctly, is way beyond the skills of a backyard hobbyist. I would have guessed more, but it only accounted for a 17% improvement in gas mileage.

Quite a bit of what we dream of is beyond some of our skills...but it certainly doesn't stop us from trying does it.





To go back to the orignal topic...it'd be nice to get a hold of one of the V8 Supercharged Mercedes cars and disassemble their setup to see how they make theirs work.





Or even better...get a chance to see the paper work on Ford's Super Stallion concept. Every year i'd hope it would show up to the local Fun Ford Weekend...and it never did.