remember that cadiallac (?) on top gear that had a V8 engine, but ran on 4 cylinders when cruising, but opened all 8 when you needed/wanted the power from it? how would it work? shutting down the injectors on 4 cylinders?

has anyone developed anything similar for megasquirt yet? think it would be a good idea, especially if it could be a different cylinder each turn of the engine?

shouldn't be too hard surely?

Wouldn't you have to open the valves on non-firing cylinders? Otherwise the pressure built up during the compression stroke on them would waste energy and effectively work against the active cylinders....

It had all sorts of controls:

Fuel and spark cut, plus some form of de-compression, valves held open perhaps??

I read somewhere an attempt had been made with a clutch in the crank to disconnect half the cylinders, whether that made it too I've no idea.....

ah yeah, hadn't thought of that, woner how the caddy did it then?

I had a lecturer at college last year who said his saxo ran on 2 cylinders at idle. I think mclaren had a system a year year or two ago that allowed them to sit at the end of the pitlane before qualifying started, running on one or two cylinders aswell.

May be worth asking on extraefi.com (megasquirt forum).

I'd say you'll need some way to decompress the cylinders though. Without combustion you'll end up with a very inefficient air pump.

yeah, a bit more complicated than i thought then. maybe some sort of electrically operated valve screwed in the top of the cylinder head, maybe thats how they do it...
never mind then
if all goes well, i might end up buying a car that will probably ruin me very soon was wondering if there was ways to make it a bit more economical lol

From what I recall, they keep the valves shut and use the air in the cylinders as a spring, rather than inefficiently pumping air through valves. To stop individual cylinders getting too hot, they alternate cylinders periodically.

Megasquirt could be tricked into doing this alread. I think you could do it using the staged injection settings.

Basically, drive your half you injectors off the normally injector line, and drive the other half of the injectors from the staged injector settings. You would want it to ramp in quickly and have a fair amount of map points around the switch-over.

The problem you would have is with AFR as when the cylinders are out of action then you would be pumping air, which would fool the AFR into elevated values.

Ideally you would want 2 (or more) AFR gauges. But there would be ways around this.

It did cross my mind as a way of saving fuel at idle in an engine that doesn't like idling at really low revs (i.e. tricky cams and lightweight flywheel). As you could rev a pair of 4 cylinders at higher speed.

If you used GSXR throttle bodies then you could close the secondaries on the throttles of the cylinders run from the staged line. In this case you would be pumping a vacuum and so minimise the loses.

I think you could put all this together for only a few quid (if you had a megasquirt). The problem would be the transition from 2 to 4 cylinder running. I doubt it would work very well, but it would be an interesting hobby!

Matt

My Mondeo used to run on 2 cylinders



but then bought a set of leads and a new coil pack and that fixed the problem d)

but yes ms can run 2 sets of injectors. So in theory it could be used to only get fuel to the second lot of cylindrs after a certain rpm
but as mentioned by others above, I think it's not that easy.

nah, doesn't sound easy, and i don't fancy megasquirting the car anyway... maybe a new job is the way forward to make it 'cheaper'

To turn the engine over you need a set amount of power, if that comes from 2 or 4 cylinders it doesn't matter.

If you're using 16 that can develop 1000bhp it's another matter as it'll be built to run at high power, i.e big bore and suitable chamber and head design.

the two options i use is to turn the engine off if i want to save fuel, and use my right foot as an 'economy device'.

Purley as an exercise, again i don't think running a 4 cylinder on 2 is very nice. It's abit lumpy and all that. On more cylinders or a very powerful/large engine it might be a different story.

F1 cars do/did indead have a similar system for safteycar/parade lap/pit lane use.

yeah, wouldn't run any less that 4 cylinders, so on a 6 cyl I6, knocking 2 off isn't so bad.

ok, balls out the bath tub, i'm about to buy a skyline if all goes well, 70k miles, £3k might be able to bring that down a bit hopefully. but at the minute i'm in a poo job getting £6 and hour... new job is always on the agenda, but it just got me wondering if there was a good way to get fun cars to use less petrol than normal

^^^^ Yes there is - put a block of wood under the throttle pedal.

Or set up your car to run on LPG (Check on t'internet: some cars dontlike it)

Regards
Hugh

quote:

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Originally posted by hughpinder
^^^^ Yes there is - put a block of wood under the throttle pedal.


Regards
Hugh

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TBH, the answer to your situation is no.
What about the cost of MS, all the fuel you'll use to map it to std, and then mapping it to your economy settings, the cost when the engine dies.

You could possibly lower the boost, thus increasing the safe AFR. Make the engine more effecient, increase CR, better combustion chamber, exhuast and inlet. Taking the turbo out of the equation when not needed would be good. Other than that, don't use it, it'll be all the more special when you do.

TBH, the answer to your situation is no.
What about the cost of MS, all the fuel you'll use to map it to std, and then mapping it to your economy settings, the cost when the engine dies.

You could possibly lower the boost, thus increasing the safe AFR. Make the engine more effecient, increase CR, better combustion chamber, exhuast and inlet. Taking the turbo out of the equation when not needed would be good. Other than that, don't use it, it'll be all the more special when you do.

hmm, turbo boost controller would be a good idea anyway i guess.
and whenever i finally get this car finished, it'll be a 2 litre n/a engine, very light, so i guess there's my economy setting there, use the truck

I thought about doing something like this before. You would just need to switch off the injectors and spark plugs to those cylinders.

You would gain an improvement in MPG but it wouldn't be massive because (as said) you'ld still be compressing air.... Seperate fly-by-wire TBs would be the best answer- close the butterfly and run the "quiet" cylinders in a vacuum. IE compressing a vacuum isn't that difficult

Bit of a hassle and would sound grotty if it was only a few cylinders running. Thought about doing it on my PanEuro because as much fun as cruising @ 8krpm is it really isn't necessary and the fuel consumption isn't the best....

interesting, wouldn't expanding a vacuum be just as difficult as compressing the same volume of air?

quote:

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Originally posted by brianthemagical
To turn the engine over you need a set amount of power, if that comes from 2 or 4 cylinders it doesn't matter.

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Out of interest, when the Ford Focus was first announced I remember them saying that on total loss of coolant, the ECU could switch to running on 3 cylinders, allowing air to cool the fourth and regularly switching which wasn't in use. Did that make it into the production models? I've not seen mention of it since and would have thought that it was a fairly good selling point.