blakep82
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| posted on 20/5/10 at 12:22 PM |
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megasquirt economy settings?
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?
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tomprescott
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| posted on 20/5/10 at 12:40 PM |
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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....
A bird in the hand....
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r1_pete
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| posted on 20/5/10 at 12:41 PM |
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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.....
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blakep82
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| posted on 20/5/10 at 12:41 PM |
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ah yeah, hadn't thought of that, woner how the caddy did it then?
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speedyxjs
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| posted on 20/5/10 at 12:49 PM |
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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).
How long can i resist the temptation to drop a V8 in?
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rost
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| posted on 20/5/10 at 12:59 PM |
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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.
Charlie don't surf!
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blakep82
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| posted on 20/5/10 at 01:02 PM |
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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
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BenTyreman
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| posted on 20/5/10 at 01:17 PM |
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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.
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matt_gsxr
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| posted on 20/5/10 at 01:21 PM |
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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
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Lars
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| posted on 20/5/10 at 01:22 PM |
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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.
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blakep82
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| posted on 20/5/10 at 01:24 PM |
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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' 
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brianthemagical
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| posted on 20/5/10 at 01:44 PM |
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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.
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blakep82
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| posted on 20/5/10 at 01:47 PM |
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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
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hughpinder
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 posted on 20/5/10 at 02:35 PM |
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^^^^ 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
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blakep82
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| posted on 20/5/10 at 02:36 PM |
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quote:
Originally posted by hughpinder
^^^^ Yes there is - put a block of wood under the throttle pedal.
Regards
Hugh
looks the most likely solution lol
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brianthemagical
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| posted on 20/5/10 at 02:37 PM |
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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.
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brianthemagical
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| posted on 20/5/10 at 02:38 PM |
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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.
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blakep82
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| posted on 20/5/10 at 02:40 PM |
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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
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BenB
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| posted on 20/5/10 at 03:40 PM |
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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....
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blakep82
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| posted on 20/5/10 at 03:46 PM |
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interesting, wouldn't expanding a vacuum be just as difficult as compressing the same volume of air?
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MikeRJ
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| posted on 20/5/10 at 04:43 PM |
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quote:
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.
The actual number of cylinders isn't as imporant as the capacity, which you are effectively reducing by cutting cylinders. This means the other
cylinders have to work harder to produce the same same power. In practice this means less pumping losses and higher effective CR, and overall higher
efficiency (assuming the losses from the deactivate cylinders isn't too large).
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SteveWalker
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| posted on 20/5/10 at 08:23 PM |
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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.
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