The Merc NA V8 with cylinder deactivation....
Discussion
Cylinder deactivation is a red herring in UK. All it does is enable manufacturers to post artificially high mpg figures on the extra-urban test cycle. If you want fuel economy you need to get a lighter car which almost certainly means a smaller engine.
Makes much more sense in USA for V8s running mega freeway miles.
Makes much more sense in USA for V8s running mega freeway miles.
It may well remove the pumping losses associated with the de-activated cylinders, but it doesn't remove the ring / piston / bearing friction as well, so the real world economy benefits are marginal. If you want to potter around, just using about 20bhp, it's better to simply buy a car that only makes 20bhp, rather than one that makes another 300 you don't ever use.........
Max_Torque said:
It may well remove the pumping losses associated with the de-activated cylinders, but it doesn't remove the ring / piston / bearing friction as well, so the real world economy benefits are marginal. If you want to potter around, just using about 20bhp, it's better to simply buy a car that only makes 20bhp, rather than one that makes another 300 you don't ever use.........
I've got an Mx5 with around 130bhp. I don't use all 130bhp all the time?. But, it's there should I feel the need.Max_Torque said:
It may well remove the pumping losses associated with the de-activated cylinders, but it doesn't remove the ring / piston / bearing friction as well, so the real world economy benefits are marginal. If you want to potter around, just using about 20bhp, it's better to simply buy a car that only makes 20bhp, rather than one that makes another 300 you don't ever use.........
....which is why turbocharging is generally a much better answer than cylinder deactivation. In Europe.Ozzie Osmond said:
Cylinder deactivation is a red herring in UK. All it does is enable manufacturers to post artificially high mpg figures on the extra-urban test cycle. If you want fuel economy you need to get a lighter car which almost certainly means a smaller engine.
Makes much more sense in USA for V8s running mega freeway miles.
Well it's 50% urban, 50% extra urban.Makes much more sense in USA for V8s running mega freeway miles.
Sounds like a reasonable test to me.
If you do more urban running, look at the urban-only results.
I'm failing to see why geography plays a part in this. Surely if the ECU recognises the parameters required for activation of the cylinder cut off it doesn't matter where you are?
My understanding is that it bleeds off oil pressure from the valve lifters,so the valves don't open and cuts off the injector and coil for the relevant cyinder? At least that's what happened on the 5.7 Hemi in my Grand Cherokee here in the UK. I guess Mercedes shared the technology when it was all DaimlerChrysler??
My understanding is that it bleeds off oil pressure from the valve lifters,so the valves don't open and cuts off the injector and coil for the relevant cyinder? At least that's what happened on the 5.7 Hemi in my Grand Cherokee here in the UK. I guess Mercedes shared the technology when it was all DaimlerChrysler??
I think it's a pretty good idea, if it makes a saving, then why not? It's never going to massively reduce the mpg but as long as the engine isn't under load for a 'manoeuvre' half the cylinders remaining closed will make a difference on a cruise.
But as has been said, smaller engines and turbocharging, also stop start technology added to the equation will make the most significant difference. The days of the V8's may be numbered...
But as has been said, smaller engines and turbocharging, also stop start technology added to the equation will make the most significant difference. The days of the V8's may be numbered...
Buff Mchugelarge said:
It's a shame really, its a good idea.
How often can most 4 cylinders pootle about on 2 cylinders without any detrimental affect?
a steady cruise, in traffic etc?
I'm surpirsed this hasn't been a bandwagon?
VW are using that very tech on a new Polo (Golf?), the name of which escapes me (GT? Blue?). It had a "Driven" article here on PH a few months back. 1.4TSI engine IIRC.How often can most 4 cylinders pootle about on 2 cylinders without any detrimental affect?
a steady cruise, in traffic etc?
I'm surpirsed this hasn't been a bandwagon?
A different engine I know but I think the cylinder deactivation does work and is useful to save fuel. I have it on a 2001 Mercedes CL600.
I haven't actually calculated it but going by the obc on a gentle run the car does around 30mpg. It depends what speed you are doing though as anything over about 80mph and the fuel use increases dramatically. Still 30mpg~ from a 5.8 V12 is pretty good! I think the official figure is a bit lower though, so maybe the OBC is telling lies.
I haven't actually calculated it but going by the obc on a gentle run the car does around 30mpg. It depends what speed you are doing though as anything over about 80mph and the fuel use increases dramatically. Still 30mpg~ from a 5.8 V12 is pretty good! I think the official figure is a bit lower though, so maybe the OBC is telling lies.
Ozzie Osmond said:
Cylinder deactivation is a red herring in UK. All it does is enable manufacturers to post artificially high mpg figures on the extra-urban test cycle. If you want fuel economy you need to get a lighter car which almost certainly means a smaller engine.
Makes much more sense in USA for V8s running mega freeway miles.
I would be surprised if the cylinder deactivation was any more of a red-herring than all this forced induction, which is great on the mpg test cycles but so far from reality on the road it's laughable. Makes much more sense in USA for V8s running mega freeway miles.
I've driven the SLK55 with the new engine - dropped a friend off at Gatwick and bought his car back home to look after it for a week.
It does work... and at busy M25 motorway speeds, it drops off four cylinders, improving your economy and range. For the most part, yes it still runs on all eight cylinders. I guess it just makes a V8 a more viable proposition as a commuter car - before any decent sized V8 would only ever return 22-27mpg when driven like a saint. The 55 engine means your V8 can return a figure starting with 3.
It does work... and at busy M25 motorway speeds, it drops off four cylinders, improving your economy and range. For the most part, yes it still runs on all eight cylinders. I guess it just makes a V8 a more viable proposition as a commuter car - before any decent sized V8 would only ever return 22-27mpg when driven like a saint. The 55 engine means your V8 can return a figure starting with 3.
Max_Torque said:
It may well remove the pumping losses associated with the de-activated cylinders, but it doesn't remove the ring / piston / bearing friction as well, so the real world economy benefits are marginal. If you want to potter around, just using about 20bhp, it's better to simply buy a car that only makes 20bhp, rather than one that makes another 300 you don't ever use.........
Totally disagree. I want a clever engine that delivers on two fronts:Firstly, excellent mpg when I am cruising / commuting and using no more than about 50bhp to keep up with the flow of traffic
Secondly, excellent power when I want it.
I appreciate that you can't have both together, but an engine that tries to give you either/or is a fine thing indeed.
liner33 said:
Matt UK said:
Firstly, excellent mpg when I am cruising / commuting and using no more than about 50bhp to keep up with the flow of traffic
Secondly, excellent power when I want it.
You have described a petrol turbo engine there, keep them off boost and decent economy can be had Secondly, excellent power when I want it.
Matt UK said:
I appreciate that you can't have both together, but an engine that tries to give you either/or is a fine thing indeed.
Yes you can, its easy. You put the engine in a lightweight car. Economy, AND high power to weight, Plus all the other benefits thatgo with it.
All well and good chasing lasts %ages of efficiency out the engines, but is the fundamentals of the big heavy cars themselves that are the problem.
kambites said:
liner33 said:
Matt UK said:
Firstly, excellent mpg when I am cruising / commuting and using no more than about 50bhp to keep up with the flow of traffic
Secondly, excellent power when I want it.
You have described a petrol turbo engine there, keep them off boost and decent economy can be had Secondly, excellent power when I want it.
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