http://www.roadandtrack.com/article....&page_number=3Originally Posted by fpv_gtho
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http://www.roadandtrack.com/article....&page_number=3
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variable valve trains comes from simple hydrolic, and electrical advancements in technology. There is nothing similar between any of them they are all different. We have Lotus and GM to thank for these advancements. Why don't i like it? Because It complicates the already complicated valve train, it puts a lot more rotating mass in the valve train, and ultimatly it isn't as good as 1 good ol camshaft, with big numbers attached, and a bunch of pushrods on top.
~Couch
P.S. I just left a forum with this e drama mess going on. Is there no escape?
Enthusiast
Actually most cam phasing system are highly similar and variable lift systems fall into only a few categories. VTEC like systems that switch between different cam lobes. Ferrari like systems that use a single morphed cam that has different lift, BMW like systems that have an eccentric link between a single cam lobe and the valves. Other than that you start getting into fringe systems like Lotus's electric-hydraulic system.
Power, whether measured as HP, PS, or KW is what accelerates cars and gets it up to top speed. Power also determines how far you take a wall when you hit it
Engine torque is an illusion.
Enthusiast
the systems ARE similar because they do the same thing, though by different methods
they change either the cam timing which or valve lift profiles themselves (or both)
1 camshaft iSNT as good because you cant vary intake and exhaust independently
you're right in that it adds more rotating mass but in the big picture the benefits are greater then the cost
Enthusiast
I hope you realise that the reciprocating mass of the pushrods kills efficiency and drains more power than DOHC...
BMW's new variable lift system can already match pushrod systems upper limits for redline. (on production cars)
Power, whether measured as HP, PS, or KW is what accelerates cars and gets it up to top speed. Power also determines how far you take a wall when you hit it
Engine torque is an illusion.
Enthusiast
I dislike it just because, like NAASBC355 said, it just complicates an engine more, and also because it basically benefits the top-end on cars, something I don't really care to use anyway. I think it would be better used as a way to boost low-end torque while maintaining HP peaks, much like Toyota has done with its 3.3l VVT-i in their minivans and sedans, for instance, rather than pushing the HP peak upwards in search of higher specific output.
Now, on a sport bike, the whole VTEC idea takes on a whole new life. There, although I woudln't necessarily like it, I could live with it. Low weight and comparatively large engines mean that low-end torque becomes less of an issue, and I think it would be really fun to see a 220hp VTEC-like system motor on a 1300 Hayabusa
An it harm none, do as ye will
Approximately 79% of statistics are made up.
Enthusiast
They do not just make engines more complicated...
And they do not just benefit top end!
The whole point of Vtec is to run a good low rpm cam for normal engine use increasing useable torque and economy and to still have good top end when you really want it.
Power, whether measured as HP, PS, or KW is what accelerates cars and gets it up to top speed. Power also determines how far you take a wall when you hit it
Engine torque is an illusion.
Enthusiast
Yeah...I know...read closely, I gave credit to Toyota for doing exactly that...boosting low-rpm torque while simply maintaining top-end...I think that's a far, far better way to use a VTEC system on an automobile.
And yes they do complicate the engine
An it harm none, do as ye will
Approximately 79% of statistics are made up.
Enthusiast
those specific examples might but in theory it doesnt affect low rpm operations at allYeah...I know...read closely, I gave credit to Toyota for doing exactly that...boosting low-rpm torque while simply maintaining top-end...I think that's a far, far better way to use a VTEC system on an automobile.
And yes they do complicate the engine
variable valve lift systems allow you to have a cam optimised for low end and one optimised for high end (or infinetly variable ones which are always optimised) which means it will ALWAYS be better then a system without this
variable valve timing allows you to boost torque throughout the rev range and again you'll always be better off with one then without
Enthusiast
An engine with a VVT and or VVL is going to be more mechically complex and will have complex electronic control.And yes they do complicate the engine
However the statement I was answering was that it ONLY complicates the engine (ie. it doesn't do any good) This is total bollocks.
Also the mechanical parts of a VVTL system are very easy to understand and shouldn't give any average person problems. The electronics are a slightly different story but they aren't any more complicated than the rest of the computer system in todays cars.
Power, whether measured as HP, PS, or KW is what accelerates cars and gets it up to top speed. Power also determines how far you take a wall when you hit it
Engine torque is an illusion.
Member
As a studying engineer all I can say in reply to this is; oh. my. god.
How wrong can one man be? I'll wait for him to bemoan the demise of carbs whilst mocking new fangled direct injection before I say he has reached the limits. But this is the bar set.
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