2nd Cam on the Toyota engine, how does it work?
Discussion
I know what it's called, I love what it does, but I've no idea how it does it.
So far my technical knowledge has been limited to topping up the screenwash, but following a recent visit to Plans Motorsport (new tyres and to discuss potential mods), I think it's time I learnt a bit about how the thing works.
So can anyone explain how the 2nd cam works? Layman's terms appreciated.
So far my technical knowledge has been limited to topping up the screenwash, but following a recent visit to Plans Motorsport (new tyres and to discuss potential mods), I think it's time I learnt a bit about how the thing works.
So can anyone explain how the 2nd cam works? Layman's terms appreciated.
My (basic!) understanding of it is that when the oil pressure reaches a certain level (a level that it will reach at a set rpm) a variator alters the cam timing in effect changig from a 'mild' overlap to a more aggressive overlap giving you increased performance.
The Honda VTEC works like this.
I also think that the Alfa 16v Twin Spark work in a similar fashion though it's a lot less pronounced in the Alfa as they're not selling it as a 100bhp per litre performance engine.
The Honda VTEC works like this.
I also think that the Alfa 16v Twin Spark work in a similar fashion though it's a lot less pronounced in the Alfa as they're not selling it as a 100bhp per litre performance engine.
MJK 24 said:
My (basic!) understanding of it is that when the oil pressure reaches a certain level (a level that it will reach at a set rpm) a variator alters the cam timing in effect changig from a 'mild' overlap to a more aggressive overlap giving you increased performance.
The Honda VTEC works like this.
I also think that the Alfa 16v Twin Spark work in a similar fashion though it's a lot less pronounced in the Alfa as they're not selling it as a 100bhp per litre performance engine.
err - wrong.... massively...
there are two different bit's here...
the 'second' cam bit is where the camshaft has two different profiles on it, and the ECU via some mecanical stuff, selects which profile to use.
On the Honda this is done by a hydralic pin that locks the rocker halves together to engage the second cam, this is also the same for the Toyota, although the layout of the followers is slightly different.
the next part of the equation is the ability some engine have to change the cam phaseing, ie. to be able to move the camshaft's timming on the fly, with the Honda this is done with a hydralic actuator in the cam pulley controled by a pulse valve (driven from the ECU)
I assume that Toyata engine has a simmilar setup to this.
the odd-one out is the Rover VVC, this used a comples excentric gear system to slow the camshaft down as the cam lob is in use effectivly changing the ramp angles and duration of the cam, then speeding it back up when the lobe is out of play (this is why the cam is split in two halves). this is controled by a hydralic 'rack' driven by the ECU.
In the old days of the first Honda Vtec's, all they had was the alternate cam profile and a hard switch-over point, the current iVtec's have both this and the cam timming control (VTC).
Phew - not a small question. Probably the more important question is "why?"
Standard engine timing is set up for an economy / easy driving wheras a dragster has an aggressive timing set up for competition use. Where the standard car set up is not condusive to high power and high revs the sports profile is not god for tickover and is hard to sit in stop start traffic.
As the engine in a standard car revs it needs more air and fuel and also the timing of the cam (opening of the valves) has to change in relation to the rotation of the bottom end. This is hard top do as the 2 aspects of the engine are carefully joined by a rigid timing belt.
What the variable valve timing systems do is to amend the valve timing to alow the engine to react more like a competion car engine at high revs and a nice sedate standard car engine at lower revs.
There are various methods and the toyota is the simplest and contary to popular belief there is only one inlet cam.
Standard engine timing is set up for an economy / easy driving wheras a dragster has an aggressive timing set up for competition use. Where the standard car set up is not condusive to high power and high revs the sports profile is not god for tickover and is hard to sit in stop start traffic.
As the engine in a standard car revs it needs more air and fuel and also the timing of the cam (opening of the valves) has to change in relation to the rotation of the bottom end. This is hard top do as the 2 aspects of the engine are carefully joined by a rigid timing belt.
What the variable valve timing systems do is to amend the valve timing to alow the engine to react more like a competion car engine at high revs and a nice sedate standard car engine at lower revs.
There are various methods and the toyota is the simplest and contary to popular belief there is only one inlet cam.
scuffham said:
My (basic!) understanding of it is that when the oil pressure reaches a certain level (a level that it will reach at a set rpm) a variator alters the cam timing in effect changig from a 'mild' overlap to a more aggressive overlap giving you increased performance.
The Honda VTEC works like this.
I also think that the Alfa 16v Twin Spark work in a similar fashion though it's a lot less pronounced in the Alfa as they're not selling it as a 100bhp per litre performance engine.
err - wrong.... massively...
I duly stand corrected! Thanks for the explanation - now I really know!
scuffham said:
There are various methods and the toyota is the simplest and contary to popular belief there is only one inlet cam.
sorry?
yes there is only one camshaft, however, it has two cam lobes per cylinder, one high one low, this is for both intake and exhaust cams.
Hence 16 valves in total. Obvious. The valve height is varied by a steped shin being inserted under the folower bucket.
gooby said:
Hence 16 valves in total. Obvious. The valve height is varied by a steped shin being inserted under the folower bucket.
sorry, your wrong again...
the two lobes for each cylinder have different profiles, not only in lift terms but also in timming.
the 'high' lobe is engaged with a slideing pin
>> Edited by scuffham on Friday 20th January 16:52
scuffham said:
Hence 16 valves in total. Obvious. The valve height is varied by a steped shin being inserted under the folower bucket.
sorry, your wrong again...
the two lobes for each cylinder have different profiles, not only in lift terms but also in timming.
the 'high' lobe is engaged with a slideing pin <imgsrc="www.scuffham.com/Temp/VVTI.jpg">
OK, how do you get an image to work???
>> Edited by scuffham on Friday 20th January 08:49
![www.scuffham.com/Temp/VVTI.jpg">](http://www.scuffham.com/Temp/VVTI.jpg">){kind=link}
I hate to sound pedantic. You are correct in stating that one of the 2 cams has more lift than the other. That is true in VVT and VVTL but the engine in the 111r is the ...
Lotus said:
Mid mounted, transverse, 1796cc, 2ZZ-GE engine, Metal Matrix Composite (MMC) & aluminium lightweight and compact construction, 4 cylinders in line, water cooled, naturally aspirated with double overhead camshafts exploiting a Variable Valve Timing & Lift - intelligent (VVTL-i) system, hydraulic tappets 4 valves per cylinder. Rocker arms with low friction followers, multi-point sequential fuel injection and electronic ignition.
This engine incorporates an additional variable lift system. When "on cam" the stepped shim (sliding pin) under the cam follower is inserted in order to give more lift to the cam lobes on the Long duration cam.
www.autozine.org/technical_school/engine/vvt_31.htm
Reading this - I think we are both agreeing!
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