vvc vvt v-tech

[TF160SA]

Why does the toyota vvt-i produce more power than the vvc with the same cc? I'v heard of the lack of time to fix gliches in the vvc but what are they and can they be over come? oh and just a tought i'v heard that 200bhp is about the highest power you should go in a k-series(?) but 214bhp would be true to the 160 name (in kw that is )

thanks John

[Stu]

Peak HP isn't the answer to it all though.

The 160bhp K series in the elise is as quick as the VVT they are also using. And from speaking to the testers is a better all round package than the VVT.

[JonathanP]

isn't vvc supposed to be more advanced than v-tech, but wasn't developed to its full potential due to B*W?

[Stu]

Swings and roundabouts really. VTEC is more reliable, VVC is probably more advanced, but is certainly more complicated and expensive to produce.

[TF160SA]

I heard about the vvc having more potential but due to damage to the cams it wasn't tuned further? i thought that v-tech did something to the timing that vvc didn't?

[bgunn]

VTEC please, it's not a childs computer.


Brian.

[Mike12345]

Hehe!

Me not guilty this time Brian!

[Scarlet Fever]

The difference is fundamentally one of timing.

As i understand it the VTEC / VVTi systems work with a pair of interchangeable cam lobes that switch at a fixed point on the rev range. Basically you get reasonable performance and good economy at low revs, but when the cam lobes switch the timing and duration of the valve opening alters allowing more fuel into the combustion chamber and thus more power is released (at a trade off in fuel consumption). These systems are simple and durable, but from a drivers point of view thay can feel a bit 'all or nothing' in a similar way to a turbo'd engine feels when driving normally and then on boost. To be fair the technology has come along a bit these days and the 'mild cam' driving experience is still reasonably quick.

VVC on the other had is a quantum leap forwards, but like everything Rover develop, is a great idea but the execution has suffered a bit. Unlike the VTEC/VVTi systems described above, the VVC only has one cam lobe profile per inlet valve but the clever part is in the rotation of the cam shaft. There are 2 epicyclic <sp?> drive gears at each end of the head, each one is responsible for driving 2 camshafts, a half length shaft, with lobes on the far end, and a quarter length shaft that is slotted onto the end of the half shaft. A bit like a hinge pin if you know what i mean. Basically this means that the VVC head has five camshafts, a normal full length exhaust cam (2 valves per cylinder x 4 cylinders = 8 valves / 8 cam lobes), 2 inlet half shafts and 2 inlet quarter shafts (1 cam shaft per cylinder with 2 cam lobes on each. 2 valves x 4 camshafts = 8 valves / 8 cam lobes. 8 inlet valves + 8 exhaust valves = 16 valves). Now you know why VVC is also known as Very Very Complicated! Anyway the trick here is as i said, 1 camshaft per cylinder and each one is independantly driven through a set of gears which varies the timing of the shafts rotation, slowing and speeding it up to produce different valve open durations. Because the system is gear driven the cam timing is infinitely variable within an upper and lower limit and thus there is no fixed point at which the cams switch, they are 'on cam' all the time to a greater or lesser degree.

This is the VVCs great advantage, and also it's weakness. Because the rotational speed of the camshaft is speeding up and slowing down per revolution to provide greater valve opening times (slow shaft speed) and shorter intervals between openings (fast shaft speed), the cam lobes wear a lot faster than in a normal engine. Rover had great problems resolving this and because the VVC F had a fixed introduction date, they basically ran out of development time. Rather than solve this mechanically they simply 'de-tuned' the engine management system so that the VVC was running within safe perameters. This is why the VVC produces less bhp than the other systems, to use a computer analogy, it is running in 'safe mode'.

This would have been OK if it wasn't for BMW then putting the kibosh on the F development programme (including the VVC mechanism) until they sold the company to MGR. Basically the VVC mechanism was supposed to had post development to resolve the issue and release it's full potential but it didn't happen during BWMs tenure. I heard that there was a lot of work going on in this area since the buy out but these are only rumours and have yet to be proven. I did hear that K2000 had caused the VVC development project a bit of a hiccup though, K2000 has a different head to the other K4 engines and thus the VVC technology isn't directly transferrable, VVC K2000 is a goal they want to achieve and thus the programmes were merged, again another rumour. The last i heard they were looking at different metals and facings for the cam lobes and experimenting with different 'hotter' maps but this was over a year ago now and i have heard very little since.

Anyway, this is my understanding of the situation.

[mike satur]

Good explanation Andrew but not quite accurate , the VVC is not engaged all the time but is controlled by the hydraulic controller when certain parameters are met,RPM/oil temp.To my knowledge there has never been an issue with VVC cam wear and I have never seen any 'worn out', in fact the materials used are very high quality. With regard to further tuning of the VVC cams it would be possible to make higher lift and revised profile cams and IMO the actual VVC mechanism would be capable of the extra work. I have heard of a tuning company producing 210BHP from the VVC engine by this method. For the standard engine to remain 'reliable' at this level of tuning then other mods would have to be done, probably one of the reasons why this has not been done for the production engines. Maybe a VHPD bottom end and a VVC with modified cams would work

[Scarlet Fever]

Originally Posted by mike satur

Good explanation Andrew but not quite accurate , the VVC is not engaged all the time but is controlled by the hydraulic controller when certain parameters are met,RPM/oil temp.

Interesting, i didn't know this.

Originally Posted by mike satur

To my knowledge there has never been an issue with VVC cam wear and I have never seen any 'worn out', in fact the materials used are very high quality.

True, there shouldn't be any wear issues because the MEMS isn't running at full potential. I suspect that once Emerald start pushing the boundaries with thier new VVC map they will encounter some cam lobe wear issues.

Originally Posted by mike satur

With regard to further tuning of the VVC cams it would be possible to make higher lift and revised profile cams and IMO the actual VVC mechanism would be capable of the extra work. I have heard of a tuning company producing 210BHP from the VVC engine by this method. For the standard engine to remain 'reliable' at this level of tuning then other mods would have to be done, probably one of the reasons why this has not been done for the production engines. Maybe a VHPD bottom end and a VVC with modified cams would work

Yep, i agree 100%, the VVC system has a lot of untapped potential, but have you been reading the Exiges.com thread on VHPD engines, blueprinting and tolerances Mike? The basic gist is that following a really well researched article called 'KingK' none of the higher spec engines are balanced to the same tolerances as the OE spec items, in particular the VHPD engine and the steel cranks have come in for serious criticism. Forewarned is forearmed as they say...

I quote from the article 'KingK', by Simon Erland

Below is a table of crankshafts measured for dynamic unbalance – F3 forces, expressed in gram/millimetres from a number of makers manufacturing steel after market crankshafts for the engine as well as standard cast iron Rover crankshafts, as measured by Steve Smith of Vibration Free. Steve uses a machine and methods which are very much more sensitive than any used outside the in-house F1 operations. He works for a number of the best motor sport teams including F1, Cart, Nascar, Le Mans and also does some of the very fine work on satellite systems. Simply, his machine and methodology achieve a sensitivity that is not common.

Crankshaft - Initial level of unbalance gm/mm

steel crank make A n°1 - flywheel 773.5 - nose 313.8
steel crank make A n°2 - flywheel 754.8 - nose 334.7
steel crank make A n°3 - flywheel 764.3 - nose 328.4
steel crank make B n°1 - flywheel 747.3 - nose 106.9
steel crank make B n°2 - flywheel 783.7 - nose 362.0
steel crank make B n°3 - flywheel 748.7 - nose 301.7
steel crank make C - flywheel 693.7 - nose 307.4
steel crank make D - flywheel 227.1 - nose 68.2
std Rover iron crank n°1 - flywheel 80.3 - nose 22.8
std Rover iron crank n°2 - flywheel 79.3 - nose 11.5
VHPD iron crank n°1 - flywheel 360.2 - nose 25.7

Balancing and blueprinting are relative terms, all engines, Ilmor V10’s to Rover K Series engines are balanced and blueprinted to a specified required level. This level depends upon the engines use and its maximum speed of rotation. If an engine is outside its balancing tolerance it will vibrate – like an oscillating hammer, and the faster an engine rotates the more violent the hammering. Any rotating mass – crank assembly will do this, the tolerance simply reflects a maximum limit. <snip>

<snip> In other words all the steel crankshafts are at least 10 times out of tolerance for a standard engine and more that 20 times out of tolerance for an engine with a raised rev limit. It is a similar story for the flywheels measured.

The article is facinating reading, i confess that some of it went over my head, but i can Email it to you if you like. The author, Simon Erland, has done an immense amount of research and has links to the original K series designers (family connection apparently) - the basic conclusion is that the tuning companies who manufacture these items (through no fault of thier own) do not have access to balancing equipment calibrated fine enough for the K series (which appears to be particularly sensitive to vibrations due to it's construction).

[Scarlet Fever]

Link to Exiges.com thread for those who have a few hours to spare...

>> link <<

[Rob Bell]

Cam lobe wear is the problem I'd heard of Mike. Piper were attempting to develop alternatives - as you probably know - but nothing materialised from it.
The other problem with the VVC at high engine speeds has nothing to do with the crankshaft - but rather with harmonic vibrations within the VVC cams - which build, if what I've been told is correct - quadricatically. The whole mechanism is very likely to fall apart if reved beyond 8k...

I guess the lack of cam lobe wear on the VVCs out there could have a lot to do with the conservative grind that Rover/BMW decided to launch the engine with?

Why does the toyota vvt-i produce more power than the vvc with the same cc?

It has a little more power than the standard VVC - but check out the torque curves: the long-stroke K has a much stronger spread of torque than the peaky Toyota engine... Besides, it appears that it is pretty easy to get 180+ bhp out of the VVC with the right work - but you could rightly argue that the Toyota does this out of the box, so why doesn't the K?

Perhaps when S&R announce the engines for the ZRX and TFX we'll get an answer for this...

[col]

Originally Posted by Scarlet Fever

Anyway, this is my understanding of the situation.

no **** dude

pretty much how i see it, i read about it on the dutch sd1 owners site soon after i got my vi.

v-tec - 2 settings
vvc - infinately variable.

bear in mind honda engines and toyota engines are far better (imo) than rover's, hence the higher power out puts of the vvti and b18c, but only rover have been able to make vvc work... after all its a 1970's concept.


Col

[Rich Webber]

Originally Posted by bgunn

VTEC please, it's not a childs computer.


Brian.

thank you beat me to it


rich

[JonathanP]

childs computer???

[Stu]

V-Tech make childrens toys.

Far more complex than the VTECH in most cases

[JonathanP]

[TF160SA]

Originally Posted by JonathanP

childs computer???

My apologies never been a very good speller but that’s brilliant compared to my knowledge of children’s computers? why would you name a car after a computer?

he he seriously though Andrew does "It is a similar story for the flywheels measured" mean that you can't use aftermarket flywheels too or that they vibrate too? on that point doesn't ptp have a lightend flywheel for the k-series? (wow nice explanaition). is there anybody who has reliably "tuned" the vvc and at what cost?

[JonnyCoupe]

The VTEC most talk of was designed 14 yrs ago and cracked 100bhp/litre then as std. Variable lift yes please.

[col]

is ivtec different?