Scottish Elises

Can any good technical people explain to someone who knows nothing about engines (i.e. me) what the VVC in the 111 k series, and the VVTi in the Toyota engine actually do, i.e. how they differ from the standard engine, and/or from each other.
Also, what about having a second cam in the Toyota engine; is this related to the above; what does a 'cam' do anyway, and how does having two result in more power.

And while we're on the subject, is the VTEC in Honda engines similar to any of above?

Wikipedia is your friend

http://en.wikipedia.org/wiki/K-series

http://en.wikipedia.org/wiki/VVT-i

http://en.wikipedia.org/wiki/VTEC

Also how cam shafts work
http://auto.howstuffworks.com/camshaft.htm

Hope it helps

Vtec, VVC, and VVTiL are all species of the same thing. Other than that, I'd direct you to wiki. Too many questions in there to be answered in a post (and I'd probably get 50% of it wrong )

VVC is constantly variable valve timing.
wheras
VVT changes at a certain engine speed hence the kick you get.

Rover showed an engine (on the same day they went under) that had no cams looked really good too, I wonder what happened to it...

Read some of that techhy stuff - think I've got the basics:-

In a basic engine, the cam shaft is covered in lobes that, as it turns, operate the opening and closing of valves (which is what affects the performance of the engine.)

Any particular cam profile provides optimimum performance only at a sepcific RPM, so is therefore a compromise at all other RPMs.

These VVC, VVTis, etc. offer different cam profiles at different engine speeds, and so can deliver better performance.

So ignoring the fact that they're two completely different engines, what would be a 'better' feature - the constantly variable element of the K, or the 'kick' of the Toyota.

Interesting Honda vtec article here http://asia.vtec.net/article/k20a/index.html

You'll get more power out of a system that alters valve lift as well as timing (like VTEC and VVTLi) The constantly shifting timing of the Rover system makes it smoother (no kick) but doesn't actually produce as much power as the valve sizes could allow (the VHPD ports and valve sizes are exactly the same as a VVC)

Lift is a bit of a red herring though. Once lift reaches 25% of the valve diameter you are at 98% flow anyway and increasing beyond that is not useful in itself.

Most high lift cams also have long duration, and it's the extended duration that is required to improve volumetric efficiency at higher RPM (at low RPM you would actually like reduced duration).

High lift cams cause other problems with valve acceleration (if they're going to lift more and sooner, then the valve must accelerate quicker).

I suspect the lift adjustment in the ivtec and vvtli engines is there to allow low lift at low rpm/engine speed and "normal" lift at high load/engine speed.

In it's second incarnation the VVC engine made nearly 160BHP which is pretty respectable for single throttle body and crappy standard exhaust manifold.

The PTP165 kit using the same manifolds makes more at the expense of being very lumpy and a bit peaky (relatively speaking).

Cheers,
Robin

Of course, the ultimate is a system where each valve is worked using an actuator of it's own and then you'd have infinite control over lift, timing and duration at all revs. It's being worked on.... (although we really need the tech to catch up on the idea, with this one)

Shug wrote:Of course, the ultimate is a system where each valve is worked using an actuator of it's own and then you'd have infinite control over lift, timing and duration at all revs. It's being worked on.... (although we really need the tech to catch up on the idea, with this one)

Renault, who came up with the idea of pneumatic valves, are working on an electromagnetic system that works with no cams or valve springs... Dont know how far down the road they've got though but it'd be pretty ideal for controlling lift and timing via the ecu.

Problem with electro mag systems is their rest state lets go of everything. there is an electro mag suspension system which is fantastic, runs on linear actuators, agile, responsive, etc, but when the power is switched off the car drops onto its suspension bump stops....

http://www.powertrainltd.com/rel_archiv ... 405ptl.htm

http://www.camcontec.com/datasheets/Dat ... motive.pdf

The rover/Camcontec system looked really good it only used power on the switching cycle