5 valves / VVL ???

[urtz]

Why with 5 valves/cylinder we can´t manage VVL??? is there any real technical reason?

[Daffyflyer]

Yup, the amount of stuff you need to run VVL (extra rockers etc.) won't fit in a 5 valve head as the 3rd intake valve is in the way

[urtz]

but, at REAL engines is it possible? i´m not an expert of mechanic

[Daffyflyer]

I've never seen it done, at least not with the kind of cam lobe switching VVL like VTEC or NEO VVL, I don't think Fiat's Multiair or BMW's Valvetronic will do it either, as they all take up a lot of space and would be really complex on 5 valve heads

[darkjedi]

VVL requires a big cam lobe in between the normal cams and at idle it would still hit the center valve. also the 3 valves are not aligned.
Audi's latest 1.4 unit has the lobes on 2 of the cylinders move out of place to disable them, running the engine on only 2 cylinders at idle and low power loads to increase fuel efficiency

[urtz]

ok, normally, i can see a car at streets.... and if i see, for example... 20V (inline 4)..... that engine looks like better than a 16V.
But now, at game... i see i can manage the VVL values in a 16V i4 engine... and get a better engine and more power than a 20V.
And there is where arises my dude.

[Daffyflyer]

Note that for example Toyota went from the 20V 4AGE (1.6, 118kw) to the 16V 2GZZE (1.8, 140kw) seemingly so they could run VVL and get more power out of it, so 16V with VVL can indeed be better for power than 20V.

[vfreire]

this seems to be the reason why audi stopped producing 20v engines for most models.

[darkjedi]

audi never used vvl systems. they gave up on 5 valve configurations because they were complicated and the heads had a tendency to crack. also they switched to roller equipped rockers DOHC systems that are take up more space and would not fit an extra valve.

[RobtheFiend]

Maybe use Porsche Variocam Plus.
This system uses no rockers, instead the lifter has a sleeve around it that is activated by 2 narrow (and more agressive) cam lobes.
At low rpm the sleeve and lifter moves independently, but at high rpm they are locked to each other so the more agressive cam moves the valve.

[xABSOLUTIONx]

quickly looked up Porsche system, looks way too complicated to be used in day to day cars

[darkjedi]

Porsches are day to day sports cars and variocam is more like a vvt than vvl. it has 2 lobes for 1 valve and at high rpms it moves one of them backwards to increase duration...besides having variable timing.

[xABSOLUTIONx]

VVL is Variable Valve Lift e.g. VTEC and Porsche system you mentioned (2 lobes on cams and all)
VVT is Variable Valve Timing e.g. VANOS, i-VTEC

speaking of VTEC, 1gen and 2gen is purely VVL and 3gen which is i-VTEC introduced VVT into the bunch

correct me if im wrong

and don't forget, they engage at certain RPM, i have no idea what will happen to that engine after going lets say 1000km in VVL
Porsche has made and still makes bulletproof engines, no doubt about it, but still, i have my concerns

[darkjedi]

yes . what you`re saying is correct except for porsche's variocam. lift does not change like the vtec system. instead 2 smaller lobes push the valve together at the same time at lower rpm. as the engine requires more air, one of them rotates back a little, increasing duration, not lift. therefore it's VVD.
usualy a manufacturer like porsche and honda will test their engine running max rpm under load for very long periods before selling them. they should last at least 150.000 km at full power.

[RobtheFiend]

DarkJedi, I have no idéa what system you have been reading about.
The Porsche Variocam +, is the normal VVT plus it has one lifter+one sleeve per intake valve, the cam lobes for the sleeve is higher lift and more duration.
Thus giving the same result as the original VTEC system. Nothing else.

In essence, a combination of Vanos and VTEC.

http://www.youtube.com/watch?v=tAITcaNP8GM