variable valve lift

[KnifeEdge_2K1]

my idea is instead of a direct connection between the lobes and the valve actuators have a very stiff progresively wound spring in place, at high rpms more force would be exerted onto the spring changing the amount of lift for the valve

this wouldnt do anything to valve timing, its valve lift im concerned with right now

any valve timing system can be implemented with this system because they're independent of each other

patent pending

[pimento]

Springs wear out and go slack though...

[Rob Mann]

sounds like it could be a good idea but as PIMENTO said springs would wear out very quickly when subjected to the force of an engine under load. there are also many other problems such as the design of the rocker arms, these would need to be addresed becouse of the changes in cam lift. also such a system would be very costly to manufacture compared to currant technology and would also need much more maintanence.

[BjD]

Don't think it'd work too well tbh. You'd end up with the valve mounted between two stiff springs, and yes, you would get a variation in the valve lift, but it wouldnt necesarily be in phase with the cam. You conouldnt accurately control when the valve is opening.

[Rob Mann]

the best systems that i have heard of are from bmw they are the valvetronic and vanos systems.

[jcp123]

OK, one question: Why wouldn't you just want as much valve lift as you can get?

Lift = how much torque
Duration = where the torque comes in

By that rule of thumb which I have heard tossed around more than a few times, and according to the Engine Analyzer 3.0, I have always thought that having the most lift you can pack into a given duration is always advantageous. This does seem counterintuitive to me (I'd think that it would hurt low-speed intake velocity)...but I haven't heard anything otherwise, either.

[Rob Mann]

the more valve lift you get the more you have to solve problems like valve float.

[jcp123]

I see...so then, you're trying to decrease the lift at higher revs?

[PerfAdv]

Long duration and high lift are best taken advantage of at high RPM, when there's a lot of fuel mixture to move, also helps in the scavanging effect to pull in fresh fuel. The way I understood it was high lift and >duration are for high HP and not torque. Such a motor would have a distinctive lope at idle and not be at its best until wound up. Also to take advantage of the more radical cam you'd need harder springs, which will control valve float at high RPMs. This setup will wear out sooner than one built for lower RPM operation with shorter duration and lower lift.

[jcp123]

I know that fundamental theory, that's not really what I was asking. I was assuming that this system progressively increases lift as revs go up, which wouldn't make sense to me, as you'd want maximum lift for whatever duration you're running (be it conservative or more radical); it's the duration that you'd most want to up as revs increase in order to keep the torque from falling off. So basically I was confused why you'd concentrate on just increasing lift as opposed to duration.

[Rob Mann]

i agree there's no point just increasing lift by a lot just on it's own

[BjD]

At lower RPM low loft will help increase the intake air's velocity, and induce some turbulence. That helps it all burn cleanly, but then as revs increase low lift limits the total amount of air you can draw in, so for the best of both world you need a variable lift system.

BMW's VANOS is pretty good at that, if a little complicated. On an aside variable lift also has the posibility of removing the throttle, if you can have full and accurate control over lift

[Matra et Alpine]

the best systems that i have heard of are from bmw they are the valvetronic and vanos systems.

FANBOY ALERT

[jcp123]

At lower RPM low loft will help increase the intake air's velocity, and induce some turbulence. That helps it all burn cleanly, but then as revs increase low lift limits the total amount of air you can draw in, so for the best of both world you need a variable lift system.

BMW's VANOS is pretty good at that, if a little complicated. On an aside variable lift also has the posibility of removing the throttle, if you can have full and accurate control over lift

OK then, thanks. That makes more sense to me, since of course less lift would increase the intake velocity. But I had never heard anyone say that categorically, which is why I was confused.