variable lobe camshaft

[thecheese429]

I read that Ferrari uses "3D lobe" cams, that change the valve timing/duration depending on engine speed. It is different from VTEC in that it is not just 2 lobes to chose from, but rather an infinitely variable change that shifts much the same way as VTEC. I read about it here.

Wouldn't "perfect" valve timing for every speed not only gain power, but also greater efficiency? What kind of applications would it be good for (other than high-performance engines)? Is there some place that custom fabs these for the more affluent engine-modders?

[GasSavers_JoeBob]

If only someone could come up with some sort of variable lift solenoids to operate the valves...infinitely adjustable lift and timing, and no camshaft or timing belt/gear/chain to deal with.

[VetteOwner]

Originally Posted by thecheese429

Wouldn't "perfect" valve timing for every speed not only gain power, but also greater efficiency? What kind of applications would it be good for (other than high-performance engines)? Is there some place that custom fabs these for the more affluent engine-modders?

in theory yes it would. and yea the solenoid idea would work but solenoids are "slow" (building and collapsing of magnetic forces) watch the mythbusters episode where a fired bullet will hit the pavement the same time as one dropped from equal height, they had a hell of a problem trying to get the bullet to drop when they fired. well a solenoid is essentially an electro magnet that shoots a metal rod either forward or back.they work great for what thier used for but would switch too slow for valves...

[theholycow]

Originally Posted by JoeBob

If only someone could come up with some sort of variable lift solenoids to operate the valves...infinitely adjustable lift and timing, and no camshaft or timing belt/gear/chain to deal with.

I could swear that such a system was already in production cars by either BMW or GM but I can't find any record of it.

Interesting reading at http://en.wikipedia.org/wiki/Variabl...mplementations though.

The slow solenoid issue could probably be ok as long as you trigger them a little early, unless they're too slow to cycle fast enough.

[bobc455]

It sounds like Rhoades lifters on steroids.

Actually there is a huge amount to be gained just by messing with the cam timing. If you could change cam timing on-the-fly, you could have a very efficient engine when desired, and a screamer at WOT.

I heard discussions of hydraulically controlled valves a few years ago, which could be completely computer controlled, but I have heard nothing on those for a few years now. (Maybe they've become mainstream and I haven't even realized it...)

-BC

[VetteOwner]

Originally Posted by theholycow

The slow solenoid issue could probably be ok as long as you trigger them a little early, unless they're too slow to cycle fast enough.

yea thier just too slow at cycling magnetic fields dont disappear and regain instantly so your gonna hit a limit eventually then either its going to start stalling or bend valves lol

[JanGeo]

Yeah there is a lot of power involved in moving them little valves up and down quickly. It's why the timing belt / chain is so big. If you had rocker arms and moved the pivot point between the valve and the cam lobe you could get variable lift and then just vary the timing with an adjustable gear like Toyota does on the VVT engines - electric controled hydralic gear timing. I don't think lift is critical as long as there is plenty of lift all the time there isn't much need to vary it.

[i-DSi]

Originally Posted by JanGeo

I don't think lift is critical as long as there is plenty of lift all the time there isn't much need to vary it.

Play with lift height has some advantages:
- less engine noise
- less power losses in the valve movement
- better 'swirl' for the mixture (opening is a smaller and mixture 'crashes' on the valve).

It's indeed not critical but an advantage if you're looking for an efficient engine.

[i-DSi]

Originally Posted by theholycow

I could swear that such a system was already in production cars by either BMW or GM but I can't find any record of it.

You are right. BMW has such a system. They don't even need a throtlle valve any longer! All is done by the openingtime of the valves.
They have it for certain in the BMW 116i (and in other cars/engines).

[theholycow]

I remember the bit about the throttle! Good, I'm not completely crazy.