Thread: The end of the road for VVL?

Well his method uses the original ramp angle to open and close the valve. That's the great part about it. What it effectively does is add meat to the cam at it's maximum lift. I don't think it affects the valve spring because it's not altering the ramp angles at all. All it does is instead of holding the valve open at max lift for a few degrees (as a standard cam would), it now "holds" it at max lift for a significantly longer period of time. With the lobe specifically designed for the engine it's being applied to, this means you won't have a power curve which peaks and then falls off, but instead you get the maximum performance that the engine can deliver at every rpm. The only constraint seems to be the ability of the other engine components to hold this power and function up to the rpm you want to rev to.

From what I gather he has run the cam in a suzuki 250 bike engine. IIRC he gained something like 40% power with lower fuel consumption. But I just scanned through the site as I'm busy prepping for exams right now.

The thing is duration is great, but there is no way to change lift... so from a performance standard (which is really all we care about) I don't see it being super useful, especially with interference engines.

good point

Lift isnt' the only way to get air into the engine. I'd rather have the valve open for 30 degrees at 12mm lift than for 5 degrees at 13mm lift.

The lift will give you gains at a certain rpm. Having variable duration will give you gains at every rpm.

The interference thing is a limiting factor I agree.

Yah I have to disagree. Duration is great and all, and variable duration is even better for many, many reasons. But variable lift is more appealing to me from a performance aspect, and obviously variable lift and duration is the cat's pajamas. If I had to pick one, I'd rather have variable lift and fixed duration, not the other way around. With variable lift you can just have the fixed duration very large, and the lift can determine how much air you get over that large duration, including no air (effectively shortening the duration or overlap).
With variable duration the best you can do is make the lift aggressive and then...

Wait a minute.

I'm thinking of variable cam phasing, not variable cam duration. You have a point that variable duration is probably one way to skin the cat. Make the max lift very aggressive, but control general air flow and overlap with the duration. Not a bad way to do it. I still think variable lift is maybe the better option just because you don't have to work with extreme ramp angles like you would with a "performance" variable duration cam in certain configurations. At least the one I'm imaging in my head.

I hate poppet valves though, so cams in general piss me off. :o

yeah theres no right or wrong its all prefferance but i feel theres not much performance options with this

Ben your second last sentence is a bit confusing? I think you meant to say you prefer variable duration as it will have friendlier ramp angles?

I know the natural tendency is to be in favour of lift. But unless you can have Continuously Variable Lift, then Continuously Variable Duration will have to win. Obviously both, combined is the ultimate.

The one advantage variable duration has over variable lift is that you can run very high static compression ratios as the guy mentioned in one of his vids. The dynamic or actual CR is then controlled with the variable duration. I do think that this sort of cams and any form of continuously variable ANYTHING is gonna have a big knock on effect on things we think we have sorted right now, like optimal valve sizes, intake designs, headers etc etc.

I did have a wrong term in there that I've corrected. Maybe that's what you're getting at?

In my head, a variable duration system would have extremely aggressive ramp angles, or ultimately extremely fast valve opening and closing speeds if it is to achieve performance aspirations. The amount of air you get would be determined by the duration at max lift. Only need a tiny bit of air? Open those valves fast and then close them fast right away. Need a lot of air? Open them fast, keep them open for a while, and then close them fast.
That's how the system in your first post would work in a performance car I believe.

See how it would have to ramp up quickly?


In a variable lift scenario, you have to lock duration so you pick a very long duration so performance characteristics can be there if you need them. And then you control lift for the amount of air. Need a little air? Don't lift the valve for the first 1/4 of the duration, open it a tiny bit for the middle 2/4ths of the duration and then close it for the last 1/4 of duration. Want a lot of air? Open it all the way for the entire duration, but you still get to control how quickly it opens (and closes) so you never have to deal with ultra aggressive opening/closing speeds if you don't want to.

In the new Ford 302 twin cam and BMW M3 twin cam 4.0L the cams have variable timing (vanos in BMW parlance but the systems are similar) and they move the cams up to 50 degrees relative to crankshaft. I think this helps with emissions but it also effects performance. The 4.0L BMW is advertized at 416 and I have seen it on the dyno. It makes all of that. The 5.0L (Boss) is rated at 440ish but I haven't seen it on the dyno yet.

The concept of these cams are completely different to Vanos and VVT systems.

VVT changes the cam/valve timing. It will advance/retard the cam so that the valves open earlier or later, but the duration of time the cam spends at max lift remains constant.

These cams do what VVT/VANOS does, but at the same time it also extends the period of time that the valve spends at maximum lift.