Okay, it's off topic, but if I post it in "off topic" no one will take it seriously.

I was thinking that instead of having two or three cam profiles to choose from like in a honda VTEC, you could have an continous amount of variation if you make the cam profile a 3 dimensional surface (instead of flat lengthwise) and then slide the cam in and out. Here's an artist's (ASCII artist )conception of the profile of such a camshaft, when viewing just one lobe from the side:

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The horizontal line is the axis of the camshaft. The bottom is flat, so that the valve will close all the way no matter how much the camshaft is slid in or out. The top changes, because if the camshaft is slid so the lifter follows the left end it is high lift and if the lifter follows the right end the lift is very low. The biggest draw back is that there is no way a conventional roller lifter can follow the cam, since it is sloped. That's why I gave up on the idea when I thought of it a few weeks ago, but I since found out that Ferrari actually uses it in real life. I don't know how the heck they can, and I haven't found anything on the web. If you had a ball bearing at the end of the lifter it would work, but then the point of contact is incredibly small.

Just think of the possibilities: At the small end you'd have a stock cam lobe profile (or even lower lift and duration), and at the big end a 235/235 .570/.570 108LSA. You could have a redline at 8000rpm, and make power all across the rpm range, with a engine nearly identical to a stock LS1. Just this special cam and the mechanism to slide it in and out are necessary.

If anyone knows about the ferrari engines that use a similar set up, please point me to the web link.

thanks.


[Modified by Miles in Michigan, 8:42 PM 8/13/2001]

 

You will need a new design in lifters...They pretty much cover the whole cam lobe. So moving it in and out wouldn't be effective. Then the other is cam journals would have to be bigger. I think a whole new top end design would be necessary.

Tony

 

That's a good point. I had assumed that there is enough space between lobes to enlarge the cam journals, so that the cam could slide forward or backward an inch.


The heads wouldn't have to change at all, beyond valve springs that could handle higher lift and faster ramp rates. Assuming the new lifters would fit in the place of the old ones, and the cam journals could be enlarged enough, and the cam gear could be made stationary as the camshaft slid in and out, and a hole could be bored in the back end of the block so that the camshaft could extend out the back to a mechanism that'd push it in and out, it should (in theory) work. Not that this is something someone could modify on their own car. I meant that GM could implement this in a year or two, if they don't end up going to electro-hydraulicly actuated valves.

Here's a pic I found online of the ferrari system:

 

Or you could.....

 

Too cool Shawn! :cool:

 

I am a little late to this conversation, but this is an idea that has crossed my mind as well, both for DOHC as well as pushrods.
Today, in the 2020's, we likely have the materials necessary to reduce the lifter's bottom cross-section so that the lobe could effectively slide on it.
How low of a contact area we could get away with, I am not sure. One would need a tool to simulate the stresses.
Perhaps, a method of supplying oil, under pressure, through the center of the lifter could help... or maybe it could not.

A more viable method, I think, would be to use the biggest cam possible, and then control the effect of the cam on the valve via 3 different rockers.
Today's materials would be there to help us reduce the rockers' sizes.
One simple(ish) way to go about it would be to have 3 rockers with different geometries side by side.
On the low end of the RPM range only one rocker is active, mid-range the second rocker is active, and so on.
One way to activate each independent rocker would be to use a fourth rocker (this is getting complicated and expensive) or a transfer bar mechanism or a rotating cylinder. There are many ways to skin this one.

Another method, perhaps with more potential, would be to have a shaped pushrod running through the middle of a small pinion. That small pinion rotates via a rack, thus rotating the pushrod, thus allowing the pushrod itself to control different arms at different times. This would increase reciprocating mass.

In summary, there are ways to do it, I am sure. What I am not sure about is if such systems would be worth the extra mass, and most importantly, the extra cost.

 

You guys are about 60 years late to this discussion.