Stupid Idea Time: Two cam profiles at once

"If only EssExTee could be so grossly incandescent" (essextee)
08/18/2014 at 23:41 • Filed to: None

When you have multiple intake and exhaust valves (see: all modern engines), each pair will run off the same cam grind, right? What would happen if say, one intake valve used one cam and the other used a second cam with a different shape? You'd essentially be running two different timings at the same time.

You could have one valve optimized for low RPM performance, and the other for high RPM. You'd have the best of both worlds, without the added complexity and weight of a VVT/VVL system. Of course it wouldn't be as efficient as VVT/L due to only having one valve optimized at a time instead of two, but it would be a lot cheaper to implement.

DISCUSSION (11)

Jake - Has Bad Luck So You Don't Have To > If only EssExTee could be so grossly incandescent
08/18/2014 at 23:43

Wouldn't they just average out, more or less? I don't see the advantage of this.

If only EssExTee could be so grossly incandescent > Jake - Has Bad Luck So You Don't Have To
08/18/2014 at 23:44

I just edited the post as you were typing that.

Frank Grimes > If only EssExTee could be so grossly incandescent
08/18/2014 at 23:45

Wouldnt the best cam profile be the best for either valve? would one run at differnt speed opening the valve at a different point in the stroke?
What would be cool would be to get rid of cams and use pneumatics or something so the cam profile itself could be variable as well as the timing of the valves.

Ramblin Rover - The Vivisector of Solihull > If only EssExTee could be so grossly incandescent
08/18/2014 at 23:47

Except for promoting cross-valve swirl, this is not meaningfully any different than having a single profile that's an average of the two. Now, if you've got two stages of induction system that have pairs of runners to each cylinder, there might be a reason - a tuned stage/valve profile that will pass more air than its brother at X rpm, and less at others... Ultimately, however, there's just too much bother, particularly for a single inlet feeding two valves. The swirl enhancement would only be significant at low to mid Rs, or situations also known as "you don't need two valves on this engine, you idiot".

If only EssExTee could be so grossly incandescent > Frank Grimes
08/18/2014 at 23:50

That's the point. One valve timed/profiled for low RPM and one for high, instead of a complicated and expensive system for changing all that on the go.

JGrabowMSt > If only EssExTee could be so grossly incandescent
08/19/2014 at 00:07

If they're controlled by a set of hydraulic lifters, you could effectively disable whichever profile you didn't want based on load. Run 2 valves around town, and all 4 for better flow under higher speeds. Or a way more aggressive cam for higher speeds, and a very very mild one for idling around town.

Completely overcomplicated though. It's very similar to the MDS system in the HEMI engines. Complicated, but also pretty successful, which is a good thing.

wabbalosthiskey > If only EssExTee could be so grossly incandescent
08/19/2014 at 00:21

But if you are running both of these profiles in tandem, then each one is defeating the other. You don't get the best performance by just having the valve open and long and as far as possible all the time, which is what you would have. The valve timing needs to be able to vary across the RPM and load range to be optimally effective.

John Bulzacchelli > If only EssExTee could be so grossly incandescent
08/19/2014 at 01:13

At low rpm and load this actually has some value - it produces more swirl and allows you to run leaner or more EGR for emissions and economy. At higher engine speeds though, you would want to be able to open both valves as much as possible.

Look at some of the early Honda VTEC systems - they essentially operated on a single valve until the cam switched. The other valve would open just enough to prevent fuel from puddling on the back of it.

samssun > If only EssExTee could be so grossly incandescent
08/19/2014 at 02:07

At any given RPM, you'd still have one valve optimized and the other not, so it would probably be about the same as just averaging the two. Still waiting to see solenoids become practical for true infinitely variable valves. Paging Mr. Koenigseggisseggggnignigsegigisegggg.

tc_corty > If only EssExTee could be so grossly incandescent
08/19/2014 at 08:24

I looked at it two ways:

Where the second valve opens less compared to the other. In this case you'll be improving flow at lower lifts. The lower lifting valve is helping until it reaches its max lift, at which point it hinders max flow. This seems an improvement over 2 valve heads, but are you getting the max you can out of the addition of the extra valves?

Or flip it around the other way and think the valve that is opening more, is improving flow at peak lift. When compared to two valves (of a 4 valve head) following the same cam profile. It is only improving it when you look at it as if you made one valve open more. But once again are you getting the most bang for buck.

It works if you look at it as one valve opening more than the other, or if you had one valve opening a little to help improve low lift flow. But looking at them in one picture they're both hinder each other in a way.

Would be better to keep both valves opening at the max amount. Then port the bowl, get a good seat cut, de-shroud the valves etc to improve flow at low lifts and also possibly high lift flow, depending on porter but normally improvements can be made at all lift.

I'm no expert but this is how I'm thinking about it. If someone of experience knows more I'd be happy to listen and learn. Hahaha and hopefully you'll understand, pictures and hand gestures help lol

davedave1111 > Frank Grimes
08/19/2014 at 15:40

Get rid of cams? How about variable shape cams? So many nutty possibilities.

Alternatively, if we are getting rid of cams, I want piezo-electric valve activation.