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Determining valve event when knowing duration LSA?

Cranky

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Can valve events be determined when you only know what the lift, duration and LSA is?
 
Great question Cranky...Gee...lets look at this;

By knowing:
"LIFT"
"Duration"
And "Lobe Seperation"....

1. Lift means "lifting the LIFTER" up.
So, if you know LOBE LIFT AND the Rocker ARM Ratio...then you have a better picture as opposed to just knowing the "LIFT"

2. Duration: Simply put "how long the cam keeps the valve open" IS THIS AT 050" ?

3. Lobe Seperation: Most of us understand "basic" LSA factors. Differences between "WIDE" seperation and "NARROW" seperation, choppy idle, less vacum, Broader power spectrum, valve overlap etc.

So, with the above factors above I would say YES...
Perhaps a DYNO spec software program can help you determine the "specifics"

But it IS plenty of info, I personally do not know how to do it.....

Check out this site: facultyfiles.deanza.edu/gems/.../Chapter174Valveeventscamterm.ppt‎Cached
 
Got to be some cam gurus here......?
 
Well, you'll be needing cam angle (of rotation) and cylinder number for sure. Otherwise, you'll have no reference.
Gravy would be to relate that to crank angle too.

Edit: Or or were you thinking less about dynamics and more about total lift, overlap, etc? I also agree that effective rocker ratio (as opposed to statistical/theoretical because geometry can change with build specifics) is critical information.
 
I read this after giving it some thought. Now it's got me thinking!
http://www.mechadyne-int.com/vva-re...ation-on-engine-performance-and-emissions.pdf

That is why I "THINK" with:

LIFT
Rocker Arm Ratio
Lobe seperation Angle
AND
Duration.....
Valve Event can be determined....

I dont believe CENTERLINE is or should be a factor simply because CENTERLINE is not static by a Dynamic feature of the set-up/build.

My suggestion is to:
A) Call CRANE,COMP-CAMS or LUNATI Tech Help
OR
b) Purchase or Down Load a DYNO type software program.
 
But events are relative to piston position and thus the cam to crank phasing is the missing piece of the puzzle. I mean, sure, you'll know when in cam rotation each event will occur. But the "crux of the biscuit" is in valve event timing with respect to TDC or BDC and that is what drives torque higher/lower on the RPM axis. Or do I got more thimkin' to do?

You can always get an adjustable timing gear set and get real gone with it!
 
if you know the duration divide it by two and subtract the lsa for the opening. opening plus 180 subtracted from the duration will give the closing.
 
Haha! He's balancing turbomolecular pumps that spin at 57,000 RPM.

This is an interesting question for sure! I'm going to say you can only get an approximate answer and that won't be accurate enough data to base any real decisions from. The lobe profiles are probably very similar if you looked at 20 different cam grinds in that same, say, 270 deg range and likely they are all very similar. But even between 20 different grinds you can have very different results (as we all know). Some cam companies like Lunati may cheat by closing the valve as soon as possible to build some cylinder pressure then rely on a fast rate upon opening to fill the cylinder. That might be what I'd call an aggressive lobe profile that builds great power but also requires a lot of spring to keep under control and with that comes increased wear. But that's a different topic.
 
Last edited:
That's reality for ya, Meep-Meep.
Hey, can I get you to pull a hard vacuum on my RV-2 AC?
;)
 
So;
Am I (Or We) to assume that Cam Event is totally Dynamic?
Another words never a "Constant" but always changing?
The Delta is dynamic?

It cant be theroritical...it has to have specifics...
 
It's only dynamic based on the different grinds. Once you pick one and shove it in the hole it is what it is. Well, unless you factor in a torsional twist and how that relates to the valve events but that would be virtually impossible.
 
Meep-meep touched upon a really good point. Duration does not have to be equally split on either side of the lobe's apex. Lobes could not only have a different rise/fall slope, they could even be physically asymmetrical. Nothing says a valve's open/close events must be centered about the point of maximum lift.
 
Can valve events be determined when you only know what the lift, duration and LSA is?

No, they can be approximated, but the lobe profile will determine everything between the base circle and maximum lift.
 
Thanks for the replies!! I'm no cam guru for sure but do understand some of the aspects of how they work. A lot of people post about what cam to use and see them posting lift and duration numbers but never valve events. I know that can change when advancing or retarding but if the cam valve events is stated according to recommended installation on the cam card, a good idea of how an engine will run can be derived based on valve events, right? Of course the engine needs to be built accordingly for a particular grind but it looks to me like if you know just the valve event timing, then all the other numbers can be figured out? One of the first things I look at is when the intake opens and closes and that generally tells me if I want to look further into that particular cam or not.....
 
Yep! I'm no guru either but from what I see far too many people are hung up on lift. It's more important to note when the intake valve closes and you start building cylinder pressure as well as the LSA (or overlap). The overlap spec is huge when it comes to street drivability. If you go big on overlap (short LSA like 108) you make more peak torque but at a higher RPM. Close the intake valve later and take advantage on the inertia to fill the cylinder and you suffer more drivability at low speed. Duration is interesting and not sure if I can totally correlate that spec as a low number = street car. The stock Road Runner cam seems to be a fairly high duration number but it runs like a bone stock cam with it's wide LSA.

As a data point I built two engines as identically as possible. One is my 440 in the green Bel and the other is a 426W in my orange RR. The heads are both big valve 915's and the cams are the same and installed within a few degrees of each other - like 3-4 IIRC. Other than the bore size the difference is the 426 has .5 point less compression (10.1:1 vs. 9.6:1). Cranking pressure on the 440 is 190 PSI and on the 426 it's about 170. I need to test the 426 with the same gauge as I used on the 440 to eliminate one variable. Once I start driving the RR it will be interesting to note if I lost or gained anything. So far tooling around the compound it feels pretty crisp and I've lost nothing but a high compression headache.

As a side note - and sorry for the minor diversion - I had a huge pinging problem with the 10.1:1 440 using the stock intake and a 750 AFB (but it ran like stink with a splash of race gas). I since put on a TQ with the basic Edelbrock performer (the one with the more squared off runners like you'd find on a truck) and it runs really well and no pinging on pump 91. With this bit of info I'm willing to bet my previous pinging problem was due to poor fuel distribution to at least one cylinder. No track results yet but if I still get at least 12.80's @108 with slicks then it's a step in the right direction.
 
Sounds great Meepster!
Thanks for the CAM info concerning Valve Event.
-Glad you solved the PING issue (PRE-DETONATION....YIKES!)

I agree with the Wide LSA on that car...I am FAR from a CAM guru...but as with everything in this HOBBY...
READ, READ AND READ MORE...
 
The whole thing is a catch 22. Yep. Read, read some more and collect data. Note my signature line!
 
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