How does someone determine whether or not you may get PTV problems with a cam? Has it become rule of thumb, an equation of some sort or do you always have to measure?

Considering cams, milling, push rod length and various gaskets....

Oh my....

 

Well, this would simply have to be an overlapping plot. An easy venture but would necessitate information that we do not have.

We can all plot piston position relative to crank angle. Simple trigonometric function that defines the slider-crank mechanism.

But to plot valve position relative to crank, that is something entireley different. We have to have insight into the mindset of that profile's designer. What was the objectives. What was the limiting factors of loadings due to accelerations, masses, spring rates and harmonics, seat and valve material properties, etc.....

There are several functions to use in order to create a cam profile, the simplest to imagine is the sine curve. This is not the best choice, as the acceleration is inconsistent (it too is a sine curve). Acceleration should be a constant value maximized to get the most accomplished at the minimum amt of time. Therefore we would want a set value, right? But what about seat impacts?? Loft, or the unfortunate event of the rocker leaving contact with the valve?? Adjustments have to be made. It would be best to change the function at the peak lift, as valve rise event and valve fall actions require two different sets of considerations.

If, however, we did have these two plots on a graph, with the appropriate inital distance between them set, we could.

Who's with me?? Fun Stuff!!!

Qn?? Do i crack into the advanced forum with this??

 

You could do it, but the cam information typically provided won't allow for it.

 

Sideiki, these fragmented functions are proprietary.

we could, however, Cam Doctor the hell out of one... reverse-engineer??

 

Or you can slap everything together and turn the engine over by hand, and if it stops, you have PTV problem

This is interesting, I am sure there is a formula out there or its plausible to come up with one.

 

The advantage of a "before" calculation would be selection knowing flycut would not be necessary.

 

Let me summarize what you just said:

Better measure

 

The actual experimentation of something as simple as interference is absolutely the best way. Validation is an irreplaceable step.