Anybody check actual valve timing events?

[BAracer]

On a typical rocker arm V-8, it's most common to degree in the cam by taking your lift readings directly from the lifter. Does anyone have any specs taken from the valve, to correlate to the lifter numbers? Preferably something with a 1.7-1.9:1 rocker ratio.

[Erland Cox]

You can find that in Competition Cams catalog with durations at various lifts,

Erland

[DaveMcLain]

It would be very easy to figure out where the events occur with different rocker ratios. Say you use the .050 cam lift events and then multiply .050 by your rocker ratio. Say you're using a 1.5 ratio rocker .050 becomes .075 theoretical lift at the valve. Take that value and divide by the new rocker ratio to see where on the cam you have the same lift at the valve. In this case a 1.9 rocker gives you .075 at the valve when the cam is only at .0394 lift. Use this lift when you check the duration on the cam to see how much it changes.

[Adger Smith]

You have got to be kidding. What does the engine see? The cam bumping up and down in its little hole in the block or the valve action created by the cam, lifters, pushrods and the rocker arms? I could care less what numbers are on a cam. To me they are just there to identify the cam and be used as a starting reference point. I DO care what is happening at the valve and how those cam numbers end up generating a lift curve. In the old days I had to plot valve movement with a degree wheel and indicator, then draw a graph. Today I do it with an rotary encoder and electronic scale all hooked to a computer that can draw a very detailed graph of what the engine sees at the valve. I'm not the only guy in the country doing this. Please remember that all the numbers in the catalogs and spec cards are theoretical. They are theoritical Due to the variations in geometry. You can't say going from a 1.6 to a 1.7 ratio rocker always produces the same lift curve in every engine. I've checked rocker geometry that was supposed to be good and found it had dips and flat areas in the lift curve. The valve couldn't possibly follow a profile being generated by that bad geometry. If you ran the engine like that it wouldn't make the springs very happy, either.
BTW in 1969 I went through 242 Chevy rocker arms to get 20 that matched and produced the correct lift curve. My chevy parts man loved me after I returned all those "out of spec" rockers. :~)
Short answer:
Get some good measurment devices and check everything at the valve. You might find a few problems you didn't know you had and pick your program up a notch or two.

[DaveMcLain]

So then the real question might be, how much difference do you have to see before it makes any difference in the performance of the engine? Do you check it with the cam fully loaded or only one valve at a time? Does the fully loaded cam behave the same on the engine stand when turned by hand as it does when the engine is running? A lot of questions and a lot of stuff that probably doesn't make much difference or does it?

[#84Dave]

Good grief Adger! I thought I was the only guy around that set up the cam in a V-8 engine at the retainers..... with lash. And all springs actuating all valves...... with lash. -Dave-

[BAracer]

Adger, you are checking things more along the line of what I'm talking about. I'm trying to compare numbers from Ford 2300 stuff to what a pushrod engine sees. On the most advanced 2300 stuff, the intake and exhaust valves will see in the neighborhood of 295/395 @ .050" and .730" lift @ the retainer. How does that compare to a pushrod V8 engine seeing 2.5hp./cu.in in a 320-350" engine?

[Adger Smith]

That is a hard engine to do comparisons with. The action of the lifter/rocker change the relationship more than a pushrod engine. I don't see any reason to try to compair them to anything else. They are just different....The only way I would think would/could is do a graph of the action at the valve. Locally we had a couple of tracks use those little screamers. I built quite a few that ran well. That is one engine that you just don't throw together the valve gear. Milling the block and head can get you in big trouble with the cam phase, if you don't use the right aftermarket parts & think about what is taking place. :~)

[BAracer]

On the most advanced 2300 stuff, the intake and exhaust valves will see in the neighborhood of 295/395 @ .050" and .730" lift @ the retainer. How does that compare to a pushrod V8 engine seeing 2.5hp./cu.in in a 320-350" engine?

Oops, that should read ~295 @ .050" on the intake, and ~305 @ .050" on the exhaust. Measured at the valve.

Would 320-250" pushrod V8's end up in the same neighborhood of duration to peak at about 9000RPM?

[DaveMcLain]

I think you're right in that measuring at the retainer is the only way to do it on this type of valve train, same for Ford Mod engine at least that's the way I've degree'd the cams in those before. Unlike the Mod engine the way the geometry changes and interacts with the profile on the cam goes two different directions on that 4 cylinder too. To get what would be "symmetrical" action at the valve requires a very unsymmetrical lobe.

[Adger Smith]

I'm thinking that there are some that don't understand the function of any rocker geometry is to add size and "shape" to the lobe that the lifter is following. The shape of the cam lobe is not what the valve actually sees. Sometimes close, but
not exactly. As an example Some engines have valve gear that adds 3 degrees @ 50 to what the cam is and then it has a total of 9 more degrees @ .500 lift. There are a lot of relationships of parts that can make these numbers different for every application. Just like the example of what the 2300 geometry does to the valve action. Valve action and the relationships of rockers and cams is an area that I think can't be packaged into one neat little box where a builder says the same thing happens in every application. You just have to study what you are working with and try to understand what is taking place. (In my younger days I would have said engines are all like women, the same but a little different) :~)

[donc]

I have to agree with Adger, to find out whats really going on, I check at lifter, check at retainer, most important all the valve train on and adjusted, with some lobes and spring pressure , cam timing will change.

[DaveMcLain]

A good example of an engine where the valvetrain geometry does change how it runs is the SOHC 427 Ford. For many years builders thought that the left cam needed to be advanced less than the right cam to make the engine run well. It was always thought that this was caused by the very long timing chain stretching out at high rpm. As it turns out what really caused the right head to act retarded was the geometry of the rocker arms. All were effected but on the left head the cam lobe moves away from the valve stem side whereas on the right head the lobe moves toward the valve stem. Since the cam follower is mounted on the end of the rocker it's relationship to the lobe/contact point moves in the opposite direction on each head.

Grinding two distinctly different cams would help to reduce the differences in the valve action and it's a better "fix" than running different cam timing between the two heads.