cams are ground (or should be) ground on the premise that the valve will follow the lobe profile X the rocker ratio. So, all cams benefit from proper geometry. All valve trains should open the valve exactly half way when the cam is at midlift.
In other words all cams are ground based on where the CAM DESIGNER wants the valve and when. Setting up the geometry is simply an attempt to accomplish just that.

Cams aren't ground to rocker geometry, rocker geometry is set up to try to follow the cam design as closely as possible.

 

So could a cam grinder compensate for an over or under arcing rocker? Knowing that the valve will be slow off the seat or whatever the situation is in relation to the crank in degrees.

 

Not necessarily. The mid lift geometry is more than just trying to follow the cams profile as closely as possible, it is also about the dynamics, as well as the load seen by the pushrod and rocker. The best cam in the world can destroy rockers and pushrods if the geometry is wrong.
But in a word, the cam grinder EXPECTS the valve to be at a certain lift off the seat at a given crank angle. The geometry can alter that, as well as the max lift of a given cam shaft. If the rocker is already past perpendicular to the valve when the cam is at midlift, it will begin losing ratio sooner and not reach the max lift designed into the cam because the rocker is way past the point it should be.

Grumpy Jenkins used to play with PR lengths to get the rocker to over and under arch with the same camshaft to help determine what the cam profile should look like. But he didn't race the engine with crazy PR lengths. He would just dyno the different setups and use them to determine what the profile and timing should look like.

If you ever dial indicate a valve with an extremely short and long PR, you will find that the changes in valve timing and max lift is very very very small. Its much more about valvetrain reliability. Unless you have dyno'd lots of cams thru your engine, I doubt you cam is THAT critical to the last HP. You cam choice can destroy the potential of the engine much quicker than the rocker geometry. But the wrong rocker geometry can destroy your valve train quicker that 99% of the cams off the shelf.

 

This motor that I am working on is the second motor that I have implemented the mid lift theory on . After all the help from the good people of this site I felt I had a grip on the general relation of rocker and valve. You can put all the dial indicators you want on the retainer and get a good sense of max lift vs P/R length as well as mid lift angles but its not until you put a indicator on the roller tip and see just how much the roller travels across the stem at the same time the valve is opening that things really start to come to light. So after a brief call to Mr. Miller "nice guy by the way"and a discussion with our very own "Lakes Only"I felt it was time to look at the P/R mid lift angles . "Comp Cams stainless lockers suck ass by the way" So after searching the web I purchased a set of miller rockers and WHALAA almost perfection on both sides of the rocker. Now that got me thinking. So if the MFG with the biggest footprint in cams and valve train components instructs their customers on choosing P/R lengths on a 123 pattern across the valve stem which only leads to slow seat timing as well as less than max lift numbers Than maybe their cam profiles must compensate for this? Evidently not.

Thank you GN-7 for not letting me call Straub and wast his time with this jackass question.

 

The 1-2-3 diagram in the Comp catalog is the laughing joke in the industry and has been for well over 20 years. And yet they have never bothered to correct it. Its not just little off, its totally wrong!!!! Keep in mind that Comp Cams is owned by a lawyer, not a motor head. I, as well as a few others on the boards, will not go near MOST Comp Cams products. When Crane cams ousted Harvey Crane (long story) the company went straight the shitter. It took a few turns getting there, but thats where it ended up. It wasn't alone in the performance industry. The number of performance companies headed by their founder, or even a gear head is getting smaller every day.

Look at what happened to Apple computers when John Scully ousted Steven Jobs. He damn near bankrupted the company and Jobs had to save it.
We have discuss this here before. There 2 types if companies. Those owned and ran by people that have a PASSION for what they do and make, and those ONLY interested in making a buck. Guess which has your best interest in mind.

 

Matching cam with rocker geometry...is there a lobe profile that takes full advantage of this ?

GN7 already covered your question, but I thought I'd add a few more extremely important build details to consider:

• Don't forget to establish bearing crush while the con rod is a maximum angularity (both the rod and main bearings)
• When cutting valve seats with carbide cutters, always remember to lift the cutter of the seat at the exact point that a cutting blade passes the 12 o'clock position (relative to intake flange side of head)
• And whatever you do, never, never, NEVER install a woodruff key backwards (it will be 180* out of phase)

There are more (tee-hee) but they escape my mind at the moment....anyone?

Merry (belated) Christmas,

LO

 

Now thats just good stuff! And yes, it dead on topic!

Hope you all have a happy and prosperous new year.

 

Thanks for some good info Bob.