Is there a way to find duration at .006, knowing duration and lift at .050? Also, can ramp rate be found using duration and lift at .050?

 

"Ramp rate" is not aprecisily defined term, AFAIK. But the concpt is simple enough. It refers to the "steepness" of the ramp. Which means, for practical purposes, how quickly (in terms of degrees) the lift goes from one point to another. So, you need either two lift/degree points or one plus a "rate" to calculate the other. "Advertised" or "rated" duration is often quoted at .006" lift, so you can use that number as a starting point. IOW, if a cam lobe goes from rated duration to say 0.200" lift in fewer degrees, it has a higher ramp rate than one that uses more degrees to go from 0.006" to 0.200".

Rich

 

So, if I'm getting this correctly, you can have two cams with the same duration and lift at a given lift point, with different ramp rates?

 

Right. For example, cosider two cam lobes as follows (real lobes, BTW).

1) 270/224/135 (rated duration/duration at 0.050"/duration at 0.200")
2) 262/224/147

As you can see, they have the same duration at 0.050" but #2 has a higher ramp rate, it is "steeper".

Rich

 

Here's what I'm confused about. Let's say a cam with duration and lift 218/228 .515/.515. Given the duration and lift, why can you not find ramp rate? The info provided tells you how much lift in a given time (expressed in camshaft degrees) Basically, I don't understand the geometry of how 2 cams can have the same duration and lift at .050 but have different ramp rates. I understand that one cam would reach its max lift value(in this case .515) in less time than the other. By time I mean actual time(minutes, seconds, etc..) Giving one cam a faster ramp rate. How would the lobes differ in shape though. I just can't picture it.

 

Faster ramps = steeper = more nearly square cam lobes.

Rich

 

BTW: I want to make clear that some people use the term "ramp" to refer strictly to the part of the lobe just off the base circle where the lift starts.

Rich

 

The basic problem here is that you are thinking about average ramp rate, when the term is used to discuss maximum ramp rate.

Look at this:



Ignore the difference in lift (squoosh the red line down a little so it has the same max lift as the blue line.) Then they have the same 0.05 dur. and max. lift, but the red has a higher (maximum instantaneous) ramp rate.

 

OK, I think I understand it a little more now, thanks. So the ramp rate is, or at least can be changing from point to point. Why is duration at .006-duration at .050 used to define ramp rate? Is there some specific reason for this? It seems that duration at .006-duration at let's say .200 would give a ramp rate more representative of the average ramp rate of the entire lobe. Don't ya think?

 

the faster the ramp speed the harder on lifters and valve train. most cams never get to that point but it can make a cam louder than others and be the same lift and duration. the steeper ramps make the valve open faster. Reason the roller cams make more power than the hydraulic and solids. that and they have less friction but mainly because of the increased flow

 

Measuring the duration at .050 is the standard way to compare cams from different manufacturers. Some rate their advertised duration at .006(comp) and some at .004(crane). Whoever grinds the cam can also tell you what the duration is at .200 if you like to give you another aspect of how the valves are opening and closing.

 

Advertised duration - duration @ 0.05 is termed intesity, the smaller the number the more aggressive a cam lobe is. It gives an idea on the ramp rate but is not it. The ramp rate varies from base circle to lobe nose.

 

Is that where "proprietary info" comes in? How exactly the ramp rate varies from base to nose. Basically giving the lobe it's exact shape.

 

Don't mean to jack... Have a couple Q's, also.
Ok, I have been following this. I know enough about cams to be dangerous. If you could be so patient to please xplain the .050. I understand now how ramp rate is found, but a couple numbers confuse me.

Taken mesurments form the base of the cam, before the lobe, and measures how much lift is created in a short rotational distance.. Correct? Smaller # in degrees to obtain max lift = steeper rate. (measured as closed to max lift/full open?)

What is the last #? Is it degrees? If so, wouldn't the smaller # be a steeper rate?

 

http://www.chevyhiperformance.com/te...39_cam_basics/

Google is your friend.