for all you guys out there who have better math skills than me. assuming a stock size base circle sbc cam. is there any way we can make a function that will tell the lobe area based on the .006 lift duration the .050 duration and the .200 duration, and max lift.

after that i was wondering if there would be a way we could map that against head flow and come up with an average cfm based on this? i just think these would be neat tools to have in the form of computer programs. if we could get the formulas worked out it wouldnt be a problem to get them into an easy to use program. and just be one more tool to use when looking at cam lobes it would be nice IMHO. so does anybody wanna take a crack at it.

on another note it would also be nice to make up a program based on dynamic stroke that would figure out what the optimum intake closing point would be without just plugging crap into the formula over and over.

 

I think you could guesstimate it pretty well by just drawing it out on graph paper with the known points that you listed and "connecting the dots". The cam manufacturer has this info, but I am not sure if they would give it to you, though I am not sure why not.

Rich Krause

 

that did occur to me why dont they just post the lobe area along with the other stuff. i know some of the lobe shape is what keeps them in business or give them an advantage over another manufacturer. i just want all the numbers i can get. i like to support my decisions with math. simply because this is science not magic. just seemed funny to me today when i was looking through the lobe catalog. the .200 number is a good indicator of the lobe's real size. but i still think theres more to it.

 

I've built an excel spreadsheet that fits a 4th order polynomial to the cam lobe. I just enter the opening and closing events at 0.050", lash duration, lobe lift, and lobe centerline. These points are charted, then I use the curve fit operation to fit a 4th order polynomial. I tried different ordered polynomials, but the 4th order seemed to fit best.

I haven't taken this equation to calculate area under the curve, but all you would have to do is perform an integral over the lash duration figure, and you could calculate it.

I'm not saying this is EXACT, but it seems to be fairly accurate. I used this system in a spreadsheet that rotates the crank/rod/piston through a revolution so that I can find max piston accelerations and velocities at different points in the rotation, based on stroke length, rod length, and rpm. The valve events were added later so I could "estimate" the valve notch depth on my pistons. I did this by linking the rotation of the crank with the valve events, basically showing the intake valve opening as the piston approaches TDC, then continuing through the lift curve and the piston accelerates away from TDC. I've checked my setup and the estimation of the program was very close to actual measurements.

I can send you the spreadsheet if you would like. It has the charted output of the lobe profile, with the curve fit printed on the chart. Or, if you give me your cam info, I can give you the curve fit equation, and you can calculate the area. I would need the following info to do this:

1. 0.050" Intake Valve Opening: ______ degrees BTDC
2. 0.050" Intake Valve Closing: ______ degrees ABDC
3. Rocker Ratio: ______
4. Lash Duration: ________ degrees
5. Intake Lobe Center: _______ degrees ATDC
6. Lobe Lift: ______
7. Valve Lash: _______

Right now, the program only does intake valve events. Let me know if you're interested.

Shane

 

I would appreciate the program! As I am a math dummy, it's something I could never do myself.

Rich Krause

 

I agree, it would be useful information.

Rich Krause

 

If you have access to Cam Doctor or equivalent data it's a piece of cake finding lobe area, but that's only the beginning of what you need. Using a simulation progrm like Engine Analyzer Pro with Cam Doc data pretty much outputs what you are looking for, however. It recalcs every crank degree or so which is useful if it has good cam lift data.

Iteration ("plugging in crap over and over") is still part of the game, but with some of the outputs you can creep up on a solution relatively quickly. That gives you a start as to what to build and test.

Unfortunately, an internal combustion engine is a very complex thermodynamic and mechanical mechanism which operates in a highly dynamic state. Even though we seek "magic bullet" solution to parts choice, it's still a calculate/test/recalc/retest ... process. Even the highest end (those with the most money) engine builders do LOTS of testing of engines after they run the simulations. Sometimes it takes them a lot of time to get where they are headed.

IMO, Renault's 110 degree (or 106 or 108 or 1??) V-10 Formula 1 engine is finally making the kind of hp they needed to become competitive. Damn, I bet figuring valve event timing and port tuning on that engine is a bugger. Perhaps every cylinder has a different valve lift curve! As far as I know they still use mechanical cams to open the valves. Non-cam actuated valves have been tested, but may not yet be on race engines in F1. But maybe they are. It's not what moves the valve that is important. It's what the lift curve looks like that counts.

My $.02

 

Calculating area under curve seems to fall into the subject of integration.... way back in my memory banks from trigonometry. Drawing rectangles and triangles ( or a trapezium) you can get a very good approximation.
Though this is considering the fact that you have a mathematical function to describe the curve, parabola, etc.. We don't have that much info with a lobe profile, so it may be better to just use the graph paper approach, count the squares or create trapezium and calculate the area.
I'm sure you could find more info by searching for "calculating area under the curve"... pretty common thing to do in trig and calculus.

-Mindgame