Cam overlap... Help me understand
Staging Lane
Joined: Nov 2006
Posts: 55
Likes: 0
Hey guys, the different advertised durations at give points (from the manufacturer) are to give the knowlegable buyer an idea of the ramp speed. If you are cam degree freak than you will understand what they mean. If not they lead to just what we have here a bunch of guys turning an already confusing question into a study that by now i am sure the original poster is totally confussed on. Cam specs are one of the hardest engineering feats to comprehend and these big terms you are using dont teach the new guys nothing. Hell you even got my head shaking. If you dont understand a camshaft and want to learn the basics and better understand what is taking place and why order a comp cams catalog sit back with a cold one and the dog and read what they have to say it will really amaze you as to how well they teach you about cams in lamens terms. good luck
My Error - cam only vs. the entire valvetrain
Originally Posted by J-Rod
Great 421 a cam is physically ground to certain specs. We all agree on that. You can't change the LSA for instance, as that is physically ground into the cam itself. Where you are in error, and grossly in error, is in your claim that lift is measured at the lobe.
Originally Posted by brad8266
Once the lifter comes off the base circle of the cam and starts to lift the lifter, the higher rocker ratio will allow the valve to reach .006 valve lift earlier through the cams rotation than if you used a lower ratio rocker. It will also bring the valve lift to .006 on the closing side later. By changing valve intake and closing points you have just changed valve events. The closing and opening points of the valves is what is known as valve events.
Having said that, calcuating 'effective lift' at the valves (as you both seem to think that is the industry standard), is dependant on a number of factors: valve lash or lifter preload, material deflection at higher RPMs, as well as other assembly issues.
As another person's research indicates:
Originally Posted by thehammer69
I have been reading the software manual today for Comp Cams DynoSim Advanced software. When I got to the part about cam specs. In the part about what exactly seat to seat duration is...it essentially stated that the .006 lift point is the point in the camshafts rotation that .006" of lift is measured at the lifter.
So based on that, one would presume it would be same that the .050" lift point is also measured at the lifter. So technically, the duration per a set lift point actually doesn't change. You just see higher lifts at the valves earlier with higher ratio rockers.
So based on that, one would presume it would be same that the .050" lift point is also measured at the lifter. So technically, the duration per a set lift point actually doesn't change. You just see higher lifts at the valves earlier with higher ratio rockers.
So, to summarize - Sorry about dealing with just the cam (with respect to my answers) vs. the entire valvetrain. If you look at the system in total, as you both did (and as I did not), then rocker arm ratios will indeed impact those things.
See, I can be reasonable! (though, I still can't seem to spell!)
MIKE
