With everything being equal, more duration will usually result in more lope but there's no majic line where lope will occur or not occur. Slightly more duration will give slightly more lope. A lot more duration will give a lot more lope. There are a lot of other factors like timing, fuel mixture, displacement, head port volume, etc., that will affect lope also. One engine may have a very noticeable lope with 220º and another may have none with 225º.
Lope is usually the result of lower intake velocities caused by longer duration and which prevent the fuel/air from mixing well or not keeping the fuel suspended in the air and also from exhaust gasses flowing into back into the combustion chamber. In the latter case, the lower intake air velocities offer less resistance to exhaust reversion and also, because both the intake and exhaust valves are open together for longer periods, there's more opportunity for this to occur.
...also, because both the intake and exhaust valves are open together for longer periods...
This, is of course, is "overlap". Overlap is the main contributor, to a lopy idle and a soggy low end. Overlap increases as duration increases. HOWEVER, for a given amount of duration, the overlap is decreased by increasing the amount of lobe separation.
HOWEVER, for a given amount of duration, the overlap is decreased by increasing the amount of lobe separation.
:confused: So by decreasing the lobe seperation you can actually "induce" lope into an engine?
In some cases, a "lope" is a desired property. In a cruising type car, not an all out race car and not a daily driver. (Street Rods for example :thumbs: )
Or, can you alter cam timing enough with a mild cam to "induce" a lope at idle?
Yup! Some people buy cams with short duration and very tight lobe separation like 106 or 104, so they get that lopey sound without killing their low end performance too much. I would never personally choose a cam for its sound. If you're gonna build the motor to sound fast, build it to be fast!
You can't induce a lope by advancing or retarding a cam. It has to have the valve overlap ground into it. You could slightly increase overlap by increasing the rocker ratio, but it would only make a very small difference.
In am effort to make a "healthy" cam more streetable, copious amounts of spark advance, can help. If you want it to sound "nasty" try retarding the timing. It won't run like it should, but it will sound mean. Personally, I'd rather sound stock and run otherwise, than the opposite. Either way, good luck, and...
Corvette Store
Cam "lope" question?
