I understand the vague generality of smaller LSAs increasing the odds that a motor will lope, and also that loping is a function of vaccuum; my question is: what aspects of cam timing create low vaccuum (which in turn creates loping)? Too much overlap?
If so, then it would follow that smaller duration profiles (say, 218 - 224) could be built into a cam with a smaller LSA and be less likely to produce a lope, yes?

Thanks, Jon

 

More overlap = more lope.

To much overlap and you gotta worry about ptv clearance among other things. Someone more knowledge can chime in on that part

 

OVerlap and ramp rate

 

Thanks, guys. That was helpful in choosing a cam to fit the criteria.

Jon

 

A tight Lsa
Lobe
Separation
Angle

The tighter ie 110 vs ie 116 the 110 will sound way meaner!

 

The "lope" or "chop" is actually caused by misfiring. Wide overlap cams don't do a good job of clearing the burned fuel/air mixture out of the cylinder at low rpm's, so your air/fuel mix is polluted, causing a misfire. Keep in mind that the intake and exhaust valves are open at the same time, the burned fuel/air mix can actually be pushed/drawn back into the intake, which causes the same misfire. Once the engine gets the rpm's up, there's no polution of the fuel/air mix, so it fires as it should again.

 

Right.

More or less, the misfire which creates "lope" is basically caused by the engine choking on it's own exhaust if that simplifies it any.

 

Thanks you guys. That was the last piece of a cam "primer" that I wrote, hoping to actually contribute something around her, rather than just ask for help all the time.

Jon

 

dont forget also, that the sound is created when the valve is opened and closed REALLY quickly. it will be about as noisy when you push compressed air through a motor to run it