Generation IV Internal Engine - What, technically, causes "loping" in a motor with a cam installed?
12-07-2011, 08:59 PM
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?
12-07-2011, 09:07 PM
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
12-07-2011, 09:16 PM
OVerlap and ramp rate
12-09-2011, 09:48 PM
Thanks, guys. That was helpful in choosing a cam to fit the criteria.
12-09-2011, 10:06 PM
A tight Lsa
The tighter ie 110 vs ie 116 the 110 will sound way meaner!
12-11-2011, 10:11 AM
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.
12-11-2011, 11:34 PM
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.
12-11-2011, 11:38 PM
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.
12-12-2011, 02:32 AM
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
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