I've always heard folks refer to cam's as having alot of lope at idle. Well I've been unable to really find a description. So, can anyone describe it or maybe some .wav/.mp3 examples and cam specs? Thanks!

 

Lope is the sound an engine makes at idle when large cam is installed.
It's kinda hard to describe. It sounds kinda like a horse running, but faster.
It's caused by the intake and exhaust valves being open at the same time (this is known as "valve overlap"). About all engines have a little valve overlap, but a "big cam" has more duration and leaves the valves open longer; so there's more valve overlap.

At idle, some of the exhaust flows back up into the intake diluting the fuel-air mixture (this is known as "reversion") and causing eng to run rough or "lope". If a really big cam is installed, the idle speed has to be raised or the eng will die. With a really large cam, the idle speed has to be 2500 rpm or it will choke itself on exhaust.

Two things effect valve overlap.

Duration; or degres of crankshaft rotation the valve is open.

LSA; lobe seperation angle, or the # of degrees of crankshaft rotation needed for the intake valve and the exhaust valve lobes to pass the same spot. Less LSA will allow the exhaust valve to open sooner, increasing the time that both valves are simultaniously open.

Maybe someone will post a good wav link.

 

For what it is worth, lope is not a desirable trait on a street car. All it means, as the last fellow mentioned, is that the engine is having a hard time idling. This means low rpm power will not be very good. Since by far the lion's share of your time in a street car is spent at lower rpms, you can see how that would grow old fast.

 

So there doesn't seem to being a really big difference between "some lope" and "fair/poor" idle? Now if there would be some way to correspond the cam specs/vaccuum/idle... Hopefully someone out there will post a wav or two!

 

I am sure you have heard lopey cammed engines before, maybe you just didn't recognize it. Ever been to a car/hotrod show, drag race, cruise night at a burger joint??? If you can answer yes to any of these, you will have definately heard at least ONE aggressive cam. I would love to post a sound clip of my new engine cause I think it sounds just perfect...

Most of the time people go with a cam that has lots of overlap because they want that lopey sound at idle. Some use cams that way for the performance aspects of it. Another thing to point out is that the "lopey" cams will make the engine have less vacuum at idle...