What is it on the cam that gives the "lope" that we love so dearly? Is it cam overlap? Lift duration? What exactly is it?

The quick answer is overlap.

I think the real answer is a lot of overlap without a lot of valve lift area during overlap.
There are also other, more arcane, things involved.

UDHarold

Thanx for the quick reply.

I had someone tell me more overlap allows you to bleed off some of the cylinder pressure so you can run a lower octane fuel. Is this so?

Also I'm wondering....when I see two cams side by side, lets say one has 108 degrees of overlap and the other 110 degrees which one has more overlap?

(kinda new to cams :D )

Originally posted by Junkyard Dawg:
Thanx for the quick reply.

I had someone tell me more overlap allows you to bleed off some of the cylinder pressure so you can run a lower octane fuel. Is this so?

Also I'm wondering....when I see two cams side by side, lets say one has 108 degrees of overlap and the other 110 degrees which one has more overlap?
(kinda new to cams :D ) =
If you are actually talking about overlap the higher number would be more.

I think you might be confusing lobe separation angle (the distance in cam degrees from the intake lobe centerline to the the exhaust lobe centerline) with overlap.
Assuming you have the same lobes the cam with the tighter separation (108 in this case) will have more overlap.
Overlap has nothing to do with cranking compression, it is on the opposite side of where you make pressure. The intake valve closing point is when you start making cylinder pressure or compression.
Overlap is at the end of the exhaust stroke & the beginning of the intake stroke when the exhaust valve is closing & the intake valve is opening.
It is the time in degrees that both the intake & exhaust valves are open at the same time.

Think I got it right,,, it's gettin late :D

Mike(WolfPlace) is correct.....

Bleeding off cylinder pressure to run a lower-octane fuel is done by closing the intake valve later, either by running a bigger cam OR by having a wider LSA, or both.
The overlap is as stated, the period when both intake and exhaust valves are open. "Lope" is caused by the effect of exhaust gas reversion on the intake of fuel and the creation of vacuum. This is why I mentioned the area 'under the curve' during overlap. Too much area under the curve FOR THE SAME OVERLAP raises the idle speed too high. Different cams, whether by different manufacturers or of different lifter types, that have the SAME overlap, may idle or 'lope', at different RPMs. A 288/296 hydraulic on 108 LSA will have a different idle from a 288/296 roller on 108. They have different 'areas under the curve' during overlap.

UDHarold

BTW, does anybody have another word besides 'different'?

Originally posted by UDHarold:
BTW, does anybody have another word besides 'different'? [/QB]Harold pick your poison:

Dissimilar
Diverse
Unlike
poles apart
unusual
special
singular

Or installing the cam retarded, (I also call it, "straight up" if it has advance made in it like say 110/106 vs 110/110 sorta deal), so the intake valve closes later to help bleed cranking pressure..

He, He!! That's how I'm hitting the wanted 551 hp with my big motor for "Brother-in-Law" bragging rights... But still it's only per D2K though..

pdq67