V-Twin Forum banner

1 - 6 of 6 Posts

·
Registered
Joined
·
2 Posts
Discussion Starter #1
Hello
My dad allways said if you dont ask, you won't know.
Where do you get the big cam lope sound, From the
lift or duration?
 

·
Registered
Joined
·
567 Posts
The lope comes from long duration. In order to more efficiently fill the cylinders to produce big power the cams of this variety open the intake valves before the piston reaches top dead center and hold exhaust valves open past top dead center. Because the fresh incoming mixture doesn't have inertia of motion at low RPM's mixture will blow back out the intake valve at low speed, it makes for the kind of idle a gearhead loves, but sacrifices low RPM torque for maximum gains at higher speeds as well as using a lot of fuel.
 

·
Registered
Joined
·
9,250 Posts
S&S 585s in a 98" had a bad-ass lope. 9b in my 117 sound normal - and I miss the lope!
 

·
>>> The Curmudgeon <<<
Joined
·
352 Posts
The lope comes from long duration...
Not to pick nits, but it's actually the Overlap area, and this is determined as much by Lobe Separation Angle as it is by duration. Within the limits of mechanical interference, a big cam with lots of duration can still idle well if the LSA can be made wide enough. Conversely, a short cam with little duration will not idle so well with a narrow LSA. (Think S&S 561).

The duration number in and of itself is pretty meaningless. It's the event timing that counts.

As to idle lope: It's as much due to the style of intake manifold as anything else on a Harley. There's so much cross-talk going on in there it's a wonder they idle at all. Listen to a Marelli EFI bike compared to a Delphi EFI bike. Even with a much bigger cam the MM bike will idle better. Why? No intake crosstalk...

The more you learn, the more there is to learn. Keep askin'.
 

·
155" R&R TwinCam
Joined
·
3,437 Posts
Not to pick nits, but it's actually the Overlap area, and this is determined as much by Lobe Separation Angle as it is by duration. Within the limits of mechanical interference, a big cam with lots of duration can still idle well if the LSA can be made wide enough. Conversely, a short cam with little duration will not idle so well with a narrow LSA. (Think S&S 561).

The duration number in and of itself is pretty meaningless. It's the event timing that counts.

As to idle lope: It's as much due to the style of intake manifold as anything else on a Harley. There's so much cross-talk going on in there it's a wonder they idle at all. Listen to a Marelli EFI bike compared to a Delphi EFI bike. Even with a much bigger cam the MM bike will idle better. Why? No intake crosstalk...

The more you learn, the more there is to learn. Keep askin'.
You want a little more lope? toss the EFI and bolt up a carb fuel leak to compliment the narrow LSA camshaft
 

·
Registered
Joined
·
567 Posts
Not to pick nits, but it's actually the Overlap area, and this is determined as much by Lobe Separation Angle as it is by duration. Within the limits of mechanical interference, a big cam with lots of duration can still idle well if the LSA can be made wide enough. Conversely, a short cam with little duration will not idle so well with a narrow LSA. (Think S&S 561).

The duration number in and of itself is pretty meaningless. It's the event timing that counts.

As to idle lope: It's as much due to the style of intake manifold as anything else on a Harley. There's so much cross-talk going on in there it's a wonder they idle at all. Listen to a Marelli EFI bike compared to a Delphi EFI bike. Even with a much bigger cam the MM bike will idle better. Why? No intake crosstalk...

The more you learn, the more there is to learn. Keep askin'.
Thanks, no offense taken at all.
 
1 - 6 of 6 Posts
Top