What affects power more in a camshaft....high lift or longer duration?

[RustyRatRod]

So the answer is 250@.050 and .530

IMO, always lift past peak flow a little if possible, Valve doesn't stay at peak lift long enough to access the flow rates there. Peak accessible is usually a bit lower .030-.050 on the flow sheet

I agree, ESPECIALLY if the .530 is a solid, since you have to consider valve lash. Also, we caint forget the crappy small block pushrod angle that subtracts "around" .020" or so lift. So yeah, the .530 would be good, I think. I think even .550 wouldn't be "too much" all things considered.

 

[gzig5]

When I was looking at getting a solid roller for my build and talking to several of the cam grinders, more than one advised that max lift should be at least .020" over the peak flow lift number. Unless the flow crashes after peak, it only makes sense (to me) that the longer the valve is open at or above peak flow, the more power potential you have.

 

[33IMP]

When I was looking at getting a solid roller for my build and talking to several of the cam grinders, more than one advised that max lift should be at least .020" over the peak flow lift number. Unless the flow crashes after peak, it only makes sense (to me) that the longer the valve is open at or above peak flow, the more power potential you have.

So, if buying rocker arms for a new combination, get as much ratio as possible?
(One of the reasons bbc and LS make good power!)

 

[33IMP]

So the answer is 250@.050 and .530

IMO, always lift past peak flow a little if possible, Valve doesn't stay at peak lift long enough to access the flow rates there. Peak accessible is usually a bit lower .030-.050 on the flow sheet

Well, the next cam I buy will be a sft for a brand-x big block, looking for roughly 260 at .050, and as much lift as I can get. .650? .700?
Street/strip, light car. 375cfm head.

 

[gzig5]

So, if buying rocker arms for a new combination, get as much ratio as possible?
(One of the reasons bbc and LS make good power!)

Not necessarily. Needs to be a balance. Higher rocker ratio increases lift but also increases valve speed and theoretically, stress on the rocker pivot because of the shorter lever arm takes more pressure to lift the valve. Faster valve speed may require a different spring to control it. If the cam already has an aggressive lobe, the higher ratio is only going to exacerbate that. Could make for jerky unstable valvetrain, or require maintenance on a tighter timeline. I'd take the advice of the cam grinder who should know what his lobe can do.

If I was starting from scratch, I'd probably try to use a 1.5 rocker and let the cam lobe determine the lift. With a roller cam, I don't think there is much of a downside to that approach.