1.) Consider two identical pushrod motors save for the selection of a camshaft. Both engines have a camshaft with the same total duration, but one has substantially more duration at .50 (i.e., solid vs. hydraulic roller). Obviously, a solid roller setup would be expected to make more power. But, with the same advertised duration, could I expect the solid roller engine to make peak hp at a higher rpm than a hydraulic roller with the same total duration?

2.) Is there a linear relationship between cylinder-head port-volume and the rpm at which peak hp will be achieved? As I understand it, the larger the port-volume, the higher the rpm at which peak hp is made. At some point, presumably, the heads can supply more air than the cylinders can demand. When this point is reached, would you expect the motor to rev any higher by going to a larger head (assuming a constant camshaft profile)?

 

It's not just duration, either total/advertised or .050 duration that determines where and how much power the engine makes. If you just want to compare SR to HR, you should look for the same area under the lift curve for both. With .020 or so lash on the SR, the lobe lift on the SR will need to be higher than the lobe lift on the HR to get the same valve motion. Otherwise wouldn't the HR have more .050 duraton for the same total duration?

It's not obvious to me that a SR with the same valve lift curve would make more power than an properly setup HR, but that's not really the point. I'd use a SR when I couldn't get the rpm I needed or the valve lift/duration combination I needed with an HR. There are some SR profiles that work better than HR profiles in certain circumstances.

Unfortunately there are very few linear relationships in engines. Well, stroke length and displacement is a linear relationship if bore is held constant. Assuming the flow follows the port volume (not necessarily true in all cases), you could expect higher rpm for absolute max hp, but you could also use the extra flow capacity and port volume to shape the torque curve (and therefore hp curve) to get a less peaky engine with a hp curve that peaks at a lower value, but holds that peak hp or close to it for 500-1000+ rpm after peak and gives more area under the curve (aka more "average" hp and torque).

As for heads supplying more air than the cylinders can demand, think about increasing revs so the "demand" goes up. There is certainly such a thing as a head that flows too much air for a given engine size if you are rpm limited, which most of us are because of the cost of extreme rpm, but if you are not rpm limited and low rpm performance isn't a requirement, more air is probably better. Even if you are rpm limited like "gear rule" Nextel Cup tracks, more airflow capacity is better.

OK, if only the head which flows more air thru a larger port is changed, the max hp and the rpm at which it occurs should climb, but you have to get everything working together, especially the valve timing. Remember that valve events depend on the the engine's airflow capacity and the requirements determined from the vehicle performance required (ideally) or by the owner (not always ideal ). The "cam profile" should be the dependant variable; choose the valve motion after all the other parameters have been selected. Not changing the cam when you changed flow and port volume would more than likely be leaving power on the table.

Not trying to give you a hard time, Elysian, but I'm not convinced there are simple answers to your questions.

My highly-opinionated $.02.