Intake/exhaust duration Paul only make sense when viewed in the context of the flow capabilities of the heads/intake/exhaust. Dual pattern cams work well (more exhaust duration) when you've got a flow deficiency, usually in the head, on the exhaust side. The Ford Racing X and Y heads are this way - their flow is intake biased, and they need help in the form of more duration and/or lift from the cam on the exhaust side to make up for the lack of exhaust flow in the head. So you see, you really need to pick heads/intake/exhaust system that are capable of enough flow to support your HP requirements, and then select valve timing events and CR such that the power peak occurs where you want it to. I firmly believe that without a professional modeling it for you, any cam choice is gonna be purely a guess. Valve timing events are what need to be selected - not lifts and durations.
Here's a link regarding rod length/stroke ratios and the implications. It's aimed at strokers, but the principles are the same. Going with a longer rod will give you a higher rod length/stroke ratio. As you'll see, the pros of a long rod engine are in your favor if you're building a high revving small block. But it's probably not a huge advantage. For the money it would cost, you'd be much better off getting Buddy or Ed to model things for you to help you select heads and cam. I'm a broken record. Here's an excerpt:
Pro:
» Provides longer piston dwell time at & near TDC, which maintains a longer state of compression by keeping the chamber volume small. This has obvious benefits: better combustion, higher cylinder pressure after the first few degrees of rotation past TDC, and higher temperatures within the combustion chamber. This type of rod will produce very good mid to upper RPM torque.
» The longer rod will reduce friction within the engine, due to the reduced angle which will place less stress at the thrust surface of the piston during combustion. These rods work well with numerically high gear ratios and lighter vehicles.
» For the same total deck height, a longer rod will use a shorter (and therefore lighter) piston, and generally have a safer maximum RPM.
Con:
» They do not promote good cylinder filling (volumetric efficiency) at low to moderate engine speeds due to reduced air flow velocity. After the first few degrees beyond TDC piston speed will increase in proportion to crank rotation, but will be biased by the connecting rod length. The piston will descend at a reduced rate and gain its maximum speed at a later point in the crankshaft’s rotation.
» Longer rods have greater interference with the cylinder bottom & water jacket area, pan rails, pan, and camshaft - some combinations of stroke length & rod choice are not practical.
To take advantage of the energy that occurs within the movement of a column of air, it is important to select manifold and port dimensions that will promote high velocity within both the intake and exhaust passages. Long runners and reduced inside diameter air passages work well with long rods.
http://www.victorylibrary.com/mopar/rod-tech-c.htm
Can't wait to hear it. Oh, for the revs/power you're talking about, I think static compression ratio is gonna need to be a good bit higher than stock.
