Honestly I want high lift because I want the excuse to mill the head down. I'm not looking to put this motor in competition use or anything, honestly it'll prob sit on a shelf until I want a new toy. I'd like the power band to be in the 4-8k range as well.
Wait.....What? You lost me there....High lift= valve to head contact or valve to piston contact.... ( depending on whether it's OHV or flat-top) but either way. ....milling the head will decrease the clearance.....
Of course- there are so many variables that we could go on with this forever- but what is your thinking behind that statement? I mean. ..I can kinda see where you could say since you are milling the head- you want higher lift and less duration to keep compression under control- but then why mill in the first place?
So- just to touch on what we have touched on. ....lift allows a lot of charge in a short time frame- duration how long the engine sucks in the charge....so now we come to timing....
when the valve opens and closes..... ( and overlap, ect....)
So again- another variable in cam design.....So in simple terms or theory....the intake valve is closed at TDC and the charge is ignited -initializing the power stroke...at BDC- the exhaust valve opens and the spent charge is expelled as the piston returns to TDC-at which point the intake valve opens, allowing a fresh charge to enter as the piston returns to BDC. Then the intake valve closes and allows the piston to compress the charge on the way up to complete the cycle.
However-that's not really what happens. The intake valve will open sometime before TDC-allowing the vacuum of the exiting exhaust charge to suck in a greater amount of charge than the piston just travelling down. . Conversely- this also helps in clearing the spent exhaust. ...
So both valves are open at the same time (overlap)....
Anyway- this is why you get interference between valves and piston.
So all this and $5 will get you a cup of coffee at Starbucks. ....Now a cam recommendation for a performance small block Ford - I could help you with- what you are doing. ..specifically, I'm almost clueless. ...
However- I can tell you that generally speaking-the more duration- the higher the rpm of the powerband and 'sid's point is very valid concerning lift and duration- which is why roller cams can sport a much more radical lobe profile than hydraulic flat tappets in cars.....
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