jeepsr4ever wroteI wasnt talking about high revs I am talking about making the power at a low rpm without having a cam fall flat on its face at 3000rpm. If you have a small lift and small duration with the large valve sizes AMC head have your velocity and the amount of fuel/air and combustion efficiency can go down. The 304 works well with smaller cams because it has smaller valves. When you take all the parts of what makeup the power in a AMC 343 or larger you will then understand why cams with less than 220 duration or .480 lift dont work as well as cams in that range. Donwag has a good example and did a good job of building his grunt motor however I believe that he could have made more power with a different camshaft. You very close to being accurate 82Wag but without taking into account the head characteristics a cam suggestion may not be as accurate as you have led it to be.
I need a set of 304 heads BTW anyone got a set they will send up here?
I just can't reconcile your points MC. High velocity and large wide open valves at low rpm do not go together. ALL flow data suggests that dogleg heads with 2.025 intake valves start to lose velocity at about .480 or so lift, and there is very little significant difference in flow/velocity between .450 and .480 lift. If a 304 in fact has a relatively smaller valve size to displacement ratio or lower flowing heads than a 360 then it would stand to reason that it would show a benefit of using a cam with more overlap than a 360 (RELATIVELY SPEAKING), assuming exhaust system backpressure did not hinder cylinder scavenging. If you are not running the rpm to take advantage of the port and valve size at max attainable lift, velocity can go down - you can get velocity back up in this circumstance by not opening the valve as far - cubic feet ingested can remain constant. High volume at low velocity, or low volume at high velocity can both equal the same CFM. High valve lift is not always, therefore, the best deal for low rpm engines.
A simple cam fact is that duration in and of itself only shifts the rpm at which peak torque is produced - raise this point and you make more horsepower, but at some sacrifice to low rpm torque due to the relatively later intake closing point. It is possible to regain some of the low rpm torque loss by raising compression ratio, but, as I have tried to convey, doing so means addressing higher octane fuel use, higher gear ratios, free flowing exhaust, etc. The question is at what point do you draw the line.
Use too much overlap with a restrictive (stock style) exhaust system and you start diluting the intake charge at low rpm - once again, bottom end power suffers.
Sure donwag could probably increase his peak numbers with more duration and higher rpm, assuming the intake closing point did not fall behind where it is now. IMO he could also increase peak torque within his current rpm range, widen his torque curve, and even increase peak hp numbers, and do all of that at a lower rpm than where his peak numbers fall now -simply by going to a cam with a 112LSA and slightly less duration.
Look, I am not trying to be a contrarian here. If there is something special about an AMC engine in these regards that I have overlooked, please enlighten me.
