Keep in mind that at 90* ABDC the piston is half away up the bore, and moving at about maximum speed, preparing to slow down and stop when it approaches TDC again. The 6900 has a closing point at about 70*. That is a very long time after BDC, and well suited to a high rpm engine.
Calculated at .050, the ICA is 34*ABDC
So from 34 after to 70 after, At idle, what is the piston doing? You guessed it pushing the intake charge back up the cylinder, past the slightly open intake valve, and up into the intake manifold (reducing the idle vacuum),until the piston is nearly half way up the bore and approaching it's maximum speed. Remember the piston had to stop at the bottom, turn around and is now heading back up to the top. This works well in a higher rpm engine. Not so much in a DD.
But then a 4.10 equipped A-body, doesn't much sound like a DD.
But then again, with a same 204cam with faster ramps, it wouldn't need the 4.10s.
On the flip side, with a 70* ICA, you could have a fast-rate cam in there about one or perhaps two sizes bigger, with little or no loss in bottom end performance, and pick up maybe 15/20 hp at peak.
To be fair, the long intake period begins to work in the 318s favor, some time after about 2200 rpm,whenever the intake vacuum peaks. So if you never run at an rpm lower than that, then the design is ramming AF charge in as may be normal on a 204 cam.
But do yourself a favor; take your car for a ride around town in your typical driving style, and see how much time your tach spends above 2200 versus how much time below. Remember all the time below 2200, the cam is operating in an in-efficient manner, messing up the AFR, costing you money at the pump; and the closer to idle, the worse it is.
Peak efficiency might not occur until after 3400, maybe 3600. This is where a 4.10 will make the difference. First it gets you up past 2200 very early,about 17 mph. Secondly, 32mph in second gear is about 2500 rpm, and 60 in third could be 3060 at zero-slip.
But with say 2.76s,then 2200 might not occur until about 25mph, if you hold it in first. If you let it shift automatically,and loafing,it will already be in third gear doing say 860 rpm (zero-slip).
Ok but, you say you have 3.55s. Aha! Then 2200 might occur at 19mph if you hold it in gear. Letting it shift automatically, the Rs might be closer to, say 860rpm, again zero slip.
But you say; how is 860=860 possible, with both gears? hang on; it occurs 28% sooner with the 3.55s, 19 mph versus 25.
Now shifting into second at say 2500, the Rs will fall to 1500 loafing (zero-slip) to whatever your stall speed is, if harder into it. So again, below 2200. In fact; loafing, the Rs in second might not get to 2200 again until 35 mph in first @3730rpm.
So, like I say, take it for a normal ride and judge for yourself.
Otherwise; a 204 cam in a 9.2 318 is a lot of fun. I'd just rather have one with waaay faster ramps. In a nominal 8.0, it just wants more gear or more stall or both,lol, cuz the cylinder pressure is way down.
