madscientist,
Ok, had to go back and read your OP. I don't know how any 408 with a 4.10 gear can be soft on the bottom. Define what you mean. I'm lost. Someday I hope to drive a car with soft bottom end so I can actually see what it is.
Alright...fair question. The current combo, which is a 360 motor with a hydraulic flat tappet cam moves pretty good actually, so this change is primarily about extra cubes, better airflow (W2 heads) and trying out the roller stuff.
Given how much time the car spends on the street I do not want to give up off-idle throttle response and part-throttle driveability. In other words, this is not an idle-to-WOT ride and must be somewhat decent on the street in a stop and go traffic. The 4k stall converter will already allow it to flash pretty good when the pedal is mashed, so when called for the motor goes right to the powerband.
By saying "soft bottom end" I mean a situation where at that part throttle the motor is not responding quickly, and really does not feel strong until the RPMs pick up.
When I experimented on my current engine setup with a switch from the Perfomer RPM intake to the Holley Strip Dominator there was a real noticable part-throttle quality/responsiveness impact. This was with a 2800 stall converter (which was tight) and a 3.91 gear though. I suppose that with the current 4k and 4.10 it would feel very different.
Ok, I'm following your line of thinking. I'm pretty sure if I was looking for a cam for that head it would be on a 109 LSA. Not because that's magic, but because if the cam grinder knows what he is doing, the opening and closing points will come out at that point.
Harold Brookshire and I went around and around over using a 109 LSA on a cam he ground for me. He said any wider and I'd be giving up middle RPM, which for me was the bottom of the gear change. I took notes but that was 1988ish. But the head is essentially the same. At your displacement, you are taxing that head unless they are fully ported with a square port window. And that may still be a bit small.
When I switched to the W5 heads, Harold had moved on and I was trying to get bullet to grind a new cam. I was 288/292 at .050 and only .640 lift on a 109. I felt like I needed at least .100 more lift and much less duration. Bullet actually spec'd a cam that was .750.750 and was 292/296. I'm thinking [censored]? I want to shift at 8500 not 9500. In the end, they had issues getting a core. I got tired of waiting and on a lark, called Cam Motion. Kip ended up 274/278 at .050 (he only split the duration because I was on alcohol...had I been on gas he would have made it 274/274) .754/.738 lift on a 109 LSA.
The point of all this is trying to save money on a cam is a bad place to try and cut a corner. You'll end up where you are. Be honest with the cam grinder and you can get a much better engine with much better drivability. It's as Grumpy Jenkins said a nebulous thing to describe and even worse to try and get fixed. How the engine takes the throttle under various conditions, loads and throttle positions can be a nightmare. I know the current trend is to blow the LSA out and throw some exhaust duration at it to keep the RPM where you want to shift at the same. I'd rather run a bit more duration, and change the timing events to close the LSA up. You'll be surprised how much you lose in the middle with the former as opposed to the latter.
Hope my rambling doesn't bore you. It's just what I've found doing this for awhile. It doesn't follow current convention, but I've never bought into the hype of wide LSA's just to try and get an idle like a 125 HP Toyota engine. If you can get the timing curve and fuel curve, you can get a fairly radical cam to idle quite nice.
