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.
