So lets back up. I feel overlap, obviously the function of duration and LSA has a lot to do with power production. So I am more likely to pick a short duration cam with a tight LSA instead of a long duration wide LSA. Since they would have similar overlap. That said, with the current cam in my 454 I am super unhappy with the low speed bucking and everything I can find says that beyond timing, too rich/lean it is a function of the rough idle. The current cam is a Erson flat tappet hyd 228/235 296/306 .542/.542 110 lsa and the wore out 454 it is in has 92 cc 215s so the compression even with the flat tops it has OK compression, it has a GM version of a performer rpm qjet and 750 marine qjet with dual upper main air bleeds. I have added a bunch of initial and limited the curve with heavier/lighter springs. Changed it to less initial with lots of mech and light or heavy springs. Changed out the idle air bleed to help fatten up the bottom. Nothing. I changed out the clutch thinking the dampening springs maybe too light and winding up at low speeds, no change. Maybe it is my rear suspension bushings (which I changed out for new rubber). It is like tightening and releasing a clock spring over and over below 2000 rpm.
I respectfully disagree here on having a tight LSA short duration cam. I think you will have a faster ride if you had a wider LSA and more duration while having the same engine vacuum, better low end, flatter torque, and less peaky. It will take off smoother, idle smoother, and make more power at part throttle and drive easier. You see all these power curves that say how a tight LSA makes more power on the whole curve, and then they only show above 3K. Well, with a big block, you can only be above 3K for a very short time, you spend most of your time with a street vehicle below 3K, because if you punch it you are going fast in a hurry.
I like to tune the duration to the RPM range needed for the vehicle/engine combination, and use the LSA to get the idle quality, vacuum, and part throttle driving needed for the application. The lift I base mostly on the head flow numbers and valve springs, intended usage ,etc. This is about the shortest possible summary I can say, and its way oversimplified as there are so many other factors, but its true. I recommended a cam after I went back and looked at your heads, vehicle, gearing, transmission, bore, stroke, compression, usage, power expectations, idle quality expectations, brake system, etc. Some of it you told me later (like the manual brakes). However, I still think with a manual trans you don't want a tight LSA, you can't hide the rough idle or low RPM harshness like you can with the right converter.
For example, the cam my regal is a 315/328 duration, 280/292 @ 050. And at 2200 RPM when I am going down the freeway, if I lock the converter up, I can still feel the car buck and kick a little, its mild, but its obviously there This is gone with the converter unlocked, or with the RPM above 2500, then it finally smooths out. This is because of the overlap, and that has a 114 LSA. It still has 93.5 degrees of overlap, if that was a 110 LSA it would be 101.5 degrees of overlap. ( like to use the adv numbers for the idle and low speed smoothness quality purposes). I use the .050 numbers for the performance and comparison expectations. Also, this car is all solid everything except the trans mount, solid front and mid motor plates, solid chromemoly cage, heim joints on all suspension arms, shocks, and steering on the whole car. The only poly bushing on the whole thing is the trans mount, which is only for longitudinal forces the motor plates don't handle, I don't like any twisting forces on the trans case at all.
I am using my app to calculate the overlap based on the adv duration. That is what will affect how the engines at or just above idle, assuming everything is tuned correctly. And the more overlap, the higher the RPM before it will feel smooth with a manual. The engine will be purring like a kitten, but it will be harsh, especially with solid motor mounts.
