Because of the roller wheel geometry compared to the flat tappet geometry, small cams like this can’t take advantage of what the roller can offer in ramp rates on bigger cams. This is why the .050” and overall lift numbers are so similar on these two cams.

If you were talking about a 260@.050” flat tappet vs. roller, you would really see a difference in lift/intensity that just doesn’t show up on these little cams. Hydraulic rollers are certainly more durable, but for most of us weekend warriors that’s of little concern.

With a heavy car/no compression, you need to error on the side of caution with the intake valve closing point because it is what will determine your dynamic compression/cranking compression/cylinder pressure.

Look at the cam events… I have both your current cam and new cam in 4 degree’s advanced for an apples to apples comparison.

Current Cam-
IVO is 14.5 ° BTDC ( - indicates ATDC)
IVC is 42.5 ° ABDC
EVO is 53.5 ° BBDC
EVC is 9.5 ° ATDC ( - indicates BTDC)
Overlap is 24 °

New Cam-
IVO is 12.0 ° BTDC ( - indicates ATDC)
IVC is 48.0 ° ABDC
EVO is 60.0 ° BBDC
EVC is 8.0 ° ATDC ( - indicates BTDC)
Overlap is 20°

Couple things to note here… First there are two things that make low/mid range torque. Earlier intake valve closing, or later Exhaust valve opening.

Earlier intake valve closing makes more torque because as the engine runs at low/mid range RPM, the airspeed in the intake port is slow. As the piston starts to come up from BDC, it is trying to push the air backwards through the intake port (emptying the cylinder). The speed of the air coming through the port is fighting the piston from pushing the air backwards. If you keep the valve open too long, at some point the piston will overcome the air speed in the port (inertia), and will cause reversion into the intake. The only way to combat this is to increase the air speed (more rpm), or close the intake valve earlier. This is where the correlation between RPM and Intake Valve closing point comes in.

Later exhaust valve opening also increases torque at low/mid RPM. This is because if you open the exhaust valve too early, the pressure is released that could be used to continue pushing the piston down on the power stroke. If you wait too long to open the exhaust valve, at high RPM the exhaust doesn’t have enough overall time to evacuate the cylinder.

So looking at the events of these cams, the hydraulic roller closes the intake valve 5.5 degree’s later AND opens the exhaust valve 6.5 degree’s earlier. These are both bad things when it comes to low/mid range torque. Since your car is heavy, not much gear, and has low (pump gas) friendly compression, you can use all the low end torque that you can get. More cam will probably make the car MPH better, but probably make the ET slower. My buddy had a low compression 318, tight converter,4.10 gear and 236@.050” cam in a dart. Used to run 14 flat at 101mph. An extream example but shows how important low RPM torque is vs. HP. The big high RPM cam gave us good HP, but the lack of torque killed the ET.

For your idle comment… Because the new cam is bigger than the old, it partially negates the overlap/idle improvement you would normally get by just changing overlap. If you look, the overlap numbers are only 4 degree’s different between these two cams which is not significant.

You are right that the vacuum might get better, but it will be coupled of lost torque at low speed driving because of the later IVC and EVO events. So overall drivability might be worse.

Make sense?