I was inspired by Tom
MSD 6530 with throttle postion sensor
I decided to swap out my old MSD box with the newer 6530, which is programmable and can use a MAP sensor. So far, it's been really nice.
Rewiring it was no big deal, but the harnesses are different. The size of the 6530 box is smaller as well, so I made an aluminum plate that bolted into the old screws, and I mounted the new box on that plate. I also had to lock out the distributor, which turned out to be harder than I thought. On an MSD FE billet distributor, the gear is press fit onto the shaft. After removing the pin, and even with a puller and a vice, it wouldn't budge. This made me think that if and when I do get it off, I won't be able to get it back on and aligned properly with the pin hole. So I took a different approach. I considered welding it at the top of the shaft, like some people do, but I wanted it to be reversible. Instead, I tapped and drilled a hole so the black hex machine bolt shown below locks the distributor, I added a dab of blue Loctite so it doesn't go anywhere. This worked perfectly.
The next thing I had to do was phase the rotor. I bought the MSD racing/phasable rotor top, drilled a hole in an old cap at the #1 post, marked the center of the rotor, and checked the phasing. Sure enough, it was off. Per MSD's instructions, I set it at the midpoint of the timing range I would be using, and I get good proximity at both the most retarded and most advanced timing settings I'm using.
The way the 6530 box works is that you set the timing at maximum advance, and you program in two retard curves. One as a function of RPM, and the second as a function of manifold vacuum. I typically run 37 degrees maximum mechanical advance without any problems, and I plan to add another 10 degrees under light load for part throttle responsiveness and cruising efficiency. My approach was to run it first without the second advance curve to make sure it's right, and then to add in the second advance curve. I also should mention you program these curves on a PC and then download them via a serial port into the MSD box. You need a USB to Serial cable, but not a huge deal.
I set the total timing at 47 degrees (maximum) and configured a pretty standard RPM advance curve. This curve retards at start and has all the timing in by 2500 RPM or so. It also retards a couple of degrees at peak torque. At this point, I hooked up the MAP sensor, but set the vacuum timing curve to -10 degrees across the board. This way, I will max out at 37 degrees. I took it out for a few runs, and everything worked perfectly.
During my test runs, I monitored my vacuum to see where I want to set the vacuum curve (and also my carb power valve). It turns out vacuum at idle with this new cam is 17 in Hg, vacuum at cruise is 14-20 in HG, and vacuum at part throttle (say 40%) drops to 9 in Hg. Accordingly, I went back and set the vacuum advance curve so I get the full 10 degrees of advance at idle/cruise vacuum down to about 10 in Hg, and at that point I start taking out timing until it is all out at about 8 in Hg. This way, if I add the two curves, I get up to 47 degrees (like a vacuum distributor) at light load, and with throttle it drops to 37 degrees, with a couple more degrees taken out at peak torque.
Last thing, I welded up a little bracket for the map sensor and attached it to the firewall using an existing heater mounting bolt. It looks fine. You can spend a lot on a MAP sensor, but you can also get them from Amazon or Summit pretty cheaply, and I don't think there is a big difference.
Between the new cam and intake, and the timing curve enabled by the 6530 box and MAP sensor, it's a different car. I'll try to post some photos later.