Manifold Vacuum Experiment

@RustyRatRod thank you for posting results on this (oddly) controversial topic. I for one don't understand why this topic gets so heated, it's almost as bad as what oil to run or Edelbrock vs. Holley carbs. A lot of this hobby is about experimentation and making things work for your specific setup. If MVA works for you, great. If not, don't use it! It's that simple and it doesn't hurt to at least try it out.

I got the exact same results as you tuning my D200 using MVA. It has a stock 1972 360 2-bbl (stock cam and heads, 8:1 or slightly more compression) with 4-bbl intake and carb (Eddy 1406), Pertronix CD ignition box and Hedman longtube headers. I played with the static idle and mechanical advance to give the best WOT and over-half-throttle performance then hooked up the VA to manifold vacuum. Had some slight pinging pulling up long hills in top gear so I adjusted the VA can down about 1/4-turn at a time until the pinging went away. IIRC the VA can pulls in a max of 16 degrees and at idle with it hooked up the engine has about 24 degrees advance, with it unhooked it's around 8 degrees. It's just like you describe, hardly needs any throttle opening at all to keep it cruising down the road or to accelerate from a stop and idles buttery-smooth.

The 360 in my Duster is also lower compression, around 9:1 with stock Magnum pistons, Edelbrock LA heads with the machined chambers for pop-up 340 pistons (no quench) and .027" Cometic head gaskets. It likes a lot of timing and I found through trial and error that MVA helps with low-speed light-throttle driving especially just off idle. I believe a while back with my previous 360 that was 10.5:1 with KB zero-deck flat tops and iron Magnum heads it didn't like extra timing with MVA thanks to the decent quench and higher compression but I also was more naive back then to the intricacies of ignition advance so I didn't spend much time dialing it in "just right".

Some engines like it, some don't. You'll never know if you don't try!