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I have a Barton built 528 hemi not a crate but it is built very close in specs. I also had a Mopar performance distributor with vacume advance since my car is a street car. He did not want me to use it he steered me to a msd pro billet locked at 32 degrees. That was the sweet spot on the dyno when testing.



Since we are talking vacuum advance I assume we are talking street?

Take the dyno data with a grain of salt. My engine showed peak horsepower at 33 degrees. The dyno tests are usually done by bring the engine up to 3000rpm, applying a load and then bringing up the rpm. What the dyno can't account for is the varying conditions on the street With a drag car it's easy. Tune it to wide open throttle until it turns the best ET/MPH, rinse, repeat. As long as you can get it to the staging lanes, idle isn't that important either.

Street is different. It has to idle, accelerate, go up and down hills. Throw in changing weather, and tuning becomes that much more tougher. The curve has to be scienced out for your particular set up (gearing, car weight, available fuel)

After all was said and done, I had to use a slower curve, and 28 degrees total timing to be able to run pump 91 octane fuel.

For years I didn't run a vacuum advance because I couldn't get it to work right. The combination of curve, total timing, and can adjustment made the engine surge too much.

After much reading and acquiring the use of a distributor machine, I got it down to where I have some slight pinging up a long 6% grade with the can connected which I can eliminate by shifting into fourth to reduce the vacuum to the can. All I have to do now is dial it back a bit more. One thing that I can say is that the general consensus of 50-55 degrees at a steady cruise, does not work. It's too much in most cases. The most my engine will tolerate in these conditions is about 44. Since my total timing is 28 I have it set to get another 16 degrees at 18" of vacuum which is where it is at 3000 rpm in 4th gear (remember the total vacuum of the can is pre set. Mine is a 9L which is 18 degrees crank. The adjustment only controls the rate. I have mine at a slow rate. It's at full advance at 20")

What I am finding is on roads with no stop light (highways, etc). My mileage is way better. In the city with stop and go traffic, it is much worse since the distributor spends very little time adding the extra vacuum advance due to throttle opening and closing.

Pinging is not a good thing to have happen. The engine will tolerate a little (I've had mine apart several times and the slight pinging it has seen hasn't caused any issues). Heavy sustained pinging will destroy and engine is short order (holed pistons, broken ring lands, damaged rings, crank pins/journals, main bearing saddles/caps, etc.)

I think the reason a lot of engine builders shun the vacuum advance is that they are taking the side of caution. With the drag guys, they don't need it. Idle and full throttle. Vacuum advance not needed. Street engines can use it, but adjusted it correctly with a fast curve and not enough octane and it could spell disaster.

As I side note, I found the older Mopar distributors had a more stable advance than the newer ones. I have several at my disposal and I tested them on the distributor machine. My feeling is the MSD would perform in the same way as the older Mopar units or better.