[davepl]

Let me tell you a story about a Ford guy with a motorhome. Similar situation. Dialed in 16 degrees timing as he was told, and it did indeed run the best there. Many of our motors will... I think I have 12-14 degrees into my 402.

Sadly he also had 28 degrees of mechanical timing built into the centrifugal advance of the distributor, so each time he went through the mountain pass on the I-90 he grenaded the motor. Broke ring lands off pistons, the whole deal. And he did this twice believe before he brought the motor in to be dyno'd.

The answer there was to put it on the distributor machine and take some mechanical advance out of it.

The lesson is that your distributor has a certain amount of mechanical advance built in. If that was designed to work with some small amount of initial timing like 4 degrees and you add another 12, you may have WAY too much at higher RPM. So if it turns out to need that much to run well, do be sure to have the high RPM timing checked with a light at least to make sure it's not wildly advanced.