Pre turbo exhaust leaks and knock. Why?

[vr3.9]

This isn't a question about will an exhaust manifold leak will cause knock, but why or is it false knock. Since I am stubborn and no matter what used the rear ebay exhaust manifold this is the 4 time I've experienced a sudden case of crazy bad knock only to find out I have a cracked weld etc. Once the leak is fixed the knock goes away and I can turn the boost back up. This last time I'm pretty sure happened because my drivers side motor mount was bad. One hard launch and it went crazy even on race gas tuned to 10.4 afr and 14lbs of boost it would still get knock, retard timing and run horrible.

So the question is why?

[vr3.9]

I hope it's false knock. I can understand how the noise might be picked up. Since race gas seems to have little or no affect it would also make me lean towards it being noise just being picked up.

[terrets]

At what point or rpm does it pick up knock? How many counts? Im leaning torwards noise since your running race gas..

[vr3.9]

Knock came on around 4k rpm would go to 25 a couple of times. After fatening it up and turning down the boost, I was still getting maybe 12 counts in second gear. Then in 3rd i was getting 2 or 3 with me letting off the gas a little to make sure it didn't go higher. Before the leak it wouldn't do that running a little leaner and with more boost on pump. Thought it might have been bad race gas at first but it does the same thing on pump gas.

[terrets]

25?! o.O ....I dont know what your problem is. Fix your leak I guess :)....It could be that.