Dear Dick,
Ah, yes, the infamous Pantera drone. In your case, a Mangusta drone? Please check this tech article from the Great Lakes Panteras website tech session. I found the approach to be unique. I followed up with Gerry and found about a handful of Pantera owners in their circle that had done the mod and they noted less "boom" and , in one case, a dyno proven increase in power. If Gerry's theory that the boom is due to a sonic Helmholtz effect is correct, then if it occurs in a Pantera, it should also occur in a Mangusta. There being so few Mangustas, I haven't heard of the boom phenomenon with them, but I bet it is there.
http://www.greatlakespantera.c...r%20Modification.pdf
Warmest regards, Chuck Engles