I have one on my race car. It works well and I notice more torque difference than power. Did not do a syno run with it...yet, but it feels faster (I think)
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Anthony Rimicci | 64 Giulia Spider | 65 GTA | 68 GT Jr.
Rex Chalmers has experimented with an exhaust crossover on the V6 and found significant HP and torque inceases. I believe this was a singe crossover "H" and not an "X" type configuration.
The location of the crossover is key to tuning the performance - certain placements will give you torque lower down, other placements will move it up in the rev range.