victor 340 vs. super victor

I have a buddy who has a 69 Dart with a 13to1 comp. 360 with max ported X heads and a Mopar Perf. 620 lift solid cam, victor jr intake and 750 trc carb, shifts the motor at 8500 rpm, Car runs consistent 10.40 et. He put a super victor on because it is suppost to be better at high rpms the car slowed to 10.7 and 10.8, tried changing the tuneup but nothing work . He went back to the victor jr and went back to running 10.40 with no other changes. The super vic might have been to much intake for the cubic inches.