I tried a Manley BBC 2.25" intake valve in my MCH ported bracket heads. I lost flow from .100" on up with the BBC valve.

Lift Manley 12850 BBC MP Intake Valve
0.050 34.30 32.63
0.100 64.84 72.37
0.150 95.38 114.62
0.200 133.03 146.00
0.250 167.33 180.72
0.300 203.31 219.20
0.350 238.87 256.02
0.400 277.49 297.30
0.450 311.57 332.25
0.500 347.93 362.21
0.550 369.65 387.22
0.600 384.86 403.09
0.650 397.97 406.98
0.700 399.91 417.61
0.750 406.40 419.97
0.800 411.12 423.20
0.850 412.29 428.24