X-heads vs J-heads: what's the difference??

69 Cuda 440 said
Jake, at your request...........

Generally Accepted Flow-Rate Numbers

Cylinder Head @ Lift______________.100"__ .200"___.300"___.400"__.500"

#2538194 ~ 'X-Head'
Intake................................................. 58 ........ 125 ....... 172 ...... 208 ...... 221
Exhaust............................................... 45 ......... 95 ........ 122 ...... 135 ...... 140

#3418915 ~ 'T/A Head'
Intake................................................. 66 ........ 123 ...... 170 ........ 206 ...... 220
Exhaust............................................... 63 ........ 110 ...... 135 ........ 145 ...... 148

#3418915 ~ 'J-Head' {w/2.02" Intake}
Intake............................................................... 118 ...... 166 ....... 193 ...... 200
Exhaust.............................................................. 90 ....... 117 ....... 135 ...... 140

#3418915 ~ 'J-Head' {W/1.88" Intake}
Intake................................................................ 110 ..... 165 ....... 190 ...... 193
Exhaust............................................................... 90 ...... 117 ....... 135 ...... 140