The LS Cathedral ports, if I found the right port length about 5.5", the stock heads seem to be in the average fps of 250-260. 260 is supposedly the ideal 250 seems to be the largest port size you want to go with 240 fps maximum. So if right the LS seem to be on the large side. Eg. If was a mopar head a 300 cfm head with 250 fps would be 234 cc. 44cc more than a trick flow 190 head.