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

X heads are good if you own a 68-71, to stay original.. some 71's had the 2.02 valve head.You need to keep in mind large valve heads like higher compression, the mixture tended to swirl if the gas quality was lower. the j head came around as gas quality went down. Today, the X head won't perform any better because the gas sucks. Actually, the 70 AAR six pack used the first 360 type smaller valve, because it flowed better, because of so much fuel at a lower RPM. It's in the books. Now, a 69' with 100 octane and X heads, watch out! I beat a street hemi with it! ( back in 1975) Chrysler called it a baby Hemi for a reason. My racer guy always said: big valves high octane and high fuel flow, small valves low octane, . at least how the were built to run then. No technology, no chips, electronic Ignition, no big fancy sticky tires. Pure muscle, and keep it on the ground. It was all light to light, over and over. 0-60 ruled, as it was hard to find a quarter mile on a city street. When you got to the boonies, then things changed. It was all fun! the cops had the attitude: If I can't catch you today, then there is always tomorrow. by 1970 I was in the military, and racing was OVER!