heads

X heads came on 340's and had 2.02 diameter intake valves. J heads came on 340's or 360's and had either 2.02 or 1.88 intake valves.

All heads for 340/360 engines up through the late 80's had basically the same port size and shape and all have the same flow potential. The 2.02 valve size is only an advantage for an engine that will be turning rpm's in excess of 6000 on a regular basis. For a street motor you will have more low rpm power with the 1.88's. Any of the 340/360 heads can be machined to accept the 2.02 itake valve (the exhaust is 1.60 on all of them).

The 302's mentioned above are a 318 head that has a closed chamber and 318 size ports. These heads are refered to as a high swirl design.

The open chamber 340/360 (i.e., X or J) heads are not a good choice on a 318 unless work is down on the short block to raise the compression ratio. On a stock 318 it will make an already low compression ratio lower.