I think its the smaller port 318 size, i was going to use this on my hot 360 but found a LD340, anyway i was told if going on a 340/360 that this intake is only necked down about an 1" in and to gasket match to the 340/360 head, the rest of the port is rather large and will work fine with a hotter 340/360 + cubic inch motor. the port window is smaller than the LD i picked up. Thanks Mike