The small port heads on the W motor look to be ample, and for street use and cruise nights they work fine.The main reason that the 690 and the 583 head make much more power has not so much to do with the port size, but the fact that the roof of the port has been raised a lot. The floor of the port is curved upward on both series heads, it is pretty dead on air flow, leaving the top 2/3 of the port left to accomplish all the air flow. The reason the Z-11 cranked it on pretty well is that the entire intake side of the head was raised and straightened, and so were the intake ports. The intake on the Z-ll was a dual plane, not good, but the entry angles and the air flow was straightened out considerably. The port entry angle on the small port W motors was so low that the roof of the ports was right about on the center line of where the center of the port should have been. Raising the roof of the port and filling in the floor to effectively straighten it out and reduce the changes in angles between the plenum of the intake and the bowl around the intake valve would have fixed a lot of things, for sure. Also, the large port intake with its square turns between the plenum and the intake surface of the cylinder heads left room for improvement. For an example of a BAD intake port, look at the intake port at the flange with the head on a cast iron 340 horse intake for the #6 cylinder. Also, the 327 factory hi po aluminum intakes seem to have square turns between the intake gasket surface and the plenum. Obviously, the factory released small block intakes that were far better horsepower makers later on with the mid '60's hi po 327's.