The HiPo 289 heads have screw-in studs for use of the solid-lifter camshaft. Otherwise, the heads were the same. Compression was higher also. The 289 4V engine was just a base 289 with a 4 barrel carb on it. This raised horsepower from 200 to 225. These 2 engines even share the same hydraulic camshaft design. By the way, the stock 4 barrel carb was only rated @ 480cfm. A larger gain could be acheived using a 600 Holley.
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