I had a 502 0.060" over that dropped a valve and destroyed the head & block. Had a hard time finding a replacement 502 block. So I found a brand new Generac 489 engine locally with scat rotating assembly.


It is a Gen 6 454 bored .030" over with scat 4.25" rotating assembly. From the manufacturer it is made to run on Natural gas or Propane and runs @1800rpm. So changing heads & cam.


I am looking for recommendations on what cam & heads I should run? and what kind of HP i would be looking at. I would like to use my dart single plane intake & Holley 850 carb so need rectangle port heads.

That is a painful way to lose a 502, but pivoting to a Gen 6 489 stroker is a solid recovery. Since you’re aiming to reuse that Dart single-plane intake and 850 Holley, you’ll want a top-end package that breathes well enough to justify the manifold without losing all your low-end torque. I’d recommend a high-quality set of aftermarket aluminum rectangle port heads (like AFR 265cc or 290cc) to keep port velocity high while providing the flow your 4.25" stroke demands. For the camshaft, a hydraulic roller with duration in the 230°/240° @ .050" range and lift around .600" will provide a rowdy street/strip personality that plays nice with your 1800-RPM-industrial-roots block. Depending on your compression ratio—which you'll need to verify since gas/propane pistons often differ from gasoline slugs—this setup should easily pump out 550 to 600 HP and a mountain of torque.