Also when I was looking at cams for my 383 build before my vortec build comp cams suggested picking a cam I wanted and stepping up about 10* in duration due to the cams predicted RPM range being based off of a 350 CID motor and the 383 needing more duration to stay in the same power band if using the same parts as a 350, heads, intake, ect. The recommendations for the cam are more than likely based on a 350. The 383 will have more vacuum and require less compression than a 350 with the same cam.

 

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