Sea level will give you about 250 - 300 RPM over the 3400 ft I was stating, if the conditions are right. I have raced in both and we try to keep acurate records. Cas is right; Try to choose a cam that will perform up to and peak at around 4500/4800 rpm. Seen a few guys that have dropped a hotrod car SBC into their jetboats and they performed REAL bad. An RV cam could be concidered too, since your motor isn't built to run into the 5000 rpm plus area. I've pleasure boated and raced only small blocks and still think they are great for the lighter jetboats. 200 lbs less weight at the pump makes a big difference.