Re: Prop Help
I believe your prop is fine. And I believe your tach is also fine. But I think something is very wrong with your motor or its setup...
Using a slip calculator, and assuming a 1.5 drive ratio (typical for 5.7's...can you please confirm your drive ratio?). With a 17 pitch prop at 3,000 rpms it has a theoretical top speed of 32 mph. You're claiming 28 to 30 which is right in range of where it should be at those RPMs.
The reason i say your motor is somehow sick is because a 5.7L equipped 19 ft open bow runabout should be able to EASILY spin a 17 pitch prop well past 4,500 rpms, and be running in the neighborhood of 50 mph...so the problem is not in your current prop. Frankly I would expect it to have no problem pushing a much bigger prop at those speeds....a 19 or 21 would be more typical.
Your motor should have a HP output somewhere in the neighborhood of 250 hp, and if it can't push a 17 pitch prop any faster than that, it's because the motor is only producing maybe about 110 hp. I feel you need to figure out why you are lacking so much power before doing any prop shopping...
Are your throttle butterflies opening fully? Compression check on the motor? Confirm plugs are firing on all cylinders? Fuel flow strong? Ignition base timing set properly? Is the ignition timing advancing properly with RPM increases?
