prop damage?
 

Curious as the what extent of prop damage will affect top speed/rpm. I had a carbed 496 in the boat previously, dynoed at 600hp/602 ft/lbs, and with my 4 blade 28p bravo prop, the best I got was 76mph on gps at 5700rpm. engine just got rebuilt. Dynoed at 592hp this time around. Same prop, but I'm only getting 5200rpm, and 69mph.. when I picked up the the boat from the shop that installed the fresh engine, I noticed some light road rash on 2 of the blades from ,what I assume, them moving the boat around with their forklift. They denied it of course, so I lightly filed the damage out. Just curious if this is enough to cause my loss in rpm/mph? Looking for input before
i just buy a new prop

just remember, brett sells very expensive depth finders...

Not sure what that means but I do happen to have a 2016 Humminbird Helix 9 and 10 I'm looking to sell as a pair. Plastic still on the screens and boxes and all paperwork included.

$1800 for the pair.

Prop damage is interesting. Some times small dings create large props issues and other time a bunch of damage doesn't affect performance that much.
Was the road rash on the faces of the blades or the leading edges or trailing edges or the back of the blades? Show us a picture if you can.
A 7 mph loss from minor road rash isn't likely. 8 HP decrease on this application doesn't cause a 7 mph loss. I'm suspecting you don't have 692 HP. Sorry.
Or something else with the boat might be happening. Did you add any weight to the boat?

Brett

I agree.

Was it the same place that built and dyno'd your 1st motor ?

yes. Same shop.

no weight added. The rash was on the tips/towards the trailing edge of the blades. I bought the prop used when I originally got it, and even then, the slip percentage seemed high with my rpm and speed. I know I should bite the bullet and just spend the money in a new prop, Its just difficult to tell right now if it's a power issue, or a prop issue

Why does a fresh rebuild have less power? Did you request less power or use different parts? If not I would start with very simple stuff like checking the timing and maybe having the cam degreed. I would agree with others that thats not enough power loss for that mph loss. Back to the prop, see if you can borrow a prop from someone to verify your baseline mph and rpm.

Chris

Try swapping props from side to side and see if the rpm difference follows. Just remember that the sticks are backwards now.

I'm running single power. And unfortuntly , up in the western Canada area, the fast boats are few and far between which makes props near that pitch pretty rare. After some research, I'm gonna throw a new fuel pump in and see if that's where my issue is. I have a feeling it may fix my problem