Prop up or down for Volvo Penta

[Fishhead-1]

QUOTE=muc;n10263952]You won't be happy with it because running this engine like you are "lugging it" will cause the valves to tulip or burn out the head gasket.
I recommend more testing, a proper compression test both cranking and running, maybe a cylinder balance test.
You are low on power or there is something wrong with the hull.
This wasn't a good year for Chris Craft and this model in particular was kind of problematic.
Maybe hull is waterlogged?[/QUOTE]

Muc is right, I have the same engine and drive ratio and was running F4 set and ended up with some tulliped intake valves. It was running around 4300 rpm max. Switched to F3 set.

 

[Scott Danforth]

Boat that big should probably be running F3s.

What elevation are you running at?

 

[SeaEsta-12]

QUOTE=muc;n10263952]You won't be happy with it because running this engine like you are "lugging it" will cause the valves to tulip or burn out the head gasket.
I recommend more testing, a proper compression test both cranking and running, maybe a cylinder balance test.
You are low on power or there is something wrong with the hull.
This wasn't a good year for Chris Craft and this model in particular was kind of problematic.
Maybe hull is waterlogged?

Muc is right, I have the same engine and drive ratio and was running F4 set and ended up with some tulliped intake valves. It was running around 4300 rpm max. Switched to F3 set.[/QUOTE]

How was performance after the switch?

 

[SeaEsta-12]

Boat that big should probably be running F3s.

What elevation are you running at?

I am at sea level.

 

[Fishhead-1]

i burn about the 13 gph neighborhood it increased using the f3 set, but engines running easier. Boats a 24 ft osprey. With the weight of you boat Scott is right you need a f3 or possible f2 set. Be nice to try a loaner set before buying

 

[muc]

SeaEsta,
I replied to your prop swap post that got deleted. Then I realized that you were the same person with this thread. So I don't know if you saw my reply about trading your F4s for F3s at a prop shop. My next post was might not be a good idea to do that because you wouldn't be sure you got a set of F3s that were true to pitch. Rebuilt props are rarely as good as new.
But, if 4000 rpm is the exact speed your engine is running with F4 prop set. Chances aren't very good F3 will get you 4800-5000 with the boat loaded the way you use it.
If you want to try new props. All the Volvo dealers I've worked for (even the bad one) would swap out props at least once to get you the props you need. Maybe it just the area i worked in but as long as you bought them from us and brought them back looking like new with all the packing materials intact we would do it. You might try working with your local dealer, they can be your friend.
Let us know how things work out for you, there are a lot of helpful people here.
But please don't continue to lug your engine. I've had to give those people the bad news (you need a new engine) too many times and it's hard to keep people happy with their boat when it starts getting that expensive.

 

[SeaEsta-12]

Hello everyone,
Well, I made the switch on my props, and she gets right up to the correct RPM's at WOT. Looks to me like the F3 was the way to go.
Expensive "tests" to make, but I finally found my right props.
My top speed with 60 gallons of fuel, one person, and a boat that weighs 6100 lbs dry, was 35 MPH or 30 knots.
I think that will be about all I get out of her with a single 350 engine.
Thanks again for all your help!

 

[muc]

Glad I was wrong about needing more than props. Happy boating.