Which prop to use on my AG290's

[Indy1K]

Hi Folks,

I have a question about Prop Pitch.
We just bought a 1985 SunRunner 310SB. The boat weighs in at 9300lbs dry. can carry 150 gallons of fuel. It is a Deep Vee hull with flat stabilizing chines. It is powered by 2 AQ260/AQ290 units. I believe they are 305 chevy small blocks. The engines were reported to have been rebuilt 2 years ago, but the boat had not been used much so the original hours must be close at 210/217 hours.

The engines run great. According to the previous owner, when he took it out, he claimed he could not get it over 3500 rpms even on plane. It has Bennetts on it, but don't know if he used them.
He said he thought the problem was the carburetors needed tuning. Then he lost the port outdrive propulsion and sold the boat.

When we picked it up, the outdrives were badly barnacled up and the reverse lock on the port drive prevented proper transmission engagement on the port side. I have picked up two Fresh water outdrives to replace those old beatup units.

Here is my question:
The props on the boat are 15" x 19" props. both right-hand. Transmissions are setup to spin opposite. If the Props are not original, as I suspect, would it make sense to think the boat is over-propped and get a set of 15"x17" props for it?

I think I read somewhere that these units should run WOT at around 4500 to 4800rpm?

Any thoughts or recommendations?

Thanks,

Kevin

 

[RicardoMarine]

.............................

Hi Folks,

I have a question about Prop Pitch.
We just bought a 1985 SunRunner 310SB. The boat weighs in at 9300lbs dry. can carry 150 gallons of fuel. It is a Deep Vee hull with flat stabilizing chines. It is powered by 2 AQ260/AQ290 units. I believe they are 305 chevy small blocks. The engines were reported to have been rebuilt 2 years ago, but the boat had not been used much so the original hours must be close at 210/217 hours.

The engines run great. According to the previous owner, when he took it out, he claimed he could not get it over 3500 rpms even on plane. It has Bennetts on it, but don't know if he used them.
He said he thought the problem was the carburetors needed tuning. Then he lost the port outdrive propulsion and sold the boat.

When we picked it up, the outdrives were badly barnacled up and the reverse lock on the port drive prevented proper transmission engagement on the port side. I have picked up two Fresh water outdrives to replace those old beatup units.
With exception to the later E drive, all AQ series transmissions will be of the same reduction.
With AQ series Volvo Penta, the lower drive unit determines the over-all gear reduction. (opposite of Mercruiser A drives)
Make dang sure that you bought drives with 1.61:1 lower units.

Also, just an FYI and FWIW........ when swapping one transmission or lower unit from one Intermediate housing to a different Intermediate housing, critical shimming must be performed.

Here is my question:
The props on the boat are 15" x 19" props. both right-hand.
The Port side should be turning a LH propeller.

Transmissions are setup to spin opposite.
It's easy enough to do a check.
Stbd side vertical rod will be connected to the Port side of the eccentric piston arm. This drives from the upper driven gear allowing for a RH propeller.

Port side vertical rod will be connected to the Stbd side of the eccentric piston arm. This drives from the lower driven gear allowing for a LH propeller.

Important: FWD gear engagement on either drive will be a result of the shift cable "extending" at the gear yoke.
REV gear engagement will be a result of the shift cable "retracing".





If the Props are not original, as I suspect, would it make sense to think the boat is over-propped and get a set of 15"x17" props for it?
You will need to perform a WOT RPM test as per OEM specs.
In order to do that:
engines must be in full tune.... including proper ignition advance at the full-in RPM (see your OEM specs for this) .
hull must be clean.
drive ratio must be correct for the engines (1.61:1).

If these are not in order.... the WOT RPM test becomes moot.


I think I read somewhere that these units should run WOT at around 4500 to 4800rpm?
That sounds correct.... but I'd verify.
(WOT RPM is a test only..... and should not be sustained for any length of time)

Any thoughts or recommendations?

Thanks,

Kevin

 

[Indy1K]

Thanks Ricardo,

I got my shim calculations done and received the shims I need. Got all new seal kits.
Yes, I verified they are 1.61:1
I will be using my original transmissions up top.
Painting up the transmissions, Intermediate components and lower units before assembling.
I was just curious about those 15 x 19 props being to high in pitch, and yes, the port side is turning a LH prop. My mistake, til I looked at them
I will probably invest in a set of 17s for testing

I will not be able to do the WOT testing until next spring. Boat is dry docked right now for the winter.

Regards,

Kevin