volvo 280B, with GM 350.. need power..

[ac680]

I have this very clean 28ft 1979 Bayliner, with a single AQ260, a 280B drive, and a sick gm350.
Its been a great boat for about 4 years, but now the rods are getting noisy, low oil pressure. Salt water got in the engine, intake manifold leak.
Anyhow, I like to replace this engine, and like to get a little more speed at the same time.
I have a new "crate" gm350 290HP engine, (GM 12499529) . I will change freeze plugs, and install all the marine accessories. I am not too worried about the rest, the cam has little overlap, so I think it will do fine. My bigger issue is that I am not shure the sterndrive likes the extra horsepower. I was planning to do a little tuning with intake, etc, I expect to get 340HP or so, at 5300 RPM.
Anybody ever tried the limits of a 280B drive?
Maybe someone has experience with this crate engine in a boat? The boat lives in salt water.

Curious.

Henri.

 

[Don S]

Re: volvo 280B, with GM 350.. need power..

The 280 will handle the HP, just keep the rpm below 5000 (for the engine and drive sake).
If you really want to make the boat work better, consider changing the lower unit to a duo prop, then you'll have something.

 

[ac680]

Re: volvo 280B, with GM 350.. need power..

is it possible to do this? a lower DP unit that fits to a 280B housing, and transom assembly? I do seem to understand that the standard 280B prop and its spine have some issues with lots of HP.

Henri.

 

[Bondo]

Re: volvo 280B, with GM 350.. need power..

Ayuh,...........

It's just the Lower Unit that's Different........

Transom Assembley,+ Upper Unit are the Same.......

Like Don says,..... Prop it for 5000rpms or Less,+ it'll be Fine...........
Even with the Same Cam,+ other components,... That should give you a Solid 300hp......

 

[RicardoMarine]

Re: volvo 280B, with GM 350.. need power..

I have this very clean 28ft 1979 Bayliner, with a single AQ260, a 280B drive, and a sick gm350.
Its been a great boat for about 4 years, but now the rods are getting noisy, low oil pressure. Salt water got in the engine, intake manifold leak.
Anyhow, I like to replace this engine, and like to get a little more speed at the same time.
I have a new "crate" gm350 290HP engine, (GM 12499529) . I will change freeze plugs, and install all the marine accessories. I am not too worried about the rest, the cam has little overlap, so I think it will do fine. My bigger issue is that I am not shure the sterndrive likes the extra horsepower. I was planning to do a little tuning with intake, etc, I expect to get 340HP or so, at 5300 RPM.
Anybody ever tried the limits of a 280B drive?
Maybe someone has experience with this crate engine in a boat? The boat lives in salt water.

Curious.

Henri.

 

[RicardoMarine]

Re: volvo 280B, with GM 350.. need power..

Henri, your 280, as Don says, will definitely handle the additional power. Have it inspected, maybe have the gear pattern checked, see if the drive gear bearings are in good condition, install new seals and use it.
The Duo Prop lower unit is a bolt on affair but only with some "critical shimming" being performed by someone who knows how this is done. A must do! IMO. The DP is your best bang for the buck if you want more performance.

You mention that you must change Soft Plugs on this new engine. A "Red Flag" came up for me on that one! It would appear that you purchased an "automotive" crate engine from GM.... (hope I am wrong!) and not a Marine built engine........ as any Marine engine would come w/ the brass soft plugs from GM. (this is not the only difference between these) I'd use caution if this is the case..... these are not designed to work in a Marine application............ especially on a 28 footer and even with a DuoProp drive.
This would be a great time to install a Closed Cooling system on this brand new engine.

 

[RicardoMarine]

Re: volvo 280B, with GM 350.. need power..

Henri, I'd also advise installing new Primary Drive Shaft bearings/seals..... also a must do since the engine will be out.

Note: on the lower area of the transmission on the vertical shaft, there wil be a split ring keeper. Your unit will use a brass one. Make sure to inspect this and replace if it shows any signs of expansion.

Sorry about the accidental Quote above..... been a while since I've used this site.

 

[ac680]

Re: volvo 280B, with GM 350.. need power..

So, I am listening, will replace primary drive shaft bearings, and inspect drive shaft joints. Now for clarity, indeed I have a factory new moderately tuned chevy 350 meant for the street. I was planning to change to brass plugs, install the deeper dipstick, and install the windage tray from my old engine, and use all the other marine components from my old "volvo350".
There is apparently a difference in gasketing, and possibly valves, however not shure marine 350's use stainless for their valves , and there was mention of different pistons, and rings. I could do gaskets, however I have bought a set of original volvo head gaskets for a previous marine 350 i did, and it seemed identical to the steet set. I could rebuild my old 350, but I simply have a hard time with knowing how much rust the engine had inside. New is faster and actually cheaper .
To pull the engine, is it best to pull the top gear case, and remove the 6 long bolts that go through the transom housing , remove the compression plate, and seal, and pull the engine?

Thanks a million.

Henri.

 

[Bondo]

Re: volvo 280B, with GM 350.. need power..

What's the Cam that's installed in it,..??.... That's what Really Matters with a "Marine" SBC.....

I've never Seen a Difference in the Gaskets,...... Composite Gaskets are Composite Gaskets....
As long as you'r Not running a Steel Shim Gasket,.... They Don't Matter.....

The Rest of the motor will be Fine too,......
The Brass Coreplugs are a Good Thing,....
The Long Dipstick,+ Windage Tray,..??.... Use them off the Old Motor.....

 

[ac680]

Re: volvo 280B, with GM 350.. need power..

I have the option to use a new short block, that is actually build and designed for marine use. It has however a one part rear main seal, and I know the bolt patern is different than the older 2 part seal, which I have.
What are my options to make this work?

Henri.

 

[Don S]

Re: volvo 280B, with GM 350.. need power..

I would avoid that short block. It has a larger flywheel that WILL NOT fit under your flywheel cover, and just changing flywheels is NOT and option. Nothing else will fit it either.