Volvo 280 DP Prop

[LegacyT]

So I purchased a 280 volvo dp lower, great condition great price... It was sold as a 1.95 to 1 for a SBC. Hovever after actually counting the revolutions from the input to prop shafts turns out it is 2.3 to 1 so a V6 ratio... I was pissed. However I was told I could compensate with some bigger props. Here are the details. My boat weights 3500 lbs with an average load and has a 305 which puts out stock 230 hp but prob a little more with edelbrock intake and ignition timing thats advanced a little bit. I figured with the right ratio i would probably need a B5-B6 set of props. I'm wondering with the V-6 ratio how much extra prob do you guys figure I'll need? Like a B7 or B8? I know most will wonder just get the right ratio!. But I got this one for dirt cheap as a repo and I can't find any in the right ratio for less than 2 grand!

Thanks,

 

[steelespike]

Re: Volvo 280 DP Prop

I probably won't be much help;I know next to nothing about dual prop drives.
I picked an arbitrary speed 45 mph I felt your setup could easily do, 4800 rpm 2.30 ratio 10% slip Prop comes up 25"
If slip was 5% a 24" prop is necessary.
Thats just using the prop calculator.If your boat can normally do 50 I think you can see prop selection may be a problem.
Others may be along and blow my thoughts out of the water, no pun intended.

 

[LegacyT]

Re: Volvo 280 DP Prop

Right now she tops out at 48 mph @ 4400 rpm with a 21 P single prop if that helps...

 

[Don S]

Re: Volvo 280 DP Prop

However I was told I could compensate with some bigger props.

If that was the case, why would Volvo (or any manufacturer for that matter) have all the different gear ratios?

It's because props also have a specific range they are good in. Too much pitch to keep your rpm down and you are slow getting out of the hole, but still have the same limit on WOT rpms as the correct engine.

Sure, you can re-prop the wrong ratio to keep from over revving the engine, but that doesn't mean the drive will act the same as the right ratio and prop set up.

Right now she tops out at 48 mph @ 4400 rpm with a 21 P single prop if that helps...

That doesn't mean anything as far as how to reprop the DP, only something to compare back too when you get the DP drive on and props on it.