Volvo 4.3L duoprop 4bbl carb. conversion???

[sarmstrong]

Im very interested in converting to 4bbl. I have a 98 chapparral 22ft with a rebuilt 4.3 volvo and a DP...can not stand up coming out of hole but lacking in top end. To change props would be $1500 ++. I currently am dyno tested at 248hp with 2bbl but would love any response from anyone who has done the swap and how it affected top end. My previous boat was a stingray with a OE 4.3 mercruiser and 4bbl and was getting 62mph on a calm day<<<< really miss that!

 

[Don S]

Re: Volvo 4.3L duoprop 4bbl carb. conversion???

What's you WOT (wide open throttle) rpm with the props you have?

 

[mylesm260]

Re: Volvo 4.3L duoprop 4bbl carb. conversion???

My thoughts:


#1. There's no way a 2bbl 4.3 is putting out 250 horse power

Maybe a built 4.3 with vortec heads and good EFI or a good 4 BBL could put out 250 HP....

#2. Dons correct, you can't simply add power and expect to go faster, you need to look at your props and WOT rpms before you look into power too much.

 

[Bondo]

Re: Volvo 4.3L duoprop 4bbl carb. conversion???

Ayuh,..

I was thinkin' the Dyno is alittle Generous,...
And,...
You're all Right,...
It's those twin Dynos hanging off the back of the boat that tell the true story...

 

[abj87]

Re: Volvo 4.3L duoprop 4bbl carb. conversion???

22 feet is a big boat for a 4.3, most boats that size have v8's

 

[180shabah]

Re: Volvo 4.3L duoprop 4bbl carb. conversion???

248hp? What kind of dyno was used? Is this crank or prop rated power?

If that is crankshaft horsepower, it really doesn't sound that far out of line. It would be less than 220 at the prop. And I have always thought the 2bbl vortecs were underated. They just seem to way too fast for the 30-35hp deficit compared to the MPI engines.

As mentioned above the switch to a 4bbl might net you 20hp or so, and willprobably not make a huge difference. Drag is exponentially related to speed. On a 30mph boat, 20hp might get you to 35mph, but on a 50mph boat you may need an additional 100hp to get the same speed increase.

You cannot compare the speed of your chappy with that of your old stingray. Apples and Oranges.