repowering... should i up the horse power?

[bardfromedson]

im ordering a rebuilt engine from rapido marine. for 50 bucks I can get upgraded pistons. for another 180 I can upgrade the cam and springs. its for a 85 Volvo penta 350. 95 percent of the time I run it at around 23-28mph trying to get the best fuel economy heading out to the fishing grounds. I do quite a few trips where there are no on water fuel stations so economy is pretty important. stock hp in the old motor was 260. the new one will be about 280 without upgrades and over 300 with. just wondering how the increased hp will effect fuel economy and if I should go for the upgrades. the cost isn't a big deal if there is some benefit. if I can get more power at the same rpm can I maybe run a different prop and be faster at a lower rpm ? any other pros and cons to upping hp?

 

[Wireman]

What type of leg are you running single or duo prop? If single you might want to consider changing out your lower leg to a dou prop that could give you about a 15 to 20% increase in fuel economy and try not to use the four barrel

 

[NootkaSounder]

Correct me if I'm wrong but it's a lot easier to make a higher horsepower motor work less the a smaller horsepower work at its max. Will be better on the internals and possibly keep you out of the four barrel with the higher compression.

I would do it and replace the leg when or if it goes unless you like fixing stuff that ant broke or have a goal in mind. If your not already rocking a duo.

 

[wolf]

Well I can tell you I went from a 350 to 300 hp to a 383 stroker 425 hp engine (on duo prop) I get way better fuel than before all the added HP does though is give you that bottom end and holding in rough water. I can hit 3 ft chop doing 3200 rpm doing about 24 mph and it doesnt flinch dont even touch the throttle, I come out of the hole at about 25 ft but the duo prop helps a lot, you will only see about 2 to 4 mph more with the added HP,
After 3 years running my engine is back in the shop for a freshen up as I got a rear main seal go so while its in there and apart everything looks great just going to throw in a set of rings and going to Vortec heads which I was able to find with a alum.manifold as well , as id rather have the more power LOL,
I get about 8 to 10 GPH depending on how many people and water conditions with a 7000 lb boat

Good luck Wolf

 

[Bennie]

Hi, I repowered a 95,24' Seasport from stock 454 with Holly carb to a 496 FI(8.1)360 hp,running a duo prop. My mileage has gone up and extra torque and hp are only positive benefits, also FI is just great for start up and idle. My mechanic suggested running diesel series props and I'm using A6 series, also installed a vacuum gauge and run at highest vacuum when on step, gives best fuel economy and normally best mph for conditions. Regard's.

 

[wolf]

But Bennie theres a big difference form a small block to big block engines especially those types my buddy had a bored out 460 in his truck it didnt matter if it was loaded with 3000lb or empty that pig got about 8 mpg but man did it ever haul alot of moose home....those engines are gas hogs.....as you know

 

[Bennie]

Hey Wolf, haven't had any experience with a 460, my 8.1l uses about 7 to 9 gals of fuel to run from Sunset to Silva Bay, appr 25 NM. I run between 2700&3200 rpm, 14 in of vacuum, depending on conditions usually a nice ride!
Regard's
.

 

[wolf]

WELL thats good fuel economy for that size of boat compared to an outboard...id be happy with that....

 

[bardfromedson]

I'm running a single prop at the moment with a 2 bbl carb. Switched out the old points ignition and carb last season. Swapping out the alternator,starter, fuel pump and manifolds along with the engine this year as preventative maintanence so I don't think the duo prop is in the budget but maybe next year. Ballpark what would a duo run me? Anyrhing else I should look at swapping out/ upgrading that might ruin a trip? Plan on keeping all the old bolt on stuff in camp as back ups. I'm all for better fuel economy. I will be packing gas with me and doing a beach fishing trip in the charlottes so the less trips back to town the better.

 

[profisher]

Man would ever be interesting to have say 6 boats all the same with various power configuration, IO stock, IO built, 4 stroke OB and 2 stroke outboard. Give them all precisely 1 gallon of fuel, line them up side by side, pick a speed that all can maintain and see how far they all go, then post the results. That would be interesting.

 

[scott craven]

Man would ever be interesting to have say 6 boats all the same with various power configuration, IO stock, IO built, 4 stroke OB and 2 stroke outboard.

4-stroke OB hands down, just my opinion.

 

[profisher]

The winner would be less interesting than the distance between them all. How much better or worse they are.