Fuel economy

[magster65]

In general terms, what uses more fuel, a single big block or twin small blocks? (Say... 2 x 305/5.0 (200 h.p.) mercs. vs. 1 x 454/7.4 (330 h.p.) merc. in a 28' 10-12000 lb. planing hull). I know at low speeds the two small blocks would use more because of the larger engine displacement, but what about as you apply power? I'm thinking the twins would have an easier job (higher vacuum readings) and that may result in them getting the same or better fuel economy at cruise (2800-3000 +/-). How much would the cruise speed differ? My thought also is that the twins would easily outperform the big block but they are heavier than a single... any thoughts? Oh why not... how do you think twin 165 merc. 6 cylinders would stack up against either of those combinations?

 

[Walt T]

Re: Fuel economy

what boat??

 

[Trevor]

Re: Fuel economy

What model of motors (hp) are we talking about you also have the Horse power to weight ratio to think about the boat will weigh more with the twin V8s and will need more snot to pull it out of the hole and keep it on plane.

 

[magster65]

Re: Fuel economy

This is just hypothecical. Let's call it a Trend, Commander or... a medium quality planing hull. I guess they may be a little lighter than what I've guessed. I'm trying to figure out how big of boat I can get to and still afford to run it. (p.s. Walt, I can't afford a powerful twin diesel or I'd surely buy one!) Thanks

 

[Boatist]

Re: Fuel economy

If you end up with the same total HP the twins will use about 1/4 more fuel. Can very a little but in every case I checked the twins used more. You also have the added saftey of twins and of course docking is easier. If you want twins and fuel mileage try two smaller motors that add up to less HP. The Chev Vortec engine is one of the few to gain HP and MPG, EFI models run better and get better Fuel mileage. Also pick a boat with a flater V at the transon. Deep V use lots of fuel. Most boat manufactures can give you speed and fuel mileage for different engine packages. If your buying new can usually get it but very hard on used.