Engine swaps for economy
 

Yes I know this sport is not cheap but.....
I burned 110 Gallons at $3.33 per gallon here in California last weekend in my 33 Scarab AVS with Modded 502 MPI 530 HP a side. I love driving. I was thinking how about an Aluminum LS or small block swap to get the weight down and improve efficiency.

I was wondering how fast the boat would go if I went down to 380hp LS engines vs my present set up and how that would affect fuel burn at cruise of 3400RPM BB vs LS> If there any efficient setups that make sense?

That equation will never work out........like trying to justify buying a 100K Tesla to save $40 a week in gas!

Just as a reference point, 32 Sunsation with 6.2 small blocks (320 HP) would burn a gallon a minute at WFO which was 70+ MPH. If you were building a new boat then it might save you two ways (one on the build, one on the usage). To re-rig your existing boat to save money is never going to work out financially.

My best suggestion is to run your engines at 3,000 rpm and head directly to whatever party cove you have close by and anchor out all day followed by returning to the dock at the same rpm.

I burnt bought the same as you if not a couple gals more with 6.2 MPI's in my 312 Fastech & we anchored for 3-4 hrs Sunday...
We ran bout 6 hrs Saturday pretty easy & 2-2.30 Sunday...

the most efficient way to boat is put $100 worth of gas in some one else's boat. same experience and they are thrilled someone gave them gas money.

other than that, if you are worried about the fuel cost, performance boats are not for you.

^^^ This, ..Like to the 15th power

+1. I can run 200 miles on 110 gallons of gas with the 400s.

I can run 200 miles with 80 gallon tank with my BBC. :flag:

You meant BBCs!

Fuel economy for me has everything to do with my right hand.:boat:

I can tell you the LS sip fuel compared to a BBC there combustion champers are just that much more efficient. That being fuel still contains X amount of BTU whether its in a BBC or LS or briggs motor. Those BTU are what drive your piston down and spin the crankshaft.

Something you can do with a LS that aren't as easy as todo with say a MPI motor is set your fuel burn at cruise to pretty lean. Due to the efficiency of the cylinder heads, the port fuel injection and your abilty with cam sensor to control end of injection events you can get the most out of each gallon of gas.

I know on my boat at 3k rpms is pretty close to 30mph and roughly 30 percent throttle, so what I did in my ECU is set my lamda to be 1 (afr 14.7) and my timing up there(each motor is different) I have a full function knock detection on the boat so I don't have to worry as much about part throttle detonation. I can actually go as lean as 15.0 and timing up 4 degree before I see any kinds of knock showing up. Plenty safe.

From the caculations I have done I burn roughly the same fuel at cruise that my boat did when it had a 4cly mecruiser motor in it.

What does all this mean, pretty much nothing. The cost and TIME you spend changing this over and hell even just dyno tuning the motor to peak performance will never pay off compared to what those BBC drink for fuel. If you think boat gas is expensive don't look at air planes.

Great points. I like the idea of:
Tuning what I have to be more efficient at cruise. I bought a LM-2 and MEFIBurn. Can anyone spend a few minutes to start me off in the right direction with this.
Alum LS engine would be efficent due to the weight and modern design.
And yes I know boating is EXPENSIVE this is my 6th boat!!! Too much fun!!

Maybe go up a prop pitch for lower rpm at cruise, trade off is your top speed rpm will be affected.

What he^^^^^ said. If your are concerned about fuel cost take up dirt bikes or something because fuel is the Least expensive part.

That's why I went with a 8.1. It's the big brother of the LS series.

Just curious what the load is at your 3000rpm cruise speed?

For 50k plus an ILMOR gets pretty good WFO MPG
110 Gallons at $3.33 = $366.30
But 50k, buys around 136.5 fill ups, at $3.33 a gallon.
At least for me thats a lot of boating.

Switching to more efficient might sound like a good idea until you really sit down and figure out the cost benefit. It's way cheaper to feed in more gas $$$$ over the long term unless you plant to keep it for let's say 50 years. Maybe then you will break even. Good luck.

8.1 isn't really the big brother to the LS, still runs BBC head. Really nothing like like a LS actually. lol

At 3k I'm roughly 30% throttle. This isn't a offshore boat and your going to laugh when I tell you but we all start somewhere. Its a 25ft pontoon and the motor is a ls 5.3l with twin turbos. Will run really close to 70mph at Wot.

Just because you are running a lower rpm does not mean you will use less fuel. An increase in pitch will more load on the engine.
Its like going from level ground driving a car and then going up hill. You have to give it more gas to maintain your speed and rpms.

I'm pretty happy if gas is the only thing I buy in a season.

New outdrive = 2 or 3 seasons of gas money
New motor = 4 or 5 seasons of gas money