23' Performance 5.0 vs 5.7 Mercruiser

[Bushwacker]

Originally Posted by FishStretcher

There is a 7.4 MPI with bravo near you on CL. Not sure if that's too much for a 23 footer? . . .

A friend of mine had one in a 23 Sceptre. Good rig if you like to burn lots of gas! On one trip with us from Palm Beach to Great Guana Cay, his 120 gallon tank was nearly empty by the time we got to Coopers Town on the main island of Great Abaco, a distance of about 120 miles!

[FishStretcher]

Originally Posted by Bushwacker

A friend of mine had one in a 23 Sceptre. Good rig if you like to burn lots of gas! On one trip with us from Palm Beach to Great Guana Cay, his 120 gallon tank was nearly empty by the time we got to Coopers Town on the main island of Great Abaco, a distance of about 120 miles!

So with a Bravo 3 on a 25, would that be as bad? Just thinking about the siamesed exhaust ports on a SBC. It still would weigh less than dual 6 cyinders.

[castalot]

I had a 5.7 efi with the bravo 3 in a 251 proline great power package would run all day at 3800 running about 35 top end about 48 at wot
Never checked but economy was great would guess about 3-4 mpg atleast

[Bushwacker]

Originally Posted by FishStretcher

So with a Bravo 3 on a 25, would that be as bad? Just thinking about the siamesed exhaust ports on a SBC. It still would weigh less than dual 6 cyinders.

Fish, even though it weighs less than twin 6's, the 454/7.4L engine is still quite a bit heavier than the small block 350/5.7L, so it makes more sense in the much heavier 27 than it does in the 25, which is known to be sensitive to stern weight. CSC member 3rd Day has a 7.4L in a 27' Seamaster and was complaining about fuel consumption in it, so you might send him a PM to get more details. I think I'd pick a FWC 350 w/aluminum heads and a DuoProp or Bravo 3 drive over the big block engine. The small block MPI heads have lots of development work in them and make pretty good power, so if you can get enough speed at an acceptable vacuum level with that combo, why run anything heavier?

[ScottM]

Originally Posted by FishStretcher

There is a 7.4 MPI with bravo near you on CL. Not sure if that's too much for a 23 footer?

Water Rat (Chris) has a 7.4 in his 23 Sceptre with a Bravo drive (don't remember which model). If he sees this thread he'll provide performance/consumption #s. I do know that with a couple guys in the back of the boat, there's about an inch of water on deck due to the extra weight of the big block.

I've been on a 23 Sceptre with a carb'd 350 and Alpha drive which seems like a perfect combo for that boat.

[cdavisdb]

Fish: I agree with Bushwacker:

" if you can get enough speed at an acceptable vacuum level with that combo"

The 5.7 with a duoprop(or bravo3) balances 0k in a 25, especially with a light load. Load it heavy and you need careful to put a lot of weight forward. The big block would definitely be worse for balance(important in the 25), but If you are looking for speed, you might consider a big block and moving the fuel tanks forward. Mine, with a 5.7 throttle body EFI, is a bit slower than I would like. Light load is fine, 24-26 knots cruise. Load it down, the vacuum drops fast and you have to slow down, 21 knots or there abouts. Fuel economy goes to hell as well. You might find a good solution in one of the higher horsepower small blocks with more modern EFI, not sure.

[FishStretcher]

So I have some of the parts. I have a bravo 3 and 300 MAG MPI. I just need to burn the valves out of it at WOT so I can justify those aluminum vortec heads... Although I am not sure there is a lot more power with those heads. Although with good valves and seats, maybe you can run harder at cruise.

With the knock sensor, I can try higher toluene content race gas and see what a bit more power will get me. If I have the prop pitch to use it.

[Daysatsea]

Hooligan, I have a Quicksilver 1916P19 prop on my alpha II. Think it is a 14.5" x 19" pitch.