454 to 350

DCALLWELD

Sunday I went out and lost oil pressure in my 1993 Rinker 260 , it has the 7.4 with a bravo one.
I'm going to pull it and was thinking on putting in a 350 for fuel millage, with the same horse power.
I have been thinking  about the lack of torque at lower rmp with a smaller engine and would it be able to push the boat up on plane?  is there any one how specializes in this type of swap , and know what all it would take?

Michael T

x

212rowboat

you're likely not going to help economy by dropping to a small block...

the small block may produce similar numbers, but it won't be able to sustain those numbers as easily as the big block can... that equates to economy when there is a constant resistance such as boating, as opposed to on land.

212rowboat

If you had a rechargeable drill with the ts/sp settings on the shaft, that is precisely a choice between torque at a cost to speed (lowest setting) or speed at a cost of torque (highest setting)... This is performed through the magic of gears, but it's still a translation of torque to work , or what we call horsepower. 

Using that analogy, and we can only because the weight of the boat and the resistance of moving it through water are constants up to the point of plane, and certainly afterward... 

The drill, set on the highest setting, and squeezing the trigger, can be easily stopped with one hand... the drill on the lowest setting, cannot be stopped by hand, but it doesn't turn fast enough to do anything to speak of... if there were two drills, both capable of the same speeds (horsepower) but one had a bigger motor behind it (big block) you could turn just as fast,  But you wouldn't deplete the torque...

disadvantage?  You gotta lug that heavy drill around... power, as in turning the same bolts, is going to be similar if not the same, as you'll find the bigger brushed motor doesn't warm up near as much as the smaller brushed motor does to do the same thing., and because it isn't working near so hard as the smaller one. ... And that is what it boils down to, in my opinion in boating -load on engine... the lessor the load you can manage, the better your economy... there comes a point where it's way too much power, mind you, but for two engine platforms in similar conditions/ranges (as far as power goes), the bigger one is almost always more economical.  Strange but true... All about the load.  

Mike_G

 My 2014 260 has the 350 MAG, but with a Bravo 3.  Cruises at ~3800RPM@~29mph.  With full water, fuel, cooler(s) and 4 people, I have to turn 4000RPM.  I did WOT it once for 20 seconds or so and the speedo-meter passed 45mph!  No water and 1/3 tank of fuel, just me on the boat.

I have no idea what my fuel burn is, but it doesn't seem bad.  The 4 times I have had it out since I bought it, I burned around 20 gallons (guesstimating based on fuel I've put in the boat/hours) each time I went out (per day basically).  I usually spend a bit over an hour at cruising speed and maybe 45 minutes to an hour at around 1200 RPM (no wake mode).

Boat is still breaking in (only 10 hours) so ??? if those numbers will go down a bit.

Not sure if this helps, but that is my experience.  My hull might be different/more efficient, and cleaner cause it's new.  No bottom paint.

If I had the extra $12,000, and was ordering a boat, I would do a Volvo V8-380 just for fun. This was a boat show/end of year deal and was the largest motor option they had in stock.  Also, I liked the all white with navy blue stripe vs. the colored hull sides, so buying the smaller engine'ed boats and swapping in a larger one didnt' make sense (and I didn't want to spend the $$$.   )

-=Mike G.

DCALLWELD

well thanks all for your thoughts and led me to the same thoughts I was having , im going to sick with the big block . I'm not one to put a smaller engine in something just was trying to get a farther range out of the boat, if that's the case I will build a additional fuel tank. Im looking at US engines INC , on the internet they sell rebuilt 454 with 415 horse , and is spose to get 25% better fuel for 4200 has any one used them befor or know anything about there build? And I just had my out drive off and rebuilt so could a bravo one handle 415 horse , im not going to be wave jumping and racing it.

Michael T

 

x

Michael T

The Bravo 1 will handle 415 HP. It's more the torque that twists drives anyway and your torque for 415 HP - unless they have put in some kind of crazy cam - which I doubt as it'd be too expensive - will be fine too. As you have wisely noted, wave jumping with a cruiser is real **** the drivetrain. IMO you have made the right choice and will not regret it. MT

DCALLWELD

well good deal , yes I called and asked about the specks to make the power and I said I don't want a wild cam , bc starting, loading up ect. they said its noting much over stock. So ill brake open the pigey bank and see if I can get the new engine delivered and swap it over the winter , will post some pictures ,  

DCALLWELD

one last question may seem stupid , but will the increase in horse power allow the top speed to increase, even thow the engine will be operating at the same rpm range ?

212rowboat

Yup... It'll allow a bigger pitched prop to work for you. 

Michael T

x

Dream_Inn

Nice to see you here again Al.

BoatAway

AL SIGHTINGGGGGGG!!!!!!!!! SO NICE TO HEAR FROM YOU!!!!

DCALLWELD

yes I am planning on running of the of factory intake , rebuilt the carb , and if the  exhaust manifolds come off in one unit I was going to reuse them as well. and distributor and time curve ? Ill adjust the timing when i put the distributor in the new engine. I just talked to the shop that machines and assembles the long block and said that this engine plat form is designed to run with all the factory intake carb manifold ect.  

Michael T

x

DCALLWELD

yes I understand and am looking around some more. Thanks for the names ill look into them . I called US marine engine and talked with them as well as stated online. on the phone he has told me that using all stock components it will make that power... and I have a flying monkey lol not saying its true, but never the less that's what he is clamming. Im open to more engine shops if any one know any , I cant use my factory block. Also im in houstion tx   

Michael T

x

DCALLWELD

Michael I knew there was a difference between car and boat engines , but I did not know what the differences were thanks for pointing them out I'm learning a lot threw this process and with the help of this form, I deeply appreciate all the suggestions and help. IM not sure on the port configuration of the intake yet but will shorty when I pull it out, I am shooting for next weekend. I trailer the boat and only had it about a year so I don't know a lot of people in the marine inboard out board scene yet. BUT!!!!! I am  not new to boats I've owned my own boats before I could drive a car, legally that is. All my previous boat have had outboards so have a good network of outboard parts... but am new to the inboard/stern drive,

I found a place in Florida, RAPIDO marine 454 long block for 3500 and talked to him yester day for a good wile and he is not making wild power and fuel savings climes in the same sentence's, which tell me he may have the truth on his side.    

frenchship

DC
if I was you I would follow Al to the letter.......

Mike_G

No basis for this other than what I have read on other forums but...

I believe others have had issues with RAPIDO marine.  Do a google search and ask around before you make a purchase.

-=Mike G.