Does More Horsepower Give You Better Fuel Economy in an I/O ?

[gsrsol84mm]

Will a new 5.7 vortec 350 motor with 315 HP give you better fuel economy than the standard 260HP motor in a 24 foot albemarle with a duo prop outdrive ? Both motors have a carb. Mostly offshore running at a constant speed and trolling.

I am getting ready to repower the 1989 24 express and am having a hard time deciding between the New 315HP Vortec with electric fuel pump, electronic dist http://www.michiganmotorz.com/Marin...engine-SILVER+Package+(1967-2010+replacement)

and a rebuilt longblock from the same company using my intake manifold and original dist with points and a new Holly carb which I got with the boat.
http://www.michiganmotorz.com/Marin...gines/5.7L+(350+ci)+marine+engine+(1987-1995)

I have the block ready to be removed and the intake manifold looks OK.

The real question is it worth the extra $2000 for the new motor with 315 hp or will the rebuilt 260hp motor work just fine.
Doing the install myself so the labor is the same.

Appreciate the input. Thanks

 

[mylesm260]

Re: Does More Horsepower Give You Better Fuel Economy in an I/O ?

Short answer: yes

You are however splitting hairs.

The vortec motor has better volumetric efficiency (breaths better). This gives you more power.

It also has better Thermal efficiency (burns better) this gives you more fuel efficiency and more power/torque.

Having electronic ignition also helps you're torque/economy, as you can have a more precise ignition curve.


Having said all that, if you're at all concerned with economy, why the @#$# are you planning on going carbed?

 

[dan t.]

Re: Does More Horsepower Give You Better Fuel Economy in an I/O ?

in my opinion and with what I have experienced, a more powerful motor running at part throttle will give better economy than a less powerful motor at full throttle,I am in the process of swapping out a 305 t0 a 350 mostly for that reason

 

[Alpheus]

Re: Does More Horsepower Give You Better Fuel Economy in an I/O ?

It depends on how you utilize the new found HP. When you install the more powerful engine it will likely increase your WOT speed. If you run your boat constantly at this new found speed then no,you will probably get the same fuel consumption. Now with this more powerful engine it also has increased torque,so it will get you up on plain faster than the old engine and if you run it at the same speed as your old engine then yes you will see an improvement.

You can boost up the HP using the 260 long block just by adding the Vortec heads. You mentioned that your old intake looks good but that will not work with the Vortec heads.

 

[Bondo]

Re: Does More Horsepower Give You Better Fuel Economy in an I/O ?

Ayuh,.... I agree with Myles,...

If you plan to keep this boat for awhile,...
The Vortec is a Major step forward in Efficiency...

There is No downside to the Vortec heads, whether you're buying a complete motor, or changing the heads on an older SBC....

 

[mylesm260]

Re: Does More Horsepower Give You Better Fuel Economy in an I/O ?

3rd option is to have you're engine rebuilt and while they're at it swap the heads to vortec.

vortec heads are a dime a dozen. You're re-builder is going to re and re a set of heads anyway, just go to a wrecker, get a set of used vortec heads, and give them to you're re-builder with you're engine.


He can machine the new vortech heads and use those, and just throw away the ones that are on you're motor now.

He's likely going to be replacing you're pistons during the rebuild, so he can use the proper matched pistons to work best with the vortec heads.

It shouldn't cost you a dime more for the rebuild, and the heads themselves can't be more than a $100-$200 at a local wrecker.

 

[cr2k]

Re: Does More Horsepower Give You Better Fuel Economy in an I/O ?

Ahh How much gas/how many days on the water will that $2000 buy?

Cuz then you are gonna want a higher pitch prop, etc. etc.

Before you know it you are up to $3000 or more. I think I could run my boat for the rest of it's life for that kind of cash.

 

[CharlieB]

Re: Does More Horsepower Give You Better Fuel Economy in an I/O ?

If your go with the Vortec heads while rebuilding your old motor just remember to also pick up a Vortec compatable intake manifold.

You may also upgrade your old points ignition with one of the aftermarket (Marine) breakerless kits which will give you a much hotter spark.

The heads, intake and ignition can all be had during your rebuilld for far less than the 2G for that 315

AND the new power output should be very nearly the same.

Plan on repropping to keep the WOT RPM with range.

 

[gsrsol84mm]

Re: Does More Horsepower Give You Better Fuel Economy in an I/O ?

Thanks to everyone for their help. I think I have found my solution.
Since I got a brand new 4 bbl Holly Marine Carb in the box with the boat and I just pulled the intake manifold and it looks OK, I am going to go with a 300-320 HP Reman motor from Rapido Marine http://www.rapidomarine.com/default....s/default.aspx
They do all the work in house and use all New US parts to build the motor. It was an additional $185 for the increased horsepower with a total of $1735 delivered. No Core charge BS which ranged from $275-$425 with other companies I spoke to. All Rapido Marine does is build marine motors.
Hands down the two very best companies I spoke to were Michiganmotorz and Rapido Marine. I spoke to quite a few other companies who were less than pleasant to say the least.
Hopefully the 300-320 HP motor from Rapido Marine will perform similar to a 5.7 vortec with 315 HP. I will just rebuild my starter and alternator which beats replacing them with new imported junk. If I didn't have a brand new 4 barrel carb and decent intake manifold I would have bought the New 5.7 Vortec Silver package from Michiganmotorz

 

[John_S]

Re: Does More Horsepower Give You Better Fuel Economy in an I/O ?

The link didn't work for me, but believe the Rapido motor you are talking about is basic 350 4brl with a performance cam added. Your original concern was fuel economy. I'd bet that the performance cam engine will be more gas hungry than a vortec, even though it has similiar peak HP.

 

[gsrsol84mm]

Re: Does More Horsepower Give You Better Fuel Economy in an I/O ?

Well, finally spoke to someone who has a mid 80's Albemarle 24 express. He had the original 260hp motor in the boat and decided to upgrade to a 5.7 Vortec. He said he did not see a huge difference in power only only gets a 5% increase in fuel economy. the boat ran 22-24 knots before and that's what he runs now. That's a new 5.7 vortec compared to a 20 year old motor. He also had to build up his engine box due to the increased height of the Vortec manifold. I now feel the best solution may be a standard motor longblock rebuild with roller cams and lifters.

 

[N0 Luck]

Re: Does More Horsepower Give You Better Fuel Economy in an I/O ?

Hmmm... this is exactly what im looking at now. To vortec or not, that silver package from MM seems pretty good, then i could rebuild my old unit and sell to absorb some of the cost.... any opinions? my boat is 25' 89 Carver, 7000 lbs. Single engine w/ alpha drive

 

[Bondo]

Re: Does More Horsepower Give You Better Fuel Economy in an I/O ?

any opinions?

Ayuh,... There'll be Plenty of 'em,...
If you post a thread of your Own...
Hi-jacking this thread, Probably won't get you many responces, because your post just blends in with gsrsol84mm's....

Welcome Aboard...

 

[fishinpa]

Re: Does More Horsepower Give You Better Fuel Economy in an I/O ?

Hmmm... this is exactly what im looking at now. To vortec or not, that silver package from MM seems pretty good, then i could rebuild my old unit and sell to absorb some of the cost.... any opinions? my boat is 25' 89 Carver, 7000 lbs. Single engine w/ alpha drive

really dont see you makin much profit ,after buying a new engine and paying for parts and machine work to re-build the old. There isnt much prfit if any gained there!
why not have your current engine rebuilt ?


fish