4.3 vs 3.0 fuel economy?

I have a '07 Larson 180 Sport with a carburated 3.0 SX drive. I don't know exactly what my fuel consumption is, but I like to keep the RPM's under 3600-3800. This is about 33-35 mph. With the same boat and a 4.3 fuel injected running at the same speed, how will the fuel economy compare?

Re: 4.3 vs 3.0 fuel economy?

I can tell you my 4.3 (carb) in my 19' Sea Ray burns about 3 gph cruising.

Re: 4.3 vs 3.0 fuel economy?

My 8.1L (MPI) burns 2.7 GPH when I'm cruising. Of course, that's cruising pretty slow.

Re: 4.3 vs 3.0 fuel economy?

Boattest.com is probably the easiest and most unbiased place to find info like this.

According to Boattest.com, a 2007 Larson 180 with a 4.3L gets 4.6 MPG at 30 MPH.

A 2008 Maxum 1800 with a 3.0L (closest thing I could find with a 3.0L) also gets 4.6 MPG at 30 MPH.

It would probably be hard to tell any difference in fuel usage between your boat and a 4.3L as long as you operate them identically. But the 4.3L would have the advantage of having the extra power if you wanted to use it.

The 3.0L Maxum will do 43 MPH@3.7 MPG, the 4.3L Larson will do 50 MPH@2.8 MPG. The 4.3L will get 3.7 MPG at 45 MPH.

Re: 4.3 vs 3.0 fuel economy?

mthieme said:

I can tell you my 4.3 (carb) in my 19' Sea Ray burns about 3 gph cruising.

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How fast and how many RPM's? Also. what size prop?

Thanks.

Re: 4.3 vs 3.0 fuel economy?

45Auto said:

Boattest.com is probably the easiest and most unbiased place to find info like this.

According to Boattest.com, a 2007 Larson 180 with a 4.3L gets 4.6 MPG at 30 MPH.

A 2008 Maxum 1800 with a 3.0L (closest thing I could find with a 3.0L) also gets 4.6 MPG at 30 MPH.

It would probably be hard to tell any difference in fuel usage between your boat and a 4.3L as long as you operate them identically. But the 4.3L would have the advantage of having the extra power if you wanted to use it.

The 3.0L Maxum will do 43 MPH@3.7 MPG, the 4.3L Larson will do 50 MPH@2.8 MPG. The 4.3L will get 3.7 MPG at 45 MPH.

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Thank you, this has been very helpful. I have to try to figure out how many GPH I burn. I don't have a flow meter, so I will just have to guess/calculate.

Re: 4.3 vs 3.0 fuel economy?

Does anyone have an opinion about fuel injection on a 4.3 vs carb?

Re: 4.3 vs 3.0 fuel economy?

Since both motors will be doing the same amount of work the consumption should be close.

on a boat ill take a carb any day over open loop efi.

Re: 4.3 vs 3.0 fuel economy?

borz170 said:

Does anyone have an opinion about fuel injection on a 4.3 vs carb?

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I am in the middle of upgradding a 4.3 to higher horse power values. I can tell you this all marine engines run increbily rich....they are some polluting SOB's.

With that said there will be little difference between a 3.0 @ 130 hp and a 4.3 at 200 hp... For now Marine engines are still living in the 60's....It seems a saftey issue..AKA cold burn engine...much to learn but

Re: 4.3 vs 3.0 fuel economy?

I prefer the FI for the smoothness and responsiveness, although as long as a carb is set up and running right you won't be able to tell any difference. My experience (hot-rodding stuff since I turned 16 in the early 70's ....) has been that carbs tend to need more maintenance than FI. And usually what happens is that the first time it's not running right people start screwing with the carb. Unfortunately, most of the time the problem is ignition related so they just make things worse.

Even though the FI is running open loop (that means it's feeding the fuel based on a pre-set table in the computer, not actually measuring the amount of oxygen left in the exhaust like a car does - oxygen sensors don't like the wet exhaust on boats), mine appears to be dialed in very well from the factory. It has the original plugs in it (2003 model, so they're 6 years old) and they appear to be a perfect tan color every time I check them. I've never had to do any kind of tune-up on it (no distributor, coils on each plug). It idles perfectly at 630 RPM, and throttle response is instantaneous!

Now that I've said all that, I'll probably have to do a total rebuild this year .....

Re: 4.3 vs 3.0 fuel economy?

A boat opperated at 30mph will require a certain amount of hp. It does not matter how much available hp there is. There will be minor variations due to differences in weight/loading, but they will be so small that you likely will not be able to quantify them without test gear. With a larger engine, you may find yourself opperating at a higher sustained speed, this WILL increase your fuel usage, but it is a result of the speed and not the larger engine.

Re: 4.3 vs 3.0 fuel economy?

45Auto said:

I prefer the FI for the smoothness and responsiveness, although as long as a carb is set up and running right you won't be able to tell any difference. My experience (hot-rodding stuff since I turned 16 in the early 70's ....) has been that carbs tend to need more maintenance than FI. And usually what happens is that the first time it's not running right people start screwing with the carb. Unfortunately, most of the time the problem is ignition related so they just make things worse.

Even though the FI is running open loop (that means it's feeding the fuel based on a pre-set table in the computer, not actually measuring the amount of oxygen left in the exhaust like a car does - oxygen sensors don't like the wet exhaust on boats), mine appears to be dialed in very well from the factory. It has the original plugs in it (2003 model, so they're 6 years old) and they appear to be a perfect tan color every time I check them. I've never had to do any kind of tune-up on it (no distributor, coils on each plug). It idles perfectly at 630 RPM, and throttle response is instantaneous!

Now that I've said all that, I'll probably have to do a total rebuild this year .....

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Thanks for the reply. What engine and outdrive are you working with?

Re: 4.3 vs 3.0 fuel economy?

180shabah said:

A boat opperated at 30mph will require a certain amount of hp. It does not matter how much available hp there is. There will be minor variations due to differences in weight/loading, but they will be so small that you likely will not be able to quantify them without test gear. With a larger engine, you may find yourself opperating at a higher sustained speed, this WILL increase your fuel usage, but it is a result of the speed and not the larger engine.

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Thanks, do you like the fuel injected 4.3 or would you go with carbs? Also, mercruiser or VP?

Re: 4.3 vs 3.0 fuel economy?

abj87 said:

Since both motors will be doing the same amount of work the consumption should be close.

on a boat ill take a carb any day over open loop efi.

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I'm going to go ahead and say the exact opposite.

I would take ANY efi, open of closed loop over a carb.

MAF based EFI only allows for about a 5% correct in a/f ratio's from the o2 sensor input anyway. All the o2 feedback (closed loop) really does in most efi systems is fine tune the engine emmisions to be catalytic converter friendly.

90% of the vehicles on the road today in states that do not have mandatory emissions testing and are over 5 years old are all running open loop. Automotive O2 sensors fail like clockwork, and most people don't replace them unless they have to.

I'm running a closed loop EFI system without the o2 sensor (so in effect an open loop system) on my boat with a 4.3 vortec pushing about 225HP. It runs absolutly perfect, I would never give that up and go back to a carb.

Re: 4.3 vs 3.0 fuel economy?

borz170 said:

Thanks, do you like the fuel injected 4.3 or would you go with carbs? Also, mercruiser or VP?

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Current boat has a 4.3 with 4bbl carb on it and I have no complaints. It pushes my 18'er to 48mph fully loaded and 51mph with me solo and low fuel(over-reving though). Instant starting? Yup, although I do have to wait 20 seconds or so before I can put it in gear. Nasty black soot on transom? Nope. Hesitation on acceleration? Nope. However I can't run at 2900RPM, 2800 or 3000, but not 2900. An issue that just doesn't exist with EFI. I also don't have the "sexy" EFI logos and increased resale value.

Would I rule out EFI, no way. In fact there are times when it is nice to have, like when someone else is starting the engine...

Most of the problems that people have with carbs stem from a lack of knowledge. A proper tune up every year and some fuel stabilizer will go a long way torward preventing problems.

mylesm260 said:

4.3 vortec pushing about 225HP.

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Is that a "dyno'd" number? Is it a crank or prop rating?

Re: 4.3 vs 3.0 fuel economy?

It's a direct drop in from a 2001 AWD astro van rated @ 200 HP in the automotive application with the restrictive exhauste and 2 catalytic converters.

It is essentially the same engine as this:

http://www.gm.com/experience/technology/gmpowertrain/engines/specialized/marine/2010_4300_Marine.pdf

Except my Injection system is "poppit" rather than what the GM marine engine has.

It pushes my 21' open bow boat to 63 MPH (GPS) @ 4900 RPMs (23P prop vs 19P that came with the boat)

Re: 4.3 vs 3.0 fuel economy?

Those are the kind of numbers that make me love the 4.3...

Re: 4.3 vs 3.0 fuel economy?

mylesm260 said:

It's a direct drop in from a 2001 AWD astro van rated @ 200 HP in the automotive application with the restrictive exhauste and 2 catalytic converters.

It is essentially the same engine as this:

http://www.gm.com/experience/technology/gmpowertrain/engines/specialized/marine/2010_4300_Marine.pdf

Except my Injection system is "poppit" rather than what the GM marine engine has.

It pushes my 21' open bow boat to 63 MPH (GPS) @ 4900 RPMs (23P prop vs 19P that came with the boat)

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Never liked to respond to these types of situation before. To think at a motor with 200 hp would be almost the same as one with 130 is abusrd. But looking into MEFI-3 and how untuned it is..its very conceivable that a carbed 130 could do as well..

Your a case in point mylesm...you have a remapped ecm and can do 63 with a 19' 4.3......That's all tuning....Makes you wonder if they are going to try to shoot those enriched gases thourgh a cat huh......

Im not being negative with efi, ive spent quite a bit of money trying to keep it and finish a 4.3 upgrade it's very intresting..

Re: 4.3 vs 3.0 fuel economy?

My Ecu has actually not been re-tuned at all.

I'm running the stock astro-van Fuel maps and Cam profile.

I basically dropped an astrovan motor into my boat, swaped the starter and alternator for marine one, and made a custom wiring harness using the astrovan harness.

I'm using all the stock automotive sensor, including the MAF, and simply did not connect the o2 sensors.

You can still plug an obd-2 scan code reader into the harness and read the automotive codes.

The engine starts, idles, and pulls perfectly. Great fuel efficiency, and lots of top end power.



The actual fuel maps for a marine application are virtually the same anyway, especially for an MAF based system.


The MAF sensor measures the air entering the engine, then the fuel "maps" are just basically to set the air-fuel ratio and the ignition timing.


More primitive EFI systems will rely only on MAP sensor inputs. This makes the fuel tables much more critical, as you are essentially estimating how much air your engine will be drawing in based on absolute manifold vacuum. If you change your intake, exhaust or cam profile, the ECU will not correct for it, and your A/F ratios will go way out to lunch.

If you took a MAP only EFI system from an automotive application and dropped it in a boat, it would run like crap.

What I would really like to do is drop a 6.0L v8 from the corvette or trailblazer SS into a boat, but nobody makes manifolds for them that work with a Bravo-1 leg

Those are LS series V8's, rater for 400 HP and 400 ft/lbs of torque. I bet they would make 450 HP in a boat, no problem (improved intake and exhaust)

Here is the closest engine GM marine has to the corvette engine....
http://www.gm.com/experience/techno...s/specialized/marine/2010_6000_LY6_Marine.pdf



They would likely get the same mileage at cruise as the 4.3 aswell... More efficient heads and combustion chambers, higher compression ratios..... better intake manifolds....

Re: 4.3 vs 3.0 fuel economy?

You have a far better grip on the subject than i do.. but a 4.3 doing 63 is out there shall we say and i attributed it to tuning. From the conversations i have had with our techs and some reputable programmer's mefi-3 has some very different mapping as compared to automotive. Anyway's this conversation is a bit off the beatn path and not to pc so good luck with your boat and have fun