Compare gas consumption

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jayjay4888

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How does gas consumption compare amongst 2 strokes, vs etec's vs four strokes given comparable hp size (150). I am looking at buying a boat equippped with a 150hp 2 stroke but it seems pretty thirsty.
 
dingbat

dingbat

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Re: Compare gas consumption

You should see a 25-30% overall reduction in fuel usage with the 4 stroke over a carburated 2 stroke. The DFI 2 strokes supposedly do equally as well, but no personnel experience with them. When my 2 strokes dies, I'm going 4 stroke

FWIW: 200HP Ocean Pro boat weighs #5.4K Cruise in good sea conditions, ~2 mpg. In not so good conditions, a little over 1 mpg. Trolling ~ 2 gph.

Good friend, same boat, 250HP Yamaha 4 stroke: Cruise in good sea conditions, ~3 mpg.... In not so good conditions, a little over 2 mpg......Trolling ~ 1 gph.
 
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H

H20Rat

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Re: Compare gas consumption

Also keep in mind most of the advantages are at partial throttle. If you take a certain hp motor and run it WOT, it surprisingly makes very little difference what type of engine, they all will suck down the fuel.
 
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jayjay4888

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Re: Compare gas consumption

Thanks guys
I had this boat out for a test run, the lake was almost flat and admittedly I was pretty wide open so maybe if I throttled back a bit I would not have been quite so shocked at the fuel consumption. I also think the boat is a bit under powered which I think would make a difference. A 233 Sea Fox with a 150 Merc.
 
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ricohman

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Re: Compare gas consumption

My 200hp 4.3 uses far less fuel than my old 80hp 2 stroke merc. I've never seen a thirstier motor than those "tower of power" mercs.
 
F

fixnfly

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Mar 3, 2010
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Re: Compare gas consumption

Remember a 2 stroke produces quicker power than a 4 stroke. It roughly takes a 250cc two stroke to produce the same HP as a 450cc four stroke. Haven said that the response time on a 2 stoke is faster. 4 strokes are heavier given the same HP rating.
4 strokes in theory are more fuel efficient.
 
Texasmark

Texasmark

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Re: Compare gas consumption

Having come up in the days of the cross flow with no attention paid to economy, I have to disagree. Compare a '60's cross flow to a 4 stroke of the day and I'll agree, having had both. I had the '88 Direct Charged 115 tower and it was one of the most fuel efficient engines I ever had. Course I ran it just over the upper rpm limit and it loved it. Had it on a 17 1/2 Ranger pad boat hull and had a 10 gallon built in tank. Never ran it out of gas, water skiing and all.

When OMC did the Looper in '68 they did a lot of things to up the economy. Some were unique to 3 cylinders, like looping and exhaust tuning, but my '71 4 cyl 125 OMC was very reasonable on fuel even though it was cross flow. It had all the upgrades other than looping. My current engine is a 3 cyl Merc looper and I run it over top end also. Very efficient.

Having had what I have had over the years, I'd take a current 2 stroke OB hands down. On operating efficiency of any engine, go to current mfgrs. wwws and look up their performance curves. Shows you right quick where to run your rig if economy of operation is your main concern.

Mark
 
L

lakegeorge

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Re: Compare gas consumption

jayjay4888 said:
How does gas consumption compare amongst 2 strokes, vs etec's vs four strokes given comparable hp size (150). I am looking at buying a boat equippped with a 150hp 2 stroke but it seems pretty thirsty.
Click to expand...

If you go to the Merc web site or Yammy site you will see that they claim that their 150hp 4 strokes use about 14/15 gph.
 
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H20Rat

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Re: Compare gas consumption

lakegeorge said:
If you go to the Merc web site or Yammy site you will see that they claim that their 150hp 4 strokes use about 14/15 gph.
Click to expand...

Which is hp/10, so pretty much exactly what the 2 strokes get a WOT.
 
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Chris1956

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Mar 25, 2004
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Re: Compare gas consumption

A carb 2 cycle motor uses more fuel than a 4 cycle motor or 2 cycle DI motor of the same displacement, due to the exhaust scavaging. There is no way to change that fact.

In a 2 cycle carb motor, the fuel/air mixture must sweep the exhaust out of the combustion chamber. To make it an efficient cleansing of the cylinder, some unburned fuel/air needs to escape out the exhaust port. This is where the extra fuel consumption and pollution come from.

In a 2 cycle DI motor, only air and a bit of oil scavange the combustion chamber. When the exhaust port closes, gasoline is injected into the combustion chamber and the spark plug fires it. All the fuel is consumed, lowering pollution and raising economy.
 
dingbat

dingbat

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Re: Compare gas consumption

lakegeorge said:
If you go to the Merc web site or Yammy site you will see that they claim that their 150hp 4 strokes use about 14/15 gph.
Click to expand...
......and a Prius gets 20 MPG at the drag strip...... how does relate to the real world usage how?

Valid data for buying a Prius for drag racing. Not so valid if your buying as a commuter.
 
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MH Hawker

MH Hawker

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Re: Compare gas consumption

Boats like a lot of gas period, you may be more interested in golf.
 
NSBCraig

NSBCraig

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Re: Compare gas consumption

Don't forget to factor in maintenance costs to.
 
ChadSD

ChadSD

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Re: Compare gas consumption

I have an '88 Mercury 115hp in-line six TOP that drinks 12 gph at WOT (50 mph gps) and about half that at cruise (3500 rpm, 35 mph) pushing a 17 foot CeeBee Avenger. She looks and sounds great guzzling though! Nothing like the sound and smell of a tower of power!
 
Silvertip

Silvertip

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Re: Compare gas consumption

I invite you to visit Yamaha's web site and look at Performance bulletins. Pick a boat, then look at the various engines tested on that boat. If you really pay attention to the fuel consumption charts. You will generally find a two stroke almost always pushes the boat faster at any rpm. Therefore if you compare fuel consumption at the same rpm the four stroke will alwas win. If you compare at the same speed you will see economy numbersare much closer. Four strokes do have an advantage at very slow speeds. The two stroke will also have tbe boat on plane at a lower rpm.
 
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crabby captain john

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Re: Compare gas consumption

Not missing my 2 stroke on a 17'er. I'll keep the 150 on the 21'er. All considered I'm not burning that much more. Quieter and more reliable but 100 hr services bite when you use the boat a lot. I'd never go back...
 
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Chris1956

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Re: Compare gas consumption

Hey Chad, I had a similar rig. Merc 1500 on a 1974 16' Avenger. I blew up the TOP a few years ago. I now have a Merc 135HPV6 on that boat. The IL6 motor sips fuel compared to that V6, however, the V6 has lots more low end power, and is not quite so "high strung". Top end is about the same, but the boat power is more predictable.
 
D

dan02gt

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Aug 30, 2012
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Re: Compare gas consumption

smokingcrater said:
Which is hp/10, so pretty much exactly what the 2 strokes get a WOT.
Click to expand...

Sounds about right. I had a lightly modded 07 Optimax 150 on a 18' fish and ski. It made around 170HP and would burn 17-18GPH at WOT turning 5850RPMs.

For comparison the MercCruiser 4.3MPI in my Stingray burns 16GPH at WOT turning 4750RPMs.

The fish and ski weighed ~2200 lbs and would run 58MPH on the GPS and the Stingray weighs ~2700 lbs and will do 56MPH on the GPHs.

I like to cruise between 35 and 40 and the Optimax was consistently better than the MPI by 1.5GPH at these speeds.

I don't know if this info helps the OP but I find it interesting. I measured fuel consumption on my MercMonitor that reads directly from the computer BTW.
 
dingbat

dingbat

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Re: Compare gas consumption

Quieter and more reliable but 100 hr services bite when you use the boat a lot.
Click to expand...
"100 hour service" is a misnomer. It assumes 100 hours of annual usage. In season, I can put close to 100 hours on a motor a week...don't get weekly service.

Oil changes are cheap compared to buying gallon jugs of 2 stroke oil by the case every two to three weeks
 
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