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02-17-2018, 07:56 AM #15000 RPM
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2 stroke vs 4 stroke - why the 4 stroke?
We see the 2 stroke phased out and the 4 stroke dominating the market, why?
Is the 4 stroke better at emissions? Fuel consumption? Power to weight? Power delivery? Torque? Top end? Total efficiency? Maintenance costs? Noise? Durability?RIB Unlimited 600/Merc 150 ProMax ss
Allison SS-2000/Merc 200xs ss
Hydrolift T-17/Merc 200xs ss
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02-17-2018, 08:28 AM #2
Simple. Smoke and oily exhaust contribute to pollution.
2-Strokes get their lubrication by mixing gas and oil. The cylinder walls, rings, piston pins, and crank bearings get their oil from that 50:1 mix that comes from straight mix or that oil-injection system installed on most outboards. The injection systems helped by reducing the ratio at idle and lower rpm to approx 200:1, but they still mix the oil with outgoing exhaust by the combustion process.
2-stroke motorcycles used to outnumber the 4-stroke bikes in the small/medium capacity 2 to 1 back in the 60's and 70's. During the 80's that visible smoke seen on the streets brought about bans, new laws, and big changes in philosophy. That smoke from our 2-stroke outboards seemed to escape the public's attention until the early/mid 90's when water quality in public water supply reservoirs started showing pollutants. Gordon
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02-17-2018, 08:59 AM #3
I'll add here too that the old barriers of horsepower to weight that used to be in the 2-stroke's favor by big margins is gone. Supercharging as used in the Mercury Verado series brings 200 and 300 reliable horsepower per liter into our near future. Kawasaki introduced it's 1 liter H2R a few years back with 324 horsepower from a 998cc four. Half-liter 2-stroke (500cc) race bikes were making more than 200 horsepower 20 years ago (400 horsepower per liter), but they smoked.........a lot.
2-strokes have 1/2 the time to intake and expel the new and old gasses so they they do both at the same time. At 6,000 rpm, this has 1/100th of a second to happen. This quick exchange finds that some of the fresh gas/oil gets out of the exhaust port along with the residual oil from the previous stroke. Oil, oil, and at 100 times a second - 6,000 times a minute = oil in our water supply.
Now, I do love my 2-strokes. I've got several bikes and outboards that love their oil. The outboards will last forever if cooling water and mixed oil are fed to them regularly. I like their simplicity and almost no required maintenance.
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02-17-2018, 10:22 AM #4Team Member
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true but simple internals , above old school, one word , DFI ................ KISS = Keep it simple stupid
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02-17-2018, 10:40 AM #5
Snowflake imbalance in today's value system ...
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tom kennedy, Davidlake, Capt.Insane-o, mrichartz, rudderless, NICE PAIR, Glasstream15, Forkin' Crazy liked this post
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02-17-2018, 12:04 PM #65000 RPM
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Gordon02, so it is a matter of lubrication pollution. I have an Optimax with about 130 hours on it and it does not smoke and there is no sot in the exhaust but yes, it does consume oil.
Outboards generally lead a hard life how about when the 4 strokes piston rings and/or valve seats wear down and start leaking... Will they not start polluting and smoking like a 2 stroke then?RIB Unlimited 600/Merc 150 ProMax ss
Allison SS-2000/Merc 200xs ss
Hydrolift T-17/Merc 200xs ss
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Capt.Insane-o, NICE PAIR liked this post
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02-17-2018, 01:32 PM #7
Non DFI 2 strokes scavenge exhaust with fuel charge meaning a substantial portion of the fuel charge goes out the exhaust unburnt on every stroke. DFI (optimax) motors do not have the fuel injected into the cylinder until the exhaust port is closed resulting in a much cleaner exhaust.
RockTeam Junk
No sparkling wiggles in here, only dump truck grinches.
"Screamin Heathen"
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conmax liked this post
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02-17-2018, 01:49 PM #8Screaming And Flying!
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And also if it weren't for the excellent exhaust port to port stuffing oiled prefuel charge would also be expelled.
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02-17-2018, 06:01 PM #9
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02-17-2018, 06:32 PM #105000 RPM
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Evinrude's E-TEC G2 series are not smokey or smelly. The low-emission computer-controlled outboards are nothing like the old outboard motors that your grandpa had.
The EPA figures show them to have the lowest total reported emissions of all current outboard motors. They also emit fewer particulates than a 4-stroke outboard according to the EPA Clean Air Award presented to Evinrude - the first outboard ever to win that.
As a 4-stroke accumulates running time, its emission output, especially hydrocarbons, increases as the rings wear against the cylinder wall and the valve seals start to allow minute amounts of oil past them. The E-TEC computer even allows for wear over time of the injectors and modifies the fuel flow to compensate. It does not pollute more as the motor gets older, that was another but unpublished reason for the EPA Clean Air Award.
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02-17-2018, 07:11 PM #11Screaming And Flying!
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02-17-2018, 08:25 PM #12
SeaHorse ,
I cant say anything about the E-tec's . And to be fair , go look on the front page and see if BRP is phasing out any 2 strokes in favor of 4 strokes . Go ahead , I'll wait ..
No ? OK .. then , I guess we are taking about Mercury's for now . And as I was alluding to with FMP , on the Opti's the gas goes in the chamber thru the head and the oil goes thru a little hole in the sleeve that the skirt uncovers while near TDC and blows into the crankcase . And then migrates up with the air flow . The seventh line on the pump feeds the compressor . I don't much care for them things , but that's how they work .
No , let me say until someone offer's a piggyback box that you can sit in the passenger seat with your Bluetooth Raspberry Dashboard and tune on the fly . All this stuff is in the stone age ....
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02-17-2018, 08:55 PM #13
Just wait till they put catalytic convertors on them..
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rudderless, powerabout liked this post
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02-17-2018, 08:56 PM #145000 RPM
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run a g2 inside a closed shop a few minutes and tell me they don't stink and pollute.
the epa test just doesn't measure synthetics.
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02-17-2018, 11:24 PM #155000 RPM
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You mean that it would be different than running your car inside of a closed garage?
At various boat shows over the years, because of E-TEC low emissions and super low CO output, the fire marshalls allowed a motor to be run inside the show booth in a barrel of water. That was a first for any internal combustion engine.
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powerabout, CRH1 liked this post
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