Another Yam v G2 Faceoff

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  • #16
    On a modern DI 2 stroke gas is never mixed with oil or circulated around the crank. Because you no longer have gas trying to wash away the oil or diluting it, you can use a fraction of what you used in the past. And since the gas is only introduced to the combustion chamber at the last possible millisecond, you can jack up the compression without the concern for knock/detonation.

    Old 2 strokes were inefficient because they had 2x the combustion events as a comparable 4 strokes running at the same speed. Their intake and exhaust were also simultaneous, and the only way to be certain the exhaust gas was clear, was by running unburnt fuel/air straight through without burning it. You could wind up burning 20-30% of your fuel in the exhaust, which is a less than ideal place to do this. A modern DI 2 stroke may still do the same thing, but only with air.

    DI runs at high pressures to overcome the combustion chamber pressures which are 100s of PSI at the time fuel is introduced, and to atomize the fuel into as fine of a mist as possible to provide instant and complete combustion. Any combustion that takes place after a certain point is simply wasted energy. To visualize this take a can of hairspray and spray it on an open flame. One quick burst gives you an instant fireball. Take the same hairspray in a pump spray bottle and pour a little on the ground. Try to light it. It may or may not burn. If it does burn, it will do so slowly. That’s the difference between modern DI and everything that came before it.

    Prior to Modern DI, you had to squirt in enough fuel to absorb the heat of compression without self igniting, and to have enough remain atomized in a fine enough mist to burn instantly and fully to achieve your desired result. To give you an idea of the prevention of knock/detonation I’ll use my old Porsche as an example. It’s a ‘85 928. ‘85 was the first year for the 32 valve engine and full electronic fuel injection. It has no knock control system. The only safe guard against knock is two wires you hook together when you only have low grade gas available. Connecting the wires retards the timing by a set amount. It uses 24lb/hr fuel injectors. In ‘87 they released the s4. It had a more refined intake. They updated the fuel and ignition ECUs (they were separate boxes on those cars back then). They added knock sensors and knock control to the new ignition box. It gained 30hp and they went down to 19lb/hr fuel injectors. So by adding proper knock control, they were able to reduce WOT fuel consumption by as much as 20% or more. Think about that. On traditional fuel systems on almost identical engines, on one you’ve got to be able to dump in 20-25% more fuel, not to get the vehicle down the road, but to act as a buffer against knock/detonation. On the other, you add two sensors and a more sophisticated ignition to detect and compensate for knock and conserve a significant amount of fuel under the conditions when knock is most likely.

    How does that relate to modern DI? Modern DI removes fuel from the equation until the exact point in time when it must be added to it. It allows extremely precise quantities to be added at a precise time with a precise atomization. Knock and detonation risks are reduced as the time from when the fuel is introduced to the time the plug fires is so minuscule, the fuel hasn’t the time to absorb the excess heat from a high compression ratio and self ignite. You’re not wasting extra fuel as a buffer against knock, nor are you pouring a puddle on top of a piston. You’re not dumping unburnt fuel into the exhaust, and the amount of partially burnt fuel is reduced drastically. You’re only using what’s required for the combustion event itself with minimal waste otherwise.

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    • #17
      Originally posted by cpflaum View Post
      Thanks, I had not even thought about the v versus inline impact. I totally agree that the meaningful comparison would be equal configuration engines on identical boats. When I look at what I am getting with my G2s compared to Yam or Merc, the fuel cost, after considering the cost of oil, is only about 5-7% in favor of the G2 (but range is 15-20%). This isn't a big deal, actually trivial in the scheme of things. I don't think that the modest difference in time to plane is important on a big boat (flats boat is a different story) either and who cares about top end (they are about the same).

      The big savings seems to be in the maintenance cycle and repairs (10 year, no hours limit in FL). I put about 20 hours per month on my engines, so maintenance is every 25 months compared to every 5 for the 4S. At $500 per engine, assuming Yam and G2 costs are similar and they appear to be, that would be $1000 for the G2 versus $5,000 for the Yam over 25 months. I have no idea regarding the frequency, type and cost of non-warranty repairs on Mercs and Yams and how to factor this in.

      Please, somebody correct me if I have screwed this up.
      You have to factor in initial cost too, how much more does the G2 cost over the Yamaha, plus oil assuming it uses more oil then a Yamaha between changes.

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      • #18
        Initial cost is about the same when you factor in the power steering and the cost difference between the Idock and the Yam/Merc joystick systems. Etec also has free Idock and rigging right now. Anyway, at this time, both of them are unobtainium.

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        • #19
          Originally posted by cpflaum View Post
          Initial cost is about the same when you factor in the power steering and the cost difference between the Idock and the Yam/Merc joystick systems. Etec also has free Idock and rigging right now. Anyway, at this time, both of them are unobtainium.
          The rigging is not available?

          Also, regarding modern DI 2 strokes, I believe there is some oil routed to the vst to be mixed with the fuel. At least with an HPDI. I still consider the HPDI to be modern.

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          • #20
            Wow! A civilized discussion without personal attacks and very informative explanations!

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            • #21
              Originally posted by Pstephens46 View Post

              The rigging is not available?

              Also, regarding modern DI 2 strokes, I believe there is some oil routed to the vst to be mixed with the fuel. At least with an HPDI. I still consider the HPDI to be modern.
              The Idock-compatible engines, 250 and 300 hp A series, have a six month plus backorder. My understanding is that there is no oil mixed with the fuel in the G2.

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              • #22
                would be nice to see a comparison of twin 150 2-strokes and twin 200 4-strokes. Top speed, MPG, cruising speed. This was just a 2 stroke vs 4 stroke thing. Maybe BoatTest is getting political. Who ever pays their fees, they stack the deck?

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                • #23
                  Originally posted by Cregeis View Post
                  Wow! A civilized discussion without personal attacks and very informative explanations!
                  It’s really not hard to see why. There’s a thread over there discussing the same test which I presume you’re referring to. That thread is over 100 posts at this point and most of it revolves around “I know more than you, my engine is better than yours.”

                  Most of the technical commentary ceases to be technical and focuses on making value judgements. (I.e. engine x is bad, engine y is good). A lot of people their have too much ego tied up in their arguments and boating purchases.

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                  • #24
                    I think it's all relative, minute and winter.
                    For the most part, most twin engine boats struggle to plane on one engine, unless you swap props.
                    And, if it planes on one engine, you stand a pretty good chance of damaging some part of that engine. Then, when that happens, you gots no engine.
                    So, buck up, smoke a ceegar, (or drink a few beers) turn on some muzac and fish.
                    This whole 2 stroke, 4 stroke, 150 is better than your 200 is for the birds.
                    The general boater wants to get in his boat, turn the key and have it run. They pretty well all do that, consistently.
                    As for wishing for "what was".
                    Well, for the most part, that is all gone.
                    Simple fact.
                    Engine Sales and Service
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                    • #25
                      Personally I think competition is a good thing. It drives research which leads to improvements. On the other hand marketing and advertising can lead to comparisons that are deceiving and full of half truths to make their product look better to the consumer. I am pretty sure Yamaha could come up with a comparison that would make their motors look better to the consumer. But since they out sell Evinrude by a large margin it is in fact it is not necessary...Charlie

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                      • #26
                        Wow, even an elderly boat salesman can learn something here and I have really nothing to add except--salesman's tongue in cheek--why would anyone want a two stroke this day and age when we have one hell of a time re-selling them on the used market? My 2 cents worth.

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                        • #27
                          I haven't been on here in several months. First post I read is 2 stroke 4 stroke comparison...

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                          • #28
                            Originally posted by Sneaky Snooker View Post
                            I haven't been on here in several months. First post I read is 2 stroke 4 stroke comparison...
                            Welcome back, he, he, he!.
                            BWP

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                            • #29
                              When and if I ever sell my HPDI I'll be looking long and hard at a new G2.

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                              • #30
                                Erie Skipper it's because of mind set just like a Diesel/Cat boat/ old 2smoke. I own 2 out of the three Ram eco diesel and yes a Cat I could give a chit about any test I have stood right next to a G2 running and owned a Yamaha 225 and like them both. Evinrude paid for the test so they win!!!!!!!!!!

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