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5.7 carbed vs 5.7 MPI

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  • #16
    So far nobody has told us why this worked for the Atlanta guys and not for anyone else. This was an actual case history. I wish I could find the details but since the study was done 17 years ago, even the forums (2) where I read it all don't search back that far.
    Mariah Shabah Z202 5.7L Mercruiser B3
    Jensen Marine 1972 Cal 21 cabin sloop
    Retired EE of 45 years

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    • #17
      Originally posted by DouglasW View Post
      So far nobody has told us why this worked for the Atlanta guys and not for anyone else. This was an actual case history. I wish I could find the details but since the study was done 17 years ago, even the forums (2) where I read it all don't search back that far.
      Because it was a publicity event. Something to drum up business. Hardly a legit "study".

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      • #18
        So just duplicating the same numbers that GM had, doesn't count I guess. More fake news?

        Mariah Shabah Z202 5.7L Mercruiser B3
        Jensen Marine 1972 Cal 21 cabin sloop
        Retired EE of 45 years

        Comment


        • #19
          Originally posted by DouglasW View Post
          So just duplicating the same numbers that GM had, doesn't count I guess. More fake news?
          C,mon..apples and oranges.

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          • #20
            EFI can compensate for changes in intake air temperature and barometric pressure. It can also increase spark advance to the optimum amount. So the possibility for increased power and fuel economy compared to a carburetor is obvious.

            Changing from a carb to EFI is a lot like going from a gas engine to diesel. There will be a payback, but you need to put on a lot of hours to see it.

            I once was involved in advising a customer on ordering a new 35 foot cruiser. He planned to own the boat for 5 years. The numbers might not be valid anymore because I had to use the cost of fuel vs gas and resale value to come up with the numbers and this was 10 to 15 years ago. But after taking into account the fuel, resale, up charge for a pair of Diesel engines and generator, the average speed he wanted and maintenance costs. He would have needed to run over 400 hours a year to see a pay back. Sales department wasn’t real happy with me because there is a bit more profit in a diesel boat. But it worked out in the end because we had a 35 gas in stock, so it was a quick sale and he come back in 2 years and bought a 40 foot with diesels.

            Moral of the story. Upgrades to a boat take along time to payback and never think that “this is the last boat I’ll ever buy”.


            Good Luck Muc

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            • #21
              Originally posted by DouglasW View Post
              So far nobody has told us why this worked for the Atlanta guys and not for anyone else. This was an actual case history. I wish I could find the details but since the study was done 17 years ago, even the forums (2) where I read it all don't search back that far.
              Did you not read the reply in post 13?

              In the late 80s. Early 90s my buds and I built many vehicles with TPI engines. Put them in everything from S10s to Chevy Vegas to a Grand AM (RWD conversion). We prefered the early motors with MAFS vs the later Speed Density

              Nothing majic about the results. You would get similar performance gains with an edelbrock Air Gap manifold, a carb spacer and a 650cfm carb
              Cheesehead boating the Gulf Coast of FLA 27.51° N, 82.53° W

              1988 Cruisers Rogue 2420 -VP 290 DP now powered by custom 468 - https://forums.iboats.com/forum/owner...988-rogue-2420

              Past Boats
              1970 Wooster Hellion - Merc 9.8
              2002 SeaRay 190BR - 5.0 - A1G2 - "Cheeseheads in Paradise"
              1984 Avanti 170DLI -3.0 stringer- "Ship Happens"

              What’s behind you doesn’t matter.Enzo Ferrari

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              • #22
                Originally posted by Scott Danforth View Post

                Did you not read the reply in post 13?
                Yes, but that doesn't explain why they could do it and you could not.
                Mariah Shabah Z202 5.7L Mercruiser B3
                Jensen Marine 1972 Cal 21 cabin sloop
                Retired EE of 45 years

                Comment


                • #23
                  Originally posted by DouglasW View Post

                  Yes, but that doesn't explain why they could do it and you could not.
                  What wasnt explained? based on your comments, it was a 1985 camaro. basically a 305 smog motor. so they took a smog strangled motor, unbolted a badly designed low-rise cast-iron intake and smog carb and bolted on TPI injection (available first that year) and it produces the same power it did that GM says it did - all 215hp. you state its EFI, however the truth is the intake plenum and a bit more timing is all it was - allowing the motor to breath and advancing the timing closer to the edge of detonation. take the same 305, bolt on a medium-rise cast iron intake and a carb and it makes 230hp as a marine motor (with a cam that has less duration, however just a bit more lift) take the same motor and bolt on an air gap intake, carb spacer and a decent carb and you get more power - about 270hp. to make more power than that, you need different combustion mix

                  its no different than the same 1985 vintage pickup truck motors producing 175hp with the smog choked TBI fuel injection and the same motor in a boat with a medium-rise cast iron manifold and a carb produced 250-260hp.

                  intake plenum size and runner size is extremely important to combustion efficiency and power.
                  Cheesehead boating the Gulf Coast of FLA 27.51° N, 82.53° W

                  1988 Cruisers Rogue 2420 -VP 290 DP now powered by custom 468 - https://forums.iboats.com/forum/owner...988-rogue-2420

                  Past Boats
                  1970 Wooster Hellion - Merc 9.8
                  2002 SeaRay 190BR - 5.0 - A1G2 - "Cheeseheads in Paradise"
                  1984 Avanti 170DLI -3.0 stringer- "Ship Happens"

                  What’s behind you doesn’t matter.Enzo Ferrari

                  Comment


                  • #24
                    rpm is a big variable. Maintaining torque to a higher rpm = more horsepower. More compression = more horsepower. More CORRECTLY MIXED fuel/air in = more horsepower. More heat converted to work = more horsepower. Less friction = more usable horsepower.

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                    • #25
                      Did you get any further forward ? Think some are getting confused with the engine you are comparing to the carb. The mpi or gxi aren’t efi or tbi. They are a whole different thing with common rail and individual injectors. Very efficient and powerful....when they are behaving.

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                      • #26
                        Originally posted by Scott Danforth View Post

                        What wasnt explained? based on your comments, it was a 1985 camaro. basically a 305 smog motor. so they took a smog strangled motor, unbolted a badly designed low-rise cast-iron intake and smog carb and bolted on TPI injection (available first that year) and it produces the same power it did that GM says it did - all 215hp. you state its EFI, however the truth is the intake plenum and a bit more timing is all it was - allowing the motor to breath and advancing the timing closer to the edge of detonation. take the same 305, bolt on a medium-rise cast iron intake and a carb and it makes 230hp as a marine motor (with a cam that has less duration, however just a bit more lift) take the same motor and bolt on an air gap intake, carb spacer and a decent carb and you get more power - about 270hp. to make more power than that, you need different combustion mix

                        its no different than the same 1985 vintage pickup truck motors producing 175hp with the smog choked TBI fuel injection and the same motor in a boat with a medium-rise cast iron manifold and a carb produced 250-260hp.

                        intake plenum size and runner size is extremely important to combustion efficiency and power.
                        I never stated it was EFI, clearly I stated MPI. ALL THEY CHANGED WAS THE CARB COMPONENTS TO MPI COMPONENTS, NOTHING ELSE. How many times do I have to mention that? And it was not 215 HP, it was 200 HP. You are thinking of another engine.

                        Might as well be talking to the wall...Unsubbed.
                        Mariah Shabah Z202 5.7L Mercruiser B3
                        Jensen Marine 1972 Cal 21 cabin sloop
                        Retired EE of 45 years

                        Comment


                        • #27
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                          Originally posted by BarryTurano View Post

                          Thinking I may have been looking at this problem from the wrong end. When I put this motor in I was still running D5's.I could not get above 4000 rpms. I dropped down to I4's. My rpm's got up to 4400 if I was going with the tide and wind at my stern (everything going in my direction short of hoisting a sail) I spoke with Ken at Prop Gods he put me in touch with Pablo at General Propeller. He suggested going down another number of pitch. He says that I should get up on plane quicker and hold plane at a lower rpm. And should bring wot to close to 4800 which would bring my cruise up to 3600 (@75% of wot) As of now 3600 rpms is 82.5% of wot. And it is possible my secondaries are slightly open. I am thinking I can probably cruise at 3400 where I am burning about 12gph. If I can get 21 knots at 3400 rpm that is the same speed I am getting at 3600 but 4gph less is a big deal. Especially on a 150 mile stream trip. I will be hauling in about 2 weeks for annual drive service. I will put the new wheels on then and report back. Stand by and thank you all.
                          Barry
                          Problem has been solved. I took Pablo's advice I put on a set of I3 props.The difference in performance is incredible. I am cruising at 3540 rpms running 26 mpg (about 23 kts) my fuel burn on the flo scan is 10.6 gph 2.52 mpg. I am running only on the primaries. The secondaries will start to open at 3850 rpms. At wot (4720 rpms) I am at 37.4 mph burning 25.3 gph.

                          It has been a long hard road with lots of experimenting. I being somewhat anal can now say with out any reservations I am HAPPY. Thank you all for the counsel and advice throughout the years. I really appreciate it.
                          US Submarine Force Veteran
                          USS Corporal SS346

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