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Any conversion to 4 barrel carb experience?-gctid404504

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    Any conversion to 4 barrel carb experience?-gctid404504

    I have the 5.0L 220hp 305cu engines on my 2006 305SB and it is underpowered without a doubt. It really should have 5.7L engines but it doesn't and I can't afford to change the engines out so I am looking for a way to get some more horsepower. It seems the only practical way is to convert to a 4 barrel carb and I was wondering if anyone has taken this on and could pass along your experience, parts depot and reflection on if it was worth it?

    I did check with Michigan Motorz and they would sell me a "kit" for around $1,000 (x 2) that had Aluminum High Risers, New Carb, New Intake Manifold and Throttle Bracket and estimated I'd get 20Hp from the effort.

    its doable.

    Why do you say its underpowered? Your the 1st 5.0L owner of a 305/3055 since I have been here that has said the 5.0's are underpowered for that boat.

    I only have about 30hp per engine on you, mine are rated at 250hp each, I dont think thats a HUGE difference from the 5.0's 220hp.

    just curious.


      Fair question and I hope I don't get too far off track from my original question. I have had issues with both engines due to being overworked and I've spoken with two dealership and three mechanics and all have said the 305 really should have had 5.7L standard. With the factory 3-blade 21" props the boat struggled with four people loaded and the hole shot was terrible. I've moved to 19" SS props which have helped the problem but I now have to cruise at about 4000 rpm and gas mileage is killing me, not that it is great to start with.

      At 4000 rpm, I am doing ~26 knots with the 19" SS props.


        I did this on a 2001 2455 with a 5.7. The estimated gain was 30-40 but I don't know how that would translate to a 5.0. I did a marine manifold that was recommended by my local shop for around $500, but unfortunately I don't recall which model it was, and a Holley marine 650 carb. I had to get a custom mounting bracket made up for the throttle cable. I spent about the same price, so assuming those products are good, the price is decent.


          I have had issues with both engines due to being overworked
          What issues exactly? This is a suspicious statement. Overworked...meaning what exactly...?

          When you are at full throttle with a light load, what is your RPM and speed?


            That is pretty terrible performance, your right. Are you using your trim tabs on takeoff? Full tabs down, then adjust up after getting on plane?

            Without tabs my 3055 takes a bit to get on plane, goes super bow high and is working hard. With tabs it can do it fairly easily and keeps the bow nice and low. Its really a night and day difference for me.


              i think a 5.0 4 barrel carb is only around 225hp a 5.7 around 260 to 271 hp


                That performance sucks.

                A 19" or 21" prop would definitely be big Hopefully it's a 15" or 16" prop or so with 19-21 pitch. (Also measured in inches, but not the usual nomenclature)

                Doesn't that sound aggressive for such a large boat with 5.0s? My 2955 runs 15x17 and does 32mph @ 3200rpm, and it's about the same size as the 305 though perhaps lighter?

                What is your WOT RPM?

                I would not fix this problem with 4-barrels... solve the base problem first.


                  top speed should be 34 mph plus... i would tune the engines and change the fuel should be getting more rpms.

                  how many hour on the motors ?


                    gary1p wrote:
                    i think a 5.0 4 barrel carb is only around 225hp a 5.7 around 260 to 271 hp
                    stock 5.0 2bbl is 220hp

                    stock 5.7 2bbl is 250hp

                    top speed with 2 5.7's is 44-45mph. (gps)

                    for reference.


                      Engine Won't Reach Operating RPM. Check

                      1. Fuel condition. Type and Octane possibly old fuel

                      2. Propeller pitch or diameter, damaged blades

                      3. Restricted fuel pickup tube or anti siphon valve Fuel System Test

                      4. Crankcase oil volume, high oil level can cause aerated oil and lifter collapse

                      5. Marine growth on hull and outdrive

                      6. Wrong gear ratio in outdrive

                      7. Restricted carburetor air intake (clogged flame arrestor)

                      8. Restricted exhaust system (broken exhaust shutters/flappers) in engine transom shield or drive

                      9. Poor cylinder compression Compression Test

                      10. Carburetor defective, or wrong type.

                      11. Fuel pump pressure and vacuum

                      12. Boat overloaded, improperly loaded, or improperly trimmed.

                      13. Engine Overheating

                      14. Engine timing and ignition system operation

                      15. Remote control cables and linkage for proper travel to open throttle plates fully.

                      Above copied and pasted from another website Don s is the author.

                      Added by Chief Alen

                      16-Valves need adjusting.

                      17-Hidden water in the hull
                      Be good, be happy, for tomorrow is promised to no man !

                      1994 2452, 5.0l, Alpha gen. 2 drive. Sold ! Sold ! Sold !

                      '86 / 19' Citation cuddy, Merc. 3.0L / 140 hp 86' , stringer drive. Sold ! Sold ! Sold !

                      Manalapan N.J


                        My cost of going to 4 bbl on 350 Vortec:

                        - Edelbrock aluminum performer manifold - $150 (do it only if you have a fresh water cooling, or plan to never leave the lake)

                        - Eldelbrock (1409?) marine carburator (Weber, actually) - $250

                        - Spark arrester ($20, Craigslist)

                        - Best in class Vortec manifold gasket (important, they tend to leak) - $100

                        - New set of stainless intake manifold bolts - $25-30?

                        - Used 4 bbl throttle bracket from 1993 Merc (Ebay) - $15

                        - Misc hoses/plugs/barb fittings -$10

                        - Total: about $580.

                        Works excellent, very pleased with the performance.

                        Anyone needs cast iron Vortec Merc Manifold, and 2bbl original Merc carb? Perfect condition, looks brand new, from a FWC engine with about 50 hours.
                        1997 2859, 7.4 MPI, Bravo II
                        1993 2452, 5.7 Bravo II - SOLD


                          I see you are in Seattle and can you recommend your mechanic unless you did the work yourself?


                            Matthew: I have the 2005 Bayliner "Boat Information Guide." This is the 175 page booklet that salesmen keep at their desk to fend-off technical and specifications questions from potential buyers. It lists engine performance and gallons per hour for all models and engine combinations. With a dry weight of 11357 pounds and tested cruise weight of 13893 pounds here are the figures for the 220 HP "base" engines. Using the 13893 cruise weight: Cruise MPH: 25.7 MPH (20.2 GPH), WOT MPH: 38.5 MPH (34.8 GPH), Max cruising range: 180 miles (with 10% fuel remaining). By comparison, The 250HP 5.7 (carb) cruises at 31.4 MPH (22.4 GPH), WOT MPH: 41.9 MPH (40.0 GPH). The 5.0MPI cruises at 33.0 MPH (28.4 GPH), WOT MPH: 45.2 MPH (46.8 GPH). The 350 MPI cruises at 34.0 MPH (29.0 GPH), WOT MPH: 47.0 MPH (50.4 GPH) So there you have it, while the 220 HP setup may be a little slow to plane, it has better GPH figures than the others. Also, there is no "silly inverted" oil filter or expenive "cool fuel" filter to deal with! Good luck and enjoy your 305, Griff


                              What am I missing? The numbers you just quoted indicate the 5.7 carbed is a winner by a good margin (in mpg terms) which is generally the objective.