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5.7 Volvo Penta GS Intake, Carb, Heads & Cam

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  • 5.7 Volvo Penta GS Intake, Carb, Heads & Cam

    Hello All, I hate to beat a dead horse, but I am needing some help. I have a 1997 Larson 206 with the 5.7 GS & SX outdrive. It is all stock except for through hull exhaust. I have had the boat about 4 years now. This past summer the intake started leaking a little oil. Ive already pulled the intake and carb. Since I’m already in this far, I’m thinking about replacing the intake and carb. I also have a set of vortec heads that I would like to install and would love to go ahead and do a cam upgrade. I am going to post pics along the way.

    1) What Intake and Carb Would You Guys Recommend ?
    2) What Cam Would Be A Good Fit ?
    3) Do I Need To Have Anything Done To The Heads ?
    4) Should I Upgrade The Ignition ?

  • #2
    Being its a 97 you should already have vortec heads (I think)

    What needs to be done depends on how much power you want to build.
    Doing a valve job is easy and doesn't cost much, but if you get into changing cams then your talking full rebuild. Could bore it out and change the crank and make you self a 383.
    94 Formula 27PC Custom 509MPI MEFI3 , B3 XR
    95 Rinker 232 w/ 7.4L Carb 0F425011 B1 0F486471
    07 Seadoo GTX
    Merc Adults Only VP Adults Only
    G-Dad always said "First Liar doesn't stand a chance"

    Comment


    • #3
      welcome aboard

      with some head work, you can change the cam to a comp Cam XM264HR or XM270HR. You need to pull the heads, convert to screw in studs and you need to cut the spring pockets for the bigger cam or run beehive springs.

      your carb and ignition are fine. no gains to be had there

      however, your best bang for the buck will be to pull the motor, build a 383 stroker.

      or....sell your boat and buy the boat you want.
      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


      • #4
        You're not gonna get much more horsepower at the same rpms you're running now without more displacement.
        HP=Torque X RPM/5252. A 4 bbl. carb and manifold will help power over 3500 rpms.

        The last Volvo 350 I took apart was a 2 bbl. Holley, flat tappet cam (even tho it was a 1 piece main seal), non vortec head with center bolt valve cover.

        Comment


        • #5
          Look carefully at your intake. If your engine has the vortec heads, it likely came with a 4bbl intake with an adapter for the 2bbl Holley. While the 500cfm(378cfm when flowed like a 4bbl) Holley is a wee bit too small for a 5.7 turning 4800 rpm, it doesn't need much more. A small 4bbl(450 - 500 cfm is plenty) would help a bit at top end. I replaced my 2bbl Holley with a Holley 650 Spreadbore 4bbl. It livened up my 5.7 with an additional 500 rpm.
          A few more HP can be gained by replacing the stock rocker arms(1.5 : 1) with some 1.6:1 versions. That effectively mimics a slightly longer duration cam.
          Click image for larger version

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          • #6
            A few updates and questions. Again, this is the 5.7 GSPLKD engine non Vortec. I’m wanting to go with the XM270HR cam as recommended. I do have the 4 barrel, but it either needs rebuilt or replaced. Also, I am looking at an intake upgrade. What should be done, if anything, to the Vortec heads I am wanting to use ? They were removed from a 98 Silverado.

            Comment


            • #7
              I’m trying to put some pics up, but it won’t let me

              Comment


              • #8
                Need a few more post before you can upload
                94 Formula 27PC Custom 509MPI MEFI3 , B3 XR
                95 Rinker 232 w/ 7.4L Carb 0F425011 B1 0F486471
                07 Seadoo GTX
                Merc Adults Only VP Adults Only
                G-Dad always said "First Liar doesn't stand a chance"

                Comment


                • #9
                  Gotcha. Thanks

                  Comment


                  • #10
                    First, find out what cam and lifters you have now, and compare the specs. Frankly, there's better (and simpler) ways to get power than changing the cam. Dial in the carb, have the distributor curve checked, get a free flowing K&N filter/flame arrestor. Start with the basics.

                    Comment


                    • #11
                      free flowing K&N filter/flame arrestor
                      Air flow thru a filter is good and the less restriction the better as we all know. There is a whole lot of K&N advertising out there but it has been proved on a Dyno that they are not the best, and in some cases the standard OEM is better. Also not many marine arrestor's are not even filters, there just stacked plates to keep large chunks out

                      But they can look pretty so that's worth something
                      94 Formula 27PC Custom 509MPI MEFI3 , B3 XR
                      95 Rinker 232 w/ 7.4L Carb 0F425011 B1 0F486471
                      07 Seadoo GTX
                      Merc Adults Only VP Adults Only
                      G-Dad always said "First Liar doesn't stand a chance"

                      Comment


                      • #12
                        Originally posted by TNParrothead View Post
                        A few updates and questions. Again, this is the 5.7 GSPLKD engine non Vortec. I’m wanting to go with the XM270HR cam as recommended. I do have the 4 barrel, but it either needs rebuilt or replaced. Also, I am looking at an intake upgrade. What should be done, if anything, to the Vortec heads I am wanting to use ? They were removed from a 98 Silverado.
                        with the motor being a non-vortec, its a left over 1995 or earlier. you may have flat tappets. if so, your limited on the cam. an XM268H is the largest flat tappet you can go. however before you buy anything, you need to verify what you have

                        how many intake manifold mounting bolts do you have? 8 or 12? if 12, non-vortec heads and you will need to pull the intake to determine which cam you have. only some of the pre '96 boat blocks got rollers.

                        if the heads are stock vortec heads from a 98 silverado... to expand on post #3

                        at a minimum, get a valve job, get the press-in studs removed and replaced with ARP screw in studs. get the guides cut for teflon seals, get the spring pockets cut for a higher profile cam.

                        I would highly recommend SS valves, however if your on a budget, dont worry too much. then again, if you look at your local racing classifieds, you can probably pick up a set of vortec heads with a fresh valve job and all the upgrades done for less than you can modifiy the heads. usually about $400 a pair

                        If you have a roller cam now, the XM264HR is a reasonable improvement over stock. this cam can be run with 1.6:1 rockers. the 270 is largest cam you can go with wet exhaust as you are then knocking on the point of reversion. recommend sticking with the stock 1.5 or the aftermarket 1.52:1 rocker arms with this cam.

                        a 2" plenum spacer will help mid-range torque

                        Originally posted by aimlow View Post
                        First, find out what cam and lifters you have now, and compare the specs. Frankly, there's better (and simpler) ways to get power than changing the cam. Dial in the carb, have the distributor curve checked, get a free flowing K&N filter/flame arrestor. Start with the basics.
                        stock cam is extremely mild. there is a bit of power to be had there. rocker arm ratio change will help.

                        the specs that GM used for the 260hp 5.7's

                        202 duration intake
                        214 duration exhaust
                        395" lift intake
                        404" lift exhaust
                        112 lobe separation.

                        k&n filter wont help, same spark arrestor is used on BBC's as the SBC's. inlet airflow is not limited

                        distributor curve is electronic
                        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


                        • #13
                          My marine cam specs (merc431-5943) show 200/212 degrees @ 0.050". 110 lobe center. 0'400/0.410 lift. 264 cam is only 212/218, same lobe center (so a little more overlap), but really high lift. In any case, not much difference for the cost (cam, lifters, timing set.....) Retard the existing cam 4 degrees, this will move the peak power up a few hundred rpm's.
                          The tell on flame arrestors is when you remove them and pickup a couple hundred rpms, as happened on my 302 Fords The K&N's are available with CG approval, and actually filter dirt. The key is a tall enough filter to allow decent airflow, or use a stub stack if you have a Holley. Otherwise, I'm NOT a K&N fan..it's just they have marine approval. NEVER! use them on an engine with hot wire MAF!

                          Be careful with used vortec heads..they are prone to cracking.

                          Will stock springs work with a comp cam with nearly 0.500 lift?

                          Comment


                          • #14
                            aimlow not a good idea to retard a cam in a marine motor. especially since it changes the piston to valve clearance and marine motors need all the bottom end torque that they can get. what is not covered in the chart below is the effect on reversion. How does it affect performance?

                            Advancing or retarding the cam will move the Torque curve higher or lower in the RPM range. Advance will improve low-end power and throttle response. Retard will improve the power at higher RPM's. See the table below for more information on advancing and retarding a camshaft.
                            Advance Retard
                            Begins the intake event sooner Delays the intake event
                            Builds more low-end torque Builds more top-end power
                            Decreases clearance between the piston and the intake valve Increases clearance between the piston and the intake valve
                            Increases clearance between the piston and the exhaust valve Decreases clearance between the piston and the exhaust valve
                            4° of advance will cause the torque to peak about 200 RPM sooner 4° of retard will cause the torque to peak about 200 RPM later
                            no one is questioning whether K&N has marine approval. they do. however they do not improve anything on a stock small block as far as air flow

                            hot wire MAF need to be cleaned on a regular basis even with paper elements. just more often with a freshly oiled gause/oil filter such as a K&N

                            NO, stock springs wont work in a vortec head on anything over 0.420" lift. at that point you bind the springs. to go beyond that, you need to cut the spring pockets as stated in post #3 and #12.
                            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


                            • #15
                              Sign up today
                              Originally posted by Scott Danforth View Post
                              aimlow not a good idea to retard a cam in a marine motor. especially since it changes the piston to valve clearance and marine motors need all the bottom end torque that they can get.
                              no one is questioning whether K&N has marine approval. they do. however they do not improve anything on a stock small block as far as air flow

                              hot wire MAF need to be cleaned on a regular basis even with paper elements. just more often with a freshly oiled gause/oil filter such as a K&N

                              NO, stock springs wont work in a vortec head on anything over 0.420" lift. at that point you bind the springs. to go beyond that, you need to cut the spring pockets as stated in post #3 and #12.
                              Not to get into a peeing contest, but SBC valve/piston clearance is not that critical. Retarding/advancing a cam a few degrees is common..been doing it for decades. Look at VVT..they are often 20 degrees or so. Moving the torque point automatically moves the "horsepower" point, since horsepower is a function of torque and rpm.

                              It's an old wives tale that gas marine and truck engine cams produce and need low end torque..just the opposite. The typical rpm range is higher that a street vehicle, so the cams are actually lumpier...more aggressive. Idle quality is not an issue on marine engines.

                              Most marine inboards are high rpm breathing limited, especially on exhaust. This is why the split profile cam profiles work so well on them. A taller air filter system will flow more air (and CLEAN air) because the air flow into the venturis is less "turbulent"..most flame arrestors require a sharp 90 degree bend to get the incoming air thru the arrestor and into the venturi. The bigger issue is not the flow thru the flame arrestor, it is the temperature of the incoming air. Cool, dense air always improves power! You'd be surprised at how dirty my air filters got on my boat engines...worse than a street vehicle, and my bilge was clean!

                              I post nothing which I haven't personally done. Decades of road racing, engine building and tuning, and hands on experience. I'm always open to discussion, though...bench racing.

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