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Cam Specs for Mercruiser 260hp?

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  • Cam Specs for Mercruiser 260hp?

    Does anyone know the approximate cam specs for the cam Mercruiser used in its 260hp Chevy 350CID. I built a new engine using Comp Cams 260h marine cam. Specs are duration of 212 @ .050 and .440 lift. stating operating range from 1800-4900rpm. I was just wondering how that compairs with Mercury's Cam. Thanks in advance, PAR1969


  • #2
    Re: Cam Specs for Mercruiser 260hp?

    Intake: .263
    Exhaust .269
    Duration is not listed
    What's the cam's LSA?
    From Mercruiser:
    Anyone who uses a service procedure and/or tool, which is not recommended by the manufacturer, first must completely satisfy himself that neither his nor the productís safety will be endangered by the service procedure selected.

    Comment



    • #3
      Re: Cam Specs for Mercruiser 260hp?

      I would have to look it up in Dennis Moore's book, but do remember that it is dual pattern cam with exhaust lift and duration being more than intake.

      Comment



      • #4
        Re: Cam Specs for Mercruiser 260hp?

        Thanks, LSA is 110. on a 1978 Searay SRV195 trimmed down I get 45mph on GPS with 4000rpm on a factory tach. Trimed up I can get 4300rpm @ 50-52mph. I was expecting more RPM on this small boat with a 21p prop. The cam MFG stated operating range up to 4900rpm but I don't don't know if I should expect more or not. I figured if I compare it to the Mercruiser cam I would know if my RPM's are where they should be or not.



        Originally posted by mkast View Post
        Intake: .263
        Exhaust .269
        Duration is not listed
        What's the cam's LSA?

        Comment



        • #5
          Re: Cam Specs for Mercruiser 260hp?

          I dur @ .050 = 200
          E dur @ .050 = 212

          I think spec was 4600 - 4800 WOT rpm, but check service manual. See adult only section. The older 70's 350's might have a lower rpm spec around 4400 - 4600. A 19" pitch prop of same make/type should get you in your recommended range.

          Comment



          • #6
            Re: Cam Specs for Mercruiser 260hp?

            Originally posted by par1969 View Post
            Thanks, LSA is 110. on a 1978 Searay SRV195 trimmed down I get 45mph on GPS with 4000rpm on a factory tach. Trimed up I can get 4300rpm @ 50-52mph. I was expecting more RPM on this small boat with a 21p prop. The cam MFG stated operating range up to 4900rpm but I don't don't know if I should expect more or not. I figured if I compare it to the Mercruiser cam I would know if my RPM's are where they should be or not.
            what are the full cam specs on the cam card...is the cam ground with an advance already in and/or did you install it straight up?

            does it say 110 or does it day 108/112 or anything like that...

            i'll bet it is ground advanced and that is why it tops out at 4900 RPM... which means it is strong midrange...

            did you change the valve springs as well or test them and when does the card say vlave float can occur...?

            Comment



            • #7
              Re: Cam Specs for Mercruiser 260hp?

              I think John S is pretty close.

              ...and like he said, you're over propped. You should gain top end with more RPM.

              Mkast,
              Your figures are about what I have for my 406(comp cams XE 262H). Not even close for a stock 260.


              Need full specs like Bowtie said.
              Charlie

              Comment



              • #8
                Re: Cam Specs for Mercruiser 260hp?

                Duration 260 advertised 212 @ .050 both intake and Exhaust

                Lobe lift .293 Total Lift .440 both Int. and Exh.

                110 Lobe Center Angle

                106 Intake Centerline

                Installed Straight up.

                Seams to work fine but with my 2800lbs 20foot, Searay SRV195 I was expecting it to pull to 4500+rpm even with the 21p prop. I though 50mph without having to trim up would be no problem. Don't really care how fast it goes just want to make the engine is making the power it should. I have a new ignition system with 12 degrees initial timing and 24 mech advance all in by a high 4000rpm(being safe) and I have ruled out valve float. Maybe I am over propped but with the small boat shouldn't turning a 21p prop @ 4500+rpm's be no problem. Thanks again for your information and help.

                Comment



                • #9
                  Re: Cam Specs for Mercruiser 260hp?

                  How much tuning have you done?

                  Still running a q-jet carb?

                  Change anything else besides the cam?

                  I might bring in timing 4-500rpm sooner and have total around 33-34 degrees. Probably not gaining anything from running that much besides more heat. Bringing it in earlier will give better midrange punch. You should be able to get more rpm in that boat with a 21p prop. The stock Merc cam is a bit smaller but is still spec'd fro a few more rpm than you're getting. I would think 4700-4900rpm would be expected in that size boat with a 350.

                  Comment



                  • #10
                    Re: Cam Specs for Mercruiser 260hp?

                    Most marine cams are dual pattern as John S said. You picked out an auto cam. Could be you torque is falling off by 4000 RPM or your boat is a lot heavier than you thought. Get it weighed at a truck scale.

                    I have Dennis Moore's book, too. It gives you a ton of information. I use it for cam selection.

                    Comp Cams are supposed to grind their cams 4* advanced anyway. I advanced mine another 4* to increase off idle torque...even though I have 450+ ft/lbs at 2500 RPM.
                    Charlie

                    Comment



                    • #11
                      Re: Cam Specs for Mercruiser 260hp?

                      Being a 70's vintage is this just a tired motor? ie what was performance before changing the cam? The cam specs are only slightly different than stock, so unlikely you would "feel" much of a diference.

                      I would expect a 19' runabout w/1.5 gearing to turn a stock Blackmax type 21" prop, but hull design, weight, etc could put you below that. A 70's vintage boat would not be surprised to have water logged foam, which adds a tremendous amount of weight.

                      Why are you running with trim all the way down? Only do that until the boat is on plane, then trim to running position. Depending on prop and water condition, going straight or making tight turns, etc, trim to just below the point where it sucks air back into prop (you will feel the slip).

                      Comment



                      • #12
                        Re: Cam Specs for Mercruiser 260hp?

                        Originally posted by jtybt View Post
                        Mkast,
                        Your figures are about what I have for my 406(comp cams XE 262H). Not even close for a stock 260.
                        These figures came out of Mercruiser Manual #3 page 6C-11 for a 260 horsepower 350, "STOCK." Close enough for you?
                        From Mercruiser:
                        Anyone who uses a service procedure and/or tool, which is not recommended by the manufacturer, first must completely satisfy himself that neither his nor the productís safety will be endangered by the service procedure selected.

                        Comment



                        • #13
                          Re: Cam Specs for Mercruiser 260hp?

                          The motor is a brand new, old one was blown up when I bought the boat so I have no idea what it ran like previously. The previous motor was a 350cid with a 2 barrel Carb running a 17p prop. I have done no tuning other than the timing and yes is has a Q-jet. The Cam was listed on Comp Cams web site as a Marine cam. As for tuning other that changing the Jets/Metering rods in the Carb what else should I look at? Should I just have to throw a 19p prop on it and see what happens? I know there are millions of variables but if everything was working proper, what speed do you think a 19ft Searay with 260hp would do? Thanks again for all the information.

                          Comment



                          • #14
                            Re: Cam Specs for Mercruiser 260hp?

                            What intake is on there now?

                            It'll most likely spin right up there with a 19p prop and be fine but unless it's waterlogged it should do it with a 21p.

                            Comment



                            • #15
                              Re: Cam Specs for Mercruiser 260hp?

                              Originally posted by par1969 View Post
                              The previous motor was a 350cid with a 2 barrel Carb running a 17p prop.
                              If the previous motor was running at correct wot rpms, going to 4brl and a very near-stock cam, would indicate to me, a 19" pitch would be about right.

                              If this is not a deep vee hull, I suspect you are carring around more weight. ie the 17" pitch was possibly installed by prior owner to compensate for it.

                              Comment

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