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1.6 ratio rockers in a SBC

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  • 1.6 ratio rockers in a SBC

    Somebody asked a question today and I couldn't give a definate answer, so I will turn to the guru's here.

    Is there any reason not to use 1.6 instead of the 1.5 ratio rocker arm on a marine 350 ('87-'95 vintage)?

    He is using the stock Merc cam(lobe lift is at or slightly below .300. I think). His thoughts are it will provide extra lift(this is a given) for a little more power. I would agree, although I doubt it would be a huge power gain. Also, since timing, duration, LSA, etc would not change there should be no additional risk of water injestion, right? What about increased fatiguing of the valve springs, or as long as they are not fully compressed will they be fine?

    The conversation just went in circles, good, bad, good.....

    So now I defer to you guys who have modified more engines than I have owned; What are the pluses and minuses of a swap from 1.5's to 1.6's?

  • #2
    Re: 1.6 ratio rockers in a SBC

    I'd say if it worked, the manufacturer would have done it a long time ago.......


    • #3
      Re: 1.6 ratio rockers in a SBC

      Dennis Moore discusses this change in his hp book. Recommends dialing the cam to: intake lobe centerline is moved to 110 degrees ATDC. Says its good for 5-10hp at 4500 rpms.


      • #4
        Re: 1.6 ratio rockers in a SBC

        Can it be done "Yes". Is it worth the cost. "Nope" Not on the above mentioned motor. The little gain would not be felt in the seat of the pants. If it were me, take the money and invest in a new bump stick and throw on a quality set of rockers. I have learned over the years that not all rockers are created equal. Just because it is stamped 1.5 ratio for example it may be well under. Some are over as well. If you enjoy reading pick up this book " How To Build & Modify Small Block Chevy's ( Camshaft & Valvetraines). There is a lot of good info in there.....


        • #5
          Re: 1.6 ratio rockers in a SBC

          I agree with riverjet, not worth doing since timing cover has to come off to install bushing to adjust cam timing. Re-installing a timing cover while engine is in boat, can be difficult. Allot of work for marginal hp increase.

          If his 5.7 is only a 2brl carb, might consider going 4brl. He would get about 30hp out of that, and would be easier bolt-on.

          Vortec heads would be the next step, but you would want to make sure the engine is good running condition worth sinking the $ into.


          • #6
            Re: 1.6 ratio rockers in a SBC

            HOLY CRAP!!!!

            That's $400 in reading for those two books. WOW!!!

            Well, there is no investment, he has both sets of rockers available and it sounds like the the 1.6's will be going on. Couldn't give him a reason not to, so it must be good.....

            Is there any negative effect of increasing valve lift, without changing, duration, centerline, LSA etc????


            • #7
              Re: 1.6 ratio rockers in a SBC

              I'd expect he would just get less than the 5-10hp increase. Duration does slightly increase on both sides of the lobes. Sounds like he is going to try it anyway.


              • #8
                Re: 1.6 ratio rockers in a SBC

                I would check my piston to valve clearance first, then check again after you install the 1.6's. (Just to play it safe) Personally I would spend the money on a new hydraulic roller cam and a pair of Edelbrock aluminum performer RPM heads. That will wake up the O'l Chevy.....


                • #9
                  Re: 1.6 ratio rockers in a SBC

                  Is there any way you can get vortec heads to fit on a pre-87 sbc? I'm guessing no?

                  Sea Ray SRV-210 - Winter refit
                  75-85 foot displacement hull trawler - gleam in my eye


                  • #10
                    Re: 1.6 ratio rockers in a SBC

                    You need the Vortec intake with the Vortec Heads.

                    I also considered the 1.6 Rockers when I replaced my intake/heads with the Vortecs but decided to stay with the 1.5's instead.

                    Would be interested to know how it works though.............
                    '84 Grady White Offshore
                    350 Mag w/ Vortec Heads
                    Alpha 1 Drive


                    • #11
                      Re: 1.6 ratio rockers in a SBC

                      Erik, as Tony stated, the only thing that changes when you add the vortec heads is the intake manifold. The rest stays the same.

                      To all:
                      Thanks for all of your responses. I wish I would be able to report accurately on the hp gain, if any, that results from using the 1.6's. Unfortunately, there is no good baseline here. The old engine was pretty weak, compression in the low 100's and one in the 90's.

                      Thnks again.


                      • #12
                        Re: 1.6 ratio rockers in a SBC

                        Vortec heads fit all small block engines produced 1955 to present, excluding LT1/LT4 reverse coolant flow engines and current LS1 style engines.


                        • #13
                          Re: 1.6 ratio rockers in a SBC

                          You will get a small increase in HP, but a better choice would be full roller rockers, 1.6 won't hurt, with a stock cam there will be no valve clearance issues, and no reason to touch the timing cover either. It is a simple bolt-on that can be done in minutes. The main benefit with the full rollers(not just roller tip) is a lot less friction and heat. Most stock stamped rockers are mass produced and cheaply made, they work fine but can sometimes be as little as 1.45 . A good set a rollers will give you much more consistant lift, add a four barrel and it will really wake up your motor, but not if your starting with a weak motor. Low and uneven comp. might just be dirty crusty valves. Get a set of Vortech heads, some good 1.6 roller rockers and a Vortech style aluminum intake, and a four barrel. Dont forget that Vortech heads need self-aligning rocker arms. It's a weekend project once you have the parts, and if your bottom end is bad, you can reuse all the top-end upgrades.


                          • #14
                            Re: 1.6 ratio rockers in a SBC

                            If you run the merc stock roller cam with stock vortec heads, and 1.6 rockers, verify the lift. I think it exceeds the recommended w/stock vortec. Some minor head work or different valve seals maybe required.


                            • #15
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                              Re: 1.6 ratio rockers in a SBC

                              One thing I have not seen anyone address is the valve springs themselves. Two things can happen: 1)In a lot of cases the stock springs cannot withstand the additional lift and coil bind will occur. 2) If the springs do not respond quick enough to the additional distance of valve movement then valve "float" can occur. Neither of these are good for making horsepower. Also the carb selection will need to come into play. If the stock carb (the Mercury version of the Quadra-Junk) is used it may need to be reworked. If the lobe overlap with the new lift doesn't work with the vacuum signal from the heads then no amount of tuning will help the carb work its best. One serious horsepower downside to putting too much cam in a motor is loss of velocity. I have seen dyno runs on dirt track motors (ie 4500 - 7000 rpm optimum range) where .520 lift shafts in a small block made more power than .600 lift shaft. It all has to do with the velocity of the air/fuel mixture entering the cylinder.