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3.0 performance increase

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  • 3.0 performance increase

    I know people have asked a million times about boosting the performance of the 3.0, but I've never seen anything about rocker arms. Can we throw a set of 1.6 roller rockers on to lose a little friction and gain a little lift? will the V8 rockers work? If so anyone want to go in on a set with me


  • #2
    Re: 3.0 performance increase

    There don't seem to be too many people on this board who have gotten deep into this motor beyond stock spec repairs and rebuilds. I've been trying to find out a little similar info on upgrading the 3.0 internally and getting little response, though the factory service manual provided by Don S wil be of great value at least for torque specs, etc upon reassembly, even if it doesn't answer my core questions:

    http://forums.iboats.com/showthread.php?t=260723

    I'm still hoping someone can answer my questions about valve sizes, since the service manual doesn't provide that info. Maybe I just need to spend a little time at a local boat salvage yard and look at the various heads myself...

    As for roller rockers, I considered the same. I did learn from the service manual that stock rocker arms on the 3.0 are 1.75:1 ratio. So I'd be surprised if changing to 1.6's would gain anything, whether rollers or not.

    I have found this company that obviously does get into 3.0's, and they sell them as complete units with an advertised 158+ hp.

    http://www.remanufactured.com/Inboar...ne_Engines.htm

    Of course they won't share their specs, but from the photos it is obvious that they have utilized roller rockers in their rebuild, and they advertise a different cam, mild head work, etc. It's pretty obvious that nobody makes roller rockers specifically spec'd for the 3.0 Mercruiser, but these people sourced them from somewhere, so I have to assume that standard V8 GM-style roller rockers must fit. I'll know more this winter when I open mine up and see what's in there. I have some GM roller rockers sitting here that I'm not using so I can at least see if they fit, though mine are not the correct ratio (mine actually are 1.6's) so I wouldn't want to actually use them in this motor anyway.

    I likely won't take my internal upgrades to the extent this reman company did, but I'll get in there and at least clean up the ports, will definitely do a 3 angle valve job, and maybe try to see if roller rockers will fit and maybe try 'em if I can find a good ratio. Even if rollers are in the same stock ratio, the reduced friction of rollers is always beneficial over stock ball/socket styles, and by nature of their design, they will actually provide a little more lift because they pivot only, instead of wasting some of their movement in a sliding motion. Rollers would give a true 1.75:1, whereas standard rocker arms waste some of their movement in a sliding motion...providing something probably closer to 1.70:1 despite their stated spec.

    Whatever you (and I) try, we need to remember that a slow speed torque-monster motor like these need to be handled much differently from a high RPM high HP motor like most people are used to building in auto racing...so we must be very careful of creating drastic airflow changes in the head (like enlarging or reshaping ports, or high lift cams/rockers, which both will often cause a LOSS of low RPM torque). While such changes may increase peak HP at high RPMS (6000?), we have to acknowledge that these motors will NEVER spin that fast, so you'd gain nothing in your useable powerband and probably would actually lose some.

    But simply massaging and smoothing airflow doing multi-angle valve jobs and port cleanup will usually increase low RPM torque, which is a much more important goal for a slow spinning motor like a 3.0 Merc. That's the course I plan to take with mine, and I'll do some good before/after performance testing to see if I gain anything. Look for results posted sometime next year. I'm not afraid to make tuning mistakes, so if I gain nothing or take a loss of performance, I'll gladly admit it. And if I do gain a little power and speed like I hope, I'll brag about it with facts.

    In the meantime, I'd love to stumble across someone else who's tried to get into these 3.0's for performance improvements so I can learn from their successes and/or mistakes, but like I said up front they seem to be few and far between.

    Good luck!

    Comment



    • #3
      Re: 3.0 performance increase

      keep in touch with me please, my email is steven.c.fletcher@gmail.com. I need to build an engine for my boat next winter (previous owner never winterized the block and I had to weld a crack last year). Supposedly my engine is cam'd and has higher compression pistons or head gasket. It does run strong (40 MPH with 3 people and a bit of extra weight - 17' Forrester Phantom 171). I'd like to share notes with you and perhaps we can uncover this mystery. Where are you located?

      Comment



      • #4
        Re: 3.0 performance increase

        I'm in Indiana. Will keep this info in mind. I would LOVE to know who makes a thinner head gasket for the 3.0...if your motor indeed has such a thing. Thought about milling the deck a couple thous while I had it off, but that's a whole lot more permanant than experimenting with thinner head gasket in case it's a mistake! So I'd be real curious to know more details about what your motor has internally and where they got the parts, although it kinda sounds like you don't really know for sure yourself. And 40 mph for a 3.0L boat doesn't really say much. That's pretty typical quite honestly, and is more a function of boat weight, hull design, and prop than anything else. Some new 3.0L equipped Stingray 18 foot runabouts, for example, are now going faster than 50 mph right out of the box, as proven by a few boat magazine tests. But Stingray is known for making fast hulls. So top speed really doesn't say much unless you do a before/after test on the same boat, with same load, in same conditions.

        Incidentally, I found the following info on a hotrodding site, which I found intriguing. They were talking about a Chevy small block V8 they were playing with, so ignore the specific numbers as they have nothing to do with the Merc 3.0. But the underlying idea is very interesting about lift ratio's impact on power:

        "One cool thing we learned from this is that smaller cams really do make more low-end power. The pushrod binding caused by the 1.6 rockers bled the hydraulic lifters down and didn't offer full lift or duration of the cam. So in effect, we were running a much smaller cam. How small? We don't know, but torque at 3500 rpm with the binding pushrods jumped by almost 30 lb-ft. How can you duplicate this low-end power increase, you ask? If you're running a very mild motor and are not worried about power above 4500 rpm you can reduce the rocker-arm ratio instead. That may not sound right to most of you, but it helps low-end power. You won't get the same peak power you would with a higher ratio rocker, but if your engine never sees that rpm then why bother? This is a great idea for tow vehicles, 4x4s, and boats that never rev very high and need all the bottom end they can get."

        Based on that, maybe sometime I'll slap my 1.6 ratio arms on this motor (if they actually fit), and see if I gain any low RPM power over the stock 1.75 rocker arms. It would be a cheap and easy experiment I can do most anytime...will report back if I do so and will do before/after performance test to document any changes.

        Frankly I have too many projects right now and my boat runs fine, so I don't expect to do much with this very soon. But I'll get motivated when boating season is over and I need a cold-weather project.

        Comment



        • #5
          Re: 3.0 performance increase

          Opinion noted.

          Lotsa old people said exactly the same about all the "kids" who started taking their Dodge Neons and Honda Civics to the dragstrip with strung out 4 bangers...many of those kids are now in their 30's and still building and racing the same small displacement motors.

          And with a little trial and error and some information sharing, they were able to build engines that are matching and sometimes beating big block V8 cars in many races. Power to weight ratio of a 4 bangers can be king in that department compared to big V8's.

          I can't speak for original poster, but for me, I'm personally equipped to do a reasonable amount of machine work...and I have friends and contacts to fill in the blanks where I'm not equipped with a little trading of favors. So I can do internal engine mods to most any engine for the cost of a set of gaskets, to the tune of a fairly significant performance increase. Real dollars? $150 or less usually for a 4 cylinder...maybe $250 to $300 for a V8. Time? A long weekend...and a weekend of pure enjoyment and problem solving at that.

          I certainly can't buy a more powerful stock boat for $200 to $300 out of pocket...but I THINK I can squeeze another 20 to 30 HP outta my rig real easy for less jing than that. And given that I personally am starting with a 115 hp version of the 3.0, I can probably do more with it than if I had originally started with a 140 version.

          And as for reliability? I gotta disagree with you completely. These boat motors are horribly under-tuned compared to their potential against something breaking, as long as RPMS are kept reasonable (and even there the weak spot is more in the Alpha drives than in the motor). And I will say that I haven't had an engine failure yet on any mild performance buildup that I've done on any vehicle. Now the 950 HP 350 small blocks on blowers and nitrous? Yeah...sometimes they break. But a 350 V8 can easliy turn 400 to 450 HP with great reliability, and that figure is about double what the stock setup usually was on the older models. And I've worked with friends to massage several 5 HP Briggs & Stratton motors to put out 14 to 15 HP on a local go-kart circuit. They almost never break even when pushed that far. So I see no reason this 3.0L can't put out maybe a 20% or 30% increase in power without any reduction in reliability whatsoever. And even if it does happen to break? So what? We're the mechanical type. We'll just fix it and learn from our mistake...I'm not taking this runabout out on the big seas where a breakdown might kill me. I'm a fair weather small lake pleasure boater. So I'll just get my oar or wait for the wind to blow me to the nearest shoreline! Or drop anchor and swim for a while first and enjoy the sunshine, then grab a friendly tow back to the dock when I'm ready to leave!

          Tuning is fun. Admittedly not always practical. And some of us enjoy wrenching as much as (or more than) boating itself. Others will never understand that, and that's OK.

          We're just here hoping to stumble across someone who has attempted and messed with this stuff on the smaller motors, and to share some info. Clearly we're in the minority, but there's a select few of us out there willing to think outside the conventional "bigger cc's is the best way to get more power" and "just tune it up and leave it stock" trains of thought...

          Comment



          • #6
            Re: 3.0 performance increase

            I don't know for sure, but if thats a version of the Pontiac "Iron Duke" 2.5 motor, at one time it could be coaxed to 300hp! With factory racing parts. I used to have the GM performance book which concentrated on parts available to build up the most popular GM engines, 1) was the small block Chevy, 2) was the 3.8 V6 Buick Grand National motor, and 3) was the Pontiac Iron Duke, But Lord knows where my book is now?

            By the way, have you looked at carb spacers, there is usually some torque, & HP, improvement with those, I'm about to put one on my 95' Chevy S-10 V6 TBI truck. I also run Mobil one full synthetic oil in all my vehicles, its a surefire boost in HP, & torque, due to less friction. I bet if I could run my vehicles at WOT, like a boat engine, there would definitely be an RPM increase.

            Comment



            • #7
              Re: 3.0 performance increase

              Originally posted by craze1cars View Post
              Opinion noted.

              Lotsa old people said exactly the same about all the "kids" who started taking their Dodge Neons and Honda Civics to the dragstrip with strung out 4 bangers...many of those kids are now in their 30's and still building and racing the same small displacement motors.
              I'm not sure if you just want to hear what you want to hear or if you're truly looking for advice.

              On the road, 100hp means quite a bit. +100hp in the water only means a few extra mph. That's not experience, that's physics. Nobody's saying don't do it, it's just the investment doesn't net near what is typically expected by those thinking in an automotive context (which you definitely are).

              Take your time researching what can net you the most speed and performance on the water, not on land.
              1989 Starcraft 171S Select "Cap'n Crunch" / OMC Cobra 4.3 V6 / 432APRMED

              If you're going to keep that OMC Cobra, please for the love of everything good in the world, get an OMC factory service manual. Not a Clymers, Not a SELOC. You can find them on eBay.

              My boat repair website: http://transomfix.dcpolk.com

              sigpic

              Comment



              • #8
                Re: 3.0 performance increase

                Might make more sense to spend the time on rigging in a supercharger.

                These guys in Europe did it on a Volvo 140 horse 4 cylinder, quoting their description "a volvo penta aq140 supercharged by a eaton m90, the engine is built by me and my brother" ....looks like quite an improvement to me.....:

                http://youtube.com/watch?v=9m0HZXQqC1M&feature=related
                1991 HydroSwift 2200 Cuddy Volvo Penta 570/DP
                1980 Glastron SSV167 90HP Mariner

                Comment



                • #9
                  Re: 3.0 performance increase

                  LOL! I love the supercharger! Certainly would be hard to pull off economically, but DEFINITELY would work if executed properly...Very cool.

                  And yes, I'm personally well aware that land HP/speed gain doesn't translate to water HP/speed gain. Did I say somewhere in my post what my specific speed and performance goals were? I didn't think I did, but I'm too lazy to re-read my long-winded posts...

                  But since it came up, I might as well throw that out there. Realisitically, a 3-4 MPH gain with no notable loss in accelleration would be nice...like being able to change from a 17p prop to a 19p prop with no loss of RPMS. Frankly I think that's quite doable with some simple and cheap engine mods. And I also acknowledge that I might be wrong.

                  I'll shut up now and go into a read-only mode. I'm definitely hijacking another guys post here. Hopefully the ideas keep flowing, and even better maybe we'll get lucky and someone will come along who's actually tried some things...whether with success or failure..instead of just wanting to continue to guess and speculate.

                  Comment



                  • #10
                    Re: 3.0 performance increase

                    I found a site that may have what you're looking for:

                    http://remanufactured.com/Inboard_Marine_Engines.htm

                    From the site:

                    This performance 3.0 liter inboard marine engine is bored oversize, has two stage Sunnen plateau honing, 3 angle competition valve job, performance camshaft and lifters, seamless cam bearings, alloy pushrods, oil pump, mildly pocket ported head and has moly Sealed Power rings, new oversized and balanced pistons, Clevite 77 main and rod bearings, gear drive, roller rockers and more! (can also replace the 2.5 liter Mercruiser and OMC)

                    Comment



                    • #11
                      Re: 3.0 performance increase

                      Originally posted by Flyin1500 View Post
                      I found a site that may have what you're looking for:

                      http://remanufactured.com/Inboard_Marine_Engines.htm

                      From the site:

                      This performance 3.0 liter inboard marine engine is bored oversize, has two stage Sunnen plateau honing, 3 angle competition valve job, performance camshaft and lifters, seamless cam bearings, alloy pushrods, oil pump, mildly pocket ported head and has moly Sealed Power rings, new oversized and balanced pistons, Clevite 77 main and rod bearings, gear drive, roller rockers and more! (can also replace the 2.5 liter Mercruiser and OMC)
                      Has anyone used their engine?

                      Comment

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