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Thread: Performance Improvements possible with newer 4 stroke outboards

  1. #21
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    Default 4-Strokes for racing

    Aside from using a laptop to modify fuel delivery & timing curves on 4-strokes, mechanical mods would be required. The motors with removable heads can increase compression by milling head surface. However, to change the equivalent of 2-stroke port timing, requires an after market camshaft. No one will engage in doing so because the volume is too small to justify start up costs. As Don has suggested, without a larger market for after market components, that will never happen.

    I believe the only road to 4-stroke success in racing is to have the rev limiters removed or re flashed, to allow lower pitch props to wind up higher than the stock limiter will allow. This will give better acceleration without sacrificing top end speeds. I know in T-750, Tom'
    s 60hp Mercury would kick our butts if he could remove limiter and run lower pitch props. When Tom gets good top end numbers, his acceleration suffers and vise versa. The only other solution to racing 4-strokes is to only allow them in the class, based upon displacement and/or horsepower.

    Just my two cents.
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    Quote Originally Posted by Ron Hill View Post
    The problem with 2 strokes, right now, there are no new one in America. And they haven't made any for 15 years or so.
    Huh? Evinrude's entire lineup from 15hp to 150hp is the two stroke E-tec engine...
    Tohatsu's TLDI is available in 40/50/90 hp and these are all still very close in weight to their old carbureted engines.
    Mercury Marine's last two stroke currently offered is the Optimax 200hp jet drive (for recreational squirt boats) but that means they still make the 2.5L powerheads.

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    WebCam Racing Cams can modify factory camshafts to a certain degree. That would be my first goto if hp gains were wanting to be had on a 4-stroke.

    Webcamshafts.com

    RobT

    Sent from my SAMSUNG-SM-G900A using Tapatalk

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    Quote Originally Posted by 25XS View Post
    Huh? Evinrude's entire lineup from 15hp to 150hp is the two stroke E-tec engine...
    Tohatsu's TLDI is available in 40/50/90 hp and these are all still very close in weight to their old carbureted engines.
    Mercury Marine's last two stroke currently offered is the Optimax 200hp jet drive (for recreational squirt boats) but that means they still make the 2.5L powerheads.
    Merc still building small engine carby 2 strokes but not for sale in the USA

  5. #25
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    Default But We Have Propellers...

    Quote Originally Posted by Powerabout View Post
    but you had gears....
    When my dad worked my props, my best props were "Shifters". They crowd in Seattle have figured this out in kneel down racing.

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    Quote Originally Posted by oledawg View Post
    T-750, Tom's 60hp Mercury would kick our butts if he could remove limiter and run lower pitch props. When Tom gets good top end numbers, his acceleration suffers and vise versa. The only other solution to racing 4-strokes is to only allow them in the class, based upon displacement and/or horsepower.
    I still think we can help Tom and other current and new racers in T750 class if we increased the minimum weight from 500 lbs to 625 lbs. Unlike our T850 class which has a surplus of horsepower that makes up for boats being 150 lbs. over weight, our T750 over weight boats have much less exceleration and that hurts lap times. If you had a new composite Critchfield at 225 lbs, an OMC twin at 200 lbs, gear at 25 lbs., and a average weight driver at 175 lbs you are at 625 lbs That should be the minimum weight!!
    Last edited by hydrospeed77; 05-23-2019 at 01:45 PM. Reason: fix quote end tag

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    I agree that the minimum T-750 weight is to light. Most boats weigh 250-260 lbs. or more. ( The Rossiter Critch is 225 lbs. w/o the 16 lb. cowl.) The rigging weighs 75-80 lbs. I know since, I just rigged our new T-750. Throw in 20 lbs. of fuel and a 200lb. twin two stroke and you have 550lbs. without the driver. That is already close to the current class legal weight. That all but eliminates any driver that weighs more than 150lbs. Our lightest driver is 140lbs. and our heaviest is 230lbs. That is a 100lb. weight disadvantage. That's tough to deal with in T-850 much less T-750. If T-850 is 725 lbs. than why is T-750, 594 lbs. The motors are only 30lbs. more in T-850. Why roughly 125lbs. less in T-750??? I think T-750 should be 675 lbs. & T-850, 800 lbs. This would attract racers that are bigger guys or gals. Why exclude a large number of potential new racers in our T-750 class.
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    Quote Originally Posted by oledawg View Post
    I agree why is T-750, 594 lbs. The motors are only 30lbs. more in T-850. Why roughly 125lbs. less in T-750??? I think T-750 should be 675 lbs. & T-850, 800 lbs. This would attract racers that are bigger guys or gals. Why exclude a large number of potential new racers in our T-750 class.
    T Class is a UIM World Class...the weights for both T750 and T850 came from those rules. APBA similar classes were DE for T750 and EP for T850...I am not sure about the DE weight but APBA EP was 850 lbs. With 3 cylinder drag in 2019 the T guys may want a heavier weight..It would be a class decision. Remember OPBRA is looking to revise T850 for the 2020 season.
    Last edited by hydrospeed77; 05-23-2019 at 01:46 PM. Reason: fix quote end tag

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    Quote Originally Posted by Hounddog View Post
    I still think we can help Tom and other current and new racers in T750 class if we increased the minimum weight from 500 lbs to 625 lbs. Unlike our T850 class which has a surplus of horsepower that makes up for boats being 150 lbs. over weight, our T750 over weight boats have much less exceleration and that hurts lap times. If you had a new composite Critchfield at 225 lbs, an OMC twin at 200 lbs, gear at 25 lbs., and a average weight driver at 175 lbs you are at 625 lbs That should be the minimum weight!!
    Tom is a great guy, he gave me alot of info on the Merc formula race, I'm finishing up my boat soon it's a 13' bullet, I'm not racing but I want the most I can get out of it. It's heavy at 400lb bare hull but I rebut it for offshore durability and all composite.

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    Default Honda 50 HP! Made maybe 100 hours since the cam is in there

    One of my customers claims a re ground cam helped his Honda, noticeably. He has a 100 hours on the cam.

    From second hand information via Mercury Marine, all their smaller 4 Stokes are tamed way down, so they can sell you newer, more powerful ones later.

    I do know the early Yamaha 4 Stokes were "Weak Sucks". BUT THE NEWER ONES SEEM TO HAVE SOME LOW AND AND TOP IN GRUNT.

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