Liberated 300R

Liberator Boats of Florida sales have soared with the release of our naturally aspirated, 4.6L V-8 300R FourStroke outboard.

Our hot new 4.6L V-8 300R has a new fan. Liberator Boats of Florida owner Randy Corson received his first 300R in June. Randy has extensive experience with our legacy V-6 300XS two-stroke. He anxiously rigged his first 300R in anticipation of its performance and he was not disappointed.

There is no replacement for displacement.

The 300R, which is 44% larger in displacement compared with the  300XS,  produces 40% more bottom-end torque and provides 25% quicker acceleration.

“The  V-8 four-stroke produces so much torque that it demands a larger diameter prop,” said Randy.

“We saw  1-1/2 to 2 mph faster top-end speeds with the 300R compared to the 300XS with comparable props. The boat topped out at  106 mph; 5-6 mph faster than the 300XS when running a 15-1/4-inch diameter – 34-inch pitch Mercury Racing 5-blade CNC outboard cleaver,” Randy said.

The popular MAX5 also ran well with low (9.7%) slip and a top-end speed of 103 mph at 6200 rpm.

Liberator Boats of Florida sales have soared with the release of the 300R.

“The engine has an awesome sound from outside of boat, yet  is uncommonly quiet inside. It’s really the best of both worlds for the modern-day outboard performance boater,” said Randy.

Randy has extensively documented his 300R experience on, a popular on-line forum for performance outboard enthusiasts. owner Gregg Terzian will be documenting the performance of his latest 300R Liberator in a video shoot later this month.

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25 thoughts on “Liberated 300R”

    1. Richard,
      What engine was replaced by the 300R?
      What prop and pitch did you use on the old engine?
      What was you top rpm and GPS speed with the old set up?
      Any other changes besides the engine?

        1. Richard,

          Great question, the 300R is going to make a lot more power than your motor but it also has a higher RPM range, up to 6400. Your 26 Bravo will be a good starting point, as it is on the smaller side of what you can expect to run. The 300R holeshot will be much better than your 250 pro XS, and you will gain at least 5 mph on top end.


  1. Scott

    I emailed you in July that i was repowering my 2007 Allison
    XB21 2+2 with a 300R. I received the engine September 11th
    I purchased the HD with sportmaster gearcase & DTS. I got it rigged
    and dealer here calibrated DTS. I took it out Saturday to run it some.
    I ran a 27P promax I had on hand. You answered my
    July email, that you thought I would probably end up around a 30P.
    I agree
    It was windy so I backed out at 6000 rpm running 81 mph.
    It got to the 6000 quick. I varied from an inch below to inch above
    pad and needed vary little trim to keep the bow up. I’m setback about 8 inches. I’m going to try a 31P. I’ll post an update on how it does.

  2. 2007 Allison 21 xtb 2+2 with 300R HD sportmaster.
    Ran with the 27P Promax 83mph 6200. Prop cavitates on holeshot
    no matter how high or low engine is. All plugs & exhaust ring installed helped a little. Ran 83 mph at 6200. Not to bad.
    Tried the 31P cavitates the same on holeshot. The prop apparantly
    lifts the stern to much. Didnt matter if I dropped motor 3 inch below pad. 5500 rpm 75mph. 18.7 % slip. Ran up to 5700. The 31P
    is to much prop. I’m thinking 29P. But I’m still concerned about the
    cavitating hole shot. Even with the 27P Promax seems like to much stern lift. What do you suggest.

    1. Rex,

      Your RPM sounds spot om with the 27 pitch. Rather than looking at the prop for your stern lift problem, lets consider the gear case. The new Sport Master has a larger diameter and must be raised higher than the legacy 300XS, ProMax and 2.5L Sport Masters. Are you running a hydraulic jack plate? I think your best bet would be to plane off with the engine low and raise it as high as possible for top end. Also, are you able to try out a Bravo propeller? The bigger barrel may help direct some of the exhaust, and the larger diameter will help keep slip low when running at high engine heights.

      We are currently testing variants of the Max5 with Bullet owners in Florida, if all goes well it will be a great option for an Allison with 300R power as well.


      1. Hi Nick

        I’m running a Bob’s extreme remote pump jack plate.
        I ran the 31P 4 inchs below and 1 inch above pad.
        It didn’t matter on the hole shot. shortly before break over the
        engine would rev from 3,000 to 6,000 to brake over to plane..
        You could light foot it to not let go to to 6,000. Just takes longer to break over. Once on plane it had decent bite up to 60.
        From there it didn’t matter if you were 4 inchs below or 1 inch
        above had a lot of slip. The faster i went the higher the slip.
        The higher I raised the engine more slip. It’s like the prop is lifting the entire boat up.
        Is it the cup on the Promax causing this.
        .I went from open holes all the way to solid plugs and an exhaust ring on the 31P and changed the cavitation very little.
        Seems like with all the torque it would help to have more prop
        blade surface and maybe less cup? I know the 27P is to little
        With the 31p Promax the engine was laboring at 5,000 and
        after that there all the excessive slip. I don’t think it would ever
        reach 6200 hooked up. 29P Bravo 1XS ? 28P Max 5 ?
        Do you think more set back would help? Thanks for your help.

        1. Rex

          As I said in my previous comment, your boat’s change in attitude is most likely due to the size of the gear case. The new Sport Master is bigger than the Sport Masters that came with the “XS” motors. By having a much bigger bullet in the water, we have found that for an application such as your, it needs to be raised about an inch higher than the older Sport Master. In doing this, the Pro Max starts to slip since it is only a 14.50 diameter. I like your thinking with the Bravo and the MAX5, as of today I can say the Bravo FS will run pretty well, but we are still doing tests with the MAX5 on single engine bass boats. If there is any way you can get your hands on a Bravo to test that would be the way to go, you will be around a 29 pitch. I will touch base with you once we hear more from the MAX5 testing this week.


          1. Rex,

            If you have the time, call Fastbass Marine and ask for Tim. He has had success with setups similar to yours.


  3. Hi Nick

    Allison xb21 2+2 300R HD Sportmaster
    Ran a 29p Bravo XS with 8 solid plugs. No cavitation on hole shot.
    Removed 2 plugs closest to gear case. Cavitated on hole shot.
    Installed 2 with 3/8 holes. No cavitation. Bravo cured hole shot issue. Best performance on top end was engine height
    Right at pad. Any higher more slip. Any lower lost speed. 1 degree
    Trim ran best. Ran up to 6460 rpm and 83 mph. Not sure if rev limiter is the 6460 rpm. Slip at 18%. Not good
    The promax 27p ran 83 at 6200. Good numbers but hole shot
    Cavitation terrible. With a 150 rpm per inch pitch. I should run
    The 6150 rpm range with a 31P Bravo. But if the slip % doesn’t
    change. Then the Bravo may not be the prop for my application.
    I thought propped right I could get to 10% or less slip.
    What prop do you suggest?

    1. Rex,

      Anything over 6400 rpm, the motor starts to pull out power, as opposed to a traditional rev limiter. I have received some data from Tim at Fastbass Marine. As I stated earlier, most people with your setup are running a much higher engine height. He ran his engine (300R) 1.5″ above the pad with a 30 Pro Max and was 92 mph on the limiter. He is going to try a 32 pitch Pro Max and he should be 94-95 mph. A standard MAX5 will have too much stern lift for your setup. Tim is going to try a 31 MAX5 with a shortened barrel, which so far has worked wonders on a Bullet 21 XRS (97+ mph, 7% slip). I will keep you updated as we learn more.


      1. Hi Nick

        When I ran the 29P Bravo XS at 1.5 above pad it blew out.

        The Promax 27 and 31 both slipped more the higher I raised
        it. I went to 2 inches above pad.
        The 27 best slip numbers was at 1/2 below pad.

        My Allison 2 + 2 has you sitting 30 inches forward compared
        to most bass boats. With my partner & I combined weight of
        525 lbs. I’m trying to dial in a different animal.

        Engine setback is 8 inches. I left some additional length in all my rigging when installing engine so I could try adding some
        more set back.
        What do you think?

        Anxious to hear how the Max 5 does. If you get more blade
        surface area with the Max 5. I would think the hole shot would
        be even better than the Bravo XS.

        1. Rex,

          Adding setback in your case makes sense to me, being that the 525 lbs farther towards the bow of the boat is changing the center of gravity. I think you need to get the stern of your boat to settle through setup before we cast aside certain props. Does you pad also still have the lip?


  4. Retromodding a 1987 MOD-VP, 700lbs bare hull, with a 300R 1.60 ratio lower unit. Any guess on what pitch/type I should use? Prior motor was original 1987 Merc150XS (2-stroke) that weighed 375lbs, ran 72mph with 2 passengers (~175lbs each) and original 1987 26″ Merc through-hub exhaust prop.
    Any help is appreciated. Thx

    1. C. Lucero,

      You’re looking at a 100 mph+ boat. What is the make of the hull? Something like a Stoker? You will be looking into the 32 pitch range. Mercury Racing offers the Bravo I OC and the Pro Max. The Bravo I OC has a very small barrel and 14.50 inch diameter for minimal lift. Both props will be good options, it is hard to be sure since you will be one of the first to put a 300R on a boat this light. Also note that the 300R comes with a large diameter Sport Master gear case and will require a jack plate and much higher engine height than the engine you are replacing.


      1. Alright! Thank you. It is in fact ‘like a stoker’… I think it’s better It’s a Lavey (LCI) 18’10” Sebring.
        I will pass this info on to Chris Camire at so we can rig it correctly. We are excited about the project and patiently tapping fingers on the desk during the long lead time. November, they say.

  5. I have a 2018 Phoenix 721. It had an Evinrude 250ho. Im putting a 300r on it now with a 12in atlas Jack plate. What prop should I run with this set up?

    1. Bryan,

      I believe we talked on the phone this morning, 27 Fury for top end speed, 29 Bravo I FS for all around performance and drivability.


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