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Response LXR 6.0 Top Speed


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Hello Everyone,

I recently purchased a Response LXR with the 6.0 liter PCM 409 engine making an advertised 410hp.

The boat will run 49 mph with an Acme 515 at 5600 rpm which is on the soft rev limiter. I swapped a 449 hoping for 2-3 more miles per hour. Much to my surprise the boat still only ran 49 mph albeit at 350-400 rpm less.

At lower rpms (3000 and 4000 specifically) I did

notice the speeds were 2-3 mph faster with the 449 than they were with the 515.

The boat is equipped with an e-throttle, e-shifting, and GPS speedometers split between the stock mechanical and the Zero Off.

Does anyone know if there is a speed limiter built into these boats from the factory?

If not, is there anything else that could be limiting my top speed?

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No speed limiter.  Drag is limiting your top speed.  The hull is designed to stay wetted in order to provide a very smooth ski wake.  You bought a tractor, not a race car.

If you really want to go faster, join @Woodski in his rabbit hole.  He's not after speed, just minimum wake.

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I have the LS1 in my Sunsetter.  It has similar power. And it runs 49 with the 515 and 48 with the 525.   If you are getting 5600 with the 515 that is perfect.  In the long run that will make your engine last longer.    The LS1 and the 6L make there torque up higher. 
 

the limiting factor is the hull.  It does not raise out of the water like a Stern drive boat.  And the prop angle and is not adjustable.   

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Never meet your heroes...

I had a 2002 RLX with a 5.7 Merc Black Scorpion factory rated at 330hp. It would turn a 449 at 4900-4950 and give me 47-48 mph.

I guess I was hoping the extra 80 hp would have pushed me into the low 50s...

I still love the boat and the mid-range is just silly. I guess I was just hoping she’d at least run 52ish.

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39 minutes ago, justgary said:

No speed limiter.  Drag is limiting your top speed.  The hull is designed to stay wetted in order to provide a very smooth ski wake.  You bought a tractor, not a race car.

If you really want to go faster, join @Woodski in his rabbit hole.  He's not after speed, just minimum wake.

The Echelite.  Equally as powerful as Sasquatch, yet twice as elusive.

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I have no doubt you could get 52ish out of it if you really want it.  Start by throwing *everything* out of the boat that you don't absolutely need.  Then put only 5 gallons or less gas in the tank. 

If you don't get 52, come back and we'll help you decide what goes next.  My vote is the windshield.  It's very heavy, and it does add wind drag. 

  • Haha 3
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1 hour ago, BoatFlyRide said:

Hello Everyone,

I recently purchased a Response LXR with the 6.0 liter PCM 409 engine making an advertised 410hp.

The boat will run 49 mph with an Acme 515 at 5600 rpm which is on the soft rev limiter. I swapped a 449 hoping for 2-3 more miles per hour. Much to my surprise the boat still only ran 49 mph albeit at 350-400 rpm less.

At lower rpms (3000 and 4000 specifically) I did

notice the speeds were 2-3 mph faster with the 449 than they were with the 515.

The boat is equipped with an e-throttle, e-shifting, and GPS speedometers split between the stock mechanical and the Zero Off.

Does anyone know if there is a speed limiter built into these boats from the factory?

If not, is there anything else that could be limiting my top speed?

For what it's worth, I have a 383hp dyno tested custom built engine and I run an Acme 425 and my top end is 49mph at 4900rpm.  I was expecting something in the 50's too, but honestly I imagine anything over 50mph getting really weird in these boats.

425   13x13

449   13x12.625

515   13x12

525   13x11.5

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3 minutes ago, UWSkier said:

I thought that engine was something like 363 HP, not 410.

I’ve heard it both ways. Dealer said 363 horsepower but then I emailed Malibu tech support. They stated it’s 410 hp.....

Coincidentally enough 363 cubic inches is six liters...

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2 hours ago, justgary said:

Bring it down here and run it in salt water.  The extra density gives you a little more lift and thrust. 

Which is why I hate slalom skiing in salt water.  Well the getting up part is easier but turning sucks.

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25 minutes ago, Eagleboy99 said:

Which is why I hate slalom skiing in salt water.  Well the getting up part is easier but turning sucks.

Having grown up in salt water, I much prefer it.  I can easily judge how salty water is as I ski on it. Several of our bayous are creek fed, so it is common to ski into what is basically a river of fresh water flowing into the salt water.  The two have different textures, and you can feel them through the ski. 

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You could grind away a bit of the hook at the transom if you want to ruin the ski wake but go faster.  You could also see if adding weight to the stern helps.  I know my dad's '01 Sunsetter VLX with a larger wetted surface but the engine in the back is a couple MPH faster on top end than my '01 Response with bow weight is.  Both diamond hulls.

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6 hours ago, UWSkier said:

You could grind away a bit of the hook at the transom if you want to ruin the ski wake but go faster.  You could also see if adding weight to the stern helps.  I know my dad's '01 Sunsetter VLX with a larger wetted surface but the engine in the back is a couple MPH faster on top end than my '01 Response with bow weight is.  Both diamond hulls.

I really have no “need” to go faster. I was simply surprised that the extra power over my old LX didn’t result in much more speed.

My primary sport is barefooting. I used to do some endurance and distance races so speed is nice but not essential.

Maybe this boat won’t lose as much speed loaded down with 5-6 skiers as my old boat did.

Edited by BoatFlyRide
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It's an LXR.  Be happy it actually goes 49.

The last thing that did 49+ consistently was a light-build Response with a Hammerhead or LS1/3 spinning 5600 rpm with a 13x12.5 prop.  Before that there was the Flightcraft Outboard....

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10 minutes ago, SmoothWaterMan said:

It's an LXR.  Be happy it actually goes 49.

The last thing that did 49+ consistently was a light-build Response with a Hammerhead or LS1/3 spinning 5600 rpm with a 13x12.5 prop.  Before that there was the Flightcraft Outboard....

I appreciate the perspective! You guys have all made me feel a lot better about my purchase.

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@BoatFlyRide - there are several factors that will determine top speed, here are some of my thoughts on it based on quite a bit of experimentation:

1.  As noted, these hulls have a lot of wetted surface area, Malibu's tend to be freer than the others in the 'top 3' category.  The hull drag increases significantly as the speed increases so small increases in top speed take a significant amount of additional power.  You are also trying to overcome the aero drag, you can see the effect by simply opening your bow access window and doing an A-B test.

2. To your question on actual power, a lot depends on where in the RPM range it actually gives you that power.  The camshaft used will make a big difference and since these boats need to have excellent idle characteristics, an aggressive cam to provide additional power at the ~6,000 RPM zone may not provide good idle quality.  If you want to bump top speed, a change that accomplishes that is a ZZ4 camshaft which has more lift and duration compared to the marine cam.  It also has really good idle characteristics.  A simpler option would be a set of 1.6 ratio rocker arms.  As @SmoothWaterMan notes that configuration accomplishes that, pretty much my previous configuration and it hit the 5,600  PRM mark (I don't have a rev limiter and see next point for more detail).  The key was airflow (camshaft) as much as anything, not so much absolute power number and the Hammerhead has a more aggressive camshaft and also freer flowing cylinder heads.

3.  Here is one aspect not a lot of people talk about relative to top speed.  Prop blade area in my experimentation makes a difference on top speed in exactly the opposite effect one would initially think.  Basically, when a prop has a lot of blade area, for example the Acme's which are the current go to prop for a Malibu, they tend to hit a wall at a certain speed which ironically happens around the 50 mph mark for ones specific to tourney boats.  My conjecture is there is not enough space (read time in this case) between blades slicing the water to allow them to operate at peak efficiency so as you approach that point of diminishing efficiency the effective power output drops off quickly.  I actually discovered that doing a 3 to 4 blade comparison many years ago and basically did not think about it that much until I observed a similar thing to a lesser degree on my boat kind of by accident (read getting caught in a thunderstorm and wanting to get back to the lift in a hurry!).  Before you rush out and get that old CVP, there are many great reasons we all like the CNC Acme's and OJs:-)

4.  Any lastly, weight.  The less the better.  You might want to do a quick compare and/or run your current prized possession across a set of scales to see how it compares to the previous generation RLX's.  The Aussie video and spec sheet has the LXR tipping the scales significantly higher than they printed for the older versions.  No idea on actual real number comparisons, the difference surprised me when I read it.  No idea where all the extra weight would be for pretty much the very same boat thus I won't consider this until it would be confirmed. 

Hope I didn't put you guys to sleep:-)

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16 minutes ago, Woodski said:

@BoatFlyRide - there are several factors that will determine top speed, here are some of my thoughts on it based on quite a bit of experimentation:

1.  As noted, these hulls have a lot of wetted surface area, Malibu's tend to be freer than the others in the 'top 3' category.  The hull drag increases significantly as the speed increases so small increases in top speed take a significant amount of additional power.  You are also trying to overcome the aero drag, you can see the effect by simply opening your bow access window and doing an A-B test.

2. To your question on actual power, a lot depends on where in the RPM range it actually gives you that power.  The camshaft used will make a big difference and since these boats need to have excellent idle characteristics, an aggressive cam to provide additional power at the ~6,000 RPM zone may not provide good idle quality.  If you want to bump top speed, a change that accomplishes that is a ZZ4 camshaft which has more lift and duration compared to the marine cam.  It also has really good idle characteristics.  A simpler option would be a set of 1.6 ratio rocker arms.  As @SmoothWaterMan notes that configuration accomplishes that, pretty much my previous configuration and it hit the 5,600  PRM mark (I don't have a rev limiter and see next point for more detail).  The key was airflow (camshaft) as much as anything, not so much absolute power number and the Hammerhead has a more aggressive camshaft and also freer flowing cylinder heads.

3.  Here is one aspect not a lot of people talk about relative to top speed.  Prop blade area in my experimentation makes a difference on top speed in exactly the opposite effect one would initially think.  Basically, when a prop has a lot of blade area, for example the Acme's which are the current go to prop for a Malibu, they tend to hit a wall at a certain speed which ironically happens around the 50 mph mark for ones specific to tourney boats.  My conjecture is there is not enough space (read time in this case) between blades slicing the water to allow them to operate at peak efficiency so as you approach that point of diminishing efficiency the effective power output drops off quickly.  I actually discovered that doing a 3 to 4 blade comparison many years ago and basically did not think about it that much until I observed a similar thing to a lesser degree on my boat kind of by accident (read getting caught in a thunderstorm and wanting to get back to the lift in a hurry!).  Before you rush out and get that old CVP, there are many great reasons we all like the CNC Acme's and OJs:-)

4.  Any lastly, weight.  The less the better.  You might want to do a quick compare and/or run your current prized possession across a set of scales to see how it compares to the previous generation RLX's.  The Aussie video and spec sheet has the LXR tipping the scales significantly higher than they printed for the older versions.  No idea on actual real number comparisons, the difference surprised me when I read it.  No idea where all the extra weight would be for pretty much the very same boat thus I won't consider this until it would be confirmed. 

Hope I didn't put you guys to sleep:-)

I was waiting for your input! I did notice the engine seems to be further forward by 3-4 inches compared to my old RLX. 

Your comment about prop efficiency makes a lot of sense. I did note that the 449 was 2.9 mph faster at 3000 rpm and 2.6 faster at 4,000 rpm.

She just seems to hit a wall at 49.

Now the question is do I run the 515 or the 449?

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@BoatFlyRide - that 3-4 inches will make a significant difference as moving center of gravity forward will pitch the nose down and add running wetted surface area (hull drag).  Should also improve the wake as many note adding bow ballast helps the wake.  As for prop, my vote would be 449 for a few reasons assuming you are focused on slalom and barefoot where the engine speed will be higher than wake or surf sports:  you will spin the engine a bit slower so better fuel economy and reduce wear, the power curve is pretty flat in that engine speed range so no issues there and Indy is under 1,000' elevation so you have plenty of air.  The Acme site has a prop calculator which is fun to play with.  If you run it across the scales, I would be very interested in hearing about the actual weight.  Forgot to mention and no idea on if it applies to your engine, but I did a test on spark arrestors many moons ago and found a 200 rpm restriction so I made my own.  You might try a quick test just for fun, I am thinking yours runs a K&N filter which is cleanable but no necessarily low restriction.

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17 minutes ago, Woodski said:

@BoatFlyRide - that 3-4 inches will make a significant difference as moving center of gravity forward will pitch the nose down and add running wetted surface area (hull drag).  Should also improve the wake as many note adding bow ballast helps the wake.  As for prop, my vote would be 449 for a few reasons assuming you are focused on slalom and barefoot where the engine speed will be higher than wake or surf sports:  you will spin the engine a bit slower so better fuel economy and reduce wear, the power curve is pretty flat in that engine speed range so no issues there and Indy is under 1,000' elevation so you have plenty of air.  The Acme site has a prop calculator which is fun to play with.  If you run it across the scales, I would be very interested in hearing about the actual weight.  Forgot to mention and no idea on if it applies to your engine, but I did a test on spark arrestors many moons ago and found a 200 rpm restriction so I made my own.  You might try a quick test just for fun, I am thinking yours runs a K&N filter which is cleanable but no necessarily low restriction.

It runs a regular spark arrestor. I’m waiting for my check to clear so I’ll be able to post pictures on the site with my membership.

My only concern about the 449 is the fact is turns the engine slower than the book recommends at WOT.

449- 5200-5240 @ WOT = 49 mph

515- 5600 (limiter) @ WOT = 49 mph

The book calls for a minimum of 5400 and that 5500 is preferred. 

The 449 used in the test was a repaired unit so maybe it isn’t fully to spec?

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run the 515 - trust me on that.    You actually won't use any more gas b/c it's easier on the engine.   

this is the reason i run the 525 on my heavier boat.   The 525 puts me about 5500 which is good b/c sometimes we take the whole family and I'm still in my range of 5200-5600.   If I run the 515 I'm around 5300 with just me but if I load up the boat it will be below the range. 

I wouldn't worry about hitting the rev limiter - mine sometimes does that this time of year with the cold water/air.  Once you add a footer or skier and some warmer air it will not be an issue.

Edited by SkiPablo
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44 minutes ago, justgary said:

You could put a little bit of cup in the 515 and get WOT right on 5500.

Who could do this for me?

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56 minutes ago, BoatFlyRide said:

Who could do this for me?

Any good prop shop.  If it was an OJ, you could send it back and they'd fix it up for you.

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@BoatFlyRide - as noted a good prop shop can do it,  Nibral is very soft so really easy to work with and adjust the prop.  The Acme spec sheet will tell you how much cup is built in to the prop and you can go from there.  Also, Acme has great customer service over the phone and will tell you the effect of each change and if you tell them what you are looking for will give you a recommendation.  You could also send it to Acme, they offer that service.    https://acmemarine.com/

You can enter your boat specifics and see what their recommendation is:  https://acmemarine.com/pages/custom-fit

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