98 and 99 Malibu Response LX Engine Placement

[MopedMedicks]

Created this post for documentation. The general understanding online is that the 98+ Malibu Response and Response LX has the diamond cut hull and the same great slalom wakes we know and love. 98 was the first year of the new hull, and 99 was the first year of the new upper deck/interior which features the rear trunk.

 

Here is the part that isn't documented as clearly (at least online, I'm sure the promos at the time were aware). To make room for the trunk in 99+, the engine and pylon were moved forward by 1.5" - 2". This drivetrain movement and change in weight distribution changes the wakes, acceleration, and top speed of the boat.

 

How would I know this? I have a 99 and my buddy has a 98, both response LXs. The slalom and trick wakes are only slightly different (hard pressed to say at all). But, his boat is over a full MPH faster than mine, particularly pulling a footer. I'll get 45.3 mph pulling front wakes, he will get 47 mph under identical condtions, and identical props (we even traded props to confirm). Furthermore, the foot tables are different, with favor going to the 98. It was a local 3 event footer that pointed this model year diffeence out to me after I said "I don't know why my boat is slower"

 

We put them on the dock side by side yesterday with the clamshells up and it was clear- you could see the power train placement change by 1.5"-2". So, if you are a footer who wants the diamond cut hull (hardcore, you really want a sportster though, or a DSII), get the 98. For a marginal slalom improvement, go 99+.

[Deke]

@MopedMedicks I'm no expert, but there are other factors that could be causing that speed difference like deformities in the hull, weight, gas tank location and shape, even shaft alignment. Also, can you describe how you could "see" the 1.5" difference in engine placement between the 2 boats parked next to each other. Did you measure?

 

BTW, I still have a 99 RLX and a friend had a 98 and I never noticed a difference. Can't say I ever actually tried to notice though.

[MopedMedicks]

I fully agree that the manufacturing tolerances on hulls is highly variable, and drastically effects wake and speed. So does final drivetrain placement and alignment, not to mention engine to engine power variation.

 

To compare, we put them side by side on a calm water dock, aligned the rear tow hooks (same lower hull) and put a bungee rope between the two pylons. The rope was deflected back towards the 98. Took a side view from the dock (with the rear hooks still constrained) and could visibly see the pylon/motor placement difference. Don't know how I could accurately measure it, but they eye ball and thumb was the 1.5" - 2".

[MopedMedicks]

I would also comment that the wake difference is most profound for barefoot 3 event, slalom and trick traditional 3 event is really hard to tell apart, if really at all.

[DW]

@MopedMedicks : Interesting observation. I don't recall either from Malibu literature or from dealer comments the engine/pylon placement change highlighted as a selling tool. Interesting that both the pylon and engine moved in unison. Did you happen to notice if the windshield followed or stayed put, makes some sense that to accommodate the truck, elements needed to be shifted? I also don't recall in the previous edition TXi thread any comment that the pylon moved with the engine shift in that model. Moving the center of gravity forward and hence the pitch point certainly can contribute to a reduction in top speed due to increasing the wetted surface at speed. Thanks for sharing.

[Ski_Dad]

are you turning the same RPM - i would think it's more of an engine difference - some come out a little stronger than others.

[MopedMedicks]

With the upper deck change from 98 to 99, the windshield design changed a fair amount. Didn't really compare their resting point because of that.

 

With the ACME 515, I'll turn 5230 at 47.0 with my 99. His boat will spin the same prop ~5100 and get 48.2 mph. To me this RPM difference indicates different hull drag between them. Both motors are making good power at those RPM ranges, and with the same prop the "thrust" output is pretty close.

[BraceMaker]

@MopedMedicks - would you consider the change enough to make it worth having provisions to shift the motor fore/aft? Or is it so little that it doesn't warrant the change?

[DW]

@BraceMaker : You could actually run the experiment yourself. Simply get a known ballast weight and move it from stern to bow and evaluate the effect. Run low fuel to simulate a certain fuel load when you add the ballast at the transom, and repeat with no ballast but the added fuel to compensate to verify your experiment.

 

The challenge on engine placement becomes the prop shaft angle adjustment or attachment & seal pass through configuration. Different hardware may be required to accomplish that adjustment.

[BraceMaker]

@DW where there is a will there is a way - longer shaft for instance and then just realign the engine coupling.

 

Since now all the ski boats have reduction gear transmissions nothing saying they couldn't have a bevel gear drive on the output to put the engine flat in the hull and free up all sorts of placement options - such as engine forwards and a torque tube to the trans or reverse V-drive with torque tube to the rear for more interior room.

 

Consider how that could impact lay out.

[vtjc]

@BraceMaker Malibu still puts 1:1 transmissions in their ski boats.

[DW]

@BraceMaker : Yes, and alternate strategies can also move the CG forward. I will say moving CG forward on the SV23 hull does change (IMO improve) the slalom wake, has worked for me tinkering with my vessel. In your example, you might need to adjust or change the shaft strut or lift the engine up and create underhood clearance as you migrate forward.