2kwik4u - I've been told that the L13 cone won't really help when the SX190 is overloaded. That it, because of the space required, actually reduces the amount of water available to the impeller.
So, this isn't quite accurate, sort of. The L13 changes the shape of the water passageway between the pump and the nozzle. The amount of water available to the impeller remains the same, as the intake side of the pump remains unchanged. What the L13 (or any modified cone) does by changing the shape of that passageway is allowing a more evenly dispersed pressure gradient across the nozzle.
So, to back up a little bit, the pump and nozzle need to be understood. Most people think the pump/nozzle work by "pushing against" the water behind the boat. This is an incorrect intuition. You can tell quickly this is incorrect by noticing that when on plane, a jet nozzle is out of the water, and there is no water there to push against. The nozzle (at high speeds) works by trading pressure generated by the pump for momentum (by way of acceleration through the nozzle) of the water. By changing the momentum of the water, you generate a small force forward. Push a LOT of water out the back, and you get a large force forward.
A good thought experiment for illustration; say you're standing in a canoe, in a still and calm pond. You're holding a large block of concrete and "throw" it out of the boat. What happens to the boat? It moves slightly forward. NOW, think of throwing a LOT of blocks out of the back of the boat at a very rapid pace. That change in momentum from moving the mass of the block is what generates the forward force. Jet pump and nozzle systems work the same way, it grabs lots of stationary water and throws it out of the back of the boat. It does this by reducing the cross sectional area between the inlet of the nozzle (outlet of the pump) and the outlet of the nozzle. If the same mass moves through both the inlet and outlet, and the outlet is smaller, the nozzle will have accelerated that mass of water.
This is where the shape of the pump cone comes into play. That smoother pressure gradient helps reduce surging and pressure waves between the pump outlet, through the nozzle to the nozzle outlet. This in turn helps prevent cavitation in the pump. To be 100% clear, the cone shape doesn't add HP, or increase efficiency, or any other "tune up" style effect, it simply helps prevent cavitation in the pump from those inconsistent pressure gradients. It is possible to "stuff the pump" where you decrease the outlet opening to such a degree that the pump can no longer flow enough water and you loose revs due to overloading. This is why I prefer the L13, as adjustments to the position and shape of the pump cone are relatively easy. I ran with all the spacers in place for many years, I've since removed a single 5mm spacer, as I think it allows just a shade of "overshoot" during initial launch and I would rather have the flow from the increased revs than the absolute lack of cavitation from the back pressure.
That all takes us to "The L13 won't really help".......This is pretty vague and ambiguous. It helped my boat considerably, however I have cavitation issues under full load. The modified cone made the boat much more consistent regardless of person/gear loading. It now launches exactly the same whether I have 8 people or 1 people on board. "traction" with the water is much improved, and I have no problems planning with a full load and pulling a wakeboarder up from a deep water start. NOW, with that said, the 190's are still low powered single engine crafts. It's not going to launch like a scared cat on carpet. It's a 19ft vessel with 180hp, so if your boat isn't planning or struggling to plane because there isn't enough horsepower (because you're at elevation, or your overloaded, or the engine isn't running right, or whatever), then the L13 won't help. If you can't launch/plane because of cavitation, it absolutely will help.
Overall, between the ribbon delete, the L13 cone, and a sealing of the pump intake tunnel; my boat is exceptionally consistent in performance. It's not setting the world on fire. It tops out around 41-43mph now, and is still VERY sensitive to the location of loading (bow weight KILLS top speed). Brand new, with zero mods, I've only ever seen as high as 42mph. However, it almost never cavitates. Traction with the water is superb. Weather no longer affects performance. It runs the same speed in the spring, summer, and fall regardless of water and air temperature. Elevation is a much larger driver in performance than anything else. It's also been exceptionally reliable mechanically. I'm not overstressing any component, and it's given me many seasons of worry free enjoyment. That's worth more than a few mph on the top end IMO.
Sorry for the novel, it's a Friday afternoon and I didn't want to send any more work emails.
