When to Use customized Impeller？

For all the time spent on this and the previous forum, I have yet to be convinced that you can do a simple impeller change and make much of a difference in performance...EXCEPTION: if you boat at higher elevations, then the balanced pitch impellers that your boat came stock with, won't have the hole shot as they would at lower elevations. And all boats suffer a horsepower loss as you get to higher altitudes...unless they are turbo or supercharged. This is due to a loss of atmospheric pressure. So if you do boat at a higher elevation lake, like over feet, then I might consider looking into them, otherwise, don't bother. Another thing to note...you can't have it both ways...a prop or impeller will either be pitched for power out of the hole or for speed. A power prop will produce more resistance and won't turn as fast at speed, so the boat won't run as fast as a boat with a "speed" prop. Conversely, a "speed prop won't get you out of the hole nearly as quick or as powerfully as a "power" prop. The stock impellers are a balance between the two. Any minor change in pitch to them will result in a loss in one category and a gain in the other. Just can't have both without balance. Now, you could have any nicks cleaned up, and that could improve your performance, depending on the need to redress them. Also, having them polished might give you an improvement, but will it be measurable? Maybe not on the speedo or gps...but your rpm's might change as well as your fuel usage. Efficiency is gained by many small improvements, not just one. As they say, it takes about $1K to gain 1 mph...if you want 5 mph, your spending $5K and so on. I did Solas on my Exciter and LX. Very happy with the results. I bought them from Group K. They have done all the testing on the two stroke boats to know what works, 13-19 and 12-18. Got perfect 7k on both motors. Much better hook up and 1-2 on top. Don't know if any one has spent the time to figure the right props for the 4 stroke boats so I haven't done my SS yet. And I'm not the speed freak I use to be. My biggest concern would be getting the right RPMs without sending them back three or four times. I agree. I have changed out impellers on a few PWC's I have had over the years. They make a decent difference and changing an intake grate can also help some in addition to the impeller.

With the boat I am not sure it would be worth the time or money. Has anyone but the cavitation kits on our boats? I did that on a yamaha PWC once and it seemed to help not get so much air in the pump. With these boats cavitation doesn't seem to be an issue but I do wonder if it would do any good to seal everything up around the grate. The following will sound like I'm being paid to write it, I am that happy with my new impellers. They were an amazing improvement to my boat. I did lose maybe 2MPH off the top end, but I dont really spend much time trying to prove differently because I could care less about going over 50. I brought it up to 50 with the new props and called it good.

I had Impros custom pitch a pair of Solas Concordes. They pitched for no top end loss and a large improvement in acceleration. Mel is right, you cant have it both ways when adjusting pitch on similar props, but the difference here is a more efficient impeller design that bites much better and much smoother than stock which equates to a significant holeshot improvement with very little top end loss. The difference in acceleration was very noticeable! I had around 120 hours on the old units and now 30 on the new ones.

Additionally my boat runs much quieter, with a lot less vibration than before... much better than new even. I use a lot less fuel and the power is very smooth at any range. My No Wake speeds are a little higher (which I like) and I have very little trouble with weeds where I did before. Those blades are like razors.

Knowing what I know now this will be a mod I will make to every Yamaha I ever may own, even if brand new. Dont hesitiate to buy custom units from Impros. They were great to work with.

Now replacing them was one of the worst things I've been through. Dont attempt this on the evening before you leave for a week-long boating vacation! One of them was stuck, which completely stumped the local Yamaha Waverunner dealer, broke all the tools they usually use, and ended up an overnight job in my friend's machine shop to get it off. The impellers are of a slightly superior design in that they can process more water more efficiently. That being said, a properly pitched stock impeller is really not that far behind. Sending them to a company such as Impros is probably your best bet if they aren't too beat up.
There are no anti-cavitation kits for our boats. What you do is take the good marine sealant () and seal all the gaps. This will sometimes make a difference and reduce some cavitation if you are experiencing a little bit. I have the Solas DynaFly 14/20 pitched at 14/19 and 14/21. Works well. I did notice more hole shot, and I still have a 52 mph top end, which for the MR-1 engines is pretty darn good. I'm aiming for more top end, but the engines have run out of steam.
I have the impellers, sealed the pumps, blueprinted the pumps, put in pump wedges, pulled the filters, put in velocity stacks. I have also tried a straight through exhaust. Gained me nothing, and made a heck of a lotta noise.
The biggest thing for top speed is seriously the weight in the boat. Get rid of the weight, you're closer to a jet ski with two engines and pumps.

Hey guys, so I’m working on a custom project and I’m trying to find the best impeller for my application. When I started looking for the right one for what I need I noticed that there are a couple of different designs out there. I searched online for any characteristics of each design, like which has better acceleration and which handles rocks better, but I came up with nothing. A quick Google images search will show you all of the different types out there.

So, can someone point me in the right direction? I’m looking for a design that handles rocks very well and also has good acceleration.

Thanks

I guess I should have explained to you a little about my project. This pump will be in a jon boat that will be ran in a rocky river. I need something that will get on plane quickly and is durable when it comes to dealing with rocks. I have access to lathes and mills and I plan to modify a jet ski pump to take a stronger impeller if theirs a better option.

I would just use an unmodified jet ski pump but I hear that they tend to get rocks lodged and seize the engine. Their blades are also very fragile and easily damaged.

Here is what I meant by different types of impellers:







What is effected when the leading edge of the impeller is straight rather than curved? How does having the blades cast in a cylinder like in the last pump effect things? These are the characteristics I’m wondering about.

Anyone have any input? I would think that the impellers with the straight leading edge would be less prone to getting rocks lodged inbetween it and the wear ring. I guess i could just go ahead and use a regular stainless steel jet ski impeller but they seem to be flimsy and easily damaged by rocks. I just figured that since i have the machinery to give it a better impeller, i might as well try.