DI 951 top rpms with 15/20 impeller rpm loss

[Seadoo rxdi]

2003 rxdi. 89hours. So I replaced my wearing ring and impeller with an aftermarket solas 15/20 due to sucking up debris and dinged up the oem impeller and ring pretty good
I use to hit 6800rpms.
Now after the impeller change I am more around 6400 sometimes 6500rpms. Is this normal?
I did kind of feel like the hole shot is now a bit more aggressive after installing the 15/20 but can't say for sure if it's in my head or not. What is the OEM pitch?
Not sure if this is directly the cause for rpm loss or not.
I am in Texas with altitude of roughly 1300' if that matters.

 

[Matt Braley]

The 15/20 Concord is hard for a stock engine to pull. A new wear ring tightens up the tolerances and causes rpm to drop but you will maintain your speed normally. A good solution would be for you to send the impeller out to a place like Impros or Skat Trak and have a degree of pitch removed.

 

[Seadoo rxdi]

The 15/20 Concord is hard for a stock engine to pull. A new wear ring tightens up the tolerances and causes rpm to drop but you will maintain your speed normally. A good solution would be for you to send the impeller out to a place like Impros or Skat Trak and have a degree of pitch removed.

So the rpm loss is normal with this impeller on a stock engine? Any idea what the OEM impeller pitch is?

 

[Sportster-2001-951C-Stock]

The 15/20 Concord is hard for a stock engine to pull. A new wear ring tightens up the tolerances and causes rpm to drop but you will maintain your speed normally. A good solution would be for you to send the impeller out to a place like Impros or Skat Trak and have a degree of pitch removed.

This is a good answer, I agree the pitch is most likely greater. The OEM impeller choice is hard to beat, they really do their homework. Not that someone can't come along later and improve it but there are so many out there the chances you wind up with something generic are high.

 

[Seadoo rxdi]

Thank you guys. I will take my oem and send it off to have repaired. And maybe even take the new 15/20 and have it re pitched. Or just keep it for a backup

 

[Matt Braley]

The pitch #'s don't line up together between brands and impeller styles.

 

[mikidymac]

Think of a higher pitched impeller like trying to ride your bike in too high of a gear. You are putting more load on the engine than it can handle so you can’t turn as many rpm.

At wide open throttle you should be around 6900rpm, that’s the sweet spot on a stock ski.

 

[Seadoo rxdi]

So basically, with this impeller I'm not even getting the most of my ski powerband? Wonder why they sell this impeller as an "upgrade" for a stock engine.

 

[mikidymac]

Yes, it’s too tall for you engine to pull. Call Impros and talk to Glenn.

 

[Sportster-2001-951C-Stock]

Or consider sending both to Glen and ask him to fix them?

 

[mikidymac]

Or consider sending both to Glen and ask him to fix them?

Good call Sportster.

 

[Sportster-2001-951C-Stock]

BTW, we have this issue with boats all the time, can't run a 3-blade on some configurations where a 4-blade works well and vice-versa. There are so many different hull and drive depth combos you just can't guess and expect a good match, and by guessing I mean the charts don't apply in all cases.

Cupped blades, no cup, chopper, 3-blade, 4-blade, aluminum, stainless, bla, bla, bla...

In some cases unless it's the same dang prop, you just don't know what to expect until you slap it on and find out. That's where someone who really knows what they're doing like Glen (of course nobody knows everything about every prop and impeller), makes all the difference.

 

[Sportster-2001-951C-Stock]

So basically, with this impeller I'm not even getting the most of my ski powerband? Wonder why they sell this impeller as an "upgrade" for a stock engine.

I'm by far an expert on Seadoo impellers, I wanna make that clear. That said, you may have actually gained something but my suspicion is you didn't or at best came out even-Steven. Lugging especially, or over speeding an engine can result in a 30% engine life if the combo is bad enough.

Oh how come my engine took a dump, it only has 100 hours on it? Well, where'd that big-ass prop come from, that might have something to do with it!

 

[Seadoo rxdi]

why would

I'm by far an expert on Seadoo impellers, I wanna make that clear. That said, you may have actually gained something but my suspicion is you didn't or at best came out even-Steven. Lugging especially, or over speeding an engine can result in a 30% engine life if the combo is bad enough.

Oh how come my engine took a dump, it only has 100 hours on it? Well, where'd that big-ass prop come from, that might have something to do with it!

I can understand over revving shortening an engines lifespan but I would have never thought lugging it would.

 

[Sportster-2001-951C-Stock]

More heat is produced as fuel consumption increases in the case of lugging, while piston skirt to cylinder wall forces are increased as well.

It's surprising how many people seem to overlook how hard a marine engine works, they just don't stop to consider if their car burned 12GPH of fuel they wouldn't be too happy yet a boat can easily consume this much, that's a hecka lot more fuel consumed and heat being produced in the process. All at 5,000RPM, not 2,500. 100% duty cycle, no coasting up to a stop light or down hills. I see people on the water with throttle to the wall, couldn't get away with doing this in a car for very long.

OEM's optimize their design as a system (for instance the tune/map of ignition timing and air/fuel ratio) based on torque and horsepower peaks, this allows them to run the power plant in it's sweet spot and achieve respectable fuel consumption, speed and engine life. Still, there's a narrower margin of safety since considerably more heat is generated in extreme conditions like WOT, and people expect their boat engine will last well beyond a couple hundred hours.

I've seen plenty of well maintained outboards with tens of thousands of hours on them, these were not abused by burning stale fuel, lack of maintenance, and storage in moist environments, they are all professionally rigged and operated conservatively, often on a daily basis in a commercial environment.

Heat is probably the biggest enemy just ahead of moisture but both are to be avoided.

 

[mikidymac]

You can also induce detonation by overproping a ski.

 

[Sportster-2001-951C-Stock]

You can also induce detonation by overproping a ski.

Correct, detonation is common if the engine is overheating, might say they go hand in hand.

 

[Seadoo rxdi]

Here is my oem impeller. What do y'all think? Would u run this? I think most of my issues were with the wear ring which was completely chewed up. But the impeller has been like this since I got the ski. Blades don't seem bent from looking at it. Just the edges dinged up a bit.

 

[Seadoo rxdi]

I'm thinking about trading in this new 15/20 solas I got on the ski now with a aftermarket 13/19 solas. Or just putting my OEM back on with the new wear ring if the damage isn't too bad according to you guys.

 

[mikidymac]

If you want to get back on the water quick then just lightly hit it with a file. The correct fix is to send it to Impros or Skat-Trak for refurbishment and balancing. There’s absolutely nothing wrong with the performance of the OEM impeller.

 

[Sportster-2001-951C-Stock]

My impeller looks maybe worse. I'm in no hurry to yank any of it apart, still works good enuff for me and if I thought it would fix the fact this boat can barely pull me out of the water on a slalom ski I'd consider it but I know better.
I've got other projects, currently shoe horning a stern drive into an old tunnel hull I found. This will have no issue pulling my arms off.