Yamaha exciter 570 into seadoo

[Anthonynytro]

Hello, guys I have a pretty unique boat I built last summer and need some help with some odds and ends! This site has helped me alot in the past and alot of the seadoo owners get really offended and angry when a Yamaha engine is swapped in.
Okay so here's the story
I own a 1995 seadoo sportster (single engine model) I bought the boat with the engine blown (cylinders scored and crank bearings destroyed) so from what the old owner told me this was the 4th or 5th engine already... So I said screw this and found a old 1989 Yamaha exciter 570 to replace the 657x
Seadoo said the 657x made 80hp
Some sources online said the yamaha made between 80-95hp depending on years and carbs.
I installed the engine but realized I can't use the snowmobile exhaust due to the under hood temps would be to much.
So I kept the water cooled exhaust but it's from the seadoo.
On the water it picks up pretty good but can't get it over 6000rpm... Specs for this boat are 7000 and up for this impeller.

Im a mechanic but not an engineer so I don't know if using the seadoo exhaust is causing a loss of top end?? Or does a snowmobile engine not have that much top end compared to the seadoo?. I know the engine can get to 8,800rpm with no load so why can't it get there in water, is there more backpressure because now the exhaust is going through water?

Would like to know everyone's input on what I should try before getting the impeller repitched for more rpm.

 

[earthling]

The doo pipe is tuned for larger displacement. The addition of water injection only makes the pipe seem even larger to the engine as the cooling effect results in a delay in the return pressure wave as the cool air makes the exhaust look longer than it physically is. You could try running your doo exhaust dry (for a short period of time) and see if RPM comes up. If so, then it is a pipe tuning problem.

 

[sxr70001]

It could be jetting as well. Did you change the jets on the snowmobile engine for the warmer temps?

 

[Anthonynytro]

It could be jetting as well. Did you change the jets on the snowmobile engine for the warmer temps?

I put the clip on the needle 1 spot up to lean it out abit and the plugs show a perfect mixture

 

[Anthonynytro]

The doo pipe is tuned for larger displacement. The addition of water injection only makes the pipe seem even larger to the engine as the cooling effect results in a delay in the return pressure wave as the cool air makes the exhaust look longer than it physically is. You could try running your doo exhaust dry (for a short period of time) and see if RPM comes up. If so, then it is a pipe tuning problem.

Thank you! I just googled water injected exhausts how they operate and I have a big feeling that's why it's loosing alot in the top end! And it's a pretty easy test to just move 1 hose and test!

 

[earthling]

I wouldn't expect a dramatic difference but it should be noticeable. The core issue *probably/maybe* is the pipe itself.

 

[Anthonynytro]

I wouldn't expect a dramatic difference but it should be noticeable. The core issue *probably/maybe* is the pipe itself.

The way I routed the water hoses put the return line through there so that means theres a 3/8s water hose right into that expansion chamber so it's probably flooding that like crazy

 

[earthling]

The way I routed the water hoses put the return line through there so that means theres a 3/8s water hose right into that expansion chamber so it's probably flooding that like crazy

It should be a controlled injection of water, not a firehose

 

[Anthonynytro]

So update.. I rerouted the water lines so the exhaust got no water injected into the expansion chamber, soon as I brought it to the water the exhaust flange broke and introduced a large exhaust leak making this test run useless. And to add to more issues the boat developed a cavitation issue.

 

[earthling]

Bummer. The cavitation is obviously a separate issue, is that common on Seadoos?

 

[Anthonynytro]

Bummer. The cavitation is obviously a separate issue, is that common on Seadoos?

Ya the wear ring is very easily damaged.
The only thing going through my mind is.. what if this engine just isn't powerful enough? Like it's running great and still is pretty quick for what it is, but not going above 6100rpm!

 

[earthling]

Under load (in the water)?

 

[earthling]

If your pump is cavitating due to poor tolerances (wear ring) it may be that the cavitation itself is causing the issue (low RPM). Cavitation is tricky and jet pumps (like 2-strokes) have a narrow operating band of efficiency. You won't know how efficiently the motor can run without fixing the wear ring but first figuring out if the wear ring issues were caused by ingesting something or some other issue (bearing? Driveshaft?)..

 

[Anthonynytro]

Update: winter is coming to an end so I'm thinking about boat season already.
Found a performance PSI pipe for the 570, I'm ditching the seadoo exhaust. From what I read this exhaust should squeeze out some more power.
Also found the cavitation issue it was coming in from the driveshaft bearing hanger seal.

 

[Anthonynytro]

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