Snowmobile swapped sportster

[Yamadoo92]

Hey guys, I finally finished my Yamaha engine swap project in my 1995 sportster
After hearing from the previous own that it has been through 4 engines and after digging into it after I bought it I found the crankshaft bearings were damaged and needs a top end...

So I found a 1989 Yamaha exciter 570cc
I used that engine to replace the 657x
The Yamaha engine produces 95hp so that's 15hp more than the 657x made.

 

[mikidymac]

Hey guys, I finally finished my Yamaha engine swap project in my 1995 sportster
After hearing from the previous own that it has been through 4 engines and after digging into it after I bought it I found the crankshaft bearings were damaged and needs a top end...

So I found a 1989 Yamaha exciter 570cc
I used that engine to replace the 657x
The Yamaha engine produces 95hp so that's 15hp more than the 657x made.

If that 570 makes 95 hp then it must have very little torque and be at very high rpm. It’s actually going to be slower in the boat and you are probably going to have to repitch the impeller as it will be too tall.

 

[Yamadoo92]

If that 570 makes 95 hp then it must have very little torque and be at very high rpm. It’s actually going to be slower in the boat and you are probably going to have to repitch the impeller as it will be too tall.

Actually the snowmobile engine has a longer stroke which indicates more torque, the 657x made 80hp at 7000rpm
570 makes 95hp at 7200rpm not that far off.
The Yamaha engine from what I've read is just a more well developed and better engineered. Sorry not sorry

 

[mikidymac]

How are you cooling the exhaust?

Also make sure that engine doesn’t have any source of ignition for fuel vapors as that could be deadly.

 

[Yamadoo92]

How are you cooling the exhaust?

Also make sure that engine doesn’t have any source of ignition for fuel vapors as that could be deadly.

I have a T fitting in the feed line to the exhaust and have a fitting at the top to drain it.
The seadoo has a blower so I run it for like 3min before starting it

 

[Whus02]

You should be using the snowmobile exhaust, they're tuned for the particular engine. At least make sure that the length is equal by messing with your manifold.

 

[Yamadoo92]

You should be using the snowmobile exhaust, they're tuned for the particular engine. At least make sure that the length is equal by messing with your manifold.

Actually it's like an inch of the stock Yamaha exhaust, I don't know for the expansion chamber the difference. I took it on the water last weekend but the fuel pump died and I didn't even make it past half throttle.

 

[mikidymac]

The home made connector pipe is going to kill any performance from the seadoo expansion chamber.

 

[Yamadoo92]

The home made connector pipe is going to kill any performance from the seadoo expansion chamber.

From the quick test I did with it by half throttle before the fuel pump died it was on plane and had plenty of power. If it does kill some power than it will be back to stock power of the 657x lol win win

 

[Raven888]

Nice job! Looks like lots of room in there to work.

 

[Yamadoo92]

so this happened

Apparently the jet pump doesn't put out that much water pressure compared to a garden hose so there wasn't enough water flowing through the exhaust.

 

[mikidymac]

It isn't the jet pump.

The seadoo pipe is cooled from the waterjacket in the exhaust manifold up into the pipe. You have eliminated that cooling path with your homemade connector pipe. The top brass fitting on the pipe is to purge air out, not supply cooling water.

 

[Yamadoo92]

It isn't the jet pump.

The seadoo pipe is cooled from the waterjacket in the exhaust manifold up into the pipe. You have eliminated that cooling path with your homemade connector pipe. The top brass fitting on the pipe is to purge air out, not supply cooling water.

View attachment 59459

The pipe is still water cooled I have water feeding to it and was using that top bleed port to drain the water back out the exhaust. From what I've read they use that port as bleed and supply the exhaust with water.

 

[Yamadoo92]

The pipe is still water cooled I have water feeding to it and was using that top bleed port to drain the water back out the exhaust. From what I've read they use that port as bleed and supply the exhaust with water.

And now I added another return line to run it in series so the water has to fill that pipe first before it can feed others

 

[Yamadoo92]

Update: so the boat did great no over heating! Running the exhaust in series for cooling did the trick. I guess the jetpump doesn't put out as much as I thought.

New issue tho..... I noticed the rideplate is broken flush to the hull. That explains the mph loss in the boat.

 

[Yamadoo92]