js550/701 conversion exhaust woes

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Yamasaki597

Location
Indiana
So I’ve been hiding in the shadows lurking through old threads for a while now. I’m finishing a 550/701 61x build that I picked up for cheap, and I’m pretty stumped on the exhaust. I do not want the stock breadbox, but from what I see a 650sx cheater pipe won’t fit? Looking for helpful insight. Should I just stick with the breadbox or try to buy some custom stuff? I can get my hands on a 550 mariner exhaust for cheap, been thinking about cutting the inlet off and upsizing it to mate up to a 650sx manifold elbow, bolted onto a Coffman style manifold. Seems like it would work out good, just not sure if it’ll be worth it performance wise….
 
hawk2989

hawk2989

Location
Greenville, SC
I used a Factory B Pipe Exhaust Manifold, with a 650SX cheater head pipe/expansion pipe and Coffman Outlet. See my profile picture. It worked amazing. I mated that with a Seadoo XP waterbox. Had to convert to internal fill, but that didnt matter to me.
 
Y

Yamasaki597

Location
Indiana
hawk2989 said:
Actually extended the 650sx expansion chamber by 2.5inches and it made a good difference in low end kick
Click to expand...
Did you have any clearance issues with the gas tank or side of hull? That’s the route I was originally looking at, modding/ welding pipes isn’t a concern for me at all. I was gonna weld a 3/8” barb fitting to the stinger on the 650sx pipe to make a poor man’s Coffman setup. How did you go about extending the expansion chamber? Got any pics? As far as water box goes, I have a J&S (I think) 550 water box that I was gonna modify to work. Not sure tho cause the inlet and outlet are substantially smaller than the stock 701
 
hawk2989

hawk2989

Location
Greenville, SC
You could be fine with the waterbox (I just dont know), may have to buy some exhaust hose that tapers or something if the end of the stinger is different than inlet for waterbox. For expanding the pipe, I used an old trashed stock 650SX pipe and cut the end off where the hose clamp normally holds the expansion pipe to the stinger then welded (I don't weld but had a small shop near me do it) to the end of the new cheater pipe, essentially creating a new space for the stinger hose clamp to meet the expansion pipe.

With regard to fitment - It was an extremely tight fit. I ground down the motor bedplate at the mount a bit to fit, then put some high temp rubber between the hull and pipe and between the exhaust manifold and pipe to effectively "wedge" it in place. Also put high temp rubber between the stinger and fuel tank to keep the stinger from melting the tank.
 
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Yamasaki597

Location
Indiana
hawk2989 said:
You could be fine with the waterbox (I just dont know), may have to buy some exhaust hose that tapers or something if the end of the stinger is different than inlet for waterbox. For expanding the pipe, I used an old trashed stock 650SX pipe and cut the end off where the hose clamp normally holds the expansion pipe to the stinger then welded (I don't weld but had a small shop near me do it) to the end of the new cheater pipe, essentially creating a new space for the stinger hose clamp to meet the expansion pipe.

With regard to fitment - It was an extremely tight fit. I ground down the motor bedplate at the mount a bit to fit, then put some high temp rubber between the hull and pipe and between the exhaust manifold and pipe to effectively "wedge" it in place. Also put high temp rubber between the stinger and fuel tank to keep the stinger from melting the tank.
Click to expand...
10-4. I’m interested at how much power loss I’d see from modifying a js550 pipe to have a larger outlet to mate up to the 650sx elbow. Seems like the 550 pipe is a smaller diameter and would fit much better in that hull. I can snag a stainless mariner pipe for cheap, maybe worth a shot, then the pipe outlet will match up with the water box as well. Main concern is it being too restrictive for the 701 though and not worth the effort over a breadbox….
 
SexPanther

SexPanther

Location
Coeur d'Alene Idaho
Breadbox kind of gets in the way of the gas tank and in my case it also forced me to flip my e box mount to clear the pipe and thus run a smaller battery that fits under the ebox.

If you really want to go fast get a factory b pipe!

I personally choose the breadbox paired with a stock SJ water box for optimal sound levels.
 
kevbo

kevbo

Location
dfw
With a good tuned pipe, waterbox flow is not an issue since the pipe needs some back pressure to work. The breadbox has no tuning so it needs less downstream restriction to work best. A stock 61x cylinder works well with the breadbox. A pipe is worth about 3 MPH. A higher ported cylinder with a good pipe will double that.
 
C

Captain Morgan

Location
Orillia
Yamasaki597 said:
So I’ve been hiding in the shadows lurking through old threads for a while now. I’m finishing a 550/701 61x build that I picked up for cheap, and I’m pretty stumped on the exhaust. I do not want the stock breadbox, but from what I see a 650sx cheater pipe won’t fit? Looking for helpful insight. Should I just stick with the breadbox or try to buy some custom stuff? I can get my hands on a 550 mariner exhaust for cheap, been thinking about cutting the inlet off and upsizing it to mate up to a 650sx manifold elbow, bolted onto a Coffman style manifold. Seems like it would work out good, just not sure if it’ll be worth it performance wise….
Click to expand...
Hey. Same issue here. Stock Yamaha manifold and riser is hitting the ebox with Rhaas set up. Can’t move engine forward enough. What did you end up doing.
 

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