750/550

[Loganight]

Hello all. Recently bought a 750/550 conversion all stock with stock 650 pipe and stock waterbox. Doesn’t have the power I would imagine it would have and am thinking it’s the restrictiveness from the exhaust system. What exhaust system would you recommend I run? And for the waterbox I just bought a 550 TDR waterbox just because of how much I love it on my superjet, curious if the box alone will give me big performance gains and if its good for the 550. Thanks!

 

[kevbo]

You may not go any faster but all the extra noise will make it feel fast!

 

[smokeysevin]

I have not tested it yet but you could take a look at my setup for inspiration or what not to do.

Sean

 

[mikidymac]

That pipe is fine. The water box could be restricted as the mesh screen inside can plug up.

What pump and impeller you running?

 

[Loganight]

That pipe is fine. The water box could be restricted as the mesh screen inside can plug up.

What pump and impeller you running?

550sx pump w/ 18.5 solas impeller

 

[mikidymac]

Everything I have seen says the minimum impeller pitch should be a 19 typically a Skat-Trak.

 

[Loganight]

Everything I have seen says the minimum impeller pitch should be a 19 typically a Skat-Trak.

I do plan on putting a 750 pump in it soon I just wanted to see what difference the exhaust would make

 

[john zigler]

We have built MANY conversion skis. 750's, and even 800's with modified 650 pipe, dried out lengthened/tuned, ext. Mid 50's with a 750 pump. I like the Super trapp water box, 18 discs with washers between the discs to space out more.

A stock 550 waterbox is going to be way to restrictive for a 750.

Also your impeller is wrong. You need at LEAST a 19p skat, if not a 20.

 

[fastgtfairlane]

I ran a 20/22 skat with a dual carb sp750 and a 69mm bored OEM nozzle. A stock 65mm nozzle would possibly work with a 18 pitch impeller. The larger the outlet nozzle diameter, the taller the impeller pitch you'll want to run. 550 pumps like a lot of pressure and can handle all the power the 750 engine can throw at it. There was a build in one of the jetski magazines back in the late 90s they did with a ported 750 that went 58mph with a 550 pump.

 

[smokeysevin]

To piggyback here, is the stock prop in the 750 pump with a stock nozzle a decent match for the 750 in a js hull or does the tunnel change the equation a little bit?

Sean

 

[kevbo]

Smaller inlet will mostly hurt low speed performance. Use a deep scoop grate on a 550 hull with 750 pump.