- Location
- Chicago
We have a 550/750 dual carb in our group with a 650 pump tunnel. Same exact motor as my current engine, same carb tuning and all, as I helped my bud set it up. No difference pump wise to the Rhaas pump swap. And when I mean no difference, i am estimating based on our differences. I have a few more tricks up my sleeve, and a better 10/16 hooker (he has a 13/18 big hub c75), so my ski is stronger off the bottom. The Rhaas kit gets the job done really well. I just don't have the time to glass stuff up anymore, so mechanically bolting up a kit was the right option for me.
As for other differences in the hull bottom beyond the pump, handling wise they will be negligible improvements if any over a 550. And I like keeping the bottom original, it really makes these high powered js hulls feel like crazy rockets. With a 93 octane pump gas non ported run of the mill 94 small pin, my ski does 55.8, up in the region of the pro mods. This year with a ported 800 I'm going for more low end and see if I can get to 60. The 10/16 was the best low end impeller from a few I tested, so it was quite a surprise that the ski went that fast!
Given the size difference, I could see a SJ pump would give more low end, if you have the time to set that up right.
Also as far as hull mods, prowatercraft sponsons should be mandatory for this hull. That's one change I wrestled with making for a while and I am so glad I did, the handling is so improved! I did notice that putting those on gives the front more turning leverage of sorts so you need a ride plate to lock the rear down more.
One last thing, the impeller choice is everything. I have no doubt you could have a good impeller in a Rhaas 750 pump swap and have more low end than a ill- set up 144 Yamaha. When I first did the swap I used a 13/18 small hub swirl which I did about 54 in my xir. It performed about equal to the 550sx pump straight 20 pitch. 13/18 c75 swirl was a bit better, and the 10/16 hooker loads better on low end and top end. I think it revs the engine out way better with my 8000 rpm big pin cdi.
As for other differences in the hull bottom beyond the pump, handling wise they will be negligible improvements if any over a 550. And I like keeping the bottom original, it really makes these high powered js hulls feel like crazy rockets. With a 93 octane pump gas non ported run of the mill 94 small pin, my ski does 55.8, up in the region of the pro mods. This year with a ported 800 I'm going for more low end and see if I can get to 60. The 10/16 was the best low end impeller from a few I tested, so it was quite a surprise that the ski went that fast!
Given the size difference, I could see a SJ pump would give more low end, if you have the time to set that up right.
Also as far as hull mods, prowatercraft sponsons should be mandatory for this hull. That's one change I wrestled with making for a while and I am so glad I did, the handling is so improved! I did notice that putting those on gives the front more turning leverage of sorts so you need a ride plate to lock the rear down more.
One last thing, the impeller choice is everything. I have no doubt you could have a good impeller in a Rhaas 750 pump swap and have more low end than a ill- set up 144 Yamaha. When I first did the swap I used a 13/18 small hub swirl which I did about 54 in my xir. It performed about equal to the 550sx pump straight 20 pitch. 13/18 c75 swirl was a bit better, and the 10/16 hooker loads better on low end and top end. I think it revs the engine out way better with my 8000 rpm big pin cdi.
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