A Back Flippin' 550!

Joined
Mar 31, 2012
Likes
50
Location
Chicago
#21
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.
 
Last edited:
Joined
Nov 29, 2016
Likes
14
Location
west mi (Muskegon)
#24
a lot going on here.
1. considering ping pong balls instead of foam, but given the age of the ski and the amount of mods done i decided to foam for added strength.
2. exhaust re routed through the hull
3. engine mill and bore by Newmiller
4. swapping exhaust for 650 with factory mod.
 
Joined
Mar 31, 2012
Likes
50
Location
Chicago
#29
Good progress. That pipe looks good, but just know it will really limit the power on the 750 engine. Those with mods are excellent 650 pipes, but not 750. Based on my experience the flow is not sufficient for a dual carb 750. PJS big 650/750 pipes go for 250-300 if you keep your eyes open and are a much better solution. Just something to think about. It would a be a shame to limit the performance at the pipe after having such a nice tubing set up in the hull. But the ski should run ok and you can always upgrade the pipe. I'm interested to see where you'll end up with jetting and performance.

Keep it up though, glad to see another 750 conversion in Michigan!
 
Joined
Jan 31, 2015
Likes
41
Location
Eugene or
#31
great build!! there is no doubt you will be able to flip the 550 hull, its been done with smaller motors and lesser pumps, you'll need some skill and some good waves, and a good set of balls wont hurt, i have attempted to flip my 440, i got a lot closer than i expected i would but the hull did not survive. reinforce your ski and especially the hood, and make sure to get a ratchet strap for the hood, that rubber hood hold will never hold up to a sideways landing, it will pop off and down goes the ski.
 
Joined
Nov 29, 2016
Likes
14
Location
west mi (Muskegon)
#40
Picked up some ridged foam to help mold the back of the tray. Also filled the front with cabosil. time for another order to US Composites.
 
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