701 vs 787

j0hnny

j0hnny

Location
detroit MI
so I know there isn't a lot of love for the seadoo engines on this forum (at least from what I can find) but im wondering the thoughts on a 6m6 with 61x cylinders and high compression head with a single 40mm carb vs running a seadoo 787. 787 has more power but will require more work to get it in there. ski is for free style. goal is by next year to have a few flat water tricks under my belt.

thanks

johnny
 
stagesrt4

stagesrt4

see ya out there
Site Supporter
Location
St Charles IL
if you have the knowledge to do a seadoo swap then i would do it

the 787 engine is a power valve setup n makes tons more power over a 701 when comparing stock to stock


Ive actually be talking with my buddy @vshockey10 about doing the same thing
 
stagesrt4

stagesrt4

see ya out there
Site Supporter
Location
St Charles IL
yea 787 is 110hp stock

951 is 130hp stock


trouble is the exhaust pipe doesnt really fit so you will most likely have to do some glass work
 
speedysprocket

speedysprocket

Alex
Location
Chesapeake, VA
And that 777 was with low compression, like 120-130 psi, and tiny Kehien carbs. What ski are you trying to put the 787 in? It's considerably heavier as it has a rotary valve and the balance shaft is like have a second crank shaft in the engine... And since it lays at a 45 degree angle, it takes of some extra room. And all the pipes seem to be bulky and point the wrong direction and the front engine mount is on the center of the hull. Not telling you not to try it, but it certainly won't be easy!
 
j0hnny

j0hnny

Location
detroit MI
my polaris pro 785 made 138. which was a powervalve 3 cylinder with 205 psi in each cylinder. but race gas in a couch got way too expensive lol.

only seadoo experience I have was my modified 717, which wasn't a powervalve engine.

exhaust will be difficult. but cheap easy good pick two lol. 787's are cheap and good..... and im not considering the 915 due to size. it would e a bitch in an am hull I feel.
 
j0hnny

j0hnny

Location
detroit MI
idea for mounting is a bed plate setup. exhaust I have no idea that is tbd. im considering it in a bob hull. if it will fit. if not second choice will be a 750sx hull for free ride.

as for weight. I notice there are lots of aftermarket motors now that are power valve on the market now. I am interested to know what the aftermarket big boy motors are weight wise.

back up engine choice for the bob is a 66e gp800 engine. which by comparison is about the same hp. difference is I already own the 787. because I have been told a dozen times that a 6m6 with 701 cylinders will be a dog of an engine.
 
speedysprocket

speedysprocket

Alex
Location
Chesapeake, VA
The power valves are not where the weight is. You've got a few extra pounds with the rotary valve shaft, and then the extra like 15 pounds of the balance shaft. You could probably get away with a balance shaft delete kit though. These aftermarket big engines don't have a considerable weight difference over the stock engines, since they're still the same basic design.
Exhaust would be easier to change direction with the earlier 580/650/720 seadoos. Maybe depending on the pipe, you could change the direction as needed.
 
j0hnny

j0hnny

Location
detroit MI
I guess because ive always dealt with couches im used to the exhaust going up and around the front of the ski. my 750 has a pjs dry system that is routed this way and it works great. we shall see. this is a winter project. the bob has a 6m6 right now and even with the "little" engine im sure im in for a hell of a shock vs my 750sx and my stock 650sx.


coupler can be made on the bridgeport
 
j0hnny

j0hnny

Location
detroit MI
dang free hulls? lucky bastards. well I will keep this going and my bob1 build thread will have info on it. but most important thing is ride time until the lake freezes so I wont get started until this winter. Unless it goes in a different hull... but that's a totally different topic.

so general conses seems to be if I can make it work it will be a better setup power wise to a 6m6/61x hybrid engine
 
rhugo21

rhugo21

Location
Hermosa Beach, CA
Draggingto said:
There was one fairly local to me that was forsale on craigslist. it had a seadoo motor swap. Ill see if i can find the link. I know @SpaceCowboy and @RivMan have seen the ad
Click to expand...

You're referring to the 97 sj with the 717 rotax seadoo motor. I talked to the guy about it and he said his friend built it. He said it was actually a real easy swap, he had to mod the coupler I believe and something else, can't remember. Ski had a yamaha pump too. But he did say that compared to his modded 701 sj, the seadoo sj was right there with the 701 and could pull away from the modded 701 on the top end. Idk if he ever sold it though, it first popped up last year on Craigslist, then this winter and recently it was back up. If I had the money I would have bought it Bc I thought it was pretty unique. Pretty sure he was only asking 2600
 
You must log in or register to reply here.
Top Bottom