Power To Weight Ratios, Engine Pros/I've go

[RocketFox650]

I've got a few extra engines around, even thinking of stripping my odd GSX, and was looking at different ideas.

So I got this ideas simply from riding my girl's first ski before I decided to sell it. It's a white 580 SP hull, probably 95. It's honestly just stupid fun. I love it's nimbleness and how reliable and powerful it is. But I'm basically riding it right at is limit constantly. I wish they'd hook up quicker for tricks, but what's really the issue is the fact it's got nothing left after 40mph/¾-WOT. Looking at all the variables, a plain 657/657x has some attractive features. I mean there's no arguing the ratio on a 787/951cc isn't great. I don't happen to have any 720cc motors right now, but I do have 5 assorted 650s, and assorted hulls, etc. Looking at the ski as a whole- the 94-95 change to the X motor increased the weight of the craft 40lbs, which is a lot tbh. At some point I think it's just gonna keep getting too heavy for what I want it to do. A 787cc here will run WOT 62-67mph, which I think is a bit much. I want all bottom end, quick hookup, basically freestyle, but with strong pullout game and to hit high 50's. Idk if the higher HP of an X motor is worth whatever added 40lbs. It's hard to figure out every change that added weight too, because 40lbs is half and again of an engine, so I highly doubt it's the engine itself, but idk what else changed that year.

 

[mikidymac]

What you are describing is a 1996 XP which is the same as a 1997-1999 SPX, the X4 hull with the 787 engine.
They don't do 62-67 mph, more like 57 mph.

The weight really doesn't make much of a difference in handling and playfulness, the 110HP does. Anyone that rides one will agree thy are one of the most purely stupid, fun skis you can ride. The jump in power from the 80 HP 657X to the 110 HP 787 is where 95% of the fun comes from.

You are much better off finding a X4 787 hull to put your engine in instead of trying to swap on into a 720-580 hull as the engine mounts and everything else is in the wrong spot.

With a 657 X4 you would basically have a 1993-1994 XP which would be the same as a 1995 SPX, 65HP-80HP

 

[RocketFox650]

What you are describing is a 1996 XP which is the same as a 1997-1999 SPX, the X4 hull with the 787 engine.
They don't do 62-67 mph, more like 57 mph.

The weight really doesn't make much of a difference in handling and playfulness, the 110HP does. Anyone that rides one will agree thy are one of the most purely stupid, fun skis you can ride. The jump in power from the 80 HP 657X to the 110 HP 787 is where 95% of the fun comes from.

You are much better off finding a X4 787 hull to put your engine in instead of trying to swap on into a 720-580 hull as the engine mounts and everything else is in the wrong spot.

With a 657 X4 you would basically have a 1993-1994 XP which would be the same as a 1995 SPX, 65HP-80HP

No, I know the ski mate. I don't disagree with you either, I'm currently looking at different XP/SP skis. That's not what I'm talking about though. I'm talking about power/weight ratios. Idk if you've ever built anything, water or not, but you have to keep in mind what you want to use it for. I built a Bronco and a Ford Nite side on once, and the Bronco got over 12" of lift, 351W bored and stroked, etc. The Nite got a simple 4" lift, mild tires, normal bolt on performance. In the end, my Bronco was the coolest looking truck in the parking lot. It just couldn't be used for a lot.

The 787 is the same thing. Look up the weight of each ski. You'll notice there's almost 100lbs or a 25-30+% increase in weight from the 580-787 models until they switch hulls for another 90lbs. If you're like me and have other skis to fill other rolls, building a purpose built one for just a specific thing is reasonable and cheap. I'm not looking for top speed, I'm not trying to race it, not trying to break records, etc. One "negative" of the X4 hull is that they made it more stable.

Idk what people have going different, but all 3 787s I have in the water run in the low 60's maxed out. It's hard to break that 65 barrier, have to have perfect conditions, but with the lake I'm on and bone stock skis, the only one that wouldn't go over 60 was down to the trim going out and one blade on the impeller was bent almost an inch up. Straightened out, cleaned the leading edges, I radar checked it last week, 63mph.

So yeah, I can't point at every change SeaDoo made year to year, but if you're trying to get your weight as low as possible but get the most power out of it that you can, what are some engine/hull combos people liked? Personally, seeing that the change from the 580-657 added 10lbs, the 657-657x added 40 more, and it goes up, I'm thinking about performance mods for 657s. I also really love my gauges and info center, but that's more weight. Maybe some of that could be replaced or a lot of the electronics eliminated to cut weight/consolidate?

Another good point you made tho- they changed out the mounts and what have you. Now I'm not at all worried about glassing in new mounts, but I bet a few people are. So there's a reason some people won't want to go that route and will stick with the smaller engines. Plus they've gotten cheaper here. I literally have 7 skis right now with some type of 657 or a white 580. The GTXs here just keep showing up. I think there's 20 on my lake consistently, plus more coming in. The GSX is rarer, and the XP/Performance variants cost a fortune with COVID. The 787 motors are actually a bit too powerful for what I'm going for, but for others, the cost gets prohibitive. Being able to buy 2 running seadoo's to cram together for a slightly less powerful ski is a pretty viable idea.

I'm looking just to purpose build something for one specific task, so my interest is a lot more selective and mostly about weight. Idk if the added few hp are worth the X motors added 40lbs. But idk what added the weight entirely either. If I want to keep the ski under 400lbs, there's only 2-3 motors. I'd need someone to chime in with actual weights of their different engines, which is kinda what I was getting at, otherwise all I have to go by is the gross weight of each model ski year to year.

 

[mikidymac]

No stock X4 787 ever broke 60 mph, let alone 63. Radar run after radar run was 57-58 mph. The fastest production seadoo 2-stroke was the 951 XP at just over 61 until the RX-X came out at 65 but was basically a factory race ski.

The 657 and 657X are not 40 lbs heavier, they are basically the same engine. And the 720 is almost the same weight as the 657's.

I am all for moding skis so if you want the lightest weight hull with the most easy horsepower then do a pre X4 hull with a 720. You don't need any gauges for the ski to run. Don't fill the fuel tank all the way, you could nickel and dime the weight as much as you are willing to.