97 Challenger motor upgrade to a V6

[Hollymax0428]

I've done a bit of research into changing the current single Seadoo 787 110Hp motor to a something like a 175 - 200 Hp using a powerhead from an Outboard similar to the Mercury Sportjet used 2002-03 etc, only retaining the Seadoo Jet pump rather than use the Mercury Pump.

Some points that I have to overcome;
1. I need a right angle drivebox with something like a 1.5:1 ratio to convert the 5,000 - 5,500 outboard motor rpm to around 7,000+ at the impeller.
I could use the gears from the outboard only reversed in a fabricated gearbox.

2. The exhaust from the powerhead needs to come from the bottom of the motor up like the sportjet setup instead of down like an outboard, and in Australia no one has any used parts, so other than buying new which would be around $2500 + just for the Adapter plate and expansion chamber, I may get stuck having to fabricate that as well.

3. The 140 mm jet pump may not be big enough to get the extra performance without trying to fit a larger pump, unless I can get an impeller to suit the 140 mm with the increased horsepower or lift the impeller rpm to 8,000 rpm (if it will take that sort of increase from the normal 7,000 rpm).

4. I need to mount the engine, but seeing the Mercury Sportjet just bolted to the floor via the Jet Pump housing that shouldn't be an issue by still using rubber mounts to lessen vibration.

Can any one offer and information or advice on the above points or any other obstacles I may come up against.
I'm trying to make it as less complicated as possible.
Powerheads in Australia second hand bring around $3500 + and another $1000 maybe to get the drive box and exhaust setup done. I'm used to fabricating machinery so I'm not phased by having to do that.

If I can get the Adapter plate etc from the USA I would probably have to use a Mercury motor rather than onother brand, but not having to re-invent the wheel may save some time and worry, so if anyone knows who I could contact in the USA to get a second hand Adapter Plate & parts I would appreciate it.

P.S. I realise it would be easier to just get another boat with a bigger motor, but I like the layout and size of this one and there is probably a jump of around $10,000 - $14,000 in price :ack:.
The 110 Hp motor has just been rebuilt so should bring part of the difference to upgrade, or I could fit it to a Jetski with a blown motor .

 

[Dr Honda]

OK... I'm all for unusual projects... but I need to get this out of the way first. It's a dumb project. If you want to do an engine swap, use an engine that is cheaper to play with. I know you say that the upgrade boat is $14k, but in the end, you will have a boat that other people won't want since it will be full of non-standard parts, and will probably be worth less later if you want to sell it. (even though you will have thousands of $$$ into it)

Now for some random thoughts.

1) You say you are familiar with fab tools, but your questions make me think that you don't have access to them. If you are going to tackle this project, you will need full use of a fab shop.

2) if you use a Merc, or other 2 stroke engine, you don't need a right angle gear box since thy can run in any position if you are using diaphragm carbs. So, if you want to run it in-line with the drive shaft... just make up some mounts.

3) what is the "Adapter" you are looking for? Nothing exists for this swap, but I may have just miss read what you posted.

4) I could be wrong, but I think the most power put on the 140mm pump was 110 hp. I'm sure you could make it work with more, but you will be machining the nozzle, and hand fitting a high pitch impeller to the housing.


OK... with that said... if I were to do an engine swap... I think I would use a +1000cc sport motorcycle engine. They are relatively light, and they are cheap compared to a boat engine. They also rev super high these days. Most of them modern engines can get into the 13,000 RPM range. In this case, you can leave it in 4th gear, and have a 7000 ish top RPM at the output shaft.

OR...

Use a 4 stroke PWC engine. You could probably find a 5 year old water craft with a busted hull, or one that has just been sitting out in the sun too much, and is ugly. Buy they entire PWC cheap, and you will have everything you need for the swap.

On that note. If you buy a Merc engine... you will still need all the support electronics to make it run.

 

[Dr Honda]

Oh... last thought. I'm assuming you want "More" of something from your boat.

If you want more top speed out of your boat... then it's simple. You need more velocity out of your pump. The easy way is with more RPM's. So if you start with an 5000 rpm engine... you are going to be disappointed. If you do an over-dive with a gear box, you will need to know if the torque is high enough to push it. Also... you will have at least a 12% loss though the gear case. That's why an 85 hp sportster could out run a 120 hp merc drive boat.

If I were to use a merc engine, I would use a set of 40SBN carbs (or three 38's), see if you can get at least 6000 rpm out of it, go direct drive, open the nozzle 5 or 6 mm, use a shorter cone, and get skat-trak make me an impeller with 5 or 6 deg more pitch that any of the 140mm impellers.

 

[Hollymax0428]

Thanks Dr Honda for your input, I always value your comments.

OK... I'm all for unusual projects... but I need to get this out of the way first. It's a dumb project. If you want to do an engine swap, use an engine that is cheaper to play with. I know you say that the upgrade boat is $14k, but in the end, you will have a boat that other people won't want since it will be full of non-standard parts, and will probably be worth less later if you want to sell it. (even though you will have thousands of $$$ into it).

Actually this is the cheapest way. We don't have access to motors and parts like you do in the USA. Getting another seadoo jetski motor here is almost non existant.
I'm not worried about having to resell, it's value in a couple of years will be fairly low even as it is, so it's more for my enjoyment rather than resale value.

Now for some random thoughts.

1) You say you are familiar with fab tools, but your questions make me think that you don't have access to them. If you are going to tackle this project, you will need full use of a fab shop.

Yes we have all the equipment to make machinery (not like your shop but enough, and what I don't have I can get done for me), I used to design and make my own machinery.

2) if you use a Merc, or other 2 stroke engine, you don't need a right angle gear box since thy can run in any position if you are using diaphragm carbs. So, if you want to run it in-line with the drive shaft... just make up some mounts.

OK I wasn't aware of that, although I would still have to run the shaft through a gearbox to increase the revs as Outboards only run in the mid 5000 rpms, and to get the shaft closer to the bottom of the hull as is the 787 motor. 4 stroke Outboard powerheads are bringing around the $10,000, so just looking a 2 strokes at this stage.

3) what is the "Adapter" you are looking for? Nothing exists for this swap, but I may have just miss read what you posted.

.
Between the powerhead and the pump on a Mercury Sportjet 200 hp or bigger there is an Adapter plate that runs the exhaust out horizontally to an Expansion chamber to mix with water, then through tubes to the outside of the hull. 175 Hp and smaller run the exhaust straight through the pump into the water which is no good to me unfortunately, I'm not using a Mercury pump (I rang about the Adapter plate & pump all over Aust last week and they don't exist second hand).

4) I could be wrong, but I think the most power put on the 140mm pump was 110 hp. I'm sure you could make it work with more, but you will be machining the nozzle, and hand fitting a high pitch impeller to the housing.

Yes I wasn't sure if just increasing the rpm of a 140 mm pump would give much increase in performance. I would have to see how high a pitch would be available as they really only quote them for twin 110 hp. I think the later ones all went to 149mm then 155mm.

OK... with that said... if I were to do an engine swap... I think I would use a +1000cc sport motorcycle engine. They are relatively light, and they are cheap compared to a boat engine. They also rev super high these days. Most of them modern engines can get into the 13,000 RPM range. In this case, you can leave it in 4th gear, and have a 7000 ish top RPM at the output shaft.

I would be interested in hearing more about what type of water cooled sport motorcycle engines that could be used.
If it were only increasing to say 135 Hp then I wouldn't be achieving much and I can get hold of plenty of Seadoo 951 motors (or actually still in the jetski relatively cheap).

OR...

Use a 4 stroke PWC engine. You could probably find a 5 year old water craft with a busted hull, or one that has just been sitting out in the sun too much, and is ugly. Buy they entire PWC cheap, and you will have everything you need for the swap.

Been trying, out here no one wrecks that sort of stuff, they keep them and rebuild them and getting a busted hull one is very very rare. If I could that would be the way I would go even if it were only the 155 Hp one.

You can't even buy an engine out here unless you are sending back one for a rebuild. I can't believe that somewhere at some stage engines have to be replaced not just swapped for another rebuild. That means there are spare boats but no spare motors as everyone gets re-used???

On that note. If you buy a Merc engine... you will still need all the support electronics to make it run.

Not sure, from what I'm told the Electronics are fairly self contained and included in the motor other than a starter box, but I will ask that question.

Unfortunately I don't have access to a lot of options out here because most newer stuff is still considered gold. Definitely my task would be a lot easier if I had the resources you have to the quantity of boats you do.
Out here a 97 challenger would bring two to three times the price you would expect to pay. Jetskis are plentiful, but Jetboats, nothing really under $10,000 and 4 stroke nothing under $25,000.

The reason I decided on the Outboard engine is that they are much cheaper and more plentifull than anything other than your 717s and 787s and that the powerhead setup was used by Seadoo in the early 2000s and apart from the Exhaust Adapter & the Gearbox all else would stay standard with parts readily available.
Only now I notice a few Jetskis with 951s are coming onto the market at a resonable price $5,000, 155 Hp Jetskis and greater are still $10,000- $15,000, and it would be a lot of work which ever way I go, but the 951 would only give a slight gain.

As I indicated I would be interested in the suggestion of the sport motorcycle engine if you could elaborate a bit more and thanks for the input, I have a bit more to work on now.

 

[Hollymax0428]

Oh... last thought. I'm assuming you want "More" of something from your boat.

If you want more top speed out of your boat... then it's simple. You need more velocity out of your pump. The easy way is with more RPM's. So if you start with an 5000 rpm engine... you are going to be disappointed. If you do an over-dive with a gear box, you will need to know if the torque is high enough to push it. Also... you will have at least a 12% loss though the gear case. That's why an 85 hp sportster could out run a 120 hp merc drive boat.

Yes I realise that that I still need to get the revs up to 6,000 - 7,000 minmum.
I'm not sure how much loss I would get from the gear case. The Sportjet uses a right angle gear drive. When I look at the videos of them, even in the heavier boat they have good performance.
I'm not looking for more top end speed as much as quicker acceleration and much more bottom end power with 3-4 people in the boat. When we are on the river there isn't places to stop and offload gear and the extra people like on the ocean or a lake, so bottom end performance is what I'm greatly lacking. If it were only for using it with 1-2 people I wouldn't be going to this trouble.

If I were to use a merc engine, I would use a set of 40SBN carbs (or three 38's), see if you can get at least 6000 rpm out of it, go direct drive, open the nozzle 5 or 6 mm, use a shorter cone, and get skat-trak make me an impeller with 5 or 6 deg more pitch that any of the 140mm impellers.

OK when you say 'open the nozzle 5 or 6 mm' is this to try an increase the volume of water rather than condense it.

I possibly can get a higher pitch impeller, I haven't got to that stage of inquiring. I having been thinking I may get a 155mm Housing and nozzle to fit, just not sure how the size already there would work opening out into a bigger pump with water flow, cavitation etc..

 

[voodoo]

If you have a working boat now make the upgrade with a 4sale sign rather than ride a frankenstien that has to be towed in when something silly that has to be machined or made over again goes sour - the mazda swap is the most popular I read about.

 

[Hollymax0428]

If you have a working boat now make the upgrade with a 4sale sign rather than ride a frankenstien that has to be towed in when something silly that has to be machined or made over again goes sour - the mazda swap is the most popular I read about.

Thanks Voodoo, this is the part I'm confused about, I looked at the Mazda 13b option and it to me is an out of this world-over the top option and huge amount of work to put one in, whereas the powerhead was fitted as an original Seadoo option.
I just don't have access to the sportjet pump and want to stay with the Seadoo Pump setup other than cutting up the hull.
Really the only change I'm making is making my own gearbox, otherwise using standard manufactures parts. The Exhaust adapter plate just allows the motor to be mounted lower rather than running the exhaust down like on an Outboard. It is still a standard part used by Mercury & was used in the Seadoo jetboats.

 

[Dr Honda]

Don't know where to start.............


OK, sport jet.

Yes, the 240 sport jet did have good performance in even a big, heavy SeaDoo boat, but their pumps were big. Somewhere around 163mm, and they would move a lot of water. Also, your thoughts on the "Adapter" are only half thought through. (it believe) From what I'm reading (about not wanting to cut up your boat for a 13b engine) you are thinking of the adapter just as the engine mount. Unlike the rotax engines, where all the drive parts are discrete individuals ... the sport jet is an "All in one" unit. The pump, gearbox, adapter, and the engine are all mounted together, and bolted into the boat. Sure... they can come apart, but they are designed as a single assembly. So, I think finding a used adapter would be pointless since you will have to fab up the gearbox anyway. It would be just as easy to make the mount into your gear box.

Thinking of the gear box. You will have to support the driveshaft of your SeaDoo in proper alignment to keep from destroying it. Your engine does that now.


On the 140mm pump. Jet pumps work well because we neck down the thrust water to get more velocity. If you want more "out of the hole" you don't neck it down as tight. If you want more top speed... neck it down more. As with everything in life... you can't have both. So, I was suggesting you open up the outlet nozzle to get more thrust (volume) out of the 140mm pump, but then add a few degrees of pitch to the impeller to make up the velocity. Also, by putting on a shorter cone, you change the compression ratio, and allow more volume though the pump.

This won't be a cure all for a small pump, but it will make it more efficient with more HP and possible lower RPM's.


Bike engines... any of the modern sportbikes over 1000cc will be making 150hp or more. I find new wrecked bikes for a couple grand all the time. Ask your local insurance company if you can buy a "Salvage" bike. (if you want to go down that path)

A 13b swap.

I don't agree with this anymore than any other swap since it's a heavy engine... but in reality, it won't be any more work to mount that into your boat over the Merc engine. In more than one instance, you hinted that "SeaDoo used the sportjet in their boats." Well... yes they did... but those boats were a completely different configuration than their Rotax counterparts. So... if you buy a Islandia with a blown up Merc... you can't just mount a 4-tech in it's place. The conversion would be just as much work as any other swap.


I'm going to now go back and re-read everything to see if I missed something.

 

[Hollymax0428]

Don't know where to start.............


OK, sport jet.

Yes, the 240 sport jet did have good performance in even a big, heavy SeaDoo boat, but their pumps were big. Somewhere around 163mm, and they would move a lot of water. Also, your thoughts on the "Adapter" are only half thought through. (it believe) From what I'm reading (about not wanting to cut up your boat for a 13b engine) you are thinking of the adapter just as the engine mount. Unlike the rotax engines, where all the drive parts are discrete individuals ... the sport jet is an "All in one" unit. The pump, gearbox, adapter, and the engine are all mounted together, and bolted into the boat. Sure... they can come apart, but they are designed as a single assembly. So, I think finding a used adapter would be pointless since you will have to fab up the gearbox anyway. It would be just as easy to make the mount into your gear box.

Yes I know the sportjet pump is larger but without knowing the ratio of the jet pump gear box I don't know what rpm they drive at. Seeing the motor only revs around 5,000-5,500 I'm thinking it pushes volume at a lower engine rpm.

No actually it wasn't the 13b cutting into the hull I was worried about it was using a complete sportjet (although at this stage that won't happen because I can't get one) because it has to be cut in, the problem I thought about with the Mazda 13b was marinising the exhaust manifold, otherwise I can get those motors fairly cheap. All the Mazda 13b options I've seen had extractor type straight out the top of the boat hull, no water cooling, which I don't want to do because it is still a family boat.

The way I look at the Sportjet is 3 components, the powerhead, the exhaust and the pump housing. Yes I can fabricate an exhaust adapter plate to mount straight on top of the gearbox so other than the material for the exhaust/adapter plate I think that part will work out OK, and also I would have to workout how the Expansion chamber works. I guess it is a matter of introducing water into the exhaust and incorporating the short tuned pipe the outboard uses. The online sportjet motor parts diagrams shows a fairly good breakdown of the components, but not the exact dimensions etc.
This is the parts I'm talking about incase we are talking about 2 different things.
"http://www.boats.net/parts/search/Merc2/Jet/200%20DFI%20JET%20DRIVE%20%28PUMP%29/0M954922%20%26%20Up/Expansion%20Chamber%20And%20Adapter%20Plates/parts.html"

Thinking of the gear box. You will have to support the driveshaft of your SeaDoo in proper alignment to keep from destroying it. Your engine does that now.

I actually have a spare PTO coupling and planed to use that on the end of the gear box shaft in exactly the same location as the one on the end of the seadoo motor and exactly in the same alignment all supported from brackets on mounts as the seadoo motor does now.

On the 140mm pump. Jet pumps work well because we neck down the thrust water to get more velocity. If you want more "out of the hole" you don't neck it down as tight. If you want more top speed... neck it down more. As with everything in life... you can't have both. So, I was suggesting you open up the outlet nozzle to get more thrust (volume) out of the 140mm pump, but then add a few degrees of pitch to the impeller to make up the velocity. Also, by putting on a shorter cone, you change the compression ratio, and allow more volume though the pump.

OK this is an area I may still have to do some work on. I'm not sure if trying to get a 155mm pump assembly mounted would be better option, but I will look at how I can modify the 140mm one going from what you are saying.

This won't be a cure all for a small pump, but it will make it more efficient with more HP and possible lower RPM's.

Actually I was planning to use the gear box to get the rpm's up to 7,000-10,000 rpm at the impeller seeing I will have extra HP to play with, so maybe a 140mm pump with the modifications to get more volume and the extra revs might still go towards top end speed (which is still 2nd of importance).

Bike engines... any of the modern sportbikes over 1000cc will be making 150hp or more. I find new wrecked bikes for a couple grand all the time. Ask your local insurance company if you can buy a "Salvage" bike. (if you want to go down that path).

Well unfortunately I know nothing about motor cycles, but I'm very interested in looking at that as an option.
Just out of interest exactly what type of sportbike motors Brand/Model etc are you talking about so I can do some research?
I'm guessing they would be water cooled?

A 13b swap.

I don't agree with this anymore than any other swap since it's a heavy engine... but in reality, it won't be any more work to mount that into your boat over the Merc engine. In more than one instance, you hinted that "SeaDoo used the sportjet in their boats." Well... yes they did... but those boats were a completely different configuration than their Rotax counterparts. So... if you buy a Islandia with a blown up Merc... you can't just mount a 4-tech in it's place. The conversion would be just as much work as any other swap.

I think the actual mounting should be fairly straight foward regardless of the motor, as I plan to leave as much of the boat unchanged just in case I ever want to go back to the old configuration, rather than making irreversible changes.
For me it will be working out the Exhaust/adapter plate to an expansion chamber water cooled and the gearbox I have to mainly get right before I start.

Thanks for the time & info on this, I'm getting more and more info and gaining confidence and getting your opinion on options helps a lot.

 

[seadooya]

Hollymax...I dig the idea, just wish i could be more of help....good luck

This guys' man enough to know, if the possibility is achievable. He's not a kid, to where he needs discipline, saying, its a dumb idea, or your crazy, cant be done....if he wants to do it, let him do it, he didnt ask for opinions on "what you think", but rather, guidance for the project....

http://www.youtube.com/watch?v=nWludxGdbD8

you could install the 951cc pump assy, its a 155mm

 

[Hollymax0428]

Thanks seadooya. Dr. Honda always has varying opinions, but good ones. One thing he mentioned & I hadn't considered, and obviously he is an expert in the field, is motorcycles motors.

I spoke to a Motor Cycle repair person yesterday (actually I was fixing their computers & thought this is a good chance), and then did a bit of research on the net and I can get access locally to several types of high revving 4 stroke, water cooled motors from Honda, Suzuki, Yamaha or Kawasaki, all around the 170 Hp @ between 9500 - 11000 rpm so I should be ble to run them at the 8000 rpm I think I need, and still at a reasonable HP. These motors seem quite a bit cheaper than the Outboard Powerhead option, and the specs of Hp/Rpm seem probably a better option.

I'm not sure what the pumps would take in rpms because normally they are limited to the engine. I see the Supercharged 4 tec runs around 8200 so maybe the pump can run at 9000. I think unlike a jetski I wouldn't be running the boat more than 1/2 max rpms most of the time, it's just that initial take off and the extra power doing it with the extra weight of people and gear onboard that I'm looking for.

With the 951 - 155mm pump, without measuring up, it's 7.5 mm larger all the way round and with the gap I have now on the outside of the 140 mm bolting to the hull, I think without much problem I could get it to fit.

Not sure whether the inside opening from 140 to 155 would cause turbulence. I suppose I could bevel the back of the ride plate ring 45 deg to give a slightly better lead in, or perhaps make a ring to fit between the existing and the new housing, what do you think?

I have no idea about the mounting bolt holes to the hull either. When I look up pictures of the housings they vary anyway in the bolt hole locations between different model 155mm housings.
I guess I could fibeglass the old holes in and redrill beside them.

 

[seadooya]

there's been numerous people/members, that have converted a X-4 HULL(96 XP, 97SPX), to a 951 powerplant, which then would need to incorporate the 155mm pump assy/housing. You can run the pump studs all the way thru and double nut it, or glass them in.

The motorcycle motor would be a killer idea, thought of it before, but considering the transmission, havn't quite thought out the process of "shifting", unless like the banshees(quad), where you cut the gears, to only have 3 gears, and no clutch, just bang them.

Wonder if possible, to eliminate the gearing in the tranning and going that route.

 

[Dr Honda]

The motorcycle motor would be a killer idea, thought of it before, but considering the transmission, havn't quite thought out the process of "shifting", unless like the banshees(quad), where you cut the gears, to only have 3 gears, and no clutch, just bang them.

Wonder if possible, to eliminate the gearing in the tranning and going that route.

In a boat... shifting gears would be pointless. Unlike a car (land vehicle) you are dealing with hydraulic resistance. The pressure/resistance inside the pump will increase of a factor of the viscosity of the fluid being pumped. This is straight Newtonian physics using Bernoulli's principles.

ie... if the pump is running at 100% design specs... the pressure in the pump will remain unchanged at a given RPM. (but we all know that the pump will unload a little at top speed)

OK... most modern sport bikes use a stacked transmission, and they are very compact. (and light) I would just pick a gear that gets you the best performance. Once the swap is done, and the proper gear is selected... I would remove the engine, and then strip out the clutch basket, and all the gears that are not needed to save weight, and improve acceleration.

That isn't going to be easy since the gear shafts are fed pressurized oil. You will have to make up a bunch of spacers to hold the pressure in, and the remaining gears in place. Also... machining a coupler to hold the 2 clutch shafts together may not be easy either. (but it would be worth the effort if the swap is performed)

Last thing... unlike the Bashee engine... a 4-stroke engine cant be easily disconnected from the transmission. Normally, the engine rotating sections aren't separated from the gear case since they use common oil. Also... the oil pump(s) are in different locations, and so are the pic-ups, and finally... under the transmission is normally the oil sump.

With that said... can it be done... sure, but you will have to perform a lot of surgery to make it happen. (along with an external oil pump, with a dry sump system)

 

[Dr Honda]

OK... I just had a crazy thought

You need to find a wrecked Buell XB9 (S, SG, SX, doesn't matter)

The 900cc engine in that can easily be disconnected from the transmission. It is capable of 7500 rpms, it already has a dry sump oil system built into it, and it has more torque than you could imagine for a 900cc engine. (easy 0.9:1 over drive using a belt or chain) The HP spec for that engine is only 85hp... but it makes about 75 Lb/ft of torque. (good for the overdrive)

The only hurtle would be making water boxes for the cylinders to make it a water cooled engine. (easy welding project)

Since Buell was shut down... the parts are going cheap. I bet you could find I wrecked bike for less than $2k, and then you could ebay the rest of the parts. Heck... when it's said an done... you may get a free engine out of it.

BTW... it will be fuel injected too.

 

[Adam X20]

A Turbine Engine would be easier & more reliable....

http://www.youtube.com/watch?v=2uLE-FgJFqM

 

[Hollymax0428]

Thanks for the ideas guys.
I think if i go for motorcycle engine it will be something like a Suzuki GSX 1300 R Hayabusa or a Honda CBR 1100 XX Super B/bird, both are starting around 1999 and both around 164-175 Hp. and reasonable priced here.
I will just be running it off top gear or 1:1 ratio, both motors have more than enough rpms to not have to run the motor at peak rpms to acheive the impeller speed.
I like the idea of removing the clutch which wouldn't be needed, and probably just something else to go wrong, and the remainder of the gears though. I don't think the difference in weight will be a factor but if it makes a difference in power then any extra helps.

At this stage I look like being able to get a 2000 model 951 jetski already with the 155mm pump, but a blown motor, cheap, so I will swap my 140mm pump and 787 motor over to it.

Actually just thought the clutch may come in handy as a lever operated next to the motor to disengage the motor from the impeller out of the water to run the motor on its own?

 

[timmafod]

I'm posting mainly to subscribe to this thread as it might help me with a future project on my '97 challenger 1800 and to add my $0.02 on the 155mm pump swap on a 140mm hull. I have read that there's some X-4 hulls with the 951 engines but haven't really researched that swap. I don't know if they just throw the larger 2stroke in there and reuse the 140mm pump with a different pitch impeller, or find a way to install the 155mm pump. If they do install the 155mm pump I'd like to see how they do it, and it give me hope of doing the same 140 to 155 pump swap on my challenger 1800 (I hope to go to twin 4tecs but it will probably be cheaper to just find a few year old 205 utopia).

When I rebuilt both 140mm pumps over this past winter I did some measuring and staring at the inlet to the 140mm. The top half of the pump inlet is the hull itself, the bottom half is a huge ride shoe that looks difficult to remove. Making the transition from 140mm inlet to 155mm pump should take some fancy glass work to the hull/top half of the pump inlet to transition into the 155mm diameter. Same goes for the ride shoe but I'm sure you could do that easier as it's plastic. Or maybe you just go in there with something big & sharp and just grind down both with a shallow 7.5mm wide chamfer/taper and smooth it out with some glass repair kit or whatnot...not sure. Or do you live with the abrupt 140mm to 155mm step? That doesn't seem right to me but I have zero real world experience.

Fortunately 155mm pump parts are relatively inexpensive brand new from seadoo, if it is easy to swap that is. I do not know if the 4 bolt pattern is the same but it looks close; as previously mentioned it might be possible to just through drill the hull and studs with nuts on both sides. You'd have to be real careful making sure the pump is centered. I also don't know if the 155mm impellers take the same splines or if you'd need custom driveshafts. Lots to consider.

 

[Hollymax0428]

Thanks for the imput timmafod.
I've actually purchased a 2000 model jetski with a damaged motor and the 155 mm pump. Comparing the 155mm to the 140mm back to back I think all I will have to do is change the bottom 2 holes as they are about 1/2 a hole out.
The rest looks OK.
All I'm going to do is put a ring with a bevelled edge to open the existing 140 mm hole out to 155mm, and put spacers on the bolts to bring out by the same thickness.
The difference inside the tunnel on a 140 mm to a 155mm is minimal. If it were that critical to performance they would use a diffuser to start turning the water before it hit the impeller.

For mine I don't think it is worth changing the ride plate and the bottom of the hull for the 7.5 mm difference.

Splines are the same, shaft lengths can differ, but plenty of varing sizes to suit.

I've also purchased a 4 stroke, 4 cylinder 165 Hp motor, ready for the changeover. It can be turbo charged to 200-240 hp but I don't think I will need to.

 

[WAJetboating]

I have to jump in on this thread...

I am experienced with both Mercury and Rotax powered watercraft.

In case the original poster still harbors thoughts of retrofitting a Mercury SportJet engine onto a Seadoo jetdrive - PLEASE let me talk you out of it. There are many, many reasons that this is a bad idea....

The Seadoo jetdrive will not be able to make use of all the extra horsepower. To at least some extent the whole drivetrain has to be designed as a system. Example: A dragster engine driving skateboard wheels will not yield dragster performance.

The Seadoo jetdrive is smaller, designed for higher RPM, higher water velocity, lower water volume operation. It's a great design for 150 and fewer horsepower. Meanwhile, the Mercury M2 jetdrive is larger (7.25 inch impeller), designed for slightly lower RPM, slightly lower water velocity, and MUCH larger water volume. It's designed for 200+ horsepower. The two are not functionally interchangable because they are designed for different operational environments.

Do some research on jetdrive theory and what you'll find is that as desired power goes up, diameter increases and RPM's decrease. This is because the efficiency of jetdrives (and props, BTW) are inversely related to RPM, and as horsepower goes up the losses become significant. So your little Seadoo jetdrive is just going to dissipate most of that extra horsepower as system losses rather than transfer it to the water stream where it can do real work.

The hull modifications to make this work will be substantial. Have you confirmed that a SportJet engine will even fit in the engine compartment? Remember, the Rotax engines "lay down" while the SportJet engines (really, they're outboards) are mounted "vertically".

There there's the questions of weight and weight distribution. A Rotax engine can be lifted by one person. A SportJet engine (without its jetdrive), while having great HP-to-weight, still weighs ~250 pounds. That's a lot more than the hull was originally designed for. And even if we presume the hull can take the weight, what about weight distribution? The boat will now be substantially aft-heavy... like having an extra ~150 pound adult riding on the back ALL of the time. You may have trouble getting the boat on plane with the center of gravity shifted aft so much.

And don't forget, you're not going to get that much extra power out of the Seadoo jetdrive. How much impact does an extra adult have on your single-Rotax powered jetboat today? That's not going to change much. The boat will likely be more sluggish, have a weird aft-biased CoG, and possible steering issues. You'll likely have to radically lower your ride plate in an attempt to compensate for the CoG shift, which will further impact power and efficiency. All of these effects will combine to reduce your acceleration and make it hard to get - and stay - on plane.

Still think this is a good idea? Please say no....

 

[Hollymax0428]

Thanks WAJetboating for the input.
No I've discounted the idea of using a Powerhead, I've already purchased the replacement 4 stroke, 4 cylinder 165 Hp motor.

I am however still trying to work out whether or not to use the 140mm or 155mm pump so was interested in what you were saying about the pumps dia and speed.

The 4 stroke, 4 cylinder 165 Hp motor developes it's maximum HP at approx 11,500 to 12,500 rpm, which when it is geared back is through it's final drive is approx 8000 rpm (I'm not running straight off the crankshaft).
I can alter that final drive rpm up or down, so I'm trying to work out if the 140mm pump at 8,000 rpm (or higher without blowing it up) with the correct impeller would be as good as the 155 mm pump.

I would have expected the 155 mm pump to be the better one in either case as it already has impeller applications to run on supercharged motors of 200+ HP that rev around 8,000 rpm.

 

[WAJetboating]

I would have expected the 155 mm pump to be the better one in either case as it already has impeller applications to run on supercharged motors of 200+ HP that rev around 8,000 rpm.

I'm not as familiar with the specs of the Seadoo jetdrives, but I agree with your reasoning. As you add power, you generally go up in diameter. As far as RPM's, those should be determined by the jetdrive's specifications; then set your gear ratio to match that. Keep in mind what Dr. Honda said about gear efficiency - you'll lose something going through a set of gears.

Keep us posted!

 

[timmafod]

Thanks for the imput timmafod.
I've actually purchased a 2000 model jetski with a damaged motor and the 155 mm pump. Comparing the 155mm to the 140mm back to back I think all I will have to do is change the bottom 2 holes as they are about 1/2 a hole out.
The rest looks OK.
All I'm going to do is put a ring with a bevelled edge to open the existing 140 mm hole out to 155mm, and put spacers on the bolts to bring out by the same thickness.
The difference inside the tunnel on a 140 mm to a 155mm is minimal. If it were that critical to performance they would use a diffuser to start turning the water before it hit the impeller.

For mine I don't think it is worth changing the ride plate and the bottom of the hull for the 7.5 mm difference.

Splines are the same, shaft lengths can differ, but plenty of varing sizes to suit.

I've also purchased a 4 stroke, 4 cylinder 165 Hp motor, ready for the changeover. It can be turbo charged to 200-240 hp but I don't think I will need to.

I like your idea about the adapter "ring" to go between the two pump diameters. this can be a ~25mm thick alum. plate with a chamfered through hole (140mm to 155mm) and be your pump spacer all-in-one. You say there's plenty of selection on drive shafts? I assume you'd need one that accounts for the thickness of the adapter ring/plate. Or perhaps there's enough length on the stock shaft splines?

EDIT: if you're installing a different engine you can place it so the stock driveshaft will work fine. silly me. I'm still thinking about my 4tec engine w/155mm pump swap.

I like your idea a lot. Streetbike engines are definitely more plentiful and less expensive even here in the states. A 14krpm bike engine should last a while at 11krpm sustained, and geared down (4th gear?) to 8krpm should output more torque than at the crank anyway.

 

[Hollymax0428]

I'm not as familiar with the specs of the Seadoo jetdrives, but I agree with your reasoning. As you add power, you generally go up in diameter. As far as RPM's, those should be determined by the jetdrive's specifications; then set your gear ratio to match that. Keep in mind what Dr. Honda said about gear efficiency - you'll lose something going through a set of gears.

Keep us posted!

Certainly will keep up the posting. I think the efficiency loss is more on a bike through the effort required to turn the rear wheel and perhaps a long chain rather than gears.

I like your idea about the adapter "ring" to go between the two pump diameters. this can be a ~25mm thick alum. plate with a chamfered through hole (140mm to 155mm) and be your pump spacer all-in-one. You say there's plenty of selection on drive shafts? I assume you'd need one that accounts for the thickness of the adapter ring/plate. Or perhaps there's enough length on the stock shaft splines?

EDIT: if you're installing a different engine you can place it so the stock driveshaft will work fine. silly me. I'm still thinking about my 4tec engine w/155mm pump swap.

I like your idea a lot. Streetbike engines are definitely more plentiful and less expensive even here in the states. A 14krpm bike engine should last a while at 11krpm sustained, and geared down (4th gear?) to 8krpm should output more torque than at the crank anyway.

Yes I think the adapter ring can only be benificial. I think there is a range of drive shaft lengths but in either case I will mount the motor in relation to the stock shaft I have.

Actually the gearing down occurs straight from the crankshaft to the gearbox. They have a primary reduction of 1.55 to 1, then the secondary reduction to the back wheel which I'm not using. I can still gear up or down from the final drive I'm using quite easily. I intend to leave the geabox in 6th gear and then work how many rpms I want the motor to max at keeping the pump at approx 8,000 rpm.
Shouldn't be too hard to calculate given that I have all the ratios, but I don't see a need to have the motor rev above it's max HP range, I wouldn't be gaining anything.
Plus as you say that way I can keep the motor lasting a bit longer at lower revs.

 

[markdsr]

Sport bike motors

Very interesting thread, sorry I am so late getting in. I have built several SCCA race cars using 1 liter bike motors. I have a 96 Challenger and a 954 Honda motor. I figured I was the only crazy who would try something like that. The only worry I have is the salt water effect on that beautiful motor.