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787 supercharger?
- Thread starter Luvme4thamoney03
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Say your intake pressure is 10 PSI, then your exhaust pressure would have to be more than that say 12 or maybe 15 psi. The reason for this is because you lose kenetic energy in air and mechanical resistance in the bearings and keep up your centrifugal momentum of the turbo. The turbo will push pressure into the crankcase and underside of the piston when the piston is towards the top of cylinder, then, as the piston comes down, the reed or rotary valve closes and the piston comes down and forces the air into the combustion chamber. But you still have that pressure on the exhaust side keeping the pressure in the combustion chamber.
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There are many theoretical ways to make more power in engines and even if it were possible to do so on our Sea Doo engines you would have so many roadblocks like blown crank seals, cooling the turbo oil, how do you cool the intercooler and increased fuel consumption. The easy answer is there are much cheaper and more efficient ways to make big power with these engines.
Dr Honda
Well-Known Member
HU????
You are still burning fuel in the middle, and expanding the gas volume, and adding energy to the system.
OK... There is a little truth to that. BUT.....
1) A properly set tuned pipe will "Reflect" the pressure at just the right time, to force the Air/Fuel back into the combustion chamber. That will give better filling than a regular exhust ever can, and still gives low, overall back pressure.
2) Yes... the turbo will make some back pressure as it spins up... but you will still be flowing air/fuel out the exhust.
3) Since you seem to have a grasp on the pressurizing of the lower end.... if you force feed the lower half, with a turbo/supercharger, to (lets say) 2 bar (1 bar over atms)... then to compress that lower volume, with take HP away from the system. This is the same reason why a supercharger is VERY low on efficacy compared to a turbo. As you build pressure... it takes more HP to keep spinning.
BOOSTING A 2-STROKE DOESN'T WORK !!
I'm not saying if you take a stock 2-stroke of some kind... and strap a turbo to it... that it won't make more power. BUT... it's not going to be a huge gain... and you will waste fuel getting it to run without detonation.... AND... you could get more HP, without the waste, if you simply tune better for the target RPM.
Last thing... You have to remember... Rotax is getting an ASS load of HP out of these engines. A tiny 2 cyl, 800cc engine is putting out 110 HP !!!!!! Without a forced induction... we are past the (hp/lr) realm of even the super expensive Hyper-cars that are being produced. AND... these little engines are expected to run and start for +10 years of abuse. (just somthing to think about)
Now... if anyone wants to prove me wrong... do not debate it. Go out and built it. Once I see a dyno sheet... I will change my mind.
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Here's a pretty slick turbo banshee article.
http://forums.everything2stroke.com/threads/47283-DirtWheels-Turbo-Banshee-Article
http://forums.everything2stroke.com/threads/47283-DirtWheels-Turbo-Banshee-Article
Dr Honda
Well-Known Member
You took it out of context. You can still achive the same power, without the boost, of tuned. In comparison... if you take a little 4-stroke... you can dang near double the HP. (give or take) You can't do that NA, and tuning alone.
There's no denying that it's a look what I built, I agree. But that is also what happens at drag strips everyday, there is always some guy with more cash in his pocket that builds a faster car, no matter how outrageous. As far as doing it to a ski, I also agree it's a waste of time and money. A 787 in an HX should be plenty good even in stock trim.
Guys are are always looking to build their next project, like this vintage drag sled. Over the top, Heck yeah! Awesome, Heck yeah! That is vintage sled speed right there.
Dr Honda
Well-Known Member
OK... the 6cyl 2-stroke is cool. (lol) That reminds me of the old Honda CBX motorcycle. The typical 70's Honda bike engine was a 4cyl... right??? Well... Honda said... if 4 is good... 6 is better. It was a goofy bike.
Oh... One last thing on the boosted 2-stroke. Sure... that Banshee ran. But for how long? I grew up in SoCal, and I was at Glamis at least once a month. There was HUGE rigs... and super EXPENSIVE toys... but never once, did I see a turbo 2-stroke. BUT... you couldn't throw a beer can, without hitting a turbo something, with a 4-stroke engine.
Personally... my Banshee had a 550 jug mounted to the stock 350 case. It came off a Kawi JS550 stand up ski. It was an easy conversion, and I was pushing well into the 100 hp range. (with the help of a 10K RPM top end)
With a 2-stroke PWC... we strive for reliabillity. I would say for the average guy... you will burn a piston or two before you get it to run properly. And then... peak HP will be questionable.
Nuff' of that.... here's the CBX: (yes, it was a production bike)
Oh... One last thing on the boosted 2-stroke. Sure... that Banshee ran. But for how long? I grew up in SoCal, and I was at Glamis at least once a month. There was HUGE rigs... and super EXPENSIVE toys... but never once, did I see a turbo 2-stroke. BUT... you couldn't throw a beer can, without hitting a turbo something, with a 4-stroke engine.
Personally... my Banshee had a 550 jug mounted to the stock 350 case. It came off a Kawi JS550 stand up ski. It was an easy conversion, and I was pushing well into the 100 hp range. (with the help of a 10K RPM top end)
With a 2-stroke PWC... we strive for reliabillity. I would say for the average guy... you will burn a piston or two before you get it to run properly. And then... peak HP will be questionable.
Nuff' of that.... here's the CBX: (yes, it was a production bike)
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Spimothy Leary
Well-Known Member
lol i'm impressed that the group is willing to devote this much time to the subject... makes me wanna bring up my "why can't we have an overdrive gear on my ski" question again
Tony how much HP was the 6 cylinder pushing out over the 4 cylinders?
lol i'm impressed that the group is willing to devote this much time to the subject... makes me wanna bring up my "why can't we have an overdrive gear on my ski" question again
sort of like "Ram air" in a Mopar....
Tony how much HP was the 6 cylinder pushing out over the 4 cylinders?
lol i'm impressed that the group is willing to devote this much time to the subject... makes me wanna bring up my "why can't we have an overdrive gear on my ski" question again
sort of like "Ram air" in a Mopar....
Jetskigoodies
Well-Known Member
Just slap this decal on it and call it a day. I see people slapping, ss and cobra emblems on stock v6's all the time. It is kind of duechy but they seem to think its cool.
Kawasaki made them too KZ1300.
http://www.motorcycleclassics.com/uploadedImages/articles/issues/2009-09-01/Kawasaki-cob.jpg
http://www.motorcycleclassics.com/uploadedImages/articles/issues/2009-09-01/Kawasaki-cob.jpg
![Kawasaki-cob[1].jpg](https://www.seadooforum.com/data/attachments/13/13059-98947d3724e2794ea4ab8ce983c436a5.jpg?hash=mJR9NyTieU "Kawasaki-cob[1].jpg")
SabrToothSqrl
Well-Known Member
Simple. Run 2 engines and 2 pumps. Don't join them end to end. Just find a big 3 seater and cram them offset in the hull!
WhiskeyD
Well-Known Member
Pretty cool, thanks for sharing. I used to own a built banshee back in the day and that thing would fly. Might have to start looking for another as a little project soon
Not a 3 seater. I think if we can find a smaller tank we could fit (2) 787"s in an X4 end to end. Would it be an X8?
This was a very great question, I don't think I've seen posted before. The 787 is my fav engine. Everything Dr. Honda said, is correct. There are ways of pumping that engine up, but not with a supercharger.
When Rotax designed this engine, they had high performance in mind. They patented the RAVE valve (which you see other jet skis use now) to create extra horsepower without increasing piston stroke or size. Where else can you find a motor that weighs about 80 pounds, that puts out 110 hp?
Lets just say you could supercharge this motor. You'd have to change everything inside it. I don't even know if the aluminum block could withstand the pressures. Piston, rods, everything. And of course, without intake and exhaust valves, with the coil designed to fire to both cylinders at the same time, it is just not feasible. You'd be better off to buy the 4-TEC motor and trying to figure out how to put it inside your ski.
Now, there are things you can do. I usually always recommend starting at your pump first. The motor creates great power on its own. On my 97 GTX, I have recorded in my info center, as my peak speed, 63 mph. Yes, we all know the dream-o-meters are not accurate. The only thing I have not stock is my impeller. I'm using the Solas Concord. IF you looked at the other pump additions, like a wedge or extender kit, you'd see more power. The extender kit would allow more of the ski to break contact with the water. Less friction means more speed.
There are several sites out there designed to help potential racers build their skis for racing. I'm to old to race and my ski is plenty fast enough for me to do what I like to do. We have an area at our creek, that is about a mile and a half long, about 15 feet at it's widest point, loaded with turns from left to right. We call it our slalom run. It's so awesome to run it. One wrong move and your in the woods. We have a person at the other end who clocks you, since only one ski at a time is allowed through, then we compare times at the end of everyones run, then give out the money. Oh yeah, there is a 5 dollar entry fee to play.
Lastly, like I've said a million times over. If you build your motor, all your doing is decreasing the life span of it. I have a 787 over 10 years old and still running at 130 psi of compression. Because I take care of it. I also use 100% synthetic "Quicksilver" oil (no TCW). I've used it for over 5 years, with no ill affects, plus my RAVE valves don't require as much cleaning.........
So, build your motor if you must, or just enjoy it for 10 years or so, and build your pump end........
When Rotax designed this engine, they had high performance in mind. They patented the RAVE valve (which you see other jet skis use now) to create extra horsepower without increasing piston stroke or size. Where else can you find a motor that weighs about 80 pounds, that puts out 110 hp?
Lets just say you could supercharge this motor. You'd have to change everything inside it. I don't even know if the aluminum block could withstand the pressures. Piston, rods, everything. And of course, without intake and exhaust valves, with the coil designed to fire to both cylinders at the same time, it is just not feasible. You'd be better off to buy the 4-TEC motor and trying to figure out how to put it inside your ski.
Now, there are things you can do. I usually always recommend starting at your pump first. The motor creates great power on its own. On my 97 GTX, I have recorded in my info center, as my peak speed, 63 mph. Yes, we all know the dream-o-meters are not accurate. The only thing I have not stock is my impeller. I'm using the Solas Concord. IF you looked at the other pump additions, like a wedge or extender kit, you'd see more power. The extender kit would allow more of the ski to break contact with the water. Less friction means more speed.
There are several sites out there designed to help potential racers build their skis for racing. I'm to old to race and my ski is plenty fast enough for me to do what I like to do. We have an area at our creek, that is about a mile and a half long, about 15 feet at it's widest point, loaded with turns from left to right. We call it our slalom run. It's so awesome to run it. One wrong move and your in the woods. We have a person at the other end who clocks you, since only one ski at a time is allowed through, then we compare times at the end of everyones run, then give out the money. Oh yeah, there is a 5 dollar entry fee to play.
Lastly, like I've said a million times over. If you build your motor, all your doing is decreasing the life span of it. I have a 787 over 10 years old and still running at 130 psi of compression. Because I take care of it. I also use 100% synthetic "Quicksilver" oil (no TCW). I've used it for over 5 years, with no ill affects, plus my RAVE valves don't require as much cleaning.........
So, build your motor if you must, or just enjoy it for 10 years or so, and build your pump end........
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