Jet boat with transmission project/compiling information

[dgie]

Right now I am compiling information for changing out my 455/jacuzzi setup over to a 350/jacuzzi setup (with a transmission.) I think this is a viable project for the future and would like to gather input from everyone. The input that I recieved already is that the engine needs to stay put where it is due to center of gravity issues. Also that the transmission needs to be light. What I am expecting as far performance is higher RPM's at the impeller, which equates to more water flowing through the pump = higher speeds = lower rpms on the engine (less wear and tear.)The reason I chose to do it with a 350 is because of availabilty of parts,fuel economy, and weight. Am I missing anything. I would like to stick with an automotive transmission due to availability. Does anyone know what the length of a 350 with automatic transmission is? vice a 455 engine length alone. Feel free to give input that you think may be helpful.

[BGMAN203]

don't do it! just build a overdrive unit to go between the flywheel and the pump, you will never get a trans in there, and even if you do you will have to sit on the motor to drive the damn thing.

[malcolm]

It would never be more than a conversation piece.
Why would you want lower gears? If you go with more impeller to use them you'll never get it in high. :confused:

[Taylor LP]

What I am expecting as far performance is higher RPM's at the impellerAre you talking about an overdrive automatic or stick?
IMO, Don't waste your money on trying to reinvent the wheel. Sink your $$$ into a decent Big Block Chevy or Ford and spend time in the water instead of in the garage. You'll be glad you did.

[dgie]

My understanding is that a transmission or overdrive unit will allow the engine to spin at, for instance 3000 rpms and be considerally more at the output of the shaft of the transmission. This will allow the impeller to spin faster with less load on the engine. There is an option of setting back the pump to accomidate the overdrive or transmission unit, but not sure how far the maximum you can set back the pump is. I would assume it could be as far back as you can support the intake of the pump. Maybe by adding an extension of the hull facing aft, a kind of ledge that the pump could sit on.

[Oldsquirt]

1.) The length of a 350 Olds is exactly the same as the 455.
2.) Using a gearbox to turn an impeller faster wont work. You are still limited by the horsepower produced by the engine and the horsepower "absorbed" by the impeller. Can't make a 350 do the work of a 455 by using a gearbox. Don't forget you will also have 10-20% power loss in the transmission.
[ August 16, 2003, 12:29 PM: Message edited by: OLDSQUIRT ]

[Jetmugg]

Dgie:
You've got it bass-ackwards. The only way to get any advantage from a gearbox in a jetboat is to run the output shaft rpm at a LOWER value than the engine rpm. This would allow an engine to spin higher rpms, reaching it's power peak, not the other way around. I believe that KZ ran a gear reduction unit like this in Risky Business with a pro-stock drag engine, to let the engine spin up to 8000 rpm or something like that. Overdrive simply will not work. Underdrive is the only way to get any benefit.
Not trying to rain on your parade, just telling it like it is.
Steve.

[DEL51]

Dgie, it is nice that your thinking this through.You just need some basic physics and economics to figure this out.You are not the first to contemplate the Idea. Gear it up it will spinn faster,I.E.Pump or prop..Hang with the idea and apply it to your first 10 speed bike.As you change the ratio, the force applied to the peddals will remain the same,Called a constant,during a "sprint".But it is impossible to spin the peddals faster in 5th gear than in first gear. Inertia and rpm will change, causing acceleration to a point.But the initial drive hasn't changed much. The Force applied to the peddals, your max torque, hasn't changed. The only that thing that changed is your rate of appling the tourqe. Your feet have slowed down in fifth gear.I hope you understand my comparison.Economics says nothing is for free and You do get losses from spinning a high rpm motor/reducing the the rpm to spin a more efiicient pump or prop.Build a big block chrysler or whatever, to spin below 5500 rpm and you will be ahead of the game.Stick with a small block and supercharge/turbo to achieve the output of a bigger motor @ similar rpm.RPM's wear out engines, especially in boats.I have 572 chev blower engine that turnes 5k @90 mph without working the engine. find a realm where your comfortable at cruise, add the cost of 15-20 mph and spend the money.Build the motor for future uprades. Also, if you like to hear the roar of your jet and think it is a slow piece.Want something faster? Do not stick a thousand bucks into making it faster without checking it out here in the forums or in banderlog, first.Make sure you know what you want.You may save big bucks if you you know what you really want.You may want to turn the pickup with the nice sounding V-8 into a corvette and end up with a gas pig with no pleasure.
[ August 16, 2003, 09:48 PM: Message edited by: DEL51 ]

[sdba069]

You are absolutely right.I donated an impeller or 2 to the Brule's when they first started R & D with the Owen's gearbox.The perfect answer for a high winding naturally aspirated motor.Run a big impeller for the holeshot and turn the motor up through the gearbox,the best of both worlds.
Jetmugg:
Dgie:
You've got it bass-ackwards. The only way to get any advantage from a gearbox in a jetboat is to run the output shaft rpm at a LOWER value than the engine rpm. This would allow an engine to spin higher rpms, reaching it's power peak, not the other way around. I believe that KZ ran a gear reduction unit like this in Risky Business with a pro-stock drag engine, to let the engine spin up to 8000 rpm or something like that. Overdrive simply will not work. Underdrive is the only way to get any benefit.
Not trying to rain on your parade, just telling it like it is.
Steve.

[Bense468]

I am probably going to get flamed a little on this one by the olds guys.
But honestly why would you want to dump all the cash and time into something with an olds and a jacuzzi? By the time you figure all this out you could build something very nice with a big block chevy and a berk style pump that will run better and more solid then the other setup would have run in the first place. Like I said this is just my opinion and flame away.

[Moneypitt]

Djie, You can't make a silk purse out of a sows ear!! I think you were talking about a 350 chevy, not a 350 olds, right?? BUT, as far as a trans and/or overdrive, GET A GRIP! If your olds jet isn't fast enough, get used to it and enjoy it. Just think of all the really really fast boats that are sitting home with their engines in pieces while you are cruising the lake/river of your choice. No one that I know of has a fast enough boat/car/truck/sandbuggy/crotch rocket, nor do you hear people talk about being rich enough. If you really want to go fast, take your time, watch for a set up that someone else can't afford to finish,ie: a flat without an engine, or a hydro that needs hull work, or a GN boat like gofastracer just bought. These boats were built for one thing, SPEED. Your jet was built as a fun boat. The key word being FUN. Keep your boat, enjoy it when it's too rough for the fast flatties to go out. Quietly accumulate some hi perf parts for the engine of your choice, shop for a compatable hull, CHEAP.(there are great deals out there if you wait for them to come to you). So what if it takes 2 years, or 3, you still have a working jet to have fun in. If you're trying to be top dog on your favorite lake, remember, there is always gonna be someone faster, no matter what any of us do, there is always some one with more money, like the old saying, $peed co$t$ MONEY, how fa$t do you wanna go!!!!!!!Moneypitt

[dgie]

Moneypitt and everyone else thanks for the input. Now that I came down to reality I descided to just stick with my setup. It seemed like a viable option but I figure that just cruising across the lake is good enough. My thinking was that I could spin a pump faster and make the boat faster. True I am still wet behind the ears on how transmissions and stuff like that works. Hell before I bought the boat I have never removed anything more then the valve covers on an engine with exception of a clutch replacement on my CRX way back when. I have learned a lot on this board from people like Moneypitt,Infomaniac, and many more. Hell I have a stringer replacement that will have priority before anything else. However my bigest priority right now is looking for a job and working on getting into Graduate school which will take up most of my time. Once again thanks for the input. By the way I broke my reverse cable today where is the cheapest place to get one? I am on a budget now frown

[Bense468]

I don't know about the cheapest but you can call Rex. Maybe mike will help you out on the cost a little. PM rexone and ask him.

[sdba069]

I'm located at Lake Whitney about 20 miles south of Cleburne.I stock all the jet boat cables.Give me a call.....254-889-3336
dgie:
Moneypitt and everyone else thanks for the input. Now that I came down to reality I descided to just stick with my setup. It seemed like a viable option but I figure that just cruising across the lake is good enough. My thinking was that I could spin a pump faster and make the boat faster. True I am still wet behind the ears on how transmissions and stuff like that works. Hell before I bought the boat I have never removed anything more then the valve covers on an engine with exception of a clutch replacement on my CRX way back when. I have learned a lot on this board from people like Moneypitt,Infomaniac, and many more. Hell I have a stringer replacement that will have priority before anything else. However my bigest priority right now is looking for a job and working on getting into Graduate school which will take up most of my time. Once again thanks for the input. By the way I broke my reverse cable today where is the cheapest place to get one? I am on a budget now :(

[pops1]

dgie:
Right now I am compiling information for changing out my 455/jacuzzi setup over to a 350/jacuzzi setup (with a transmission.) I think this is a viable project for the future and would like to gather input from everyone. The input that I recieved already is that the engine needs to stay put where it is due to center of gravity issues. Also that the transmission needs to be light. What I am expecting as far performance is higher RPM's at the impeller, which equates to more water flowing through the pump = higher speeds = lower rpms on the engine (less wear and tear.)The reason I chose to do it with a 350 is because of availabilty of parts,fuel economy, and weight. Am I missing anything. I would like to stick with an automotive transmission due to availability. Does anyone know what the length of a 350 with automatic transmission is? vice a 455 engine length alone. Feel free to give input that you think may be helpful. If I understand you right! you are going to higher gear ratio on the Drive. If you do this you are going to decrease your torque factor to the pump. you are also going from a torque motor to a higher rpm torque chaser motor.
your only hope then is to put a big cut on the impeller making it less efficient overall.
You might get away with a 7-10% overdrive on cruise speed yet i have big fears as to the final outcome plus the added weight factor.
Don't listen to me my wife won't. Dave

[UBFJ #454]

Seems to me that a tranny isn't needed if you build your high Tq/Hp motor so that its max output is relatively flat and occurs in the 5,200 to 6,200 rpm range. That's what we have done.
The reason for trannys in the "Biz" and "Head Over Heals" is that their motors had/have to go way "Upstairs" to get their Tq & Hp.

[Hallett19]

just go big on the impeller, I think an agressor AA is the meatiest impeller you can get, that will make your motor spin at lower rpms. Or you could do a powerglide, push the motor forward, move the pump back and use a D cut impeller, spin it low, then high......that might work :D

[kojac]

A few years ago I came up with the idea (probably been thought up by a hundred jetboaters) that I needed to spin a "b" impellar in my jet 7200 rpm's to reach in the 120's mph to be in race contention. I did not like the idea of having to use a big cam with all of the big cam problems i.e. broken valvesprings, busted roller rockers,lifters,cam 2 expense and also wanted to run the jet on the lake on pump gas. So I had an overdrive gear made based on turning the motor 5500 rpm' that would hopefully turn the "b"cut impellar 7200 rpms. I had built a 572 with a 871 blower set on top prior to the gear idea. The motor was built to achieve 7200rpm's with a long cam duration and two dominator ll50 and low compression 7.5 to 1.
I hooked the gear up in line with the motor and could only turn the motor 4000 rpm's. The pump turned 5520 rpm's The boat only ran 79 miles an hour. on 6#'s of boost. I believe the problems were due to the combination of to much cam duration, to much carburation, and not enough compression to pull the power range down to work in the low to mid range. :)
I wasn't able to go any further with my experiments due to a loss of job and diminished income. But if I could have gone further I think I would have shortened the cam duration and used smaller carbs for a better low and mid range torque and raised the compression to 8.5.1 or 9.1.1 like the outdrives use and maybe cut the impellar to a "B/C". This may have achieved my goal of a pump gas motor running into the 120 mile an hour range on pump gas with only a few of the destructive problems associated with turning the motor 5500rpm's with a friendly hydraulic cam. Don't know for sure. Still have the gear drive. The motor is still running in a 19 ft stealth. Someday "if" I might be able to get back to my experimenting with this project.
Kojac.