Reply With Quotedon'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.
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.
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.
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.
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.
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.
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 ]
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.
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 ]
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.
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.
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