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View Full Version : is it possible to put a overdrive on a jet ???



Doug H.
08-06-2003, 09:53 PM
just wondering if someone has put a gear vendors overdrive unit on a jet boat ? will it work ? and why it wouldn't, seems to me with some of these RPM's you see this would be a great addition. i would like to hear what you have to say, good or bad. :)

Mandelon
08-06-2003, 09:58 PM
As long as it is a "hydro-glide"... :)

superdave013
08-06-2003, 10:19 PM
sure you could. Why not? I've seen Casale Z drives in a few jet boats. But they were underdriven so they could turn a big impeller and still buzz some high RPM.

FryJet
08-06-2003, 10:40 PM
I saw a guy running a z-drive up at Ming. It was a under drive delio though like super said. I believe it was a Daytona but I could be wrong. That boat came apart half track in a bad way, I have some video of the reckage getting towed by and at the pits. I think a twin turbo deal that made gobs of torque would work really good but that z-drive takes up alot of space. Hmmm, a nice daycruiser, say a Eliminator Sport tunnel open bow with a 588 twin turbo and a over drivin z-drive might make for a nice fast jet with alot of room. Sounds good in theory, anyone else?
F.J.

Moneypitt
08-07-2003, 09:05 AM
I don't think the engine in a jet boat is the RPM limiting component. Most jet pumps are actually the "governer" when it comes to revs. To overdrive the jet, would limit the engine down to an area of less torque,(less power) and would certainly hurt throttle response. If you're thinking of "high gearing" once up to cruise speed, I guess that might save high RPM wear and tear on the motor, but most jet boats only rev around 5K anyway, so a 20% over would lower that to 4K. Not alot of difference. Now, if you were to put an overdrive on a v drive, the result would be a higher top speed at max rpm, or a lower rpm at the same speed, assuming the motor could maintain enough torque to keep the prop turning the same speed and keep the boat on plane in "high gear". I'm sure these possibilites have been tried, and if sucessful the boat makers would be cashing in on the higher speeds with less $ in the motor. Everyone likes a little more speed!!!

Hallett19
08-07-2003, 11:50 AM
once a jet turns a certain rpm it looses all efficiency, I think somwhere around 7500 rpm's it will just start to cavitate. The only thing a underdrive would be good for is keeping the revs down on the motor and toast all throttle response like moneypitt said, might save some gas though, but what fun would that be not hearing your big block scream @ upwards of 5000 rpm's while cruising along the water ?

superdave013
08-07-2003, 12:01 PM
FryJet:
I saw a guy running a z-drive up at Ming. It was a under drive delio though like super said. I believe it was a Daytona but I could be wrong. That boat came apart half track in a bad way, I have some video of the reckage getting towed by and at the pits. I think a twin turbo deal that made gobs of torque would work really good but that z-drive takes up alot of space. Hmmm, a nice daycruiser, say a Eliminator Sport tunnel open bow with a 588 twin turbo and a over drivin z-drive might make for a nice fast jet with alot of room. Sounds good in theory, anyone else?
F.J. I think we are talking about the same boat. The Blade Runner was the name of it I'm pretty sure.

eliminatedsprinter
08-07-2003, 04:36 PM
Sure, here is how you do it.
1. Remove car motor.
2. Remove pump.
3. Plug whole and re-enforce transom.
4. Hang powertrain made for boats off of back.
5. Use new space for more people, toys, and Beer.
wink :D :D wink wink
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Sorry, I love jets, but I couldn't resist this one :cool:
[ August 07, 2003, 05:38 PM: Message edited by: eliminatedsprinter ]