SoCal Jet Boats
Tech Talk => Jet Pumps => Topic started by: surfaholic on December 19, 2012, 03:33:28 PM
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why is it that powerglides work for vdrives and prop boats but not for jets??? i just cant wrap my head around how a second gear for cruising in my tq curve would b a bad thing :banghead:
ex: peak tq at 4000rpm at 450ish
peak hp at 6000rpm at 600ish
now with a gear that turns ur motor at 4k rpm and impeller at 5k rpm that would be absorbing about 450hp at full throttle according to impeller charts, our big blocks make very flat tq curves usualy only droping 100-200 from peak to 2000rpm, so if i have 450flbs at 4000rpms and say 300lbs at 2500rpm that would be more than enough for my boat at cruising speed.. i usualy cruise at 3200 rpm because that is a nice riding speed but according the impeller chart it is only absorbing 118hp, and if 2500rpm is making 300lbs of tq then why cant i get one gear 1:1 for all out speed and the other gear overdriven just for my cuise speed at little under half throttle
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33 views and no opinions??
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read more here:
http://www.riverdavesplace.com/forums/showthread.php?36659-2-speed-Jet&highlight=transmission (http://www.riverdavesplace.com/forums/showthread.php?36659-2-speed-Jet&highlight=transmission)
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http://www.marinejettech.com/
Not a second speed but with the adjustable pitch or "cut" impellar and the adjustable nozzle and intake I think it could be a good alternative to trying to overcome the physics of putting a trans in a jetboat.
Though I think a trans would work in addition to the setup.
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You could possibly make the jet function off of a transmission, but the handling issues caused by pushing the engine forward enough to fit the trans would likely make it undriveable (IMO).
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We are trying to get the RPM's UP not down!
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the idea is only to drop rpm for cruising mpg and using the tq curve to pull the boat, then go back 1:1 for hard wide open runs... i would like to start running a dart aluminum block and already running aluminum heads, intake, scoop, valve covers pretty much everything else it aluminum to shave weight even my rails and fuel tank.. i think if i got rid of the back seat and moved the motor forward it would weigh as much as two people and a small cooler.. i just don't get why it wont work
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Gear Vendors ain't TOO long to fit.
This was the one on my Ford. A guy could get shorter adapters.
Sent from DROID RAZR MAXX HD
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Weight and handling come into play, like Crewchief said. $2k+ on a gear box set-up, and unknown handling/driveability, could go a long ways towords a "AA" or larger impeller and adding more HP. For fuel milage, get an I/O, or a smallblock/berk set-up.
I like the simplicity of a jet setup, and a trans -may- be more headache than any gains seen at the fuel dock.
I have thought about an overdrive unit for a diesel/berk setup, to have the pump turn the req'd rpm, say 5K, and the motor turning 3300 +/- against the governer. 900+ lbs of diesel motor and an o/d unit (in an 18 footer) prolly wouldnt keep up with a stock smallblock.
Daniel
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that gear vendors configuration looks pretty good! i figure if it doesnt work out ill just keep it for another project, and 2k cant buy u much hp, id have to change pistons and run boost to gain any more as im running high compression and meth as it is
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I agree with Crewcheif on that weight placement piece of it being a big issue. Marc has it also with the RPM requirements of the jet drives, although I think 5000-6000 RPM is typically the target @ max HP you want to aim for and then "impeller" the pump up to challenge the motor. I know Marc likes his engines to run like at 7000-7500 RPM, so that's a different animal to tackle, and when you start messing with this kinda edgy stuff you need to add pressure taps into the suction housing and bowl areas for guages to monitor potentially disaSSterous pressure levels.
Not quite as simple as "spin it faster, push more water though, go faster".
On V-Drives, the advantage is built in with the engine backwards to begin with. Most of them equipped with the TH400 or the Powerglide are set up with manual valve bodies. The boats, props, gear ratios in the V-Drive case, etc are setup for the boat to fly according to the engine setup in High gear. Low gear is typically only used in the No Wake Zones, etc. TH400's add that third gear that can get crazy, insane fast and require nuts the size of bowling balls to do it. I had a RaysonCraft with a TH400 that I never even hit third gear in before selling it.
Also, on V-Drives, you're not dealing with an enclosed pressure pump. Just an open propeller that, the harder and faster you spin the most agressive cut you can, the better and faster. Faster spinning on THOSE, though, also wears out the V-Drive cases, bearings, bushings, seals and shafts also, so there ARE limits there.
So there you have it. For the most part, the Jet Drive is simply designed not to need all that. It's impeller and inherent design is intended to work at the max efficiency it can whether idling in a NWZ or flat-footing it at max speed. Think of how the centrifugal clutches work on Snowmobiles, Old Rupp Mini bikes, older Kawasaki Mules, etc. that use the goddam huge belt.
That's kinda how a Jet Drive operates.
Also, understand that if a transmission were used on a jet drive, when it shifts from say .65:1 to 1:1 or whatever, that is also 35% more HP needed to spin it at the same RPM........ :sly:
Ray
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thanx ray thats exactly the info i was looking for and one of the only answers iv read there than it just doesnt work
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ok good if that is the info you are looking for than i can keep my pie hole closed... ;D but i can say i hope you get it dialed in . puttin a gluid inbetween a motor and a berk pump seems to be a tall order to me but anything can be done. i say give her a go and get alot of pics and keep us posted . 8)
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Advanced adapters has gear spliters there shorter than a trans but why not run a vdrive and trans but instead of goin to a prop angle it back to the pump?
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Nvm that wont work now im thinkin to hard