SoCal Jet Boats
Tech Talk => Jet Pumps => Topic started by: r1ver_rat on November 18, 2012, 09:37:52 PM
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Took the cobra out for the first time this weekend in Havasu. The weather was perfect, and the boat ran good. The best I could get from her is a steady 55 mph. Only issue was the boat likes to porpoise under 40mph. I can trim out if it but is very sensitive. Beyond that perfect. I need your guys recommendations to get more top end. 55 mph is a little slow for me. the boat ran Arty 4,900 rpm with an aluminum A impeller. The Motor is a Kodiak 496 HO 420 hp using an American Turbine 12 td pump. Everything is stock on the boat.
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Took the cobra out for the first time this weekend in Havasu. The weather was perfect, and the boat ran good. The best I could get from her is a steady 55 mph. Only issue was the boat likes to porpoise under 40mph. I can trim out if it but is very sensitive. Beyond that perfect. I need your guys recommendations to get more top end. 55 mph is a little slow for me. the boat ran Arty 4,900 rpm with an aluminum A impeller. The Motor is a Kodiak 496 HO 420 hp using an American Turbine 12 td pump. Everything is stock on the boat.
That sounds about right considering its a 23' u lose a lot of power with a jet on a boat that size, my boat would porpoise also I added a droop and also ride plate with two wedges... Problem solved. As far as power u may wanna think what u want reliable and 55 or build it to do 75-80 and have issues.
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How much are you looking for speed wise?
Gonna cost you a small fortune for not a lot of gains.
Got a Blackhawk outdrive in the shop, the boat will do an honest 70 MPH with your current engine and draw the same amount of water at speed as the jet.... ::)
Just don't even attempt to pull a tube or a wakeboard. :thumbdown:
Where are the heavy items in your boat? Battery(s), fuel tank(s) and so on. Believe it or not, weight placement and total weight is important for both ride quality and top speed, unfortunately forward weight is f=good for ride, but destroys speed, and weight aft is good for speed, but the ride suffers.
GT
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Don't do it. My Cobra runs the same way. Unless you have deep pockets I don't believe any changes will be for the better.
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How much are you looking for speed wise?
Gonna cost you a small fortune for not a lot of gains.
Got a Blackhawk outdrive in the shop, the boat will do an honest 70 MPH with your current engine and draw the same amount of water at speed as the jet.... ::)
Just don't even attempt to pull a tube or a wakeboard. :thumbdown:
Where are the heavy items in your boat? Battery(s), fuel tank(s) and so on. Believe it or not, weight placement and total weight is important for both ride quality and top speed, unfortunately forward weight is f=good for ride, but destroys speed, and weight aft is good for speed, but the ride suffers.
GT
I would like to hit an honest 65 MPH.
All the weight is in the aft of the boat. 4 6 volt batteries, 1 12volt battery, then all the gear under the rear seat and ski locker.
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I would like to hit an honest 65 MPH.
All the weight is in the aft of the boat. 4 6 volt batteries, 1 12volt battery, then all the gear under the rear seat and ski locker.
How is your Cobra set up?
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I was thinking a procharger kit that is mild around 2.5 - 3 psi with a shoe and ride plate, and an AA Impeller?
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I'm not 100% u can do that with ur pump droop, ride plate and impeller u can not sure about shoe tho. And the gas mileage will suck major balls.... Lol
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I'm not 100% u can do that with ur pump droop, ride plate and impeller u can not sure about shoe tho. And the gas mileage will suck major balls.... Lol
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Ya, I filled up the tanks which is about 50 gallons. I launched at Windsor Beach. Drove straight up to Pirates Cove, then back down to Steam Boat Cove through the channel and back to the launch ramp and all I have left is about 1/8 in each tank. I was full throttle about 85% of the time.
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And some one said it won't get bad gas mileage in your other thread
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I SAID if you cruise you would get good mileage. I do with my Cobra. I ALSO SAID if you have a lead foot you won't dumbazz :screwy:
I was going to try the Place diverter droop with a ride plate that attaches to the droop until TIM PLACE SCREWED ME. I tried it on my Rogers and it was the wrong direction. To small of boat for what that thing is. Buy it from someone like Tom at JBP and you will get a fair deal.
I don't believe a shoe and ride plate would do you any good. Call somebody who does this for a living and ask. Fuel injected Procharger would get you there. 5 or 7psi would work good with that engine. How much are you willing to spend? Are you able to do the work yourself? If not it's really expensive. Have you ever heard the phrase "Expect to spend $1000 for every mile an hour to go above and beyond your stock set up" I've lived it for a long time and found this to be pretty accurate.
Or you could do what I did. Buy a small jet boat for going fast.
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I SAID if you cruise you would get good mileage. I do with my Cobra. I ALSO SAID if you have a lead foot you won't dumbazz :screwy:
I was going to try the Place diverter droop with a ride plate that attaches to the droop until TIM PLACE SCREWED ME. I tried it on my Rogers and it was the wrong direction. To small of boat for what that thing is. Buy it from someone like Tom at JBP and you will get a fair deal.
I don't believe a shoe and ride plate would do you any good. Call somebody who does this for a living and ask. Fuel injected Procharger would get you there. 5 or 7psi would work good with that engine. How much are you willing to spend? Are you able to do the work yourself? If not it's really expensive. Have you ever heard the phrase "Expect to spend $1000 for every mile an hour to go above and beyond your stock set up" I've lived it for a long time and found this to be pretty accurate.
Or you could do what I did. Buy a small jet boat for going fast.
I talked to Greg Shoemaker at GS Marine. He told me if I leave the motor alone to just add a droop snoop, 4° wedge, loader grate, and a smaller insert in the nozzle. He said only get a shoe and ride plate if I build more power and to stay away from the bolt on ones out there. He also said, if my engine isn't a left over 04' model I can't get the 3.5 psi Procharger. If I can, I can get about 580hp from it. If its an 05' motor my only option is the Raylar kit or a new motor.
What are your guys opinion on this?
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Follow Greg's advice
I tried a loader grate in mine and noticed absolutely nothing
Droop, wedge, loader & insert will be a reasonable expense, let me know how it goes, I might try the same
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Follow Greg's advice
I tried a loader grate in mine and noticed absolutely nothing
Droop, wedge, loader & insert will be a reasonable expense, let me know how it goes, I might try the same
His quote was 880.00 he said that was worst case scenario. Said it should be a little less. only problem is that I like the rooster tail. If I add a wedge and droop snoop, there will be no more rooster.
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His quote was 880.00 he said that was worst case scenario. Said it should be a little less. only problem is that I like the rooster tail. If I add a wedge and droop snoop, there will be no more rooster.
Wha? You will NOT lose any roost :sly: ..... But, roost is NOT fast. I can see your "one of those".... Who the hell told you that you will lose rooster ability?
I talked to Greg Shoemaker at GS Marine. He told me if I leave the motor alone to just add a droop snoop, 4° wedge, loader grate, and a smaller insert in the nozzle. He said only get a shoe and ride plate if I build more power and to stay away from the bolt on ones out there. He also said, if my engine isn't a left over 04' model I can't get the 3.5 psi Procharger. If I can, I can get about 580hp from it. If its an 05' motor my only option is the Raylar kit or a new motor.
What are your guys opinion on this?
All this to pick up 5 or 6 MPH? Your friggen nuts. :screwy: You think your going through a lot of fuel now? ::)
GT
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Wha? You will NOT lose any roost :sly: ..... But, roost is NOT fast. I can see your "one of those".... Who the hell told you that you will lose rooster ability?
All this to pick up 5 or 6 MPH? Your friggen nuts. :screwy: You think your going through a lot of fuel now? ::)
GT
The loosing the roost ability was my assumption. I figured if you use a drop snoop and a 4° wedge, this well lower the center of the nozzle and its pitch. So i was thinking you would loose that ability. Yes, I do agree that the rooster tail does nothing for speed.I was always told best performace comes with the roost just barely breaking the surface.
5 -6 mph with all that would be false. with the supercharger I would also have to go from the aluminum A Impeller to a stainless 9.25 to keep the boat at the same max 5000 rpm. Here I can see a little more gas use. But with just a droop snoop, 4° wedge, loader grate and nozzle insert reducer should get me from around 3 - 5mph. But I dont see how this would waste more gas. As all I would be doing is making the boat more efficient by making the boat run less wet. I think I should see a very small improvement.
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Or you could do what I did. Buy a small jet boat for going fast.
best advise you have given yet :thumbup:
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Don't fool yourself here. You will NOT go any faster with these changes. I have your boat in the 21' model. Your thoughts of 5 to 6mph will not happen. Our boats are pretty big and heavy. The stock design seems to be well thought out by the builder. I don't see any easy way to get more out of it. I have never reached out to Cobra. Maybe you can get a hold of a someone there who has the experience to point you in the direction you want to go.
If your going to add a supercharger with the low boost your talking about I wouldn't change the pump at all. Adding rpm's will be your additional speed. Why do you want to keep it at 5000rpm? Do you think 5300 or 5400 would cause any problems? My 496 could take it just fine.
The droop I tried already had wedge built into it. Go up another 4 degrees and you will have serious up angle at your control. I'm sure you already know max speed comes with your roost just above water level.
Based on my personal experience you may end up with a slower loose riding experience. I only post here when I have experience in the discussion. My experience and opinion - take it for what it is.
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The loosing the roost ability was my assumption. I figured if you use a drop snoop and a 4° wedge, this well lower the center of the nozzle and its pitch. So i was thinking you would loose that ability. Yes, I do agree that the rooster tail does nothing for speed.I was always told best performace comes with the roost just barely breaking the surface.
5 -6 mph with all that would be false. with the supercharger I would also have to go from the aluminum A Impeller to a stainless 9.25 to keep the boat at the same max 5000 rpm. Here I can see a little more gas use. But with just a droop snoop, 4° wedge, loader grate and nozzle insert reducer should get me from around 3 - 5mph. But I dont see how this would waste more gas. As all I would be doing is making the boat more efficient by making the boat run less wet. I think I should see a very small improvement.
Or, make it a pig out of the hole and have the same top speed... I was referring to the adding of HP as far as the using more gas, you can't get something for nothing.
Your going to be better off IMHO putting the boat on a major diet... Your RPM at the top does not tell me your in need of a loader, may help, may not. As for the droop, you may see some attitude adjustment and get some more hull out of the water, but unless you get a few hundred pounds out of the boat, not sure you will see the expected speed gains.
The largest hurdle that you will learn on a jet boat, there is always some give and take, when your dealing with a big heavy hull, unless it is a stupid efficient design, the adjustments make a much smaller (relatively speaking) difference than on a smaller, lighter hull.
Just some more directions for you to potentially peruse;
Have you checked the bottom of the hull for a hook? Many times these hulls have a pretty substantial hook molded into them for drive-ability, don't know if this is the case for you or not.
Have you driven the boat with a light fuel load and nothing other than a driver in the boat? (goes without saying, but also a life jacket, fire extinguisher and a throw cushion :sly: )
IMHO you are trying to get that boat to do a bit more than it was designed to do, if it was easy, there would be a lot more jets out there... Just food for thought ;)
As for roost height, every boat and every hull design "likes" different parameters. If it were a tunnel bottom, they like about 6' off the water, if a modified vee, they seem to be closer to two or three feet, this changes with the amount of HP available and weight load.
Not beating you up, just trying to throw some useable information your way. I have been playing around with jet boats since the mid '80's, the "tricks" have not gotten very far in that amount of time.
Good luck!
GT