72 MX15 NEED JET DRIVE ADVICE

[johneebass]

Hello All !

So I got my 72 MX15 in 1998 and used it 2 years w/ 50hp 2cyl evenrude (NOT ENOUGH).

Had my first child in 2000, and with all my hobies, boating was one that sat on the back burner. So I sold the 50hp in 04 with the intent of a 150hp MERC "ToP" but changed my mind in 05 and was leaning towards jet drive w/ a fuel injected 4.3 , then played with the idea of a 4.3 to powerglide to a v drive(which I have)..........

anyways now here we are in 2008 and I want to start this restoration project in august (thru winter of 08/09) of which I have found many usefull topics here, so first off thank you all for the info so far.
The resto will consist of a total tear down, transum fix, depending on motor restructure of top to add motor cover and new interior, with new gell/flake and new smoked windshield. BTW I just love this boat, will not resell for those wondering.

My delema is I know nothing about jet drives, so I am curious if anyone here has done this, knows of someone who has or has any knowlaage of jet drives. I have been watching Berkeley drives on ebay for months and trying to learn as much as possible, I will build my own motor (I have built dozens of race and hotrod motors) so hp is totally at my discretion but I am not sure on sizing the jet drive and how much Hp to build into motor.

Any info will be greatly apreciated,
and any one with a drive for sale or controls please speak up.

Thanks
Jon

 

[Big Red]

For starters anything smaller than a big block is useless. Jet boats need more torque than hp. It takes more torque with the combo of hp to get the boat to move. Your best bet maybe to shop around and find a old jet boat that has a blown or missing engine. Your going to stick 10 times the amount of money in your boat than you can buy one for. I would just get a outboard and ride.

My 1976 Checkmate factory 455 jetmate

 

[johneebass]

Ok, thanks for the responce.
So what I saw on berkeleys' site stated "10-27# require 1 hp"
so do you think I should call them to get torque info?

This MX15 is is max rated at what?? 1200 pounds so even on lite side
120hp will thow it around. I mean those jet skis are what 600/700 pounds with 2/3 cyl 100hp motors?
A mild 4.3 can make 240 hp/265 Ft#T.
I believe a full dressed 4.3 is 460# 350 is 640# and 454 is pushing 800#
so never mind the boat can't handle it the wieght of the BB would suck up alot of the power so I believe the smaller motor is a better alterative, if the jet drive will run on it. But your saying it might not. As far as money forget about that aspect I am more interested in the mechanics.
So have you ever installed a JD in a boat that didnt have one prior?


BTW Nice looking CM!!

 

[Big Red]

Its your boat what ever makes you happy. I just think its not a good idea. I would never consider changing one, its not worth the time and aggravation. Why would you convert one when you can buy 1 for a 1/4 of the cost your going to spend. You need to sit down and add up every part your going to need to convert your boat. And when you get done building it you can never in 100 years get your money back. Besides a outboard will smoke that jet drive when you get done

These our just my thoughts

 

[TheNerd]

I agree with Red. Restore the boat, put a recent 150+ outboard on the back. If you are still set on a jet boat, buy the one BigRed is selling, will be cheaper in the end.

 

[johneebass]

ok no tech from you, its all about the $$$ thanks....

ORIGINAL QUESTION
"My delema is I know nothing about jet drives, so I am curious if anyone here has done this, knows of someone who has or has any knowlage of jet drives. I have been watching Berkeley drives on ebay for months and trying to learn as much as possible, I will build my own motor (I have built dozens of race and hotrod motors) so hp is totally at my discretion but I am not sure on sizing the jet drive and how much Hp to build into motor."
The money is not the subect here.... so set that aside.

Here is a good debate.......I am interested to how you come up with the fact that an OB on my boat will smoke a jet drive????? PLEASE do exsplain.

 

[TheNerd]

Well, there is no tech from me, so I am not going to bother, keep doing your research and you will find out.

 

[johneebass]

Well, there is no tech from me, so I am not going to bother, keep doing your research and you will find out.

Thank you for your opinion.

 

[Big Red]

Well here you go nobody knows a Jetboat better than Tom Morrow of smithville Mississippi. He has been racing jetboats since the sixites and is familar with Checkmates and also sells his own custom impellers and kits. I bought all my parts from him for my jetboat, impeller, pump, cables, foot throttel, gate and complete steering, and shifting. He will also sell you some used parts.

phone 662-256-4018

The web page=== http://www.jetpumprepair.net/

 

[johneebass]

Thank you for the info sir!

 

[supergenius74]

I believe you may run into a problem with the jet conversion that a lot of people have experienced, the hull is not really disigned for the pump. The MX-15 is a small pad V bottom and rather short on space underneath in my opinion, when properly trimmed out you might be cavitating. I have looked at a 77 jetmate hull and compared it to my mx-15 and they were very different in design. Nothing like this is impossible but you might not be able to achieve your goal unless you were converting a hull that was designed and or sold for both types of power. I think it would be equally fun to go blowing past a jetboat in your mx-15 with an outboard, i have done this before and with the right HP and setup that boat can hit 70 on fairly calm water. She is a bit light in the nose and does not need a lifting prop nor setback with a heavy engine. A center steer would be ideal for max speed.

 

[83PREDICTOR]

If you are set on the idea of jet power I think you should find a wrecked jet ski (like a RXT or GP1300R or even a turbo Honda) and use the engine and pump out of it. I have seen this done before and worked out ok.

 

[daren34]

If you are set on the idea of jet power I think you should find a wrecked jet ski (like a RXT or GP1300R or even a turbo Honda) and use the engine and pump out of it. I have seen this done before and worked out ok.

there was a discussion about converting to a jet afew years ago on the board

prob. the best power to weight would be twin jetski motors or a pair of merc sport-jets

you can run a berklley with a smallblock you just have to match the impellar

the problemb is jets drives are not efficient at 5,000 rpm
they are at 15,000 to 20,000 but it would be impossible to build enough power in a small package
jetski's use a 5 inch dia impellar at 10,000 rpm
at an idle you are moving very little water so you have no steering unless you goose the throttle! if the motor dies no steering!

the other problemb will be finding an intake grate that will work with a pad v
most jets are rounded keel

 

[Old Navy]

I am a former jet boat owner. Those boats are really fun, but they also suck gas, and are loud. I had the cops visit me on numerous occasions due to complaints. You will put hundreds of hours in the conversion and thousands of dollars, to go much slower than you expected. I think I worked on mine about 5 hours to 1 hour on the water. I enjoyed it, but would not do it again. My back has gotten better since I sold it. If you are really sold on getting a jet boat, there many for sale easier and cheaper than making your own out of an outboard hull. Southwind Tunnel, 455 Pontiac, 75 mph gps.

 

[johneebass]

I believe you may run into a problem with the jet conversion that a lot of people have experienced, the hull is not really disigned for the pump. The MX-15 is a small pad V bottom and rather short on space underneath in my opinion, when properly trimmed out you might be cavitating. I have looked at a 77 jetmate hull and compared it to my mx-15 and they were very different in design. Nothing like this is impossible but you might not be able to achieve your goal unless you were converting a hull that was designed and or sold for both types of power. I think it would be equally fun to go blowing past a jetboat in your mx-15 with an outboard, i have done this before and with the right HP and setup that boat can hit 70 on fairly calm water. She is a bit light in the nose and does not need a lifting prop nor setback with a heavy engine. A center steer would be ideal for max speed.

Thank you very good info here!! I thought that cavatation may be an issue, the keel on my 72 is maybe 6/7 inchs wide, I would have to fabricate a SS intake/adapter. Also the twin jet ski motor/drive is interesting, I think when cornering it would be an issue or at least a sight to see.....lol
As far as lake patrol, I dont need issues, good point... I will have to look at the bottom again and think about this a little more..
Than you!

 

[remlinger]

If your hearts set on a jet boat buy an outboard with a jetdrive lower unit like the ones used on shallow rivers, that way you don't have to convert and you have a jet boat.

I know it's just not the same.

 

[Chris E]

personally, i think this would be a very interesting project, don't know if it would work, i like the idea of pwc motors twins or for something really cool - try squeezing triples in there - that i'd like to see

 

[remlinger]

This starting to sound like a bad mythbusters episode when they retro fitted a boat with a compressed air as a jet propulsion system. Need less to say, it really didn't work.

 

[supergenius74]

I always wanted to take my mx-15 and put twins on it, just to be the only boat like that. A couple of 75 rudes counter rotating if that is even possible, would have looked and sounded cool and made it more stable.