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Offline Lord Icon

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looking for specs
« on: August 31, 2012, 09:10:21 PM »
looking for specs for all engines. please post here with findings, printed and real life.
Looking for max rpm, max rpm under jet drive load. Here is my issue.
We are all looking for better output. As i understand it, the max rpm is about 5000 for the jet drive. All our engines have a max rpm and the max rpm under jet load. Does anyone have the max required ft lbs to spin the drive to full rpm? I think the Honda has 8.8 ft lbs , the Subaru like 11 or 12 . My new 2012 es Subaru still seems sluggish.
Looking for the magic number. Why remove the governor off the engine if it never spools up under load?
Lets keep this post to just facts please , no bashing one brand over another. And no sales pitches....

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Re: looking for specs
« Reply #1 on: September 02, 2012, 12:36:34 PM »
I know the GC190 maxed out at 3660 rpm, my warmed over GX200 gets 4400 rpm, Subaru EX21 is at 4100 rpm (w/o governor) and I've heard reports of the Subaru KX21 getting up to 4500 + rpm. Beyond that it would take some serious power to ever see 5000 rpm, I'm not sure it's feasible while retaining reliability, in my opinion. I have no doubt it is possible, I just don't know if it's possible to trust that combo at WOT for hours on end knowing I would make it home without a paddle. I believe it would take a water cooled two stroke to make the needed power with any degree of reliability, but I could be way off. I also don't think the pump bearings would survive long at a sustained 5000 rpm, under load.

Think cars for a minute, are you driving on the highway... or the dragstrip?

Knowing all of the engines with the correct shaft size and mounting footprint would be good info to have.  :)

Tom

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Offline Gipsy666

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Re: looking for specs
« Reply #2 on: November 26, 2012, 07:41:17 AM »
How about http://www.kx21.com.au ?? They have some rather neat stuff. Am trying to find out if it makes sense to fit a KX21 or are the benefits to small and the headache to big? Is it value for money or just plain pimping the ride without real benefit. I do not want to reach jets ski level at all just have a bit more speed on nice and calm water or up the river would be great.

By the way the specs of the standard Kx21 you can find at http://subaruengines.com.au/product/SUBARU-engines/KX-karting-engine/kx21.crm

Cheers
Raeto

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Re: looking for specs
« Reply #3 on: November 26, 2012, 01:04:02 PM »
Welcome Raeto.

Many people have used the KX motor with excellent results. I'm sure more would use it if they were easy to acquire and didn't have EPA restriction hassles to worry over. You might find neither of those issues apply since you are not in the USA.

Would love to see some pictures from your Country.  ;D
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Offline Hillbilly

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Re: looking for specs
« Reply #4 on: November 26, 2012, 02:34:16 PM »
Hello Reato,
Welcome.  It looks like people are enjoying the Mokai all over the world.  I have owned and use both the EX21 and KX21 motors in my boats.  The EX 21 is a good motor and can be given more power with a high compression head, better carburation, and low restriction exhaust.  The KX certainly is a more powerful unit, and is in my opinion, the ideal motor for the boat.  If you have a newer boat, with the EX21 motor, you can change over to the KX in about an hour, using the throttle and choke hookup from your EX.  Simply make a throttle rod out of heavy wire for the direct throttle without the governor which is attached to the EX.
I would suggest electric start, if you buy the KX.  The higher compression on the KX makes it more difficult to pull start.  Electric start is great.

Offline watercat

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Re: looking for specs
« Reply #5 on: November 28, 2012, 01:55:00 PM »
looking for specs for all engines. please post here with findings, printed and real life.
Looking for max rpm, max rpm under jet drive load. Here is my issue.
We are all looking for better output. As i understand it, the max rpm is about 5000 for the jet drive. All our engines have a max rpm and the max rpm under jet load. Does anyone have the max required ft lbs to spin the drive to full rpm? I think the Honda has 8.8 ft lbs , the Subaru like 11 or 12 . My new 2012 es Subaru still seems sluggish.
Looking for the magic number. Why remove the governor off the engine if it never spools up under load?
Lets keep this post to just facts please , no bashing one brand over another. And no sales pitches....

Its not ft lbs of torque its HP your after. A stock 200cc honda is 6.5hp @ 4000 rpm right out of the box. this is from Mike Clements racing and his dynometer. makes since i think i read a soob is 7 or 7.5 and they were getting 4500 rpm or so.

So far I think the video posted of the briggs and straton machine with the 14hp? shows about where you need to start out at to be at the bottom of the performance curve of the mokai. But since we dont seem to have any other info the 14 hp rating could easily be wrong since the engine looks exactly the same to 18 hp i think. we have some on here with 10 and 12 hp that dont get any where the results of the briggs conversion. plus to think they started with a new engine is probably not the case? so to think it could have been a older used riding lawn mower engine with many good years of service it would have to show some age in the fact that it could be a bit low on compression if its a used engine. The reason i say this is lets just say its 10 or 15 years old runs great but we know it will probably be 25% down on power if it was used regularly ( just from what i have seen on there engines of this type). so down 25% would be 3.5 hp low at wot which the video seems to be showing. that would make it 10.5 hp and we don't have another boats with new 10.5 hp or bigger engines putting out that performance at all.

So based on those numbers it seems a mokai will need at least 15 hp to see that performance and since its almost the same money to build 20 hp as 15 hp it makes no sense to even build anything under 15hp if you are hoping to achieve plane out and long life not beating the engine to death at some huge rpm. 

Remember the more hp you have the lower your cruising rpm will be and the longer the service life. On that same not my engine builder said my 20 plus hp engine will run virtually forever at 5000rpm on the dynometer with out any signs of wear. He races the engine at 8500 plus at 30hp on methanol and there good for one day of racing. were also talking world championship racing not some go cart rental place.

I posted this because since we have no boats yet running the corrected jet pump so the engine is at the correct rpm at wot specs on engines can not be compared unless every one takes there engine after it is modified to the cart shop for a dyno run. if not we have to compare stock bigger engines specs and make guesses at what more or less hp would do for a particular boat.

Also all the specs for speed should be done at 3600 rpm so we can some what scale them. then if you have after market cam or dynoed custom built engine it should be run at the RPM the builder showed the most HP at. But at least if a boat had more or less thrust you could tell if a part helped or hurt.

 The only real way to test would be using bathroom scales. nose it to the dock or trailer and with some one holding it or it tied safely take it through the rpm range and see how much thrust it puts out. The only thing every one has in common is the pump. This takes out body weight fuel load windshields etc etc. But in the end we know from above what i wrote you need a 15 to 20 hp and 20 hp is about the same as 15hp if your looking for a mokai that properly operates like a boat would if set up by a manufacture.

I'd love to see some some ways to tie up a hull and hold a bathroom scale and a object that weighed say 50 lbs so we could see the scale is correct or very close.

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Re: looking for specs
« Reply #6 on: November 28, 2012, 02:47:42 PM »
When you find somebody to re-pitch your impeller, then the discussion about hp vs. rpm vs. torque can mean something in relation to top speed in a Mokai.

For the rest of the world, it's going to take approximately 4400 rpm to make the average Mokai travel 14-15mph with a current, and it won't matter if that 4400 rpm has 7 or 20 hp behind it.

With my motor at 4480 rpm, sitting as far forward as I can, I can tip the scale at 16mph coming down river in the straights. I can't wait to see what rpm and speed you get from yours once you get it running.
Tom

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Offline Gipsy666

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Re: looking for specs
« Reply #7 on: November 30, 2012, 08:09:48 AM »
Thank you all.

Very interesting reading. Once you get into it you cant let go. At least I know now that the KX21 e-start would be a good choice to install at least for some time. Getting max 16 however is a bit hmmmm. The boys from jet buster manage 22 even for the double seater with less noise.

Cheers
Gipsy666 

Offline Dragon

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Re: looking for specs
« Reply #8 on: December 17, 2012, 10:21:34 AM »
Does anyone have the engine spec number for the Subaru 21ex motors???  Don't Have a Mokai yet but Iam window shopping for parts already!!looking for a stock large muffler ?
« Last Edit: December 20, 2012, 01:52:44 AM by Dragon6 »