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Old 05-10-2009, 01:18 AM   #1
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Default I have a batshit crazy idea

So I have a 9 foot power boat. Its effectively the miata of the boating world; two seats, roll over hoop thing, very light (250-300lbs) excellent draft and turning abilities. It was originally developed to handle 9.9-15 horse, currently I have a mercury 25 2 stroke on the boat. How hard would it be to turbo it? I know that I could do it with a 4 stroke, but is it even possible with a two stroke? I know this is crazy, but I can't add much weight without ******* up the handling and I already have a bigger engine than it was meant for. If I could get another 10 or 15 horse I think I could probably hit 45-50 miles an hour. Thoughts?
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Old 05-10-2009, 01:50 AM   #2
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it would work just fine i would be intereseted in the octane for your mix etc. And who would make a manifold but a small t1 should be able to do it i gues
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Old 05-10-2009, 05:15 AM   #3
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What does this have to do with a Miata other than possibly just trying to get your post count up??!!
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Old 05-10-2009, 05:22 AM   #4
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I have no idea where to post this, if you or anyone else doesn't think it fits the character of the forum, please delete it. Sorry to bother anyone.
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Old 05-10-2009, 05:26 AM   #5
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Old 05-10-2009, 11:19 AM   #6
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I like this thread. And this is the DIY Turbo forum.

gaius49, got any pictures of the hull?

About 5 or 6 years ago, when I lived in Maineville Ohio, I recall driving down a back road one day and seeing a smallish boat parked on a smallish trailer in front of a house. It seemed to have an abnormally large engine hanging off the back of it, and I remember thinking "well, that must be fun."

Since than, I've never seen anything quite like it.

Turbocharging a 2 stroke engine is indeed a different animal. I've never done it, but I can understand why it presents some of the challenges that it apparently does.

A lot of the mixture would probably just blow right out the exhaust port. Not sure how you'd solve that problem.

And putting a turbine into the exhaust would **** up scavenging pretty hard, I'd think.

Might improve cylinder fill efficiency, but I don't see how you'd actually achieve much more gains than that.

Any 4 cycle engines of acceptable weight you could throw on?
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Old 05-10-2009, 01:31 PM   #7
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Default Lots of fab involved

It is my experience that two stroke outboards are really conducive to turbocharging.

I've got an 85hp Evinrude on my fishing boat. The exhaust on my motor, and most of the 2 stroke outboards I've seen is actually a cast part of the crankcase. It makes sort of a plenum that dumps into the mid-section. You'd have to figure out a way to split the plenum, routing half the plenum to the turbine inlet then routing the turbine outlet to the other half of the plenum. Another option would be to scrap the thru-prop exhaust and VTA thru a muffler. Probably would be hella loud, though.

IMO, the better option would be to supercharge it. You could mount a sheave to, or cut a belt drive into the flywheel and run a blower off it.

I say you outta do it. Awesome project.
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Old 05-10-2009, 02:00 PM   #8
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Quote:
Originally Posted by gaius49 View Post
...roll over hoop thing, very light (250-300lbs) excellent draft and turning abilities. It was originally developed to handle 9.9-15 horse, currently I have a mercury 25 2 stroke on the boat.


On second thought, don't do it. WHEN you capsize in the bay they'll find your body 5 miles out to sea. Or WHEN you capsize in the Columbia river, your severed feet will wash up in Vancouver.

FWIW the roll over hoop thing doesn't do **** on the water.
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Old 05-10-2009, 03:03 PM   #9
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Quote:
Originally Posted by bryanlow View Post
FWIW the roll over hoop thing doesn't do **** on the water.
Nope, rollbars have no place on small, lightweight, overpowered, high performance powerboats.
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Old 05-10-2009, 03:24 PM   #10
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You would be better served by increasing compression and working the transerfers if you are willing to get in there and cut on the piston/cylinder.
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Old 05-10-2009, 03:25 PM   #11
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ib4[in before] your **** flips over.
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Old 05-10-2009, 06:20 PM   #12
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get a small turbo off of a kabota diesel or any other small tractor. I have one we took from a spare motor for a large mower at work. We are throwing it on a 10 horse OHV briggs.

The housing actually says TD04 but it has like a 1.5" inlet and its TINY. Ill have to get the specs off of it.
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Old 05-10-2009, 08:06 PM   #13
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It has been my findings that it is easier to buy a jet ski, and leave the small boat dependable. LOL

Otherwise it will break in the middle of the lake.

Fun thought though.

Why don't you leave the stock motor on there and make a homemade jet engine that run off a B-Q grill tank.

I'm for real. Look it up on You-tube.
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Old 05-10-2009, 09:28 PM   #14
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You can make an air to water intercooler placing the air intercooler under water.
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Old 05-11-2009, 12:23 AM   #15
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Thanks for the responses. It seems that it is possible. The smallest garrett is designed to for .4-1.6 liters and the mercury 25 is 399cc. I may give it a shot. The intercooler idea is fantastic. Even just running a single tube would probably do wonders. For reference the boat is a mercury watermouse which was designed and built for disney world. here is a pic of such a boat. Thanks again.
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Old 05-11-2009, 12:40 AM   #16
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Every guy I know with a scooter has a crazy exhaust, jet-kit, ported head, etc... and makes about double what the thing came with.

I'll admit my marine 2-stroke knowledge isn't that great, but before I dove in to a turbocharged setup, I'd see what it would take to do a full out NA build. A different exhaust manifold, carb, new head, p&p, hi-comp piston, etc... can't be that expensive. Find a local machine shop in your area that specializes in jet-ski performanc and see where it takes you.

I'd also check online into a 2-stroke performance tuning book. Somebody has to have written one. Make yourself smart before you spend any money.
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Old 05-11-2009, 01:31 AM   #17
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so how do you plan on keeping the turbo oiled with the two stroke engine?
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Old 05-11-2009, 01:32 AM   #18
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run the gasoline/oil mix through the turbo, duhhh
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Old 05-11-2009, 02:27 AM   #19
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That thing looks gay, so it must be the Miata of the marine world! lol
I am ignorant to 2 strokers, but I'd do what Sam says, knowledge is key.
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Old 05-11-2009, 09:58 AM   #20
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Quote:
Originally Posted by samnavy View Post

I'd also check online into a 2-stroke performance tuning book. Somebody has to have written one. Make yourself smart before you spend any money.
I have a scanned copy of this manual. It's old, but still very sound two stroke tuning advice. It's an 83 page PDF, 8 MB so I can't attach. PM me your email address and I can send it.
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