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?
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?
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.
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.
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.