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Old 05-11-2009, 10:48 AM   #21
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my from teenage experience with dirt bikes 2 strokes respond well to engine building mods. i would have it bored out as much as the engine will alow and try to find a higher compression piston. on a small engine youw ill probably only get about 5hp but you would be suprised how big of a difference it will make
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Old 05-11-2009, 12:09 PM   #22
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^Again, I'm talking out my ***, but you see all these Youtubes of guys taking those little Go-peds bikes, modding the **** out of them, mini-nitrous bottles and ****.

I'm taking about a full out build... stroker crank, bored to the limits, headwork, big ports, hi-octane gas, forged ****, tuned exhaust... the works.

I bet you can manage 50hp out of 500cc's with a no-compromise motor. Maybe I'm delusional, and it might be a little more expensive than a full custom turbo setup, but I bet it would be easier and more reliable in the long run.
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Old 05-11-2009, 11:01 PM   #23
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That thing is 399 cc's. OH-YEA!.

I had a Quadzilla 500cc two-stroke. FTZ Racing can get 88hp out of those.

I don't see any reason you can't get high performance reed valves to start. Then read up on hp boat exhaust.

Remember, right now you can run wide open forever. Once you turn this into a dirtbike motor. They overwind quick and blow up. Try to figure out a way to raise the rev limiter without doing away with it.

I know a little about dirtbikes. Haven't messed with boats.

But The dealership will tell you the only differance between some 25-30 or 35hp motors is the carburator. That would be a quick easy 5-10hp. YOu might could find one in the boat yard or ebay.
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Old 05-12-2009, 12:30 AM   #24
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Quote:
Originally Posted by Stein View Post
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.
It'd be killer and greatly appreciated if you'd host a file for everyone. Here is a link to do such Free file hosting by Savefile.com. If your not up for it just say so and I will PM you my email address.
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Old 05-12-2009, 12:49 AM   #25
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Just spray it!

N2o easy!
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Old 05-12-2009, 01:44 AM   #26
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Why not just retro that honda 450cc 4 wheeler bad motherbitch to a jet pump? THAT would be scary...

Btw, like the boat!!
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Old 05-12-2009, 09:54 AM   #27
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Quote:
Originally Posted by NoiseRacing View Post
It'd be killer and greatly appreciated if you'd host a file for everyone. Here is a link to do such Free file hosting by Savefile.com. If your not up for it just say so and I will PM you my email address.
Cool. Just did it.

Manual is here: http://href="http://savefile.com/pro...le.com project
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Old 05-12-2009, 10:17 AM   #28
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Use a Rotax 493 or 494 twin-cylinder with a tuned pipe. 100+ horsepower easy on a stock engine.
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Old 05-12-2009, 10:27 AM   #29
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That tuning manual Stein posted is extremely useful. Well wort ha read if you're looking into tuning a 2 stroke, IIRC there was some talk about use of a super charger in the book.

I've recently finished rebuilding/restoring a 250cc 2 stroke sports bike, and its making 60hp. 400cc 2 stroke bike engines have been comfortably tuned in excess of 100hp. And these are engines that can take beeing wound open for much longer periods than dirt bikes.

I suspect your biggest gains will be made by sorting the tolerances out, getting the ports nice and even, get the squish band set perfect then getting a decent expansion chamber exhaust on there.

http://www.rgv250.co.uk/forums/index...howtopic=31131 - there's some useful discussion and link through to other discussions about turbo charging 2 strokes there.
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Old 05-12-2009, 10:27 AM   #30
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A turbo would require a separate pressurized oiling system with a tank, pump, cooler, lines, etc.There is no good way to reroute the factory exhaust. You would not be able to use the factory engine cowling and mount a turbo right on the engine. Two-strokes are very picky about their tuned exhausts. If it is an oil-injected motor you will not be able to match the increase in fuel and air with oil. Etc., etc.

Many times a particular engine will have different horsepower variants as noted by someone else. The compression ratio and/or carbs are sometimes all that are changed. Deck the head and then run premium gas is one of the simple things I've heard to do...
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Old 05-12-2009, 10:34 AM   #31
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The other thing that you have to look at is your prop. It's likely too low of a pitch. Most motors that size are pitched to push around a 14 ft aluminum fishing boat with two fat guys and gear in it.

The pitch should be stamped on the prop as two numbers - "diameter x pitch" The pitch is how far the boat would go through the water in one revolution in inches, assuming zero slip. Of course that is impossible. Figure 80% of that. You will also need to know what gear ratio you have and what the max RPM is. BOth should be available online or in your manual for the motor. After that, you can enter that into any of the online boat speed calulators and get a theoretical speed.

Let me ask you this as a gut check, does it seem to get to max speed quickly? Like 5-6 seconds? If so, you are likely under propped.
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Old 05-12-2009, 02:42 PM   #32
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+1 to what Stein said. You are probably making plenty of power for the weight and drag of your boat. You could buy a cheap prop of a higher pitch and make it even more likely to be fatal when you crash. You might get another 15-20 mph depending on how limited you are now and the pitch you move up to.
A higher pitch would make it come up on plane slightly slower out of the hole, but would make for a higher top speed. The automotive equivalent would be accelerating and then cruising in 2nd gear vs. 3rd.

Then you will also have a spare prop for when you hit something with yours.

There are some inexpensive composite props out there now, too.
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Old 05-12-2009, 02:52 PM   #33
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I think his biggest problem will be finding one steep enough. They just don't make them that small for that size motor in a steep enough pitch. He could likely have his repitched, though.

I actually make some parts for COMPROP Propellers. They make composite propellers. He gave me one for my bass boat, but the steepest that he had for my motor was a 15 pitch. I normally run a 23. It gets out of the hole, but tops out at 45 vs 59 gps. I still keep it in the boat as a spare when we go to Canada each year as it weighs nothing. Beats being propless in the middle of nowhere.
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Old 05-12-2009, 03:00 PM   #34
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In terms of prop pitch, I don't remember what prop is on there but by adjusting the trim I can change top speed by 5mph and how quickly it pulls out of the water. I tend to set trim to setting 2 of 3 and leave it there. The goal here is to increase power, not to swap torque for speed. When playing on waves, fast planing is far more important than top speed. That's why I was thinking of adding more power.

Thanks a ton for the two stroke manual, I have looked through it briefly. I will really read it after finals are over. Thanks again folks!
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Old 05-12-2009, 03:12 PM   #35
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The trim is just for the angle of attack on the motor. Trim down and it helps get it out of the hole but makes the front plow more at speed. Trim up raises the nose. Good for high speed but harder to get out of the hole. Is it a hydraulic trim or "set a pin in the hole" trim?
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Old 05-12-2009, 08:51 PM   #36
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its "set a pin in the hole".
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