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Thread: Expansion pipe on two stroke marine engine possble ?

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    Default Expansion pipe on two stroke marine engine possble ?

    Hi there all,
    i have a 40 hp mercury(jap spec) short shaft 3 cylinder,3 carb engine on a 3.90 mt alloy tinny.
    i have done quite a few mods so far to it,jack plate,hydro foil plate,mercury ss 15 " 4 blade balanced,cupped,thinned prop,50 d2 carbs,50 hp d1 larger stinger exhaust,60 thou shaved of head,irriduam spark plugs,removed air box,disconnected rev limiter wire,lightened flywheel,carbon reeds,ram tube velocity stcks,removed 2 lighting coils,exhaust relief hole mods in leg,cut air vents in cowl,amsoil full synthetic @ 50:1 ratio,bp 98 octane fuel
    future mods will be in next few months,
    1 mm over size wiseco forged pistons,full race porting,balanced crank shaft.

    ok,so is it possble to make/modify and fit a expansion pipe to a out board marine engine ?
    i realize the expansion part of the pipe will not fit in lower leg,but i would use the smaller ,later model stinger manifold,add some pipe length to end of it,then run a cylicone adaptor pipe,cut off the old curved pipe/flange and position it so the pipe comes out of side of leg ,near where the lower 2 bushes are,then make bracket/brace to bolt the out chamber to the engine.
    i have ben looking at using a jet ski 800 cc expansion pipe,the jet ski pipe shoulld work ok i beleive as the engine on jet ski are similar size,bore,stroke and rev range.
    although they usually rev to 7,000 rpm.
    here is what im looking at buying and modifying to suit/fit,
    www.factorypipe.com
    http://www.factorypipe.com/p_kawasaki.php
    http://www.factorypipe.com/p_yamaha.php
    http://www.factorypipe.com/p_seadoo.php

    is this going to be possble some how ??
    out of the pipes above,which would be the best one to choose ??
    i like that kawaski 750 SX/SXi Limited
    i really hope so,cause a nice decent expansion pipe would cain hard!!
    i luv the sound of two stroke pipes!!
    so do you reackon the perf from a expansion pipe would be be on par with say just the normal exhuast stinger or worse ?

    out of the pipes from factory pipe website which one would have the most chance of working ?

    you know how jet ski's have 2 or 3 cylinders,and they have only one expansion pipe for all cylinders,why is that and they work on them ?

    i cant buy bigger engine ,say for example a 60 hp as they are far to heavy for my boat !!
    as it is my boat is meant to have only a 25 hp size engine on it
    .
    but i have had my rear transom braced and modified for extra weight and power force.
    i have tried doin extensive google search on this topic so far,nothing much.

    do you please have any other links of info/pics of expansion pipeson small outboards ?
    it is not possble to make seperate manifolds for my engine is it ?


    why cant you keep bliping the throttle to keep revs up,say like shift gears??
    jet ski's dont have gears either,and there power expansion pipes work dont they ??
    they dont have a chamber for each exhaust port do they ??,no the ones iv seen any way!!
    what is a sliding style pipe mean ?
    so if the pipe does not act/perfom like it should do on a marine out board,if it was fitted,would it run worse then ?
    what about the nice tinny rev sound a expansion pipe makes,will it have it ?
    if i buy the centre bleed in the links above i provided,the pipe should kick in lower rev range than the end bleed pipe!!

    hope to hear some replies/helpful comment or may be some links!!
    cheers guys

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    Sam Cullis Mark75H's Avatar
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    Expansion chamber pipes have been used on racing outboards since about 1960, a couple years after they were first used on motorcycles. Using the search function on BRF should bring up a lot of answers to this.

    A sliding pipe is like water injection, it makes power at more than 1 rpm, unlike a fixed length pipe.

    Location of the bleed pipe is irrelevant.
    Since 1925, about 150 different racing outboards have been made.


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    thanks for reply back
    so would a jet ski pipe of similar size engine cc,bore and stroke work on a 40 hp 3 cylinder two stroke mercury outboard and perform or make it worse or just the same ?
    thanks

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    Outboarder on this site has done quite a bit with this. And i think Cheney has done the same. These guys may have some insight?

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    Quote Originally Posted by ultrafast30 View Post
    Outboarder on this site has done quite a bit with this. And i think Cheney has done the same. These guys may have some insight?
    hi mate,ok thanks for that info!!
    i might give them a p.m then
    cheers

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    i just tried to p.m outboarder,his msg bank is full and cheney member cant be found!!

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    Sam Cullis Mark75H's Avatar
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    Quote Originally Posted by dart View Post
    thanks for reply back
    so would a jet ski pipe of similar size engine cc,bore and stroke work on a 40 hp 3 cylinder two stroke mercury outboard and perform or make it worse or just the same ?
    thanks
    Port timing and engine rpm are as or more important than matching bore & stroke. You need to google "The Two Stroke Tuner's Handbook" by Gordon Jennings and learn how exhaust tuning works
    Since 1925, about 150 different racing outboards have been made.


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    Default SkiDoo 700 HO pipe

    Quote Originally Posted by dart View Post
    thanks for reply back
    so would a jet ski pipe of similar size engine cc,bore and stroke work on a 40 hp 3 cylinder two stroke mercury outboard and perform or make it worse or just the same ?
    thanks
    http://www.boatracingfacts.com/forum...rd-quot/page28

    Go here and know that the headpipe shown did not work well. It was replaced with a short stub collector and the pipe was shortened/rotated as well. In the end it worked great - after a summer's worth of trial and error. It gets a short tower this winter for racing summer 2013. Good luck with your project!

    Tim

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    Quote Originally Posted by Tim Kurcz View Post
    http://www.boatracingfacts.com/forum...rd-quot/page28

    Go here and know that the headpipe shown did not work well. It was replaced with a short stub collector and the pipe was shortened/rotated as well. In the end it worked great - after a summer's worth of trial and error. It gets a short tower this winter for racing summer 2013. Good luck with your project!

    Tim
    hi tim,great thanks for the link mate!!
    the pipe you are talking about above is the black one in post # 280 is it ???
    i have a " westcoast" brand expansion pipe im modding at the moment to fit and try out!!
    if you have any other info,facts or links r.e expansion pipes please let me know.
    btw,that black pipe,what brand is it ??
    whats it off ??
    is it loud ??
    what rev range does the pipe kick in at ?
    should the end bleed stinger outlet on expansion pipes be similar diameter to the stock engine stinger that it comes with ??
    would turning a end bleed pipe into a centre bleed give more low end power ?
    cheers

    glen

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    Question: How do those Formula One hydros run so damn fast without expansion chambers? All they have is a crude tuner built into the towerr.

    Jeff

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