Expansion pipe on two stroke marine engine possble ?

[merc_racer]

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

ok so your thoughts,ideas please guys.
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!!
cheers

[rock]

The idea of an expansion chamber has been explored on outboards but I have no idea how well any of them have done. I do however know the pricipals involved and doubt you could get a correct response from a pipe designed for a different motor. Might get some gains but not to the extent possible with a correctly designed pipe. There is a book by Gordon Jennings (Two Stroke Tuners Handbook) that details the design and construction of an expansion chamber and it is intense to say the least. I think I would look into what some of the other racers have done. I know I have seen pipes on many of the small motors over the years. Some of them chambers and some of them just megaphones and man are them dudes loud. Good luck.

Rock

[pyro]

They're pointless unless each cylinder has its own dedicated chamber. One guy built a set of six for his Merc V6 back in the day...

[PanRonnie]

if you don,t have a problem with your outboard looking like this
http://quincylooperracing.us/subpage40.html

the manuals are already on the forum
have fun with it
but it,s cheaper buying a bigger engine

[merc_racer]

g,day guys
thanks for your replies,link and help,much appreciated!!
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 ?
thanks fellas
cheers

[dragboatracer]

John Lentzkow did this years ago when I still raced. Each pipe was tuned for the cylinder. He had said at one time with proper tuning it would add about 100 horses. The bottom of the block was machined to accept the lower chambers. There used to be a video of testing.

[Markus]

There used to be an article here about John Lentzkow's expansion chamber experiment.

It was right on the S&F start page, where there is now only marketing spam from Mercury.

Maybe you can dig it up somewhere.

[pyro]

Here's the archived article:

http://web.archive.org/web/200109210...pe_project.htm

[audiobill5]

Back in the day weren't there chambers on about all small outboard alcohol burning hydroplanes?
I remember A.J.'s Auto Body in CT had a set up where the length of the pipes were not fixed, so they would move a little handle in the cockpit to change the length of the pipes. Coming out of the turn they would get an extra boost in power!
Love to smell CAM2 burinng on a wicked fast boat!

[Dave Strong]

Tuned pipes also only work well at a narrow rpm range, give great power around the peak hp rpm range but kill the lower rpm power, work great in sleds and others that use CVT clutch systems that keep rpm at peak and use secondary clutch to change the final drive ratio.

Dave

[rude tim]

The only way to make a expansion chamber work without being able to shift gears to keep the engine on the pipe is to have a sliding style pipe. Could be done but you would need a pipe guy that is willing to work with you and a pile of cash.

[merc_racer]

The only way to make a expansion chamber work without being able to shift gears to keep the engine on the pipe is to have a sliding style pipe. Could be done but you would need a pipe guy that is willing to work with you and a pile of cash.

hi guys
thanks for your continue interest and replies!!
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!!
keep the chat/replies coming guys if you may!!
cheers fellas

[930turbo]

Individual expansion chambers - per cylinder - deliver the strongest positive induction charge. It is possible to share the energy wave between multiple cylinders, it's been done many times - jet skis being one of them. SCCA F440, then 500 used a Kawasaki and Rotax motor with a chamber and wye pipe and they haul the mail. However, as mentioned here earlier, the power band is narrowed with the chamber. It sacrifices power away from the peak curve as it adds power in the sweet spot. Jet skis actually do operate in a much narrower band than an outboard, getting the outboard on plane will be difficult with the chamber unless you have sliders. Two-stroke motorcycle manufacturer's came up with several creative and complicated methods of negating the adverse effects of the chambers off peak to try to improve drivability. Also, the distance from the piston to the belly of the chamber is critical. Placing it somewhere convenient will not give the results you seek, it has to be just right. The power potential of the expansion chamber is impressive but the practical application will wear you out trying to get it right.

[pointer]

Yes, a single pipe can serve multiple cylinders. Most of those applications have gearing or slip in some fashion to keep the pipe working to its potential. Jet Skis despite having the jet without gears will let the engine spin up better than an outboard with a conventional prop. Just the nature of the beast.
An alternative to sliding the pipe(s) is to inject water into the chamber itself. In the right quantity it will effectively "shorten" the length of the pipe, which allows the pipe to "work" at a lesser RPM or greater load on the prop. This has been used on 2 stroke RC boats for a few years now, taking a few records in the process.
There is a ton of work involved in getting the pipe dimensions correct - a friend of mine does this for RC boats. Most pipes work better than no pipe, a great pipe is a game changer. Funny part is most guys spend the money for the pipes but don't take the time with set-up to ever get the engine "on the pipe"!
What you need to know is in the handbook attached in a post above. Happy reading!

pointer

[merc_racer]

hi guys
thanks alot for your advice and info.
great im happy to hear that it can be done and that the one pipe can share between 3 cylinders although not ideal and not as good as a pipe for every cylinder!!
but any way,it sounds/looks like it has potential!!
cheers
glen