more fuel needed when adding expansion pipe ????

[merc_racer]

when adding a expansion power pipe to a two stroke,for example a marine engine,is it
required that you need more fuel ,as in bit larger jets ??
with the pipe on,the engine is working harder and reving more,so would you there fore say a little more fuel would be better !!
my jets are as follows,132 top,132 middle and 135 lower carb.
so when i finally add my modified westcoast brand expansion pipe soon,should i change out top and centre carb main jets to match the lower 135 jet ??
thanks

[pointer]

My experience with expansion chambers is limited to small ~26 cc engines and snowmobiles, no experience with outboards.
The small 25ccs have needle jets - and do require some adjustment in my experience to get them "on the pipe". A good running engine on a canister muffler (think chain saw / line trimmer) may be off a tad on jet adjustment and you'd be hard pressed to notice it. Have do just that, ran a canister and then later swapped it out for a tuned pipe. Plug looks good, no piston wash (Klotz mixed very rich). Have to listen to the engine on the pipe and final adjust from there, easy with needles!
Newer snowmobiles for the most part comes with a fuel management system of some type, either EFI or a carb compensator for temp and altitude, which will compensate for the increased fuel flow the pipe is pulling. On older snowmobiles, pipe and jetting go hand in hand, and most people use a "dial a jet" to get them running well. Otherwise it is a fixed jet change.
As I stated in your other post most people do not take the time to set up properly after installing a pipe to get it working 100%. Having a pipe pulling the fuel does take some adjustments to get the engine "on the pipe" and not just crackling or making it sound "sweeter". I can remember dialling in a 42" cat with a heavily modded 26cc, it took a few hours to get the engine on the pipe. Many small adjustments to both Hi and Low speed jets, and a drop in prop pitch to make the process easier. Once we had it on the pipe we propped back up and a few more adjustments were required. Truthfully, temp and humidity are factors in jetting for the pipe as well. That particular model boat was working awesome in late summer but fall took it out of tune, and the process started over. I recorded the temp, jet adjustments, prop adjustments etc for every adjustment. That being said, a 26cc engine spinning 12K with a 1/2" bore carb making ~5.5+ HP is a finely tuned animal to begin with. On the pipe it would pull 15.5K, minor adjustments. Take the pipe off and revert back to the canister and it would just as well as it did before installing the pipe and doing all the set up work - in other words to get the pipe working the "sweet spot" in jetting is very narrow and the stock canister would run on a much wider range of jetting.
By "on the pipe" I mean the engine acts like it has a turbo or supercharger effect. The pipes sound cool and all, but one working properly is noticeably better. Again, most guys don't ever get their pipes pulling properly. The engine has increased RPM, power, and noise!
On an outboard with fixed jets yes jetting will be required. You won't know until you pipe it, and then start reading plugs and piston wash. I'm not sure I'd have the patience to dial in three or more cabs with fixed jets. The little 26cc was fun, we did it in a couple of afternoons, but it was on cylinder, one carb and one pipe, and if we roasted a piston or cylinder, easy and quick fix, let alone fairly cheap - we didn't, but the engine was way fat (rich) to begin the process. I honestly believe a little more forgiving of heat than an outboard. Piston top was ceramic as was the pipe.
Don't let my experience take away your enthusiasm foe doing this. Just know that it isn't a bolt on an go mod to work to it's potential.

pointer

[rude tim]

When you have an engine with a single gear (no trans) installing a expansion chamber "pipe" is real tricky. The pipe will make more power at peek but less everywhere else. A good sliding sliding pipe will be your best bet for all around power. Problem is getting someone that knows a lot about pipes. A good stash of cash helps!

[merc_racer]

When you have an engine with a single gear (no trans) installing a expansion chamber "pipe" is real tricky. The pipe will make more power at peek but less everywhere else. A good sliding sliding pipe will be your best bet for all around power. Problem is getting someone that knows a lot about pipes. A good stash of cash helps!

hi tim and pointer
thanks for reply/info

so how come jet skis with power expansion pipes then run so well ?????
as they have no trans either ?
i have brought and modded a jet ski expansion pipe and fitted it already!!!
it starts very well,it idles very well.
will test it out on water this weekend!!!
i have 2 types of bleeds to try out,end bleed and centre bleed,and i have also different inner diamter bleed inserts to try as well.
i fitted slightly larger jets in the carbs,it didnt agree much,plugs wet and dark in color!!
so i changed back to 132 in top and centre carb and left the stock 135 in bottom carb
will let you know the results after the weekdend with gps and tiny tach rpm guage!!
cheers
glen

[merc_racer]

can you convert a conventional expansion pipe into a " sliding pipe " some how ??
thanks

[pointer]

hi tim and pointer
thanks for reply/info

so how come jet skis with power expansion pipes then run so well ?????
as they have no trans either ?
i have brought and modded a jet ski expansion pipe and fitted it already!!!
it starts very well,it idles very well.
will test it out on water this weekend!!!
i have 2 types of bleeds to try out,end bleed and centre bleed,and i have also different inner diamter bleed inserts to try as well.
i fitted slightly larger jets in the carbs,it didnt agree much,plugs wet and dark in color!!
so i changed back to 132 in top and centre carb and left the stock 135 in bottom carb
will let you know the results after the weekdend with gps and tiny tach rpm guage!!
cheers
glen

A jet drive is a whole different animal - as long as the intake grate gets water all the jet has to do is spin that water. Jet drives do not load up like a prop drive.
Take a plug wrench and flashlight with you when you go. Should your setup allow you to pull some RPMs you'll want to shut it down, pull plugs and read piston wash and plugs. Before any long runs at any RPM you'll want to check the wash and plugs.
In theory the bleed location doesn't matter I've been told, that part of theory I'm not up on!
Bleed size does matter, the Tuners Handbook is the bible for determining size.
Sliding pipe? The "header" pipe is cut, and a slightly larger pipe is welded on one side only. When the pipe moves the peak RPM and torque moves as well. As I said in your other post, water injection into the chamber will do the same - a little more complex but same end result.

Good luck with it, have fun and remember to check the burn!

pointer

[Mark75H]

Correct info!

The reason you need bigger jets is because the pipe only pulls in more air when it works ... its up to you to let in the matching amount of gas.


As has been mentioned, most pipes don't require more gas ... because they don't work. The change in fuel need as evidenced by leaner mixture indicated on the spark plugs (or a hole in your piston) is proof that the pipe is working.


Water injection is a second way to change the pipe tuning/effective length.

[merc_racer]

thanks for that extra help.
so should i turn my jet ski pipe into a water injection pipe then by adding a brass outlet and redirecting water outlet into the pipe ?,i could re-direct colling system outlet hose from upper engine to the brass fitting in pipe!!
yes stinger bleed inner diameter important over length.
in gordon jennings book he mentions 1/1/4 " inner or a tad smaller
i heard end bleed over centrer bleed are louder,produce more power,better flow,tuned for more wide open throttle ??
so if add a brass barb fitting into start of expansion pipe,will this help much in any way please ?,where would i position this water inletn first part of chamber cone/belly ?
thanks for your kind help!!

[pointer]

Try to establish a baseline first. You have to know what you have before making adjustments.
Know before you start this that parts failure is highly likely.
I'd leave the water injection for later, there is a lot involved in getting that right, and you need to control when it gets the water.
In the book he gives the math to calculate the bleed diameter - important. The small 26cc engines I referred to in the other post use ~ 7/16 bleed, in the 20,000 RPM range. The quieter pipes do bleed form the belly, and direct towards the prop roost / water surface. The loudest pipe I've witnessed was a rear bleed. Depends on what your after - performance or sound. Other ways to get loud if thats your thing. Not positive on performance of center vs rear. Consider it good enough if you can get your setup working well.
When you get some performance and want more low end either slide the header or inject water. Water is injected into the front of the divergent cone. Makes the pipe act like a shorter (more torque less rpm) pipe.
Back to basics, take a note pad, plug wrench and flashlight and head to the water. Record air temp, speed, rpm etc. Make one change at a time, in measured amounts so you can revert if not positive. If you are used to your current setup less pipe no one will need to tell you when it is "on the pipe". You'll know. Again, the book is the resource. Happy reading!

pointer

[rude tim]

A properly tuned pipe helps the intake charge from the expanding exhaust gasses and actually pulling some intake charge into the pipe than reversing that charge back into the cylinder just before the exhaust port closes. Typically a shorter pipe gives more top end and a longer pipe more low end. Head pipe taper cone shapes etc all effect performance. Water injection works great to spread out the power at bottom end. The location of the spray nozzle and how much you spray in and how long you let it spray is critical. If you spray to much and run it to many rpm before shutting it offthe pipe can force water into the cylinder.

[merc_racer]

hi pointer
you have been a great help mate r.e this pipe project!!,thanks alot
r.e water injected in to front of the divergent cone,is that close to where the pipe begins or in the first belly of cone ??
i can use the tell tale water outlet and run it into the pipe,i have a brass 360 degree nozzle that will spray a nice " mist ' of water constanly to help keep cool.
do i need in only one location the water injection please ?
apart from end bleeds being very loud,they do provide flat out full throttle hp/power apparently.
any way,all the mods i have done,can be temporary as in i can put a plug in the water injection hole or a plug into the eithyer end bleed or centre bleed to try one thing out at a time!!
the motor starts up very well with this pipe so far and it idles very well as well,so fingers crossed on weekend things will go ok or even better still go great,lol,wishful thinking that is!!
my centre bleed is 1/1/4" diamete rout let,the end bleed is another 5 mm more in diameter which im making up a alloy sleeve to go inside to make it also 1/1/4 " diameter!!
thanks
glen

[merc_racer]

hi tim,
thanks also for your great help,much appreciated!!
r.e water is it better to have the water a nice fine spray as appose to a constant stream of water ??
i have fitted a brass 360 degree spray nozzle which the water will go thru.
r.e how much you spray in and how long you let it spray is critical,i thought with water injection pipes it stays on all the time,not just when you want it as i wont have a tap to turn it off thats all!!
cheers
glen

[rude tim]

You need a spray not a stream.
For drag racing you have it start at the hit of the throttle and turn of at a set rpm. for other types you will need a way to activate it by rpm both on and off.

[merc_racer]

You need a spray not a stream.
For drag racing you have it start at the hit of the throttle and turn of at a set rpm. for other types you will need a way to activate it by rpm both on and off.

yes i will have a spray as i have a brass 360 degree nozzle located in top off start of pipe!!
but my westcoast pipe/jet ski's dont have a switch to activate it on or off!!
it sprays the whole time.
thanks.

[merc_racer]

i spoke to a mobile marine mechanic here in oz,and he has knows of some one that has fitted and modified a expansion pipe and he said that the ideal length from manifold to end of bleed of pipe should be approx 1,100 mm long.
well my modded fitted west coast marine pipe is about 900 mm long.
any way im taking the boat for a spin/testing on sunday,new redline race oil and redline synthetic gear box oil as well!!
cheers
glen