hydro forming expantion chambers

fred · Post by **fred** » Fri Dec 05, 2008 10:14 pm

ive been welding and mucking about with bikes for 31 years now,i read a article on leon moss years ago in pb magazine ,he worked out the plate development in flat form so when the seams was welded and the fabrication was pressurised with water(a jack but with a water feed)he expanded the plates into the single plane expantion chamber ,then cut and shut it ,downpipes,twist under the engine and ect ect.does anyone have any experience of this,cheers fred

Post by **alimorg** » Sat Dec 06, 2008 1:07 am

Aparently its pretty easy, weld up your 2 halves attach a pressure washer (no need for the pumpy thing from the PB article - was it the TS250 flat tracker?) and hey presto hydroformed chamber - the difficult bit is geting the flat shape correct!
Cheers
AL

JanBros · Post by **JanBros** » Sat Dec 06, 2008 1:07 am

haven't tried it yet, but that's on my "one day when I have the time I'll try this-list"

http://www.eurospares.com/frame8.htm

Post by **alimorg** » Sat Dec 06, 2008 1:29 am

Oh yes forgot to mention - do not leave any air in the pipe or it might explode!

TwoStroke Institute · Post by **TwoStroke Institute** » Sat Dec 06, 2008 5:32 am

A fantastic waste of water, time and steel. A well known fact is stamped and hyroformed pipes lose 3-5% against a good cone pipe of the same dimensions. Hydroforming the header pipe is the only part worth the pain.

fred · Post by **fred** » Sat Dec 06, 2008 7:43 pm

if a true cylindrical cone is best(i understand why ,ish,pulse wave and a equal sort of wave returning back to the exhaust port) why do so many stick to standard kr1s expantion chambers,it would be easier to develop the blanks for cone`s and just roll em. and about the pressure washer pump ,i saw one on you tube done and it looked too fierce and is to much like a switch(on and off),and i recon if you presurise the fabrication slower you might be able to sort any distortion and kinks n ripples with a bit of heat and good old hammering.
my first project on this is ,ease of making and make it lighter,and have a bit of fun learning on the way

TwoStroke Institute · Post by **TwoStroke Institute** » Sat Dec 06, 2008 9:35 pm

No hyrofromed pipe can get the junction between diffuser and belly then belly and baffle cone correct, see above .
Pipes work from changes in cross sectional area(even parralel wall pipes have a reflection), the sharper the change the sharper the response from the pipe.Return wave is never as strong as the exhaust pulse because it's a reflection/echo. I think nobody has put the time in to develop the design for a KR, something that will change in the new year hopefully.

fred · Post by **fred** » Sat Dec 06, 2008 9:41 pm

cheers janbros,that was a good read,like he says ,you can fettle the distortion while forming .
just a quick question ,i decoke my exhausts maybe once a year and repaint them with some ship silencer paint from a old job,i use oxy/acetaline and give it a good bake and then use a airline to clear all the carbon ,But on the standard kr1s exhausts it seems to me that there may be a diverter plate somewhere .

fred · Post by **fred** » Sat Dec 06, 2008 9:47 pm

thanks for your time and information lads,cheers fred

ScottaKR · Post by **ScottaKR** » Sun Dec 07, 2008 12:18 am

TwoStroke Institute wrote: No hyrofromed pipe can get the junction between diffuser and belly then belly and baffle cone correct, see above .
Pipes work from changes in cross sectional area(even parralel wall pipes have a reflection), the sharper the change the sharper the response from the pipe.Return wave is never as strong as the exhaust pulse because it's a reflection/echo. I think nobody has put the time in to develop the design for a KR, something that will change in the new year hopefully.

Thanks for explaining the reasons why Hydroformed pipes are less efficient.
I do have one small correction to make though. JL (Jim Lomas) have put the time in to create better performing pipes for the KR which have been tested by members on back to back dyno runs against both standard and most of the best other aftermarket pipes. Unfortunately, these can cost more than some of us have paid for an entire KR, and besides that, many of us just like faffing around with that sort of stuff.
I must admit though, after reading the article, it seems that it would almost be easier to to make a roller to form the cone shapes from a template then weld them up.

JanBros · Post by **JanBros** » Sun Dec 07, 2008 12:25 am

TwoStroke Institute wrote: Pipes work from changes in cross sectional area(even parralel wall pipes have a reflection), the sharper the change the sharper the response from the pipe.

I totally agree with you on that, but that is only theoreticaly true.

if you follow what you are saying, the best way is to have as sharp changes as possible which finally leeds to a "staircase modell".

downside off that model is that each change only works on it's correspondend rev's , and so the rev's in between the changes will have to do without the benefit off the exhaust.

and we don't want that, so the way to go is make it very smooth so you have proper power all through the rev-range the pipe is designed for.

kr1stars · Post by **kr1stars** » Sun Dec 07, 2008 11:01 am

Just thought I would drop a link in hear and some interestin reading.

For all those interested in making there own pipes there are loads of web sites with info on making cones, ive got loads saved in my fav's so I can go back and use them for referance. As for the software for printing flat cones it will be in the link ive posted below, there are a few links within there but there is a free one if you read through.

From what I have read Software for developing expansion chambers is hit and miss. A good pipe will always look good if entered into the software BUT a pipe developed on the software will not always be good.

Im sure for the KR1 there would be a few people who would put up there cone dimentions of there performance exhausts. Also there are a few clever people out there that can design a pipe from scratch and will work very well, its not that hard to deveate from the original design slightly to get closer to how you want the power curve. Just takes some reading and understanding on what each cone does with relation to dimentions and lenths.

Hear is a link for my findings and a similar post but for the RD.

http://www.yamaha-rd.com/forum/topic-54934.html

Hope this helps.

Just thought I would edit this and drop another link in. This one is very usefull for fabrication.

http://rrracing.co.nz/pipe/index.html

TwoStroke Institute · Post by **TwoStroke Institute** » Mon Dec 08, 2008 4:15 am

OK let's clear up a few misconceptions.
Having made a 100 or so pipes or so I think I am qualified enough to speak on what makes a good and not so good pipe.
Aftermarket manufacturers don't spend hours and hours perfecting a pipe design.They employ a few tricks like a bigger belly,steeper rear cone or smaller stinger diameter to out perform the standard pipe(the process is explained in Eric Gorr's book).The rest is getting them to market as fast as possible,looking good/clearence and making sure the pipe comes out fitting on the bike perfect from the jig.Otherwise they go broke very quickly.
Software hit and miss? Well if you call dyno print outs shape and outputs corresponding to the simulated curves(but down 2-3HP due one a rear wheel and the sim a crank figure) 'hit and miss' then you might care to explain what is .
Software for pipes is like any other software ie $hit in= $hit out. However software will let you examine something that can't be seen the 'pressure time history' of the engine. Examining and making educted changes to optimise the pressure/time history allows a optimised ignition/carb/port/comp/pipe combination, works spot on every time.
It also helps to know what to look for in a sim also.
Sorry Jan but cone pipes with distinct and defined ends to each section consistently out perform 'smooth' stamped or hydroformed pipes of the same dimensions.Dimensional accuracy is difficult also with hydro forming.

Sheik Yerbouti · Post by **Sheik Yerbouti** » Mon Dec 08, 2008 10:13 am

For what it's worth (as in bugger all) I'm with twostroke Institute on this, I've only built a couple of pipes, but hydroforming is only any good for mass production, to get the pipe right you always need to fiddle with lengths, angles etc.
Good info in a book called "two stroke performance tuning" by A Graham Bell. Good starting point info on all things smoky and peaky

EDIT:

Just checked the link above showing techniques and pics. They were only making a "look pretty" megaphone for a 4 stroke. And it looks about as dodgey and dangerous as anything I've seen. Real pressure forming is done in two halves. A solid steel core (or cavity) is made, the shape of the inside of the wanted pipe half, it is covered with a flexable diaphram and hydraulic pressure is applied to force the steel over the core. (or cavity)

Post by **alimorg** » Mon Dec 08, 2008 10:30 am

Wow - I never knew we had so many clever people on here, makes me feel quite thick!
Cheers
AL