Designing and manufacturing of exhaust pipes

[diesel pig]

Is it really important that header pipe is cirkular?
Exhaust leaving cylinder during blow down time is very rectangular.
Pressure in exhaust systems does not exeed 2 bar absolute.
To my eyes it can be made of four very funny shaped pieces of steel edge welded together and then blown with water.

Well history tells us flat sided two stroke exhausts do not handle the pressures present in a two stroke exhaust very well at all. The first TZ750s with all four pipes under the bike had flat sides so they would all fit, in the first Daytona 200 they raced in almost all of them cracked before the end of the race.

[Hemi Makutu]

AFAIR, header pipe is important to flow - in being shaped regular section/smooth internally/focussed into exhaust nozzle..

Dents, weld spatter-lumps adhering, irregularities & what-not in the fat section do not matter so much..
..this factor was tested by dyno - on dirt bikes.. .. if interested, maybe check 'motocross action mag' site?

[Hemi Makutu]

http://www.amsnow.com/how-to-tech/20...oo-inside-look

Latest hi-po 850 twin, uses 2-into-1 with header making geometric/conformal change from port to junction.

[Hemi Makutu]

http://l3s9113.zeus09.de/RD350/Auspu...2_englisch.pdf

The bloke credits a couple of the 'brains trust' regulars here too, as it happens.

[aljaxon]

http://l3s9113.zeus09.de/RD350/Auspu...2_englisch.pdf

The bloke credits a couple of the 'brains trust' regulars here too, as it happens.

i know this is an old post but i have been making my own pipes since 2012 for my rd350A and lately for 50 and 70cc mopeds. i just wondered if anyone can recommend good cheap software? at first i used Blairs calcs in his book and since then tried FOS, and 2t calc. the pipes work well but only just compare to universal off the shelf pipes such as doppler streetcups. yet i am inputting precise info. i can now tig weld a pipe and it has zero leaks. i can roll them so there are no gaps. i get my cones dxf files cut by a local laser company.
with me baing a diy hobbyist i cannot justify forking out for $400 software. plus the cylinders im using are poorly designed with little scope for improvement in various areas so any simulation software would be bigging them up too much and i'd get an inflated simulation and skewed output for any pipe.

a pal showed me torqsoft which has a handy header angle altering facility almost real time changes the angle at part of the downpipe saving me hours doing it with autocad and a calculator.

has anyone used torqsoft pipe designer? or any other software?
cheers