porting and pipes

[TonyB]

Lozza, in simplified terms what would make a given bike - (eg mine the IT465 barrel), have a long big powerband, it seems to me that there is allways a trade off, more power equals shorter peakier band? Everryone raves about the Maico powerband and yes i had one it was great nice big power from bottom to top without being peaky ( no comments from the maico peanut gallery),  . Also what does the "fatty" pipe do? ie larger diameter fat pipes? Could you port my barrel or modify my exhaust to produce wider bigger power?

[Freakshow]

Arent Fatty short ? as in short and fat ? that would give you very peaky power.  To get a long curve you need long pipes.

[Lozza]

Geez you only ask the hard questions eh Tony
Ok I'll do my best without "boffinating" on and on .
The answer to part A is, part of the equation is the intended use.When the engineers sit down to say "OK the marketing department want the new HGF 125  to cart a fellow backwards and forwards to work, with a milk crate strapped to the back all for under $5 a week in petrol" That dictates the design of the engine the above wouldn't need an R1 engine with an ultra close gearbox.So the IT would have had a similar design brief,there a fairly easily established port/pipe/ignition combinations that fit the IT design brief.However is all dictated by the gearbox, wider 'box=wider power and vice versa.As with the Maico which had 4 sp( ) that had to have a broad spread of power to make the 4 speed work.Similarly a 6 speed 125GP road race 'box is mighty close so the spread of power can be closed up considerably.
More power doesn't necessarily mean peakier power, it is possible to make more HP through the rev range without sacrificing ridabilty. Again it comes down to the gearbox
With pipes in general terms short fat pipes rev hard and make short powerbands, long thin pipes have broad spreads, but the combinations are endless.With off the shelf pipes the fat bit would add some volume but it's more about the tuned length, same length more volume will pump up mid range , fat pipe with shorter length means power shifted up the rev range, the combinations are endless.So are the combinations of port shapes and timings but here the 'trade off' rules.
Of course    

[TonyB]

   thanks lozza I realise its hard to put decades of research into a nutshell, but one of the reasons I asked was I had a 490yz pipe from retro rocket and decided to use that on the 465IT barrel instead of the 465YZ DG pipe I used to use. I tested it tonight on a lonely stretch of industrial estate and the mid range is almost too much , it is hard for me to stop it wheeling as it goes into the band even even in 4th?? ges i even had some clutch slip in 4th which I never ever had,,, but the top end seems to sign off too early. It may have something to do with the fact that I had advanced the timing to the more advanced graduation ahead of the std timing mark, but I am amazed that the pipe works so well on an engine very different to the one intended. I will test with the timing in the normal position to compare with the dg pipe. The retro rocket pipe is noticeably fatter in the middle than the dg pipe.