I'm in the process of building a 4-2-1 exhaust system for my Blackbird powered 7.
Pictures I've seen show the 4-2 section pairing as 1&2 and 3&4 but as 1&4 are on the same coil as is 2&3 I would have thought that the pairing should be 1&4 and 2&3.
Does anyone know what's best?
I'm using a 38mm primary then 42mm for the 2-1 bit

1 with 4 and 2 with 3 is obviously beter, since these cylinders are oposite in the cycle and fire at constant intervals.
Optimizing exhaust consists of using the acoustic wave of one cylinder to trim the pressure at exhaust valve, when open, to optimize the filling of the oposite cylinder.
To fullfill this, you must know the exhaust gaz temperature curve along the pipe to calculate the propagation speed of the pressure waves (the sound speed) and find the wavelenght.
The ideal figure can be achieved only for a particular revs, up to you to chose to increase peak power, peak torque, peak efficiency, torque curve shape etc.
I know only book in french about this, but I'm sure there's plenty of english information.

4&1 and 2&3 joined is supposed to be the way to go in the theory but I have only read it.

Phelpsa on here has a gsxr1100 with them 1&2 and 3&4, his exhaust was made by the same guy that made my exhaust for my gsxr1100 and he made that one 1&4 and 2&3. Phelpsa (Adam) has power figures from dyno, I don't (although our engines are different so we couldn't usefully compare). It is certainly complicated, and that guy only makes exhausts so one would guess that he knows something about all this stuff.

One practical option would be to find the most expensive/best exhaust that is available for the bike (Yoshimura in the case of Suzuki's) and duplicate that design.

Matt

Thanks for the info

I was going to copy the exhaust that I had pictures of - A Westfield Megabird with a very expensive looking exhaust system, but that has 1&2 and 3&4 paired which I am now convinced is not the correct way to do things.

I will be proceeding with 1&4 and 2&3 keeping all the lengths as even as I can and closest to a length I have written down somewhere which is supposed to be good for low-middle range torque

David

I my be wrong here, but do check the firing order. It may be different to normal?
Plus I would use the dimensions that the factory used. Their research is going to be much better than guessing.....Unless you have the proper calculations or figures from a rolling road. "looking" right does not usually work with exhausts.

these guys thing 1&2 and 3&4 for the cbr1100xx

http://www.carpimoto.it/Images/Products/Pdf/HO_CBR1100XX_04-Sport.pdf

and they could have connected them either way.

Once more proving that it is more complicated than you might think.

Matt