Advice on building a 4 into 1 exhaust

[stucknarut]

I've got an old rusty spare exhaust set for my 750. How hard would it be to chop it up, adjust length as needed, buy a 4 into 1 formed collector and bullet, and put it back together? My father's a pretty good welder but neither of us have built an exhaust. At worst I waste the $30-40 for a collector and the rusty as hell exhaust. At best I build a custom exhaust, which would be pretty cool. Anyone ever try this and have advice?

[Big T]

You can do that, but how well it will work is open to question

Gas flow, volumetric efficiency, header length - the parameters of the designs are set by engineers

[verde]

Are the old exhaust parts you have double walled? You'd be bumping up to the diameter of the outer pipe I'm guessing. Here's a good base line idea of lengths and diameters to shoot for. You may also want to consider a tri-Y set up depending on use, and take note what they say there about pairing 1-4 and 2-3 together:

http://www.mez.co.uk/mezporting/exhaust_length.html

I haven't done much legitimate exhaust work, but one trick I have used is pipe clamps to hold pieces together for tacking (harder with MIG than TIG to not mess up your clamp). Example from here, note the holes for tack welding:

[stucknarut]

Are the old exhaust parts you have double walled? You'd be bumping up to the diameter of the outer pipe I'm guessing. Here's a good base line idea of lengths and diameters to shoot for. You may also want to consider a tri-Y set up depending on use, and take note what they say there about pairing 1-4 and 2-3 together:

http://www.mez.co.uk/mezporting/exhaust_length.html

I haven't done much legitimate exhaust work, but one trick I have used is pipe clamps to hold pieces together for tacking (harder with MIG than TIG to not mess up your clamp). Example from here, note the holes for tack welding:

Thanks, appreciate the link, the pic (good idea there) and the info for inline fours. I noticed that the commercial 4-to-1 exhausts all have 1+4 and 2+3 paired on the same side of the collector, wonder if that makes a different when all share the same collector. I hadn't thought about 4-2-1 setups, might be more complicated than I want to make it for now.