Exhausting question

[aerojack7654]

Hi folks,
Yet another issue to be addressed while bringing my 350 back to life. As I've mentioned in earlier posts, I purchased a race built motor and frame and am trying get it roadworthy. I'm trying to get the exhaust system functional (among many other things). The deal is, the bike came with an exhaust that is pretty beat. This unit, besides being ugly, did not line up properly to allow foot control installation. I cut and re-aligned the header pipe, which worked out as far as re-routing, but now, I've made it uglier (my TIG welding is still a work in progress). Anyway, I'm trying to find a pipe that fits that looks nicer, I ordered a "250, 350 and 450" header from Guzzino and after getting it, found that while my exhaust pipe is effectively a 1 5/8' diameter pipe, the one from Guzzino was approx 1 1/2". I checked back w/ Guzzino and they said that theirs was standard, I must have a larger pipe for the race application. I don't imagine that my head was modded enough to use a different header flange (the thing at the head juncture that the exhaust nut screws down on), mine is 1 5/8" diameter just like the exhaust pipe. Does anyone out there know if this is correct, and if so, where a possible commercial source for a 1 5/8" header pipe might be? I've got some pre-bent tubing parts coming that I could use for welding up a pipe, but as I said, my TIG skills still need work, and my goal for this thing is for it to look good as well as go good...

Thanks!
Jack

[Dave450]

Hi there, I'm guessing you are in the US, but I called Keihin in the UK, which will make you a custom pipe to your specification. I wanted my pipe to be standard diameter but shaped differently because my Desmo has longer rear shocks, so the pipe had to be a little more upswept to maintain the good lines of the machine. They did a superb job. What you would have to do is find a custom pipe builder Stateside and give them some drawings to work from. Or, tack weld something together that gives you the right lines and send it to them as a template. They will bend it to those angles.

One other option you might consider is to find a scrap standard pipe and cut the pipe about 1.5 inch or so from the flange as a stub. The slightly larger diameter pipe you want to use should slip right over the standard diameter stub and it can be held in place with a spring. You just need to weld a loop (or two) onto the pipe to hold the spring(s) and drill out the pre-existing holes in the exhaust gland nut to accommodate the spring(s) at the other end. This would give a race look and a little more flexibility regarding mounting. From experience, I know it also helps preserve your exhaust threads because the vibration from the engine is not transmitted so much to the header pipe and silencer, thereby putting less stress on the exhaust gland nut, which often works loose. It will never work loose using this system.

If you are going to get it back on the road you will have to use a silencer and this will take the edge off the performance of the race motor at the top end. Try the larger diameter pipe and see how you go, but it might be that it won't make much difference with a silencer and you might get a better midrange with the smaller diameter pipe.

[aerojack7654]

Thanks Dave for the suggestions. I've looked into getting a custom bent exhaust at a mandrel bending concern, a little pricey and they want an auto cad drawing which is the bigger deal. I have access to guys that can use the software, but characterizing the shape is a problem - your suggestion about welding up a template is a good one, I can probably handle that.
Your alternative about using a conventional head pipe is also good, especially since I do want to ride this thing on the street. I'll have to mull that over as an alternative. I may have over carburetored the thing with a 32mm mikuni, but in the scheme of things going to a 30mm one won't be that big a deal (having already dropped stupid money in this thing!)

Thanks again for the suggestions

Jack