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Yes the pipe is shorter if done as DB mag describes.  According to their instructions nothing is taken away from the center.  The outer shell that is removed is from the last 1/3 (or so) of the exhaust...from the last weld on the fat part on back. Basically they are saying that there is a pipe within a pipe.  I'm looking at the article right now and it makes sense.  The finished product is 1-2 inches shorter than stock depending on the length of the silencer that is used.  The point was to make the bike profile narrower without the bulky protrusion of the stock pipe and also to make things a bit lighter and improve performance once jetting was adjusted due to the new pipe configuration. I can't be the only person who knows about this mod.  I have to admit I didn't know about it back in the day.  I only discovered it recently while reading the old mag.  If anyone has the Aug. '74 issue of DB...check it out.

Oh yeah...my pipes are '72-'73

O.K....here's some info that may help us figure this out.  Back in the Aug. '74 issue of Dirt Bike mag (page 36) there was an article where they described a mod of the early Penton exhausts. They said it would work on any of the early pipes. They said to grind off the outer shell starting with the last weld which would reveal an inner cone with the perf pipe attached.  You then were to cut off part of the perf pipe and attach a silencer.  The idea was to cut down on weight, narrow the profile and improve performance.  What I am wondering re: my exhaust is whether this was an attempt to do this and they just welded the outer shell back over the attached silencer.  Does any of this ring a bell with anyone?

I have an early Jackpiner exhaust that I want to refurbish.  I removed the end to take out the old packing and found what looked like an actual silencer inside the pipe instead of just the perforated pipe with the packing around it.  Anybody know what this is?  Was this something that was done at some point in time for these exhausts?

Your help will be appreciated!!