Restrictive Stock Exhaust

8 replies to this topic
  • RipperFox

Posted March 30, 2008 - 09:46 PM


Was thinkin':crazy: What is it exactly about the stock pipe that is so restrictive? Can it be modified to significatly improve it? I have spent my total authorized(wife) allowance on my "blood sucker" (I now know why honda is red). Sooo...A $400 pipe is months in the future.:prof:

  • Purcell69

Posted March 31, 2008 - 02:03 AM


Ripper, if you want to improve flow on the cheap, pull the headpipe off and have a look inside where the flange mates with the head. The weld around the inside where the tubes are mated to the flange rings is pretty restrictive. It is very common to take a dremel tool to the welds and grind them down. Leave yourself about a 1mm tall lip for exhaust backpressure. I have read a post either here or on 4strokes that the weld, as delivered, restricts the exhaust by about 6%. That doesn't sound like much but it is free horsepower if your are willing to spend an hour with the grinder. I did mine when I did the Dynojet kit. I think the 4strokes site had pics.

The other big restriction and unnecessary weight is the stock muffler. The opening at the back is small compared to aftermarket slip-ons. There are some who have cut the weld at the rear cap and removed the baffle. I have read that it doesn't do much other than change the sound. Also you still have the added weight of the steel muffler.

I'm in the same boat. I can't spend any more green for a while, so the stock pipe will stay a while longer.


  • Huffa 2

Posted March 31, 2008 - 03:15 AM


There is a XR 650L super trapp muffler system on ebay right now, needs some cleaning up and has a few minor dents on the part you don't see but it's still totally useable, bet that goes for pretty cheap!

You don't have to spend even close to 400 if you buy used, about 1/2 that for a nice muffler system, that's what I did anyway.

  • Purcell69

Posted March 31, 2008 - 04:34 PM


Ripper, here is the link from the other site, complete with pics. It was originally listed as an XR400 mod, but applied to the XR650L as well.



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  • cleonard

Posted March 31, 2008 - 09:10 PM


The worst part of the stock system, is the baffle with the tiny dime sized hole. There used to be some aftermarket baffles that flowed a lot better. Still relatively quiet.

  • Donkk

Posted October 05, 2008 - 08:01 AM


The worst part of the stock system, is the baffle with the tiny dime sized hole. There used to be some aftermarket baffles that flowed a lot better. Still relatively quiet.

Where would one fine these aftermarket baffles?

I always grease the muffler bearings to prevent the dreaded- bipolar transitional phase lock:bonk:

  • Kenzo

Posted October 05, 2008 - 09:07 AM


IMO the stock headpipe ain't that bad it is just a design that helps the bottom end...without bumping the compression and/or a cam upgrade an aftermarket header doesn't get u much over the stocker...that being said a free-flowing exhaust and grinding the welds does improve flow and power with the stock headpipe...but some say u'll lose bottom-end if u grind the welds with the stock exhaust.

now the stock exhaust/muffler is designed for one thing, noise reduction. compare it to a free-flowing exhaust even totally gutted it's not designed/shaped to flow well plus it's a pig weight-wise.

i'm running a supertrapp race with the constant diameter mid-pipe, 11 or 12 disks and have been quite only worry is noise when i want to ride in the national forrest or other area with sound level regulations...time will tell.

i don't plan on buying a header until camming and/or bumping the compression :lame: ...unless some smoking deal comes along :lol:


  • Horri

Posted October 05, 2008 - 12:01 PM


Spending huge dollars on all the associated new bits for bikes is fine an dandy if you have the cash. If you haven't you make do by buying used and adapting it for the purpose..My example would be my 86 600 where I grabbed a used Pro-Circuit T4 from a 250 CR , got a few bits of piping from an exhaust shops bin with the appropriate angles..cut them to the lengths and attached them and the muffler to the bike,,no welding needed..It's loudish but nothing a bit more packing won't solve.It's called DIY,,Do it yourself,, and in these financial times is the way to go..In saying that the 86 600 headers end in a one pipe attachment from the header to muffler section which makes the job sightly simpler than in the twin pipe header to muffler setup on the more modern 600's/650's..but in that case all you do is get the headers from the earlier model and use them,,thus simplifying the task.

  • Kenzo

Posted October 07, 2008 - 09:38 AM


i don't plan on buying a header until camming and/or bumping the compression :lame: ...unless some smoking deal comes along :lol:

welllllllll...looks like i'm going to be adding the HotCam soon...just picked up a FMF header with heat shield off FleaBay for $160...


P.S. was the seller one of u guys???

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