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Katana Header Flow & Grinding Page:

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   This page started as a small how-to by Trinc (Tim) and has been modified by The CyberPoet to show more information and images. Enjoy!

The Sloppy Weld Problem

   Stock Katana (GSXF - GSX600F, GSX750F, etc) headers are mig welded on the inside of the header port of the exhaust header. This welding process is manual and often leaves undesirable amounts of weld build-up in the port:

Stock Katana GSXF Header with typical factory weld seam exposed
  I have no reason not believe that this same thing is true of most Suzuki headers, including those for Bandits, Hayabusa, V-Strom, SV650, etc., as well as possibly being true for other brands of motorcycles as well. Personally, I'd take a look at those seams, whatever type of bike you have.

Understanding the Quest For More Flow

  The more restriction in the exhaust passages, the higher the low-end torque will be (in part because it helps close the exhaust valves earlier). The larger the area, the less low-end torque there will be, but the more high-end HP you will net (because the chambers can flow their exhaust out better at very high speeds, where blockages and uneven flow mean interference).
  After-market headers generally add approximately 32% - 40% cross-sectional area to the header down pipe compared to the stock headers, which can drop the low-end torque heavily, but greatly increases high-end through-put. Unfortunately, this much change in exhaust flow also normally requires serious rejetting to match, and for most street riders who aren't constantly pushing it, the loss of low-end torque may be undesirable. Trinc and I both went looking for a compromise. We found a few solutions for our 98+ Katana's:
(Option 1) Remove the excess header weld seams. Depending on the amount of excess, this can increase flow by anything from 8% - 15% easily, while smoothing the exhaust flow path to remove undesirable turbulence right at the start of the header.
(Option 2) For the Kat 600's, replace the stock header with the stock header from the Kat 750's. The cross-sectional area difference between the down-tubes on the headers are approximately 23% larger (although to be fair, the port-flange and collector-to-midpipe size remain the same, so the amount of change in flow is smaller than the 23% difference might imply -- but it also means that it will bolt right up in exactly the same fitment). I suspect the oil-cooled GSXR 1100 and Katana 1100 headers might provide the same kind of size upgrade for the Kat 750's, but without measuring them, I can't tell you definitively.
(Option 3) Combine both options, placing the 750 stock header on the Kat 600 engine after grinding down the 750 header weld seams. This gave us the best of both worlds -- more flow, but without losing too much of the low-end torque or the need for heavy customized rejetting (some minor rejetting or use of a jet kit is still recommended; I'll get back to this later).

Removal Made Easy

  The idea is to remove as much of the excess weld as possible without removing so much of the weld as to make the part no longer welded into place securely. Since good welds penetrate down into the metal they are holding by a significant distance, you should be able to grind out the weld to flush or almost flush without significantly compromising the strength of the weld to the point that it becomes an issue (figure a normal industrial mig weld is at least 50,000 lbs strong per linear inch). What we intend to remove:

The amount of the weld seam on a GSX600F GSX750F header weld seam we want to remove.


  • Dremel or other rotary grinding tool.
  • Sand barrel drum attachment for the above with both course and medium/fine grit sandpaper barrels (several of each; you'll need at least four 60 grit drums or six-seven 80 grit ones to start):
    Dremel sanding drum attachment used as step 1 of sanding out the Katana header weld seams.

  • Aluminum oxide (pink) grinding stone (dremel attachment 8215, or equivalent -- medium/hard grit stone for steel use) stone grinding attachment for the dremel or rotary grinding tool:
    Dremel Aluminum Oxide grinding attachment #8215

  • Gray (dremel 425 emery-impregnated disk, or equivalent -- fine, for metal polishing use) stone grinding attachment for the dremel or rotary grinding tool
    Dremel Emory grinding attachment #425

  • Safety Glasses, shop glasses or other eye protection (we're talking about fine metal bits being flung out at speed)
  • Paper filtration mask or at least a fine-weave cloth bandana over nose & mouth (lots of dust that will go into your nose & lungs otherwise and be coming up for days).
  • High Temp Anti-seize paste (used during reinstallation)
  • Replacement mid-pipe gasket if the old one is damaged or becomes damaged during disassembly of the mid-pipe to collector. Replacement header port gaskets if desired or missing (these don't normally get damaged during the process because they sit down inside the engine's header port area and never get touched).
  • Allen-key for header bolts PLUS a pair of vice grips. An impact driver and/or MAPP gas/propane torch & Kroil or PowerBlaster or other penetrating oil may be needed if the bolts are rusted or seized.
  • Torque wrench and allen key socket attachment for the header bolts.
  • Optional Alternatives to dremel or rotory grinding tool: Set of metal-use bastard hand files, some sand paper & lots of manual work.

Standard Disclaimer: Although these instructions are generally complete and do include warnings of obvious pitfalls you might encounter, we are not responsible for any work you choose to undertake on your own, any issues, injuries, mechanical failures, breakage or other issues which might in any way connote liability on our part. This page is for informational purposes only and by reading onward, you agree to hold anyone involved in writing, posting, hosting or otherwise being involved in the creation, sharing and delivery of this information to you or persons you may pass the information onto absolutely free of any liability for any actions which you undertake. In other words, if you do something stupid and hurt yourself by trying to follow these instructions without adequate protection, equipment or know-how, you are solely responsible for all consequences. Sad state of affairs that I have to mention this at all.

  • Remove belly pan if installed on motorcycle, as if you were doing an oil change. Collect all the bolts in a zip-lock bag so they can't get misplaced.
  • Unbolt header flange bolts where the header meets the block. Collect them up in a zip-lock bag so you don't misplace them. If the bolts provide any serious resistance to turning, don't strip out the allen head -- instead you can try these tricks in order:
      (A) Using a pair of vice grips, grasp the outside of the bolt head and try turning using a bit more force. If this doesn't work, stop and use the next trick instead (don't shear the bolt off!);
      (B) Take an impact driver ($9 - $30 at any auto parts store & through HarborFreight), every Katana rider who does their own work should have one), set it to "tighten" (clockwise) and smack it lightly with a hammer a couple times (this should break the bolt's threads free of any corrosion). Then set it to "loosen" (counter-clockwise) and smack it as hard as you can. This should start the bolt backing out. If it just starts to eat up the allen head on the bolt, go to the next step instead.
      (C) Remove any fairings that might be affected by the hot air rising off the flame. Take the torch and light it. Place the hot spot of the torch onto the bolt or directly next to it and heat for approximately 15 - 20 seconds, then remove the heat. Allow to cool some (5 minutes?) then douse with WD-40 or other penetrating oil. The heat should expand the bolt, then contract it when doused, pulling the penetrating oil into the threads. Doesn't always work, can be done repeatedly. Use trick A or B again after doing this a couple times.
      (D) If you do snap or shear off the bolt, you're going to need to use a bolt extractor after the heads are out of the way. It's a PIA and the reason I recommend everyone coat their header bolts with high-temp anti-seize when they first acquire their bike, as well as any time you drop the headers.
  • Optional but recommended: loosen the bolt for the clamp at the mid-pipe to collector junction as far as possible.
  • Having removed all the header bolts, place something soft under the exhaust system (cloth, piece of carpeting, old sweat shirts, etc), especially if you are removing it by yourself (an extra person at this instant is useful). Remove the bolts supporting the muffler and midpipe, then preferably with one person on each end of the exhaust, move the exhaust forward by about 1/2 inch and bring it down to the ground.
  • It's a lot easier to grind out the weld seams if you're holding the header without the midpipe and exhaust can attached (you're also far less likely to scratch up the can & mid-pipe). This is why you loosened the clamp bolt two steps ago. Have one person hold the muffler or midpipe and rotate one way while you grab the header and rotate the other. This should break any seizing or rust in the connection between the header and mid-pipe. Now rotate and forth while pulling the two parts apart to separate the header from the mid-pipe.
  • Now it's time to play dress-up. Put on an old long-sleeve T-shirt or work shirt, slap on your protective eye wear, and the particle mask. The dremel is going to be spitting out a ton of very fine metal powder that will inevitably want to seek out your delicate bits and invade them.
  • Starting with barrel sander attachment with the course sand paper and have at the weld seams:
    Dremel sanding drum attachment used as step 1 of sanding out the Katana header weld seams.

  • Stick your finger down the exhaust header tube and feel for any weld slag that may have splattered on the inside of the tube at time of welding. Grind those bumps off as well, if you can reach them readily.
  • Repeat for every header weld seam until you have them down to within 3/4 mm (say about 1/8th to 1/16th of an inch) of the height of the metal tube under the welds. You may well have to replace the sand paper several times during this step, as the grit wears away.
  • Switch to the finer grit sand paper and repeat, taking down half of the remaining height, give or take. Again, you may well have to replace the sand paper several times during this step, as the grit wears away.
  • Now switch to the pink stone attachment (Dremel 8215 or equivalent) and go down to virtually flush.
    Dremel Aluminum Oxide grinding attachment #8215

    Caution: the dust spit out by this attachment (or any other, but particularly this one) can be red-hot and may burn bare skin, carpeting or flammable clothing.
  • Finally, move to the grey emery attachment (Dremel 425 or equivalent) and buff out the remainder to a smooth mirror-like finish. This final step is just to smoothly polish the grinds which should already be very smooth in general.
    Dremel Emory grinding attachment #425

    At this point, when you run your finger over the result, there should be no sharp edges that you can feel and the surface should feel like a smoothly flowing polished surface.
    Katana GSXF Exhaust header after sanding & grind out the excess weld seams.



  • Do not remove the weld past the surface of the metal, or you can significantly weaken the weld. Leaving a slight build-up is fine if you want to err on the side of caution, although if the piece was welded correctly, you should be able to grind it down to flush or just a hair's width above flush.
  • Particles being ground away by any attachment may be hot enough to burn skin or flammable surfaces, and may enter your eyes, nose, mouth, lungs or other body openings. Be wise about protecting yourself, use appropriate safety gear, and do not grind over carpet or other flammable surfaces.
  • This entire grinding procedure will generate a large amount of very fine metal particles (fine metal dust), many of which will be airborne and float all over. As a result, the grinding should only be done outside of common living areas (outdoors is preferred). Do not do this in your living room, kitchen, bathroom, bedroom, nor any place normally inhabited by pets, humans or used for food preparation. Use ventilation as necessary. An extension cord and a seat out in the lawn or driveway is a good place to do it.

  • Time to prepare for remounting. Examine the mid-pipe gasket to ensure it's not damaged (if damaged, replace). WileyCo mufflers bought off eBay will generally not have a mid-pipe gasket. Get the high-temp anti-seize and smear it lightly on the inside of the collector gasket if you separated the header from the mid-pipe (this will make rejoining the midpipe easier later, although it will smoke for a few minutes when you fire up the bike as a result).
  • Check the header port gaskets with your finger to ensure they are all in place and flush/smooth (should not have any sharp little wires sticking up). Replace as necessary. These normally do not require any attention during this operation.
  • Get the header bolts back out (replacing any that have gotten mangled in the process). Many Ace Hardware stores carry stainless-coated replacements in the same metric size and length at about $2 each, and it's a small upgrade that may be worthwhile to you, especially if you mangled any of the bolts. Smear the threads of the bolts with the high-temp anti-seize compound:
    Suzuki Katana GSXF header bolt with anti-seize applied before reinstallation.

  • Now there are two choices: you can reattach the midpipe at this point, or you can install the header by itself first. I tend to reassemble them both if I've got someone around who can give me a hand lifting the whole exhaust into place while I bolt it up, and install just the header by itself if I'm working alone. So do these steps in whichever order is best for you:
    • Coat the lips of the metal of the header that will contact the engine with a light coat of high-temp anti-seize (or exhaust gas sealer permatex compound 1372 -- see factory service manual for details on use of this product). Yes, the anti-seize may smoke for a few minutes after starting the engine, but what gets left behind will help ensure these pieces never bind permanently. Lift the header into place, and ensure that the engine-side of the header ends sit down into the engine holes for them. If fit correctly, they should fit into a slight recess in the engine's exhaust ports. Bring the clamps for the header up to the top of each pipe and start the bolts in by hand, turning each of them at least two full turns by hand. Do not force them; they should turn with virtually no resistance if the threads are mating correctly at this point. Get all the header bolts started before going to the next step. Examine the header to make sure it's mounted flush into the block. Now using the torque wrench, install the bolts to 16.5 lb-ft (2.3 kg-m). The factory manual calls for using exhaust gas gasket sealer permatex compound 1372, but I never do (perhaps you should).
    • Reassemble the mid-pipe and muffler to the collector end of the exhaust header, rotating slightly as you seat it into place and taking care not to damage the exhaust gasket in the collector area. Rotate into final alignment. If installing the complete exhaust with header, get the header flush into place and have whoever is holding up the muffler/midpipe start hand-threading the muffler & midpipe exhaust support bolts (at least 2 full turns) before inserting the header bolts at the engine. If installing the header by itself first, install these bolts after installing the muffler into the midpipe. After torquing the header bolts to spec, torque the muffler and pipe support bolts to spec (21 lb-ft, 2.9 kg-m)

  • Fire it up and check for exhaust leaks. Address any exhaust leaks before riding.
  • Reinstall the belly pan.


   Having opened up the exhaust flow some, engines which were set particularly lean may be pushed into a "too lean" condition. This will be noticeable by difficulties starting after this modification, and possible after-fires (exhaust popping) during deceleration or starting. To correct for this, there are two basic options:
(Option 1): [use with the stock OEM jetting if needed:] Modify the existing jetting by increasing the turns outward on the pilot screws for each carb by one-eighth to one-quarter of a turn (be consistent on all of them), plus adding an 1/2 height shim under each diaphram needle. See Jet kit installation guide to help understand what I am talking about here.
(Option 2): [use in place of the stock OEM jetting for additional power:] Install an aftermarket jet kit to improve fuel delivery and increase engine power. For the 98+ Katana's, I recommend specifically using the Ivan's Jet kits. For the 1988-1997 Katanas, I recommend the FactoryPro brand Jet kits. These recommendations for the 98+ models are based on personal experiences comparing the Ivan's and DynoJet (sometimes sold under the K&N brand name) jet kits directly to each other. For a general installation guide to jet kits on the Katana, see Jet kit installation guide.

=-= The CyberPoet
Owner of


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