Surge Tank Mod, by Ryan

This is a performance improvement that doesn't hurt stock appearance, only the most critical eye can detect this improvement.

Before you begin, order the gasket that goes between the two tank halves, if you are into better performance, the stock throttle bodies can be sent off & bored out, or if you want the maximum performance possible you'll need a set of 1982 -1984 GPZ1100 throttle bodies (the whole rack) and the correct rubber intake manifolds. Another optional item is a compressor bypass valve. Take some time to think about what hardware you want, stainless steel socket head bolts etc.

Once you have all your hardware & surge tank off, remove the Philips head screws around the two halves. You'll have to wedge a thin scraper between the tank halves ruining the gasket in order to separate this. Once open you'll see five rubber air horns, these "horns" come very close to the rear cover plate restricting the air flow. The most minimal improvement would be to cut some off these to shorten them, therefore allowing the air more space to turn entering the throttle bodies. A bigger improvement would be to remove all five of the rubber manifolds from the front tank half, on the outside of this front half of the surge tank you'll notice two risers on either side of each manifold on the outside, these stubs need to be removed from around all the openings. The object here is to make the manifold openings as flat as possible all the way across but still leaving a raised ring around the opening where the manifold fit. I used a large 20" back sander, have to be steady and make sure to hold the tank half flat against the sanding wheel, 36 grit sandpaper can remove aluminium real fast (and fingers). The inlet boost hole was the last opening I sanded flat. While the sander is still going you can sand the rubber manifolds flat also, after you cut off all the air horn. There are other ways to remove these "bosses", risers, stubs. When you are done you should have a ring left around the manifold openings, you don't want a totally flat surge tank on the outside, you want the risers smooth with the hole openings raised thickened area. I found that I had to sand further then I thought, to get a flat ring for the manifold to seal against. A file (Vixen) would work but it would take a while, I read where one guy rubbed his on the driveway cement to get it sanded flat.

The next level is to "port" the manifolds to get the most performance possible. The 1100 throttle bodies are 34mm, it's possible and not too difficult to grind the manifolds open to match these 34mm openings. Mount the four manifolds to the front half of the surge tank. These rubber manifolds have a thick steel flange inside them, sandpaper sanding drums don't last very long trying to "open" these up. It cuts the rubber fast but you'll need a serious one inch carbide Vixen rotary file in a Dotco air grinder or similar tool to get done before the beer warms up ;-) The sanding drums work well on the rubber but not on the steel, the rotary files work well on the steel but not the rubber.........Whatever ends up working for you is ok, just finish up with sanding drums. Every now & then I'd use compressed air to blow the tank clean of sanding dust, fit the 1100 throttle rack onto the manifolds and feel with a finger all around the manifold for areas still needing sanded. You can port the stock inlet manifold but I don't think it will be 34mm when you get done. After I was happy with all the manifolds I removed them and kept them in order so they can be installed to their respective "ported" holes. I then sandblasted both of my tank half's with iron oxide media to help the paint stick better and clean it up like new again. I used Demkote flat black, which isn't that flat and matches most factory black painted parts on motorcycles. I let the paint dry for a few hours then baked the halves in 350 degree heat to cure it. Reinstalling the manifolds I used black RTV (silicone) need to let it cure for 30 min. before installing the manifolds.
If you bought a compressor bypass valve and want to install it yourself, you need to know where it has to mount. Mike Chestnut installs it on the front half of the surge tank right next to the inlet (boost) pipe. It's a tight fit because if you get it too far away from the inlet manifold it will hit the cam chain adjuster. I'll tell you this much, I ended up cutting exactly half way into a stiffener inside the surge tank. I'm a little too far away from the manifold but I'm using the manual cam chain adjuster so I'll have more room then the automatic (stock) adjuster gives you. You use the valves gasket as a template for the holes, bolt holes get tapped into the surge tanks aluminium. The bypass outlet needs to point at an angle towards the left of the bike, I can't describe without showing, I'll say one ear needs to be higher then the other to point the outlet below the inlet pipe. The bottom of the valve should be visually level, but 3/16 inch from the bottom of the tank. So to put it to you like it was put to me...1/4" away from the inlet manifold, 3/16" from the bottom of the tank, one ear should be higher then the other, tap the bolt holes right into the aluminium tank, use the gasket as a template for the holes sizes & locations, use Gasgacinch sealer on the compressor gasket and surge tank gasket.

    

This is for the do-it-yourself kind of guy. If you ever needed to know why people charge so much for this work, now you know, it's not that easy. There are "hidden" problems that can throw a kink in you riding time, if you thought you'd just throw on some 1100 injectors in a half hour and fly over to the local hangout & show the guys your new tune-up, you'll have to choose another day. It's well worth the time to do this but at least know in advance what your dealing with. Sanding the surge tank inlet area for the manifolds would be the most difficult, like I said, a vixen file would work good but take some patience. A bastard file is fine btw, vixen's are coarse and bite into aluminium sometimes leaving a gouge, ouch.

Ryan