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Here are some various things to do with exhausts that I have seen. These are for 94-95 styles but the observations extend to 96-97. Let's call the section of pipe over the wheel the "over" pipe and the muffler is across the back of the truck.
All of the designs remove the last series of bends to the stock muffler and the high restriction in the muffler itself. The stock muffler weighs like 40 lbs or something. Plus, the darn stock muffler was always asking to be smacked into stuff.
Personally I have run 1-3. I noticed no huge gains in power, but it sounds faster now :). I seem to notice a little more power at the higher rpms starting at maybe freeway speeds. I feel that it does breathe better but only at high rpms. I also run a K&N.
John runs #4. After the mod, he didn't notice any big performance gains but obviously likes the new sound. After adding a K&N, he did report a slight performance increase.
The bottom line is that changing the muffler does not result in huge power gains. The stock muffler is very restrictive but does not seem to be a big issue until higher rpms that the diesel does not achieve. I suspect that if we dynoed the changes, we would see a little more hp from more free reving to the higher rpms.
Removing the cat would help but I seriously doubt a huge improvement is possible. Even headers are questionable. Most people who report power improvements via exhaust changes (in a diesel) start with a stock setup that is smaller diamater and with more "kinks". The Hummer is not all that bad. The tubing is pretty large and well bent throughout. I don't think it is possible to gain very much. Turbo motors might gain more. Tim, can we take off your exhaust? :)
Special thanks to John who is running #4 in a 94 Wagon.
IMHO, YMMV, etc.
Gerald (#3 in a 95 opentop)
I just though I'de mention another alternative for an exhaust upgrade. I did one of these for a local owner a month or so ago, after he dented and crushed his factory muffter/tailpipe. I cut the pipe going over the wheel at the point where it becomes horizontal. Here I welded in a high flow glasspack, and exited the pipe straight back through the rear of the body. The exhaust dumps out on the verticle surface to the right of the rear marker light. The noise isn't too noticeable, according to the owner, and he swears he feels a performance increase. Maybee it was just because his wallet was a little lighter and he was therefore lugging around a little less weight :) A friend of his is stopping by in a few days for a similar upgrade. We are considering using a supertrapp located in the same area. These mufflers are about 6 inches thick, and you can vary the note by removing or installing disks. I'll let everyone know how it sounds/looks.
Mark Kincart ran a supertrap across the back of his kind of like where the stock muffler goes. It was pretty loud and he eventually removed it. He even has a 2 door. He didn't really rave about performance increase, just sound "quality".
> Jeff Baudin wrote: > > Those all sound like good options, Gerald. What do you think of the idea > of a controllable cutout? > > I should probably mention that mine is a gas model, unlike yours or > Scott's. Maybe my results would vary?
Gas engines are really loud w/o a muffler, louder than a diesel. I am not sure why but it must be something to do with the combustion process. I don't think the sound would be acceptable inside or out. Plus, I once again question the performance increase from such a drastic mod. Why don't you pull off the over pipe and take a quick spin. You could hear the sound level and get a quick seat of the pants feel for acceleration.
Oh, gas engines are more picky about backpressure than diesels. You don't want to have too little b/c you lose your torque. However, at higher rpms you get more power from the higher flow. Too little back pressure can also burn your exhaust valves but I think the cat might provide enough.
Sorry I can't be more helpful. My last no muffler/cat setup was on a much smaller gas engine.
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