I have...and recommend the 788500S...it's the stainless steel version of the longest of their "superflow" mufflers. Reasons for this particular muffler:
- The stainless version is made from slighly heavier gauge steel. So, in addition to being much longer lasting than the aluminized version, it's much less likely to produce the dreaded 2k drone.
- Gibson mufflers work like no other aftermarket muffler. Basically there's a perforated tube running the entire length of the muffler case that's attached to the inlet pipe; a 2nd perforated tube running parallel to the inlet tube is connected to the muffler outlet. The perforations on the inlet tube are not just holes but more like scalloped "scrapers" such as you find on on a cheese grater...and are pointed toward the inlet to essentially scrape the incoming gas out of the tube while simultaneously breaking up the sound waves. The outlet tube has similar "grater" type holes except these are aimed toward the outlet and (1) further break up the sound waves while (2) producing a laminar flow in the outlet. There are no chambers per se (the entire muffler cannister is a single chamber) and there is no sound absorbing material like fiberglass. The muffler muffles sound by fracturing the the sound waves through the graters and causing the gasses to cross between the two tubes. Because the gas transfer effectiveness between the tubes is related to tube length, the longest case (24 inches) that Gibson makes has (1)the least backpressure and (2) is also the quietest.
The net effect of this unique construction is the muffler has a soft rumble at small throttle openings when the RPM is below 1200 (basically just a bit louder than stock). Between 1200 and about 2000 RPM at small to moderate throttle openings, it makes a sort of growl (not a distinct rumble) that is definitely louder than stock but still much quieter than any other aftermarket muffler. At RPMs over 2000 or at high throttle openings, it just makes a "whoosh" that's a tad louder than the stock "whoosh" but has no rumble or growl effects at all. It is
not a muffler for someone who either wants the nearly complete silence of the stock system nor the characteristic "V8 sound" of most aftermarket mufflers. But though detectably louder than stock (especially between 1200 and 2000 RPM), it's still quite bearable for extended periods of towing...and that's coming from a guy who has both sensitive hearing and very little tolerance for noise.
Yes, muffler
only and for two reasons.
First, low end torque will be best maintained if you keep as much as possible of the OEM 2 3/8 inch pipe. Like most aftermarket "catback systems", the Gibson Single Sideswept system uses slightly larger 2 1/2 inch pipe. Larger pipe...even that 1/8 inch...reduces low end torque.
Second, I strongly suspect that the dreaded 2K drone is minimized if you keep the OEM 2 3/8 pipe. I have a bit of that drone but it's not obtrusive at all. Comparing the reports from those who installed the complete bolt-on Gibson SS "system" with those of us who simply replaced the muffler, my impression is those with the "system" and its 2 1/2 inch pipe are far more likely to complain about 2k drone.
There's a donut connector just behind resonator on the stock system where the stock muffler can be disconnected. The shop that did my install (1) cut the OEM pipe just behind the stock muffler and (2) disconnected the stock muffler at the donut connector. They then welded the rear of Gibson to the remaining pipe and welded in approximately 10 inches of 2 1/2 pipe between the front of the Gibson and the donut connector (the stub pipe was welded here as well). I won't be able to readily go back to the stock muffler but have zero interest in doing so either.
Final notes: Unlike most people, I installed the JBA headers first...before changing the muffler. I was working from the concept that the stock manifold is the largest restriction in the exhaust system. So I can't speak to any increase in sound of using the this muffler with or without headers but suspect it won't be much. I can definitely state that you will
not (as Ken notes in his report) get much, if any, torque increase until you have headers installed...for the very reason that the OEM muffler is muchly secondary to the OEM manifold in terms of restriction.
That all being said, I definitely noticed a torque increase from installing the muffler in addition to the JBAs...the gain was somewhere around half the gain of the JBAs by themselves. And even better, the muffler had the unexpected effect of lowering the peak torque RPM by about 100~200 RPM: my engine is now making peak torque at 3200 RPM and the point at which the torque increase from the headers starts is closer to 2500 RPM than the 2700 it was before the muffler. And, of course, the lower the RPM that peak torque is obtained, the better for towing.
The bottom line is that Gibson muffler + JBA headers is a very good combo for towing.