It is all 65mm diameter polished stainless steel piping, muffler, and tips. All the welds are beautiful; HKS uses a special computerized pulsing welder that makes the welds look better than a stack of dimes. It follows the same path/configuration as the stock exhaust and it replaces the mid-pipe and rear sections. The Y-pipe remains stock. It has a 4 year warranty against manufacturer’s defects. I think it says a lot that they stand behind the products for that long and I don’t think you have to worry about them going anywhere since they have been around for 35 years! The retail price is $1225.00

It sounds great and is on the conservative side. Sound is hard to describe but my impressions are that over the whole RPM range the HKS system is louder than stock, but does not have as much peak "bark" at 3500, where the stock is loudest. It is more of an even increase throughout the range. Over all it sounds good and definitely has a tuned sound. That being said, it is no more intrusive vs. the stock, no buzzing or vibrations inside. For those of you who want a nice tuned sound but still want a system as unintrusive as stock this is an excellent choice! They achieve this by using a new packing/sound deadening material called Advantex. It keeps the system quieter while also providing more durability. A lot of systems get louder over time, this will to hold up better. Part of the reason why is that most packing materials consists of small pieces while the Advantex is one large piece so it can’t get blown out easily. I did note that after a short break in time it got a bit deeper probably from heat cycling it a few times. When I went on a factory tour a few Tokyo Auto Salons ago I also noted that most HKS systems use a special mesh around the perforated pipe on the interior of the muffler to keep packing from getting blown out over time. My opinion is that sound wise it’s probably a great starting point, you’ll be happy with the subtle tuned sound alone, and later if you plan to change Y-pipe and/or cats and/or headers it probably won’t be outrageously loud.

They test fitted the first article on my car and it Dyno'd at about 7.5 at the wheels. This is an average gain. Like most responsible companies HKS gave me a dyno chart that showed the average gains of 6 pulls. There were other pulls that showed more peak power but they prefer to show a realistic representation of the product rather than throw up an inflated #, you get in trouble that way. When I made the original post on G35Driver I was actually told verbally by them it was a 5-6 hp increase. After getting the chart you can see peak is actually about 7.5 at the wheels peak, so again they were being conservative.

One thing to be aware of is the picture on the HKS website for the RX8 is not an accurate representation of the G version. The G version has similar quality piping and muffler but the tips are a rolled edge oval type, not round like stock or the RX8 picture. The tip style is called "Da Moda" and measures 115mm wide x 70mm tall. They also have the "HKS" logo laser etched on top. It has more of a subtle look, not huge coffee can style. I think it flows well with the shape of the tail lights. Here is my link to Sony Image station showing 5 pictures and 1 dyno pull. I hope this helps!
Link To Pictures