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Discussion Starter #1
If I can find a GT I like, I plan to keep the exhaust stock or return it to stock. I like to stay under the radar.

This is a picture of a supposedly stock 2009 GT exhaust system between the transmission fluid pan and the differential. Somehow, the picture got rotated upside down during the upload.



I understand that coming from the exhaust manifolds at the heads, there are downpipes to the catalytic converters alongside the transmission bell housing. Then the pipes go back to a center thing just behind the transmission that has two inlets and two outlets. It would seem that this could function as an H or X pipe plus a muffler or resonation reducer.

Then, there are two elongated bulges in the pipes just behind the center thing. What are these two bulges? They almost look like small catalytic converters or straight through "Bullet" mufflers.

Then I understand that the pipes continue back behind the differential/axle with two more muffler/resonators, one on each side just in front of the exhaust tips.

Are these cars considered to have one muffler and two resonators? Or one resonator and two mufflers? Or three mufflers? And how do the elongated bulges behind the center muffler/resonator figure into the picture?

Thank you for your help.
 

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That first one is the mid muffler. Replacing it with an X-Pipe with everything else stock behind it changes next to nothing. I didn't notice a difference after replacing my mid with the X after the baffles broke loose inside the muffler. It does function as a pulse equalizer.

Right behind there are resonators to cancel out drone that the muffler behind and in front didn't handle. Just your typical (but stock) bottle style resonators. I'm not sure what the internals look like...

The mufflers in the back are huge and are quite good at muffling the sound to "Average Driver" levels.

So it's a mid muffler followed by a resonator on each pipe, and then the rear mufflers to complete the catback.
 

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if 2009.5, add in second set of cats in front of the midmuffler.
 

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Discussion Starter #4
Thank you both for your info.

The reference to the 2009.5 brings up a question I have.

Is there a serial number after which a G8 was a 2009.5?

Or a date or month of manufacture?

The only definitive thing I've seen for the 2009.5's is "all GXP's and other G8's with the cup holders that pull out of the rear seat".

I've seen 2009 G8 GT's on Autotrader with door jamb certification stickers showing manufacture in July, August, and September, 2008. Serial numbers have ranged from 153,117 to 233,364. That's more than the total number of G8's. Apparently, G8's shared a serial number sequence with other Holdens. And I've seen GXP's, definitely 2009.5's, with serial numbers like 311,689, manufacture date 12/08.

So, how can I tell a 2009.5 G8 without looking for the cup holders. The reason I care is that reportedly the 2009.1's do not have blue tooth capability. So getting a 2009.5 would save me having to chase down a compatible blue tooth box.

Thanks again for the exhaust system info.
 

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The rear mufflers for sure do the most amount of noise control, followed next by the single center resonator. The additional bullet style ones are possibly a means to combat the drone due to DOD kickdown, but I don't have a source.

Also FYI, the Bluetooth found in the 09.5 is not for streaming media to the radio, it is solely for hands free phone calls. Not sure if you knew or not, but didn't want that to be the reason you avoided a potentially good car otherwise.
 

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Discussion Starter #6
Thank you, L_Alvis. Yes I've read that the Bluetooth is for phone only. That is my interest. I will use it as my daily driver when running errands by myself, which is 80% of my driving. I wouldn't turn down a good GT for mot having it. I understand that there are a bunch of boxes available now from other GM vehicles that can be used. It would be a plus not to have to chase down and install a salvage yard unit.
 

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Is there a serial number after which a G8 was a 2009.5?

Or a date or month of manufacture?

I've seen GXP's, definitely 2009.5's, with serial numbers like 311,689, manufacture date 12/08.

So, how can I tell a 2009.5 G8 without looking for the cup holders.
The VIN will have 9L3... 3 is the sequence for the mid-year changes.
 

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There are 4 restrictive points in the stock exhaust. First is the inlet to the stock Cats .choked down to 1 3/4". Next is the Mid muffler. On the G8 GT exhaust you see the hot spot on the mid muffler. Its a straight through resonator in the front and the rear with the middle section open to spoil the flow.
Right after that is the crushed pipe to clear the brace under the driveshaft support. Again it chokes down to 1 3/4". The bullet mufflers are no restriction, a smooth perforated bore like a magnaflow. The 4th is the flex joint before the rear muffler. It is the exact same choke as on the stock cats. Again 1 3/4"
Now inside the rear muffler. Flow comes in from the right. first chamber is packed with fiberglass. second chamber is open . All the flow is forced to bleed out the the perforated tube in the middle chamber. I cut that section out in one of my sets of mufflers. It improved flow and tone too
 
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