I have yet to see an assessment of a full G8 GT exhaust system, head to toe. Has anyone else? I'm wanting to see where the restrictions are.

Exactly how many mufflers does the G8 have? What do they look like on the inside? What might benefit from replacement?

I've seen a couple of pics of the final muffler (axle-back as it has been called) and this is certainly one source of restriction. What/where are the others?

Please post here if you have knowledge, links, etc. I'd like to assemble of the data here in one thread, perhaps to be made a sticky of later.

The piping on the exhaust is restrictive. LOL Would have really liked to have seen 2.5" throughout. I didn't see the resonator's inside but I am sure getting rid of it and adding an x or h pipe helps.

The middle oval resonator is straight thru, 2 pipes in/out with perfs. SF has the setup. Adds H pipe and less restrictive mufflers at rear. Sounds mighty fine too.

The middle oval resonator is straight thru, 2 pipes in/out with perfs. SF has the setup. Adds H pipe and less restrictive mufflers at rear. Sounds mighty fine too.

Dude! What are you doing? This was the perfect time to push the $66 exhaust mod! :thumbsup:

Sorry couldn't help myself. :gr_jest:

I thought I heard the pipes were pretty good, just the muffs were real restrictive. Mandrel bent from the factory correct?

Mandrel bent from the factory correct?
Stolen Fox could answer this for sure, but from what I've seen from under my car, and pictures others have posted, they do look mandrel-bent. It actually looks like a well-done exhaust.

Even the cast iron headers look nice, although they are not equal length.

I wish to hear more exhaust note but don't want it to sound like a pick-up truck. Did you switch out both the resonator and axleback mufflers at the same time or did you do one before the other? If so, can you tell me how it sounds and do you hear a drone in the car at cruise? I like the exhaust look from SF but not sue if I want to do both for fear it will be too loud or it will drone when not pushing it.

I saw the in-car video but it sounded loud and truck-like to me.

jcar

The only exhaust systems I have ever dealt with (I have installed systems from most manufacturers on either my own or friends' cars) that didn't have an interior drone somewhere in the RPM range have been Corsa. Unfortunately they do not offer anything for the G8 yet.

Back to the OP;

I crawled under a v6 car on the rack at a dealer Monday. It is a true dual exhaust system and from what I could see there were two cats right behind the manifolds, then a large common muffler/resonator about in the center of the car under the front seats, then two small resonators, then the mufflers/resornators behind the bumper. From what I can see on my GT it is virtually the same.

The stock axlebacks (rear mufflers) as the single largest contributor, and the 2" piping between the large 2-in / 2-out resonator and the bullet resonators is really lousy. The system is 2.25" which isnt great in itself. Precisely why a straight through muffler is important.

The big resonator is not a restriction as it is a straight through design however it offers no help in balancing exhaust pulses between the cylinder banks for improved scavenging. Doesn't do anything good for sound quality either! :D

S.F.

S.F,

Do you have any flow numbers or dyno info for your products compared to stock?

S.F,

Do you have any flow numbers or dyno info for your products compared to stock?


Unfortunately I don't have that information. Since I am just one guy building this stuff in his garage there is no R&D budget for this kind of testing. Magnaflow has flow data for the mufflers (#12226) i'm using on their website.

I believe one of my customers here works for a speed shop and is planning a before and after test once he gets his axlebacks. I think he will be dynotuning as well.

S.F.

Does anyone have photos of the entire stock system front to back? That would be useful to have in this thread.

Does anyone have photos of the entire stock system front to back? That would be useful to have in this thread.

http://i152.photobucket.com/albums/s190/angelajeanmessina/G8pics006.jpg

http://i152.photobucket.com/albums/s190/angelajeanmessina/G8pics007.jpg

http://i152.photobucket.com/albums/s190/angelajeanmessina/G8pics008.jpg

http://i152.photobucket.com/albums/s190/angelajeanmessina/G8pics009.jpg

http://i152.photobucket.com/albums/s190/angelajeanmessina/G8pics010.jpg

http://i152.photobucket.com/albums/s190/angelajeanmessina/G8pics011.jpg

http://i152.photobucket.com/albums/s190/angelajeanmessina/G8pics010.jpg

http://i152.photobucket.com/albums/s190/angelajeanmessina/G8pics013.jpg

Not pictured are the two bullet resonator just after the big oval resonators shown above

S.F.

Not pictured are the two bullet resonator just after the big oval resonators shown above

S.F.[/COLOR]

Interesting.
Are the 'bullet resonators' somehow covered
\ shielded from view from below?
Thanks for posting these...
- Ray
Ready for axle-backs - just need a G8 GT...

Interesting.
Are the 'bullet resonators' somehow covered
\ shielded from view from below?
Thanks for posting these...
- Ray
Ready for axle-backs - just need a G8 GT...


My digital camera is a piece of crap and it "ate" that picture.......

S.F.

That last pic is bad ass.

You guys are awesome! I was too lazy to crawl under my GT and now I don't have to. Thanks ! AG

Official Magnaflow pictures to be released shortly ... I will have a complete disection of the system as we do for all of our development pieces.

Official Magnaflow pictures to be released shortly ... I will have a complete disection of the system as we do for all of our development pieces.

Sweet!:gears:

Official Magnaflow pictures to be released shortly ... I will have a complete disection of the system as we do for all of our development pieces.

Sweet. :popcorn2:

I've had my GT since it came out and so far I've added 3-chamber flowmaster mufflers and i cut out the large middle resonator, replacing it with two straight pipes. The car is louder but not too loud....and i did notice a performance increase haha. the car seems to gurgle a bit when the active fuel management system kicks in but i may experiment with H-pipes and X-pipes to see if that eliminates it.

I've had my GT since it came out and so far I've added 3-chamber flowmaster mufflers and i cut out the large middle resonator, replacing it with two straight pipes. The car is louder but not too loud....and i did notice a performance increase haha. the car seems to gurgle a bit when the active fuel management system kicks in but i may experiment with H-pipes and X-pipes to see if that eliminates it.

I have an H Pipe and S.F.'s axlebacks and it does not eliminate the sound when DoD kicks in. It doesn't really bother me too much though.

I've had my GT since it came out and so far I've added 3-chamber flowmaster mufflers and i cut out the large middle resonator, replacing it with two straight pipes. The car is louder but not too loud....and i did notice a performance increase haha. the car seems to gurgle a bit when the active fuel management system kicks in but i may experiment with H-pipes and X-pipes to see if that eliminates it.

I have an H Pipe and S.F.'s axlebacks and it does not eliminate the sound when DoD kicks in. It doesn't really bother me too much though.

Unfortunately I think that is going to be the trade off with any G8 GT running aftermarket exhaust with DOD still active in the PCM...........

A nice comparison would be fuel economy bone stock (no mods at all) vs a more efficient L76 due to high flow exhaust, CAI and a custom tune.......

S.F.

We picked up our new G8 on Thursday and started tinkering with it on Friday :D

Stock exhaust system has 2 cats, 3 resonators and 2 mufflers.

Removed all 5 of the resonators and mufflers. Also removed the portion of the exhaust tubing that necks down to 2-1/4" between the resonators. We added a 2-1/2" X-pipe where the dual resonator was located. I wasn't crazy about the stock tips, so we welded on a set of used Trans Am oval tips.

I expected the sound to go from dead quite to really loud, but I wanted to see the extremely loud side of things since the stock exhaust is obviously really quite.

Next we swapped the stock 90mm throttle-body with fully ported 90mm TB.

We then took a K & N CAI from a GTO and modified it to fit the G8.

Lastly we downloaded the stock tune and tweaked it via HPTuners.

We also tried an SLP underdrive pulley, but the offset was wrong for proper belt alignment so the stocker went back on.

The difference is dramatic! The tune is definitely the single largest improvement since the stock settings are really conservative. The car now pulls to 6400 in first. We added between 3 to 12 degrees of timing across the board. This could only be done with proper tuning of the transmission settings since the stock timing was showing knock retard due to the extremely lazy shift points and converter lock-up settings.
There are countless other tweaks that were done with the tune to transform it to a much more responsive & efficient tune.

We will be doing so more mods very soon and also putting it on our dyno for some HP, Torque & 1/4 mile numbers.

First on the list is to add a set of resonators to reduce the sound of the exhaust since it is a tad on the loud side. :wall:

Here is a link to pictures and a video of the exhaust sound.

http://www.mongillomotors.com/Pages/2008_G8_Pics.html

So you removed resonators to add some back in? Kind of confused. Is that soundclip with no mufflers at all?

So you removed resonators to add some back in? Kind of confused. Is that soundclip with no mufflers at all?

We wanted to hear the exhaust with all the mufflers and resonators removed.

That video is with them removed. Just the cats into an X-pipe and out the tips.

Now that we know how loud it is, we can pick and choose what to add to get the right sound and flow. The power with this setup is very good, but the sound is to loud. Especially when headers will be installed.

We bought this car for the shop to do R & D and to showcase what can be done with the G8. Although we do a lot of custom turbo, twin turbo & supercharger systems, that is not the plan for the G8, for now.

We are basically developing our cat-back system and stage 1 package for the G8.

I'll add more sound clips as we change the setup.

Dude! What are you doing? This was the perfect time to push the $66 exhaust mod! :thumbsup:

Sorry couldn't help myself. :gr_jest:
HAHA! Well, SF makes his systems for a living and does a fine job too.

If I did the $66.00 mod for a living I'd have to charge $67.00, and besides, it DOES sound like crap! :p

We wanted to hear the exhaust with all the mufflers and resonators removed.

That video is with them removed. Just the cats into an X-pipe and out the tips.

Now that we know how loud it is, we can pick and choose what to add to get the right sound and flow. The power with this setup is very good, but the sound is to loud. Especially when headers will be installed.

We bought this car for the shop to do R & D and to showcase what can be done with the G8. Although we do a lot of custom turbo, twin turbo & supercharger systems, that is not the plan for the G8, for now.

We are basically developing our cat-back system and stage 1 package for the G8.

I'll add more sound clips as we change the setup.

Oh ok I was confused, I thought you were going to jut add a whole lot of restriction back. I agree, the car sounds like a truck lol. No way I would want my car to sound like that. Are you going to add 2.5" piping after the cats? What kind of mufflers are you looking at?

Oh ok I was confused, I thought you were going to jut add a whole lot of restriction back. I agree, the car sounds like a truck lol. No way I would want my car to sound like that. Are you going to add 2.5" piping after the cats? What kind of mufflers are you looking at?

As of now, we will be adding some of our 2-1/2" stainless steel resonator mufflers. It's a straight flow-through design so it will have little effect on back pressure while quieting down the sound.

The exhaust flows well with the current piping which is 2-1/2" and just a tad smaller in some areas. I don't think there will be any performance gain by going with a large system. At least not with the stock manifolds, cats and cam.

After a cam and headers/high flow cats, then there may be a HP gain at the top of the rpm band, but sound will also increase again so it is a balancing act.

It's pouring today so I didn't drive it in to workl today. The rain should let up by Wednesday.

Ed

Ah I thought it was a 2 1/4 system. So basically right now all the pipings are good on the G8 its just the mufflers and resonators that decrease the sound and hp on the car, am I correct? The exhause on these cars are WAY too quiet, thats the first thing I'd do.

Ah I thought it was a 2 1/4 system. So basically right now all the pipings are good on the G8 its just the mufflers and resonators that decrease the sound and hp on the car, am I correct? The exhause on these cars are WAY too quiet, thats the first thing I'd do.

I stand corrected! I just went over to the resonators and measured the smallest diameter piping of the system. What I thougth was 2-1/4" is actually 2" :eek: And what I thought was 2-1/2" is actually 2-1/4".

So yes, the cat-back is 2-1/4" and it actually necks down to 2" at the bullet style resonators.

I apologize for the mis-information. The X-pipe and straigth pipes we installed are 2-1/2" so the smallest diameter must be the stock mid-pipes at 2-14".

I'll check that tomorrow and let you know.

Ed

Can we change the subject matter just a little bit? How did you modify a CAI for the GTO to make it fit? Any pictures?

Can we change the subject matter just a little bit? How did you modify a CAI for the GTO to make it fit? Any pictures?

Here are the pics of the install. There is no heat shield used as of now. The intake tube needed to be cut down some to fit the filter which is not the standard GTO filter but a longer one. We only had the intake tube to work with, I think the stock K&N filter would work since it is shorter, but we haven't verified that yet.

Cold Air Intakes & Heat Soak are two very debated issues on internet forums so I expect many different opinions on this. Our experiences on the street, on our dyno, and at our track events tell a different story from what many people think about heatsoak and CAI.

The majority of the power found is not from cooler air, it is from a less restricted airflow.

This isn't to say that a properly sealed cold air box isn't beneficial, because it most certainly helps make more power.

What I am saying is that one system is not better than the next based on how cold the air is or how sealed off the filter is. Ultimately, what matters is the net rwhp & torque increase across the ENTIRE RPM range.

With that said, there is another vendor on this forum how has a CAI kit that looks to be very well made and engineered.

We just needed something right now. I would like to do a back-to-back comparison on our dyno between what is on there now and that kit.

http://www.g8board.com/forums/attachment.php?attachmentid=875&stc=1&d=1209486517

http://www.g8board.com/forums/attachment.php?attachmentid=876&stc=1&d=1209487261

http://www.g8board.com/forums/attachment.php?attachmentid=877&stc=1&d=1209487201

http://www.g8board.com/forums/attachment.php?attachmentid=878&stc=1&d=1209487201

We wanted to hear the exhaust with all the mufflers and resonators removed.

That video is with them removed. Just the cats into an X-pipe and out the tips.

Now that we know how loud it is, we can pick and choose what to add to get the right sound and flow. The power with this setup is very good, but the sound is to loud. Especially when headers will be installed.

We bought this car for the shop to do R & D and to showcase what can be done with the G8. Although we do a lot of custom turbo, twin turbo & supercharger systems, that is not the plan for the G8, for now.

We are basically developing our cat-back system and stage 1 package for the G8.

I'll add more sound clips as we change the setup.


Any more clips on your progress? BTW loved the sound of the "open" exhaust but not for an everyday driver.

Any more clips on your progress? BTW loved the sound of the "open" exhaust but not for an everyday driver.

Sorry for the delay, but we have been real busy with customer cars.

I added a set of flow through mufflers (resonators) to tone it down some. We figured it was going to be on the l;oud side, but we had to see how loud it was.

I'll try to take new pics tomorow and vids of the sound now that there are some mufflers on it.

I've been installing a little something extra in the trunk :wink2: as well as a few other non-performance items.

http://www.g8board.com/forums/attachment.php?attachmentid=1025&stc=1&d=1211259647

http://www.g8board.com/forums/attachment.php?attachmentid=1026&stc=1&d=1211259647

http://www.g8board.com/forums/attachment.php?attachmentid=1027&stc=1&d=1211259647

We will probably get it on the dyno by the end of the week for some before and after dyno runs.

HID lights are installed and some molded mud-flaps are on the way.

We will also install a couple of subs in the spare tire well and a light metallic tint.

We are in the process of becoming a forum sponsor so I'll probably start a thread of some of the tweaks and things that we find that is useful info.

Ed

stock cats are the biggest restriction in a GT's exhaust. overall, the system is pretty well designed and aftermarket axle backs will gain you no more than 2-3 hp over stock.

stock cats are the biggest restriction in a GT's exhaust. overall, the system is pretty well designed and aftermarket axle backs will gain you no more than 2-3 hp over stock.

Foxbat, you are right on with that statement.

The stock cats are the biggest restriction. Axle backs is basicaly for more sound. A good complete cat-back does pick-up about 10 rwhp though.

Can anyone repost these pics of the stock exhaust because they are not showing up because the persons Photobucket account has been inactive for 90 days according to what it says where the pics used to be. I'm trying to figure out what the first owner of my car did to the exhaust. Thanks!

I feel another DRONE attack coming out of the past. What is the going price for a NEW SF H-Pipe in the box?

I feel another DRONE attack coming out of the past. What is the going price for a NEW SF H-Pipe in the box?
You want to do all those mods without a drone goodluck.A cam?Get use to listening to your motor its not a lexus.!!!!