2.5" exhaust w/ Flowmaster 40's & 4" mid-pipe - Pontiac G8 Forum: G8 Forums - G8Board.com
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post #1 of 6 (permalink) Old 07-21-2009, 04:42 PM Thread Starter
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2.5" exhaust w/ Flowmaster 40's & 4" mid-pipe

Here is something new, I built a 2.5 stainless exhaust from the manifolds back with a 4" mid-pipe that has a single 4" Magnaflow muffler followed by a pair of 2.5 Flowmaster Delta 40's in the stock location. Also used a pair of 3" cats to make it "clean".

Here is a video link to see/hear it. Hope to have a driving version soon. It sounds great and very quiet for Delta 40 Flowmasters. The 4" mid-pipe with the Magnaflow muffler has a slightly larger sq in area that seems to slow down the air some to give it a deep sound without the dreded 40 Series drone. The Magnaflow coupled with the 4" mid-pipe really quiets it down alot and gets rid of that poppy sound under heavy load and deceleration.

http://www.youtube.com/watch?v=5Yg_fHb7ejI

Don't mind the smoke, the MAF was way rich with the new exhaust plus the j-bends I used to make the exhaust were soaked with oil inside.

Even though it still breaths thru manifolds, it made a big difference for power. It would be nice to see dyno numbers, but the track should be able to show the pickup. I built it with flanges in stock locations in order to add headers later or change the axle-back setup.

2009 G8 GT- Rick Crawford
1.50 60ft, 10.41 @ 131.4 Comp 234/243 111+0 6.4 N/A
1.53 60ft, 10.59@ 129.7 ALL MOTOR!!! N/A G8 Record Holder
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post #2 of 6 (permalink) Old 07-21-2009, 10:59 PM
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wow that sounds really good, thats wat im lookin for. How much did that setup cost u?? Cant wait to see some videos while driving. Great setup man.
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post #3 of 6 (permalink) Old 07-21-2009, 11:46 PM Thread Starter
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Originally Posted by njsfinest View Post
wow that sounds really good, thats wat im lookin for. How much did that setup cost u?? Cant wait to see some videos while driving. Great setup man.

Spent $60 for 3ea Magnaflow j-bends, $200 for the stainless Flowmasters, $100 for the Magnaflow 4" muffler. The rest I scrounged from the shop. Cats were leftovers from a 3" BBK Ford Lightning exhaust kit, most of the 2.5" pipe was from 3 stock newer Mustang H pipes that are all 2.5". The 4" stainless was leftover from all the diesel exhaust kits(still have plenty of 4" leftover). Tips and flanges were off the stock G8 exhaust. I have a TIG welder and porta-band saw to put it all together.

$360 total investment.

If you can get your hands on newer Mustang "H" and "X" pipes from guys buying aftermarket, you can cut them up to fab up your own but it takes a little skill.

I am extremely impressed with how good it sounds, and just as impressed with the power gain. Never had a wheel spin problem until now, and on my marked off 1/4 it picked up 3-4 mph. I have a short driving clip but you can't hear anything with the window down for the first street. Then found out I was a little close on the cross member and it will touch under WOT. It should be fixed now but don't have time to record a new one...

2009 G8 GT- Rick Crawford
1.50 60ft, 10.41 @ 131.4 Comp 234/243 111+0 6.4 N/A
1.53 60ft, 10.59@ 129.7 ALL MOTOR!!! N/A G8 Record Holder
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post #4 of 6 (permalink) Old 07-22-2009, 12:18 AM Thread Starter
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It a ruff first video since I cut it short to fix the exhaust rattle against the corssmember at WOT. It's hard to tell how loud it is in the car until I start talking. Definitely far from being considered loud at all in the car.

http://www.youtube.com/watch?v=FLRqdBwodSo

2009 G8 GT- Rick Crawford
1.50 60ft, 10.41 @ 131.4 Comp 234/243 111+0 6.4 N/A
1.53 60ft, 10.59@ 129.7 ALL MOTOR!!! N/A G8 Record Holder
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post #5 of 6 (permalink) Old 07-23-2009, 02:48 PM
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I like that, very nice job. What did you use to merge the 2.5" pipes with the 4" center pipe?

Andy
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post #6 of 6 (permalink) Old 07-23-2009, 04:08 PM Thread Starter
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Originally Posted by realsquash View Post
I like that, very nice job. What did you use to merge the 2.5" pipes with the 4" center pipe?

Andy
The one 2.5" factory Mustang exhaust had an "X" pipe that I cut in half to used for the back 4" to 2.5". In the front I just angle cut the 4" then "formed" it around the 2 pipes merging in. Just had add a small strip down the middle to fill the gap. Used a 2.5 hole saw, drill two holes side-by-side on a spare piece of 4" with a gap between them to match the space I had to fill, then cut out the strip and welded it in. It would have been easier to use the other half of the merge but it wasn't too hard.

It would be interesting to see what it sounds like without a the 4" muffler since it is easy to add one. Even a different style like a bullet. The DOD is a bit loud (a very low tone, sub 100Hz) at 55+ cruise speed but I have mine tuned to stay on longer so stock it may not be bad. NON-DOD is great at any speed with this exhaust. This exhaust doesn't have any bad NON-DOD drone to me. Maybe if the 4" muffler was is in the back it would change the tone. With it in front, the exhaust gets quiet under hard acceleration.

2009 G8 GT- Rick Crawford
1.50 60ft, 10.41 @ 131.4 Comp 234/243 111+0 6.4 N/A
1.53 60ft, 10.59@ 129.7 ALL MOTOR!!! N/A G8 Record Holder
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